Thursday, January 4, 2007

Renal Masses

INTRODUCTION
Detection and characterization of renal masses is one of the most vexing problem encountered by the radiologists in a large teaching hospital. In any radiology department hardly a week goes by without the detection of a few renal masses, most of which are asymptomatic or detected incidentally.
The term renal masses include a large variety of space occupying lesions, which are composed of nonfunctioning renal tissue. Many of these are neoplastic, while some of these are inflammatory, congenital, cystic or traumatized tissue. A renal neoplasm can be either benign or malignant. Of all the malignant lesions renal cell carcinoma account for 2-3% of all malignant neoplasms and 85-90% of all kidney tumours. Wilm's tumour is the most common childhood tumour. Other important neoplasms are Angiomyoliomas (commonest benign neoplasm), Oncocytoma, Multilocular Cystic Nephroma (MCN), Hemangioma, Lymphoma, Sarcoma, Metastases, Transitional Cell Carcinoma (TCC) and Squamous Cell Carcinoma.
The usual clinical presentation of malignant renal neoplasm is in the form of hematuria, flank pain or lump abdomen. However, most of the benign lesions including benign cortical cysts remain asymptomatic and are discovered incidentally on USG or CT.
In the past, renal neoplasms were usually detected late in their course when the lesions had already metastasized. Surgical exploration was done in the less aggressive lesions to establish histopathological confirmation. but the reliance on surgical exploration and histological diagnosis was challenged increasingly. Simultaneously various studies claimed that sequential use of radiological investigations can identify the nature of renal masses with diagnostic accuracy comparable to that of surgical exploration. Clayman and his colleagues (1979) also stated that surgical exploration was rarely indicated since the non-operative approach was precise, cost effective and had almost no morbidity.
The past two decades have witnessed tremendous advancement in the visualization of urinary tract disorders. In the detection and characterization of renal masses too, a high detection rate can be achieved by the sequential use of various recent diagnostic modalities. These modalities including plain radiography (KUB), excretory urography (EU), ultrasonography (USG), computed tomography (CT), helical CT and MRI are useful in achieving the radiographic objective in studying renal mass lesions as described by Zemen et al. (1981).
The advent of USG and CT in recent years has led to the early recognition of small asymptomatic lesions during the examination performed for the reasons other than for a suspected renal mass. Also such masses are less likely to be locally advanced or to have metastasized thereby increasing the chances of surgical cure.
The plain abdominal radiograph may rarely be the first study to alert the radiologist to the presence of a renal mass; similarly, intravenous urography (IVU) may sometimes be the initial study to depict a renal mass.
Ultrasonography is the most common screening modality used for the evaluation of a suspected renal mass. Ultrasonography in addition to being helpful in detection and localisation of the lesion also helps in differentiating solid from the cystic lesion and further characterises them. The modality is devoid of ionizing radiation and unlike CT, no intravenous contrast injection is required. Thus USG is valuable for children, pregnant women and those who have impaired renal function or sensitivity to iodinated contrast media. It is portable, relatively inexpensive and readily available in small towns and is thereby the best screening procedure for detection of renal lesion especially in our country where 40% population is below poverty line. Recently, pulsed doppler USG and colour doppler flow imaging (CDFI) has shown promise in not only differentiating between different types of renal masses by intralesional blood flow patterns but also the intralesional extension of the tumour.
Of the modern modalities, CT has a profound impact on diagnostic uroradiology. It has proven useful for imaging the complete spectrum of renal and ureteral disorders. Despite the continued availability of less expensive imaging methods and despite advances in sonography and MRI, CT has continued to play a major role in the diagnosis and follow-up of patients with urologic disease. It is more accurate in delineating a renal mass and in differentiating between a pseudo mass and a normal anatomic variant from a tumour. It allows studies in patients who have dense renal calcification or in whom USG is technically difficult. CT should be used in many areas for definite evaluation of lesions suspected from other studies, for example IVU or USG. But for many disorders, like Angiomyolipoma, calcified renal mass or parapelvic cyst etc., the diagnostic power of CT is so definitive that its use as the primary diagnostic procedure is justified and other studies are not required. Dynamic thin section CT is highly accurate in evaluating tumour extension into the renal vein or IVC.
Though conventional CT has proven to be the most sensitive modality for detection of renal masses and their further characterization into solid lesion, simple cyst or complex cyst, a variety of problems can be encountered like variation in patient respiration can cause motion artifacts or gap in the scanning. The former may compromise image quality while the latter may lead to failure to image portions of kidney and masses within these portions. Partial voluming of renal masses with surrounding normal renal parenchyma or with perinephric fat can result in inaccurate attenuation measurement particularly if a small lesion is not centered perfectly within an image. Partial voluming can also hinder the evaluation of subtle features within cystic lesions such as minimal wall thickening, thin septations or tiny areas of nodularity. The duration of conventional scanning sequence is relatively slow with scan times usually lasting less than 2 seconds and interscan delay of 3.5 to 8 seconds. Even under ideal circumstances, more than a minute is required to image the kidneys in their entirety. Therefore, selective imaging during the earliest (cortical) phase of renal enhancement, during which time the renal cortical enhancement is maximal is not possible.
Helical CT has many potential advantages over the conventional axial CT. Rapid and continuous scanning allows an entire sequence to be obtained during a single breathhold. At the most commonly used pitch of 1:1, most kidneys can be scanned using narrow (5 mm) image collimation in less than 30 seconds. Scanning during a single breathhold also prevents misregistration, thereby eliminating the chance that portions of kidneys (and therefore renal masses) might not be imaged. The ability to retrospectively shift the level of reconstruction is an additional major advantage of helical CT. Although the collimation and pitch must be determined at the time, that scans are acquired, raw data can be reconstructed at any level. This allows the technologist to reconstruct an axial image at that level which precisely includes the centre of a detected renal mass. The rapid scanning time of helical CT also permits renal imaging during any of the three phases of renal parenchymal contrast material enhancement i.e., the cortical phase (CP), nephrographic phase (NP) and excretory phase (EP).
Recently helical CT has evolved as a new minimally invasive diagnostic tool for the detection of vascular pathologic conditions for example in the pre-angiographic workup of patient with renal artery stenosis. Helical CT has overall accuracy of 90% in the abdominal staging of renal cell carcinoma. The sensitivity of CT in lymph node staging is reported to be 83 to 89%.
Inability to determine accurately the presence of extra capsular or perinephric tumour extension accounts for most of the CT staging errors. Venous tumour invasion can only be definitely diagnosed on CT if there is identifiable thrombus in the renal vein or IVC with or without venous enlargement. If the CT suggests vena caval tumour extension but the cephalic extent of the tumour is not identifiable, MRI or USG may be of help. Following the treatment of renal mass CT is the method of choice for post nephrectomy renal fossa surveillance.
MRI is not routinely recommended for renal mass imaging. However, it may be useful (or perhaps superior) in staging renal neoplasm or where renal arteriography is required for vascular road mapping in patients undergoing selective (partial) nephrectomy or where CT findings are equivocal or where patient has sensitivity to contrast agent. It is, however, costly and not routinely available.
This study was undertaken with the purpose of evaluating the role of helical CT in the detection and characterization of renal masses.

REVIEW OF LITERATURE
Renal masses are expansile space occupying lesions which are aggregates of non-functioning renal tissue. Pseudotumors are made up of normal functioning renal tissue so that they will concentrate renal cortical radio-pharmaceuticals such as 99 m TC GA or 99 m TC DMSA, while true masses (tumour, cyst, abscess) will instead produce proton deficient area on radionuclide imaging. Most common renal tumour is Renal cell carcinoma (85-90% of all renal masses). Wilm's tumour is the commonest malignant childhood tumour. Angiomyolipoma is the commonest benign tumour. Clinically the most common presentation of a patient with renal tumour is hematuria, other complaints are flank pain and flank lump. The classic triad of hematuria, flank pain and lump is present in only 19% of patient with renal cell carcinoma.
In 1885, Wilhem Conrad Roentogen working in a Physics laboratory in Wurzberg Germany discovered a previously unknown ray, that could see through substances impervious to the ordinary light to whom he named X-rays. From this discovery of the X-ray, evolved the modern speciality of radiology. In the past century especially in last two decades most of the evolution and advancement in radiodiagnosis like ultrasonography, CT, helical CT and MRI has come into existence.
In 1927, Shaw studied the result of 1326 roentgen examinations for suspected urinary calculi and concluded that the pyelogram, properly made and interpreted offered the most valuable and conclusive proof of large number of renal lesions than any other diagnostic method and also advocated its use in all lesions of doubtful nature.
In 1957, Evans used the term nephrotomography to define a method in which tomograms of the kidney were obtained at predetermined level after administration of intravenous injection of contrast material.
According to Elkin (1963) within a few years of discovery of X-rays, roentgenography was used to demonstrate radiopaque urinary calculi and the next step was the radiologic demonstration of the course of ureters and renal pelvis by inserting radiopaque catheters, with metallic stylets threaded into their lumen retrogradely into the ureters. This technique eventually evolved to the RGP later on.
In 1965, Rabinowitz, Wolf and Goldman observed that the past decade had witnessed the advent of nephrotomography as a routine procedure in the evaluation of renal masses and noted that Chynn and Evans in 1960 and Levine et al. in 1964, reported as high as 95% accuracy in distinguishing renal cyst from tumours using this procedure.
The application of infusion excretory urography or drip infusion urography for urologic diagnosis was initially described by Harris and Harris in 1964 and more studies were conducted on the following years by Schencker (1964), Danford (1964), Wendth (1965) and Becker (1966). Double dose urography was described by Amar in 1964 and Benness in 1965.
According to Hendren (1964) and Grossman et al. (1968) excretory urography had long been the traditional modality for the evaluation of the renal mass and still remained the primary tool for the radiologic diagnosis of renal lesions. The application of ultrasonography to urologic diagnosis was initially described by Holmes et al. (1965), Howry (1965), Holmes (1966), Ostrum, Goldberg and Isard (1967), West (1967), Goldberg, Ostrum and Isard (1968) and Damascelli et al. (1968).
Schreck and Holmes (1970) and Mountford et al. (1971) applied ultrasonography in the problem of differentiating renal cysts from neoplasm and reported similar success in distinguishing these two types of masses. Also in 1974, Goldberg and Pollack showed that by means of non-invasive A-mode ultrasound it was possible to differentiate solid renal tumours from simple cyst according to the presence or absence of internal echoes. These researchers alongwith the others like Rosenberg et al. (1971), King (1972) and Doust et al. (1973) in their respective studies applied ultrasonography to the problem of differentiating renal cyst from neoplasm and reported between 76%-90%. Overall accuracy in differentiating these two types of masses.
Asher and Leopold (1972) suggested a method for streamlining the diagnostic approach to renal mass lesion by the use of ultrasound, as the method had the advantage of eliminating many angiographic procedures and surgical risks and when combined with renal cyst puncture suffered no loss of diagnostic accuracy. They proposed that the use of ultrasound and renal angiography could be extremely helpful in detecting solid renal masses of varying etiologies and that ultrasound could frequently indicate the extra renal nature of a mass which caused displacement of that organ by virtue of its location.
As early as 1977, the findings of Sagel and colleagues indicated that while excretory urography remained the primary uroradiological imaging tool which satisfied most diagnostic needs, they believed, however that computed tomography (CT) would often give additional or conclusive diagnostic information when an abnormality was detected on urography. They emphasised that CT was useful in permitting more definitive evaluation of renal mass or ascertaining the cause of non-functioning kidney with the result of CT examination often dictating which diagnostic procedure (if any) should be used next.
According to Petkovic (1980) expansion of renal tumours through the fibrous renal capsule, which signified extra renal extension meant a very bad prognosis and therefore correct evaluation of tumour expansion beyond the renal capsule was of great importance. In this context, the statement of Karp and Associates (1981) that ultrasound staging of renal tumours was mainly limited by its inability to appreciate extra capsular extension and infilitration to adjacent structures and thus CT should be the primary method, assumed significant importance.
Sherman et al. (1981) corelated CT findings of 17 patients of AML with their pathologic findings. They described that CT scans usually demonstrate a large fatty mass intermixed with areas of tissue density which may represent non-fatty parts of the tumour or area of haemorrhage. In those AML composed primarily of smooth muscle or in which intratumoral haemorrhage has obscured the fatty parts of the tumour, the CT appearance is indistinguishable from other solid renal tumour.
Pariently et al. (1981) described three cases of MCN that were demonstrated by CT MCN appears on CT scan as a well marginated rounded or polycystic cortical mass that extends beyond the normal renal outline. This mass contains cyst that vary in size and number. It may be a cluster of few large cysts with thick wall or septae or it may be a denser mass composed of tiny cysts. This CT pattern is suggestive of MCN, but is not sufficient to obviate surgery. However, as part of a complete pre-operative work up, CT provides information that may be valuable in limiting the surgical procedure, perhaps avoiding unnecessary laparotomy.
Weyman et al. (1982) in a study of 21 calcified renal masses found the ability of CT to evaluate the cystic or solid component and to precisely locate calcification within renal masses, which resulted in more accurate evaluation of the calcified masses by CT than by standard radiography technique.
In a prospective study of 23 cases of renal cell carcinoma in 1982, Cronan et al. found that staging of the tumour was correct with CT in 91% of the lesions, with ultrasound in 70% and with angiography in 61%. They went on to state that CT of the abdomen was the optimal technique to stage renal carcinoma and to determine direct extension to adjacent organs, draining lymph nodes and venous tumour extension.
Levine et al. (1983) compared CT and pathologic features of three incidentally detected renal oncocytomas with those of 6 RCC of comparable size, RCC appeared on kidney as a solid mass that generally had an indistinct interface with the normal renal parenchyma, a lobulated contour and a non-homogenous pattern of contrast enhancement. These features correlated with pathologic findings of an irregular tumour margin and the frequent presence of tumour haemorrhage and necrosis.
Oncocytoma on the other hand, generally had a distinct margin, a smooth contour and a homogenous appearance on contrast enhanced CT scan. These findings correlated with the smooth tumour margins and the absence of tumour haemorrhage and necrosis on pathologic examination. They concluded that demonstration of these findings by CT should alert radiologist and surgeon to the possibility that a renal mass may be an oncocytoma. Such a presumptive diagnosis than can lead to a surgical approach that allows for renal conserving surgery.
Madewall et al. (1983) presented clinical radiographic and pathologic findings of MCN in 58 patients. The lesion affects predominantly the boys in childhood and women in adulthood is usually solitary and it commonly occurs as an asymptomatic mass. Tumour may grow slowly over years or rapidly within months. A mass that is usually identified in plain radiography occasionally has curvilinear calcification. Angiography showed an avascular mass (6 lesions), a hypovascular mass (14 lesions) or hypervascular mass (3 lesions). US is helpful when multiple circumscribed sonolucent areas are identified. Similarly, a multilocular mass with septae is usually identified by CT (six of the seven).
The study indicated that this lesion is a neoplasm that can be strongly suspected pre-operatively if pelvic herniation or a multilocular pattern is noted on imaging findings.
Pamilo et al. (1983) compared the features of 20 RCC lesions as seen with US and CT CT demonstrated necrotic tissue area in 12 tumours. On US imaging, the necrotic area were markedly echogenic in 4 tumours, moderately echogenic in 3 tumours, minimally echogenic in 2 and showed mixed area of marked and minimal echogenicity in three. CT showed hypervascular areas in 11 of these, the hypervascular area of one tumour was markedly echogenic in US image and 5 were moderately echogenic and 3 were minimally echogenic.2 had mixed area of marked and minimal echogenicity.
These results confirmed the earlier findings of no clear correlation between vascularity and echogenicity and that necrosis varied widely in the US appearance.
In 1984, Dunnick and Korobkin observed that CT had become an essential imaging tool for the evaluation of the kidney and perirenal space as the transverse plane of the CT image complimented conventional urography. The superior contrast resolution of the CT allowed identification of specific tissues such as fat, fresh haemorrhage and radiolucent stones and the addition of dynamic sequencing had resulted in the display of vascular anatomy as well as demonstration of the sequential organ involvement. They also mentioned that the use of intravenous contrast material simplified the detection and evaluation of renal masses and was essential for the staging of renal carcinomas.
Stephenson et al. (1984) compared the ability of excretory urography and computed tomography (CT) to detect renal masses in 20 consecutive cases and found that CT consistently provided more information than excretory urography, usually was able to distinguish renal tumours from cysts and provided additional useful information regarding staging of renal neoplasm and presence of unsuspected associated pathological conditions.
Quinn et al. (1984) evaluated radiographic studies of 18 pathologically confirmed cases of oncocytoma and compared findings with the results of CT, US and angiography of 18 RCC cases. They concluded that oncocytoma can be suggestive if a stellate scar is identified within an otherwise homogenous tumour on US and CT. If the mass appears homogenous, but no scar is present, angiography could be performed. An oncocytoma can be suggested in these cases if a spoke wheel configuration and homogenous blush are present. These criteria which are reliable only if the mass is 3 cm or larger would have resulted in the correct diagnosis of oncocytoma in 16 of the 18 cases.
Pariently et al. (1985) performed diagnostic and staging CT examination on 15 cases of renal adenocarcinoma including 15 cystic forms. All of these were confirmed with nephrectomy. During the same period, they observed about 400 patient with one or more renal cysts. 15 cases of cystic renal cancers accounted for 10% of patient with renal cancers and 3.75% of patient presenting with renal cysts. Excretory urography showed avascular mass suggestive of cyst. USG revealed a cystic mass with thickened and irregular wall, sometimes with echoes within the mass. Thus USG was unable to distinguish between a complicated cyst (infected/ haemorrhagic) and an extensively necrotic cancer. The differential diagnostic CT features of these cystic cancers included size > 10 cm, localised thickening of cyst wall, with contrast enhancement in atleast one scan of the series, hetereogenous cyst contents with suspended slightly denser areas and irregularity and poorly defined implantation in the kidney.
In 1986, Bosniak proposed a useful classification of cysts and cystic renal masses in an attempt to define precisely the radiologic findings for lesion not requiring further evaluation and for those that should be explored surgically. He proposed the following CT criteria for a benign hypodense cyst —
1) The lesion must be perfectly smooth, round, sharply marginated and homogenous.
2) The lesion must not enhance on I/V contrast administration and its configuration must remain unchanged.
3) The lesion must be 3 cm or less in size.
Lang et al. in 1986 carried out a prospective study of 22 patient to assess diagnostic ability of CT, Dynamic CT arteriography, USG and radionuclide scanning in renal cell carcinoma. The dynamic CT proved to be the most sensitive, specific and accurate modality for diagnosing contiguous extension of primary neoplasm. The dynamic CT correctly characterised neoplasms confined to the kidney, their perirenal extension, involvement of the renal fascia and contiguous extension into the adjacent organs in all 22 patient.
Choyke et al. (1987) presented clinical and radiologic features of 27 patient with renal metastasis arising from eight different types of non-lymphomatous primary malignancies. Renal metastasis were generally detected late in the course of malignancy. In 23 patients there were no symptom referable to the kidney. Radiologically metastasis were usually multifocal. However, metastasis arising from the colon, the lung and the breast carcinoma were sometimes large, solitary and indistinguishable from primary renal cell carcinoma. Three of the four melanoma metastasis and three of the seven lung metastasis, infiltrated the perinephric space. CT was the most sensitive modality in depicting the renal metastasis in all 24 cases followed by US and IVU. The study indicated that a new renal lesion in a patient with advanced noncurable primary is more likely a metastasis than a primary and that biopsy in this setting is unlikely to yield any help.
Bosniak et al. (1988) proposed that angiomyolipomas of the kidney could be diagnosed non-invasively and with greater accuracy by modern imaging techniques since fat within these tumours was usually detected readily by USG and CT thus establishing the diagnosis, as it was the only radiologic finding that could differentiate between angiomyolipoma and RCC and save unnecessary surgery.
Hartman et al. (1988) analysed CT and US findings in 23 cases of renal lesions in which the abnormality was infiltrative rather than expansite. They concluded that analysis of the margin, architecture and effects on the collecting system and renal sinus by the mass are helpful in the diagnosis of those disorders that characteristically infiltrate the kidney.
Amendola et al. (1988) performed a retrospective review of the medical records and diagnostic imaging studies of 39 patients with pathological proved RCC case 3 cm or less than 3 cm in diameter. They concluded that small RCC are more frequently encountered in clinical practice than realised and they are best imaged by CT.
In 1989, Levine and colleagues retrospectively reviewed the clinical and pathological imaging findings in 20 patients with surgically confirmed solitary renal neoplasms that were 3 cm or less in diametre and found that 18 lesions were first found by CT, 3 by sonography, and 1 by I/v urography. They reported that small renal neoplasms were most often found incidentally by CT performed in patients without renal complaints and that all the neoplasms were visible on CT although characterisation of these lesions sometimes required combination of CT and USG and occasional angiography.
Kioumehr et al. (1989) studied 29 cases of adult Wilm's tumour reported in literature from 1975-1981 to identify clinical and radiological criteria for pre-operative diagnosis. All patients were either equal to or more than (³) 15 years of age, the mean age of patient was 30 years. 80% were < 35 years older. Each patient presented with a large rapidly growing abdominal mass (average duration of symptoms < 2 months), had no constitutional symptoms and otherwise was healthy. Twenty-three patients showed a non-specific mass effect on IV urography or retrograde pyelography. In remaining seven of the nine patients (78%), abdominal CT scan showed a large inhomogenous mass with large areas of low density and increased enhancement of the compressed remaining normal renal parenchyma, which resembled a pseudocapsule. In 5 (63%) of 8 patients sonogram showed a complex mass with large cystic components. In 18 (82%) of 22 patients arteriogram showed a hypovascular mass with fine, many or zig-zag neovascularity.
They concluded that a rapidly growing renal mass in a younger patient (< 35 years old) that is shown to be complex and cystic by CT or US and that is hypovascular with few zig-zag lines of neovascularity extending to the mass on arteriography is suggestive of adult Wilm's tumour. Such presentation may be helpful in diagnosing this unusual tumour before surgery.
Levine et al. (1989) reviewed clinical, pathological, US and CT imaging findings in 22 patients with solitary renal neoplasm which were less than 3 cm in diametre retrospectively. All the neoplasms were confirmed surgically (15 were RCC, 6 oncocytoma, 1 lymphoma). All carcinomas show contrast enhancement. All the neoplasm were visible on CT However, characterization of the lesions sometimes require a combination of CT, US and occasionally angiography.
The carcinomas, oncocytomas and solitary renal lymphoma could not be distinguished radiologically. On follow-up metastasis did not develop in any patient with carcinoma indicating that small carcinoma usually have good prognosis.
In 1991, Bosniak noted that an increased number of small renal masses were being detected in general population because of the increased use of CT and US and that the radiologist had the burden of detecting these masses, accurately diagnosing them and giving direction to the clinician regarding their management. He advocated that if a small lesion was not a cyst, pseudotumour, angiomyolipoma, lymphoma or metastatic carcinoma, it must be considered as a small renal carcinoma and should be removed unless the removal was clinically contraindicated.
In 1993, Zemen et al. concluded that helical CT scanning should be the preferred means of acquiring routine abdominal CT images.
Davidson et al. (1993) studied the hypothesis that oncocytoma and adenocarcinoma of the kidney can be differentiated with the CT criteria and that differences would become more apparant as tumour enlarged. On contrast enhanced scans, homogenous attenuation throughout the tumour and a central, sharply marginated stellate area of low attenuation were considered predictors of oncocytoma. Any area of decreased attenuation in the tumour, except for a stellate central area was used as a predictor for adenocarcinoma. The author concluded that CT criteria used are poor predictor of the diagnosis of oncocytoma or adenocarcinoma regardless of the tumour size.
In 1994, Silverman et al. stated that spiral CT can show many of the key imaging features of the small renal masses and should be used to distinguish between benign and malignant lesions. He concluded that typical spiral CT appearance of small renal cell carcinoma is that of a non-calcified mass with an attenuation value of 20 HU or more, that enhances with contrast medium and heterogenous enhancement correlates with acellular regions.
Gohji et al. (1994) reviewed 25 RCC patients with tumour thrombus in the IVC and right atrium to determine the relationship between the IVC diameter on CT and tumour invasion of the IVC wall. IVC thrombosis on CT was classified as supradiaphragmatic in 6 patients and infradiaphragmatic in 11 patient, 7 of whom had tumour thrombi near the hepatic veins. Thrombi were also detected around the renal vein in 8 patient. Of the 25 patients 18 underwent radical nephrectomy and tumour thrombectomy. The resected specimen were pathologically examined to determine the degree of tumour invasion of the IVC wall and relationship between IVC dilatation as measured by the CT and tumour IVC wall invasion. Their result indicated that the IVC diametre of 40 mm or more on CT probably indicates extensive tumour invasion and outcome in these patient indicated that partial cardiopulmonary bypass is necessary to decrease mortality and blood loss in these patients with an IVC diameter of larger than 40 mm on CT
In 1995, Curry noted that in the era before CT was available, renal cell carcinoma (RCC) were usually 7-8 cm in diameter when they were first detected, with tumours smaller than 3 cms representing only 5% of the lesions. With modern imaging techniques like USG and CT, however 9-38% of RCC, were discovered when they were 3 cm or less in diameter, while small (1.5-3 cm) and very small (< 1.5 cm) lesion in the renal parenchyma were frequently being discovered incidentally, with this early discovery having possibly improved the survival of patients with these tumours.
Kopka et al. (1995) and Cohan et al. (1995) had concluded that combined evaluation of 2 perfusion phases allow better detection of renal lesions and tumour staging of R.C.C. than either phase alone.
Einstein et al. (1995) reviewed records of 225 patients with a renal mass, retrospectively. These masses were shown by IVU and followed up by either US or CT They concluded that US is the most cost effective imaging method for the work up of a renal mass detected by IVU. The number of US examinations in which findings were indeterminate or positive were not sufficiently high to warrant replacement of US by CT
In 1996, Zemen et al. stressed that because of significant risk of missing a renal mass especially a neoplasm on early cortical phase scans, use of additional delayed scans appeared justified when a renal mass is suspected on the basis of other imaging tests or clinical history.
In 1996, Biranbaum et al. concluded that enhancement of renal neoplasm is time dependent and may not be evident in hypovascular tumour analysed during the early corticomedullary phase.
Platt et al. (1996) stressed that renal helical CT is a suitable replacement for intravenous urography and angiography in the assessment of living renal donors.
Murphy et al. (1996) performed a retrospective study to determine the incidence of Gonadal vein recruitment for collateral venous drainage in patient with RCC. They analysed and concluded that Gonadal vein recruitment signifies well developed A-V shunting, and high flow collateral venous drainage pathways, and may be used as an index of tumour vascularity. This finding may have clinical potential in triaging patients towards pre-operative renal embolisation.
In 1997, Brink et al. stated that introduction of spiral CT 5-6 years ago has revolutionised the way established CT examination are performed today, and has broadened the horizon of CT applications to perform new forms of CT scanning to detect lesion like aortic-aneurysm, various type of arterial stenosis and endoscopic repair of ureteropelvic junction obstruction.
Ferrozzi et al. (1997) described CT findings of renal metastasis in 1997. They described findings in seven main categories.
1) Classically multiple hypodense lesions generally small (10-15 mm) and bilateral showing only mild contrast enhancement.
2) Single generally voluminous lesion with fluid or fuid like content, due to colliquated necrosis with irregular and ill defined borders displaying infiltrating characteristics.
3) Lesion with involvement of the perirenal space.
4) Haemorrhagic lesion with mild contrast enhancement. Depending upon whether bleeding is acute or chronic, the lesion may exhibit a variable appearance ranging from hyperdense texture to pseudocystic appearing mass (from hypervascular primaries e.g. melanoma, choriocarcinoma, phaeochromocytoma, leiomyosarcoma and hemangioma).
5) Lesion with foci of calcification (from osteosarcoma chondrosarcoma and mucoid and papillary carcinoma).
6) Single, solid, homogeneous and hypovascular lesion of variable size generally displaying well defined, irregular contours.
7) Diffusely infiltrating hypodense lesions.
They described that close association between the histological appearance of causative primary tumour and structural aspect of the metastasis as seen on imaging is at times evident and knowledge of this may be extremely helpful in characterization of secondary renal lesion.
Urban et al. (1997) described the CT appearance of TCC of the renal pelvis. The CT findings of early stage TCC of the kidney consist of a central solid mass in the renal pelvis that expands centrifugally with compression of the renal sinus fat. TCC are typically slightly hyperdense to the water density renal pelvis, where they can be detected as masses with a density less than that of renal parenchyma but greater than that of urine. TCC typically show minimal enhancement after contrast material injection and most TCC are hypovascular on arteriogram.
In 1999, Yuh et al. stressed that a dedicated renal CT performed for the detection of suspected renal masses or for the characterisation of known renal masses must include images obtained during later phases of enhancement (i.e. NP or EP). Nephrographic (NP) or excretory phase (EP) images appear to be similar to one another, but superior to corticomedullary phase (CP) images in the ability to both detect and characterise renal masses. Corticomedullary phase (CP) images should always be obtained when information about the renal vasculature is desired or when there is a possibility that a detected renal mass may represent an aneurysm or an A-V malformation or fistula.
In 1999, Coll et al. stated that nephron sparing surgery requires a detailed understanding of renal anatomy. Pre-operative evaluation must delineate the relationship of the tumour to adjacent normal structures and demonstrate the vascular supply to the tumour for the surgeon to conserve as much normal parenchyma as possible. They proposed that helical CT combined with 3-D volume rendering provides all the information required for pre-operative evaluation and intraoperative management of nephron sparing surgery cases.
In 1999, Takebayashi et al. assessed the usefulness of CT nephroscopy in the diagnosis of renal pelvic cancers. They performed surface rendering CT nephroscopy after I/V contrast administration and furesemide injection in 32 patients with suspected renal pelvic carcinoma. Retrospective review revealed that 23 patients later underwent nephroureterectomy. CT nephroscopy revealed 22 carcinoma (92%) and CT demonstrated 20 (83%). They concluded that CT nephroscopy is useful to visualise the complex morphology of renal pelvic carcinoma non-invasively and is superior to axial CT for the detection of infiltrating and pedunculated carcinomas.
Dahlman et al. (2000) investigated the detection rate and characterization of renal lesion during different phases of renal contrast enhancement. They pointed out that NP detected more cortical cyst and the EP detected more sinus cysts and all solid lesions were detected in all phases. Renal parenchyma tumours were best characterised in cortical phase and angiomyolipomas in the native (preconstrast) phase.
Coll et al. (2000) showed the importance of preoperative use of 3-D volume rendering of helical CT to demonstrate renal tumour and anatomy. They emphasised that helical CT with 3-D volume rendering helps ensure complete tumour excision and conservation of adjacent normal renal parenchyma. The radiologist should be familiar with the current indications for nephron sparing surgery.

AIMS AND OBJECTIVES
The main aims and objectives of this study were as follows :-
1) To evaluate the role of helical CT in detection and characterization of renal masses with special attention to the following —
a) to confirm the renal origin of the mass;
b) to determine the nature of the mass; and
c) to determine the extent of the mass.
2) To assess the role of helical CT in the management of renal masses.
3) An attempt was made to compare the helical CT findings with the clinical impression and operative finding in cases where surgery were taken up.

MATERIALS AND METHODS
This study was conducted in the Department of Radiodiagnosis and Imaging, Government Medical College, Jammu. The study included all the patients admitted during the course of study in various surgical and medical departments of the Govt. Medical College and Associated Hospitals, suspected of having various types of renal masses, irrespective of age and sex of the patient.
A detailed clinical and radiological examination was performed in each case along the following lines.
1. CLINICAL EXAMINATION
This included :—
Name
Age
Sex
Address
Occupation
Chief Complaints : Nature, Site, Mode of Onset, Duration of Complaints
Any Significant Past / Present History
General Physical Examination
Systemic Examination
Local Examination
Laboratory Investigation
a) Blood for Hb, TLC, DLC, BT, CT
b) Blood Urea
c) Serum Creatinine
d) Serum Cholesterol
e) Blood Sugar
f) Serum Electrolytes
g) Urine for R/E
h) Urine for Culture
Clinical Impression : A provisional diagnosis was made clinically, keeping in mind various other possibilities, before the patient was subject to various radiological and imaging procedures.
2. RADIOLOGICAL & IMAGING INVESTIGATION
Ultrasonography (USG) : Ultrasound examination was done using 3.5 Mhz and 5 Mhz linear and sector probe on the following real time grey scale scanners.
i. Siemens Sonoline SL2
ii. G.E.R.T. 3200 Advantage-IIx
Preparation : Patient was asked to report fasting with full urinary bladder.
Method : The right kidney was scanned in the supine position though the liver longitudinal views in the prone position was assessed where necessary.
The left kidney was scanned in the left side-up lateral position with the patient leaning slightly forward (coronal view). The spleen was used as an acoustic window. Longitudinal views were taken in the prone position, wherever necessary.
Alternate Position and Techniques : included —
* Erect or prone views in patients with high liver or small spleen.
* Suspended maximal inspiration views for visualisation of upper pole.
* Intercostal views.
* Visualisation of left kidney using fluid filled stomach as an acoustic window.
* Films were taken on attached multiformat camera.
Helical Computed Tomography : Helical CT scanning was performed using G.E. Hispeed CT Scanner (General Electric).
Preparation : Patient was asked to report fasting.
Contrast Media : Urograffin 76%.
Method : Patients were given 1 ampoule (20 ml) of urograffin orally 2-3 hrs before the start of the actual procedure to pacify the bowel and produce contrast. The actual intravenous dosage was given as per the age and weight of the patient.
Scanning Technique : Preliminary unenhanced scans were obtained to localise the kidney, obtain attenuation values where necessary and to optimise the collimation used for the study. After this step was completed and informed consent taken, contrast medium was injected rapidly as a bolus (at the rate of 2-3 ml/sec) into the median anticubital vein using a 20 gauze scalp vein.
A scan delay of 100 seconds was used from the time of onset of injection of CM to the initiation of helical scanning to allow for the homogenous enhancement of renal cortex and medulla.
A collimation of 5 mm was used at a pitch ratio of 1:1. Scan parameters were 220 ml at 120 KVP. The helical exposure duration was 20-30 seconds i.e., during a single breathhold. Helical sections were reconstructed retrospectively whenever necessary.
Films were obtained on attached multiformat laser camera.
Radiological Diagnosis was established.
Operative & Histopathological Diagnosis was noted in all the cases where either surgery was performed or biopsy taken and patients were followed-up.
Radiological diagnosis was compared with clinical impression and operative & histopathological findings.

OBSERVATIONS
The present study was undertaken with the aim to characterize the image morphology, define the extent and nature of renal lesions on spiral CT examination and to correlate the imaging findings with the per operative and histopathological findings.
Renal masses can be classified as —
Benign :
Adenoma Multilocular cystic nephroma
Angiomyolipoma Lipoma
Oncocytoma Fibroma
Hemangioma Leiomyoma
Lymphangioma Papilloma
Dermoid
Malignant :
Parenchymal Renal cell carcinoma
Wilm's tumour
Sarcoma
Fibrosarcoma
Liposarcoma
Leiomyosarcoma
Osteogenio sarcoma
Lymphoma
Metastatic disease
Urothelial Transitional cell carcinoma
Squamous cell carcinoma
Adenocarcinoma
In most of the cases, final diagnosis was confirmed on FnAB or by post-operative biopsy. In rest of the cases, final diagnosis was made on classical imaging features based on spiral CT findings.
The study comprised of 44 suspected cases of renal mass. These were evaluated mainly by spiral CT and where associated cystic element was visualised on CT, ultrasound examination was also done. Plain X-ray-KUB was done in those cases where exuberant calcification or soft tissue mass density was noticed on CT examination.
For the sake of accuracy and close comparative analysis and better understanding of correlation between the clinical, radiological (CT imaging), operative and histopathological findings, the patients were grouped as under :-
Group Type of Lesion
I Renal Cell Carcinoma
II Wilm's Tumour
III Angiomyolipoma
IV Miscellaneous :
Metastatic Disease of Kidney
Oncocytoma
Transitional Cell Carcinoma
Nephroblastomatosis
Multilocular Cystic Nephroma
V Inflammatory Masses
VI Complex Cystic Mass
Out of 44 suspected cases under study, 37 cases were of neoplastic origin while 7 cases turned out to be benign on CT examination. Twenty-five out of 37 cases belonged to renal cell carcinoma, 4 cases were diagnosed as having Wilm's tumour, 3 cases were labelled as angiomyolipoma. One case each was having metastatic disease of kidney, oncocytoma, multilocular cystic nephroma, transitional cell carcinoma and nephroblastomatosis with Wilm's tumour.
Among 7 cases which after spiral CT turned out to be benign on typical CT features, two cases were of perinephric abscess and two of pyonephrosis, while one case each was having polycystic disease of kidney, bilateral renal calculi with emphysematous pyelonephritis and ureteritis, and third having xanthogranulomatous pyelonephritis. A single benign lesion of adult polycystic kidney disease was grouped in complex cystic masses. All the cases were diagnosed either on FNAB or post-operative biopsy where surgery was taken up.
Table 1 : Type of lesion (n = 44).
Lesion Group No. of %age
Lesion Cases
Neoplastic RCC 25 56.8
Wilm's Tumour 4 9.0
AML 3 6.8
Metastatic Disease 1 2.27
Oncocytoma 1 2.27
Transitional Cell 1 2.27
Carcinoma
Nephroblastomatosis 1 2.27
Multilocular Cystic 1 2.27
Nephroma
Inflammatory Pyonephrosis 2 4.5
Masses Perinephric Abscess 2 4.5
B/L Renal Calculi with 1 2.27
Emphysematous
Pyelonephritis &
Ureteritis
Xanthogranulomatous 1 2.27
Pyelonephritis
Complex Cystic Polycystic Disease 1 2.27
Disease of Kidney
The largest group in our study comprised of renal cell carcinoma constituting 25 cases followed by Wilm's tumour (n = 4) and AML (n = 3).
Renal Cell Carcinoma
Majority of the patients of RCC in our study presented in late stage of their disease with chief complaints of large palpable lumbar mass, flank pain and hematuria.
Most of the patients of RCC were in their fourth and fifth decade with a mean age of 51 years and a range of 21-75 years and male to female ratio of 14:11. Eight cases were between the age group of 40-50 years while 4 cases each were in the age group of 20-30 years and 50-60 years. The age distribution of various neoplastic cases under study is depicted in the table below.
Table 2 : Age distribution (in years).
Type Age Distribution (in years) Mean
of Lesion 0-10 11-20 21-30 31-40 41-50 51-60 61-70 71-80 Age
RCC — — 4 2 8 4 4 3 51
Wilm's 4 — — — — — — — 5
Tumour
AML — — 1 — — — 1 1 54
Metastatic — — — 1 — — — — 35
Oncocytoma — — — — 1 — — — 45
TCC — — — — — — 1 — 68
NB with — — 1 — — — — — 25
WT
MCN — — — 1 — — — — 44

Sex Distribution
Out of 44 cases studied, the largest group belonged to RCC. Among these, 14 patients were male while 11 were females establishing an overall male predominance in RCC group.
Male predominance was also seen in other neoplastic groups as given in the table below.
Table 3 : Sex distribution.
Type of Lesion No. of Cases Total
Male Female
RCC 14 11 25
WT 4 — 4
AML 1 2 3
Metastatic Kidney — 1 1
Disease
Oncocytoma 1 — 1
TCC 1 — 1
NB with WT 1 — 1
MCN — 1 1
Clinical Manifestations in RCC
The common presentation of patients with RCC in our study was flank pain and heaviness followed by flank mass, hematuria, lymphadenopathy, weight loss, anorexia, malaise, anemia and fever. Other signs and symptoms of uremia and paraneoplastic syndrome like hypertension were also noted in a few cases.
Table 4 : Clinical manifestations in RCC.
Signs & Symptoms No. of Cases %age
Flank Pain/Flank Heaviness 18 72
Flank Mass 14 56
Hematuria 12 48
Lymphadenopathy 11 44
Anorexia / Malaise 8 32
Weight Loss 8 32
Anemia 6 24
Fever 2 8
Hypertension 2 8
Nausea / Vomiting 2 8
Raised B.U.N. 1 4
Incidental Detection 1 4
Flank pain and heaviness was the most common symptom noted among the patients with RCC being seen in 18 cases (72%). Flank mass was the next most common symptom seen in 14 cases (56%), while hematuria was seen in 12 cases (48%). Lymphadenopathy was noted in 11 cases (44%). Anorexia, malaise and weight loss was noted in 8 cases (32%) each. Anemia was observed in 6 patients (24%), while fever, nausea, vomiting and hypertension was seen in 2 patients (8%) each. Raised blood, urea, nitrogen was seen in 1 case (4%) only.
In our study, the typical triad of symptoms of flank pain, flank mass and hematuria was seen in 6 patients. Incidental detection of renal mass was seen in only 1 case, which was suspected as focal renal mass less than 1.5 cm on USG performed for some other abdominal complaint. The patient was then subjected to spiral CT examination for the detection and characterization of the small lesion.
All the patients of RCC had unilateral renal mass. Out of 25 cases, 14 were seen involving the left kidney whereas 11 were involving the right kidney. All the portions of the kidney were equally involved, however, lower pole involvement was seen in slightly more number of cases.
Most of the lesions were larger than 4 cm in size at the time of presentation (22/25) (88%) with the range of 1.5 cm to 13 cm as depicted in Table 5.
Table 5 : As per size and side of lesion (RCC).
Less than 4 cm 4 cm - 8 cm More than 8 cm
Right Left Right Left Right Left
2 1 3 8 6 5
Spiral CT Findings in RCC
Spiral CT findings in RCC cases vary and depend upon its size, vascularity and the extent of necrosis or cystic changes within the tumour as well as spread of the tumour.
On unenhanced CT scan the appearance may be hypodense, hyperdense or isodense as compared with the normal uniform nephrogram of the renal parenchyma (AV +30 to +40 HU). On contrast enhanced CT scan most of the RCC tumours enhance, but to a lesser degree than the normal renal parenchymal (AV +130 to +170 HU) contrast enhancement.
In our study, most of the lesions of RCC were irregular, lobulated masses exhibiting variegated appearance which was caused by tumour necrosis and/or old or fresh haemorrhage. The tumour was thus heterogenous in appearance and heterogenicity was caused by presence of many small to large irregular area of hypodensity within the iso- to hyperdense stroma of the tumour.
Some foci of hyperdensity (AV ³ 50 HU) suggestive of fresh-haemorrhage were also seen in 4 cases. Calcification in the form of amorphous sheet-like or peripheral curvilinear plaque-like specks were also noted in 4 cases (16%). Two cases also showed presence of fat (AV -5 to -2 HU). CECT showed irregular and inhomogenous contrast enhancement of the tumour mass, accenuating the heterogenicity of the tumour. However, the contrast enhancement was less than the normal renal parenchymal contrast uptake. Irregular parenchymal interface between the normal compressed renal parenchyma and the tumour margin as well as the pseudocapsule formation was also clearly seen after intravenous contrast injection.
Out of 25 cases of RCC, two suspected cases of small (£ 3.5 cm) renal cell carcinoma in our study were largely well defined solid looking sharply marginated homogenous lesions on spiral CT which showed minimal contrast enhancement of the tumour on CECT. The diagnosis was confirmed histopathologically after post-operative biopsy.
One suspected case out of 2 cases of cystic renal cell carcinoma in our study was a 54 year old male who exhibited a well defined large 12 cm cystic mass with homogenous appearance, smooth contour and thin peripheral margin. However, the base of the cystic mass showed a irregular localised thickening of the posterior part of the wall with few septae which were seen projecting into the lumen of the cystic mass. The wall and the septae showed partial contrast enhancement after intravenous contrast administration.
On NCCT, the density of the cystic mass varied between +7 to +20 HU in different scan of the series. In addition the cystic mass had an irregular and poorly defined origin within the kidney as nearly whole of the kidney was transformed to cystic mass. The mass turned out to be an adenocarcinoma on histopathological examination after surgery.
Another case of cystic renal cell carcinoma was seen in a 24 year old male patient. Spiral CT examination showed a large 11 cm mass with rounded, lobulated, irregular contour. The mass exhibited irregular, mural and septal calcification with numerous thick irregular septae and uniform with nodular thickening of the wall showing minimal contrast enhancement. CT scan of the cystic mass revealed an attenuation value ranging from +10 to +20 HU.
Spiral CT findings in renal cell carcinoma and other renal masses are shown in Table 6.
Spiral CT Staging of RCC
Depending upon the spiral CT appearance of RCC and its extension into the venous system, adjoining organs and distant metastasis, Robson classification was followed as per the table below.
Table 7 : Spiral CT staging of RCC.
Robson Stage Tumour Extent No. of Cases
Stage I Tumour confined within 7
renal capsule
Stage II Tumour invasion of perinephric 5
fat, but within Gerota fascia
Stage IIIA Tumour involvement of renal 6
vein and/or renal vein & IVC
Stage IIIB Tumour involvement of regional 6
lymph nodes
Stage IIIC Tumour involvement of both 11
lymphnodes and venous system
Stage IVA Direct tumour involvement of 2
adjacent organs outside
Gerota fascia
Stage IVB Distant metastasis including 2
retroperitoneal lymph nodes
Dynamic contrast enhanced spiral CT imaging is the most sensitive modality for tumour staging of the kidney.
The tumour was seen confined within the renal capsule in 7 patients (28%). Breach of the renal capsule with tumour extension into the Gerota fascia was seen in 5 patients (20%) as an irregular thickening of the Gerota fascia which is most abundant in the posterior and lateral aspect of the kidney while medially invasion of the renal sinus and hilar fat was also noted in 3 cases.
Regional lymphadenopathy including renal hilar lymph node enlargement was seen in 6 cases (24%). Renal vein involvement by tumour thrombus was seen in 6 cases (24%). Left side RV involvement was more clearly seen than the right side RV involvement because of the longer course of left RV and the development of collateral vessels. Tumour thrombus in the inferior vena cava was seen in 2 cases (8%), though it is more commonly seen with right sided tumour.
Distant metastasis constituting Stage IV spread was seen in 4 patients (16%) in the form of involvement of liver, lung, ipsilateral psoas muscle and retroperitoneal lymph nodes. One patient had distant metastasis in the form of mediastinal lymph node involvement. Overall, abdominal spiral CT scanning has an accuracy of 90% in abdominal staging of renal cell carcinoma.
Wilm's Tumour
All the 4 cases of Wilm's tumour under study in our series were male, 3 out of 4 cases were less than 4 years while 1 case was a 10 years old male child. The main presenting features were palpable abdominal lump, flank pain and hematuria. Fever was also seen in 2 cases.
Two of the four cases involved the left kidney and appeared as large spherical masses arising from the lower pole and the middle portion of the left kidney. The masses were largely heterogenous in appearance with one of the case showing multiple small and one large 5 × 3.5 cm hypodense cavitating area having attenuation value ranging from +22 to +28 HU suggestive of tumour necrosis. Both the masses exhibited a pseudo capsule which showed partial enhancement of the margins after intravenous contrast injection. Overall contrast enhancement of the tumour and the thick wall around the multiple cavitating lesions was less than that of compressed normal renal parenchyma. One of the case showed tumour thrombus in left renal vein and the inferior vena cava alongwith regional lymph node involvement constituting Grade IV spread.
Rest of the two cases involved the right kidney with one case showing a large 13.5 × 9.6 cm lobulated exophytically growing renal mass, crossing the midline, mainly solid looking with a few linear cystic areas (AV +28 to +30 HU) arising from the upper pole of right kidney and causing encasement of right RV with displacement of IVC. Contrast enhanced CT scan exhibited a fairly homogenous mass with a few cystic areas and a well defined pseudo capsule showing enhancement (AV +88 HU) which was less than that of normal compressed renal parenchyma. A spiral CT staging of Grade III spread was noted with the tumour.
The 4th case showed a large 10 cm heterogenous mass arising from the upper pole of right kidney with involvement of the perinephric fascia and displacement of right RV. The mass was graded as Stage II Wilm's tumour. All of the cases were confirmed histopathologically after percutaneous needle biopsy of the lesion.
Transitional Cell Carcinoma
The patient of transitional cell carcinoma under study was a 68 year old male automobile mechanic who presented with complaints of pain abdomen and intermittent hematuria. Ultrasound of KUB region revealed a mixed echogenicity mass in the left renal pelvis which was dilated with evidence of selective upper pole caliectasis. The mass caused expansion of the echogenic renal sinus with internal echoes. Extension of the mass distally into the upper ureter was also noticed.
On non-contrast CT the soft tissue mass (AV +30 to +32 HU) was seen located centrally in the left renal pelvis causing obliteration of renal sinus fat with dilatation of water density renal pelvis. The mass (approx. 4.0 cm) was slightly less dense than normal renal parenchyma (AV +38 to +40 HU), but the attenuation value (+15 to +18 HU) was greater than that of urine. After intravenous contrast injection there was mild enhancement of the soft tissue mass (AV +60 to +65 HU) which was less than the briskly enhancing normal renal parenchyma. On delayed images, the mass was seen extending into the ureteropelvic junction causing its narrowing. Cranially some centrifugal expansion of the mass within the renal sinus and the invasion of renal parenchyma was also noticed. The diagnosis was confirmed after surgery as papillary type of transitional cell carcinoma.
Angiomyolipoma
Two out of three cases of angiomyolipoma under study in our series were both females of 25 years and 71 years of age, respectively. One patient presented with complaint of heaviness in left flank with dysuria. While in other, the lesion was diagnosed incidentally on routine USG performed for non-specific complaints.
On enhanced CT scan, the lesion appeared as a large 12 cm well defined heterogenous, expanding mass arising from the upper pole and middle portion of the left kidney containing multiple small areas of low attenuation (-8 to 0 HU) suggestive of fat density, lying between the isodense to slightly hyperdense stroma of the tumour. The tumour showed minimal inhomogenous contrast enhancement after intravenous contrast injection. No breach of the renal capsule was seen. A tentative diagnosis of renal angiomyolipoma was made which was confirmed after CT guided FnAB.
Another patient of renal angiomyolipoma was a 71 year old female who presented with non-specific complaints of generalised weakness, anorexia and malaise. Routine USG was performed and showed a small 2.5 × 3.0 cm hyperechoic area in the upper pole of left kidney. Patient was then subjected to spiral CT examination. Unenhanced CT scan showed a well-defined upper pole low attenuation area (-15 to -10 HU) suggestive of fat density surrounded by irregular rim of isodense to slightly hyperdense area (AV +40 to +45 HU). The lesion showed minimal contrast enhancement varying from (+10 to +50 HU) in delayed CT films except at the periphery, where enhancement was similar to that of normal renal parenchyma. A radiological diagnosis of renal angiomyolipoma was made which was confirmed after percutaneous needle biopsy of the tumour.
A single case of bilateral angiomyolipoma in our study was a male 67 years of age. The patient presented with complaints of pain with heaviness in right flank and intermittent hematuria. No other clinical stigmata suggestive of tuberous sclerosis was detected on physical examination. Routine USG revealed a well defined diffusely hyperechoic mass with posterior shadowing measuring 14×6 cm arising from the lower pole of right kidney. The mass was more echogenic than central renal sinus complex. No dilatation of pelvicalyceal system was seen and outline of right kidney was preserved. Simultaneous US examination of left kidney showed a well defined round highly echogenic lesion in the lower pole measuring 3.0×2.4 cm.
Unenhanced CT showed a well defined heterogenous hypodense mass with attenuation value of +10 HU in the right kidney and a small round very low attenuating area (-30 to -60 HU) in the lower pole of left kidney. No significant contrast enhancement was seen in both lesion on CECT. Whereas, the invasion of the perinephric fat was noticed on right side, no such extension was seen on the left side. No regional lymphadenopathy or evidence of haemorrhage was seen in either lesion.
Multilocular Cystic Nephroma
The only patient of MCN under study in our series was a 44 year female who presented with complaints of pain in the left hypochondrium. Routine USG of the abdomen showed a large 6 × 8.5 cm lobulated cystic mass arising from the lower pole of left kidney with multiple small (cystic) hypoechoic areas separated by echogenic septae with poorly defined cortical margins.
The patient was then subjected to spiral CT examination. On contrast enhanced CT scan, the lesion appeared as well marginated largely hypodense mass with trabeculations and septae. Some internal calcification and mild to moderate enhancement of the capsule and the septae within the mass was also seen. The final diagnosis was made after post-operative histopathology as multilocular cystic nephroma.
Nephroblastomatosis with Wilm's Tumour
The patient of nephroblastomatosis with Wilm's tumour under study in our series was a 25 year old male who presented with complaints of heaviness in both flanks and hematuria. USG revealed multiple small hypoechoic to isoechoic areas (£ 3 cm) involving both the kidneys and situated in the periphery of renal cortex. One large lesion (approx. 7.8 cm) in the right kidney revealed a mixed echogenicity area with heterogenous solid structures in it. No appreciable displacement or distortion of pelvicalyceal system was seen in either kidney.
On unenhanced CT scan both kidneys showed multiple well defined small (< 3.5 cm) hypo to isodense areas surrounded by normal renal cortex in the periphery of both kidneys especially on posterior and lateral surfaces. One lesion in right kidney was a large hypodense area (6 cm) which demonstrated inhomogenicity. After the intravenous contrast administration, the small foci were seen as homogenous hypodense areas in between the briskly enhancing normal renal parenchyma in the periphery of both the kidneys. The larger lesion in the right kidney showed heterogenous appearance with few area of low attenuation (AV +35 to +40 HU) suggesting tumour necrosis and exhibited sharp demarcation from normal residual renal parenchyma. Some foci of calcification were also noticed. A radiological diagnosis of bilateral multifocal N.B. with induction of Wilm's tumour in right kidney was made which was confirmed by percutaneous needle biopsy of the larger lesion.
Oncocytoma
A single patient of oncocytoma under study in our series was a 45 years male who presented with complaints of pain abdomen and heaviness in right flank. Routine USG showed a large 7 × 8 cm, well defined mass which was fairly homogenous in echotexture, with a central echogenic stellate area having few specks of calcification arising from the mid portion of right kidney.
Unenhanced CT scan showed a well defined lobulated, homogenous (AV +32 to +35 HU) mass with a central hypodense area (AV +12 HU) with some calcification in it. After intravenous contrast administration the mass showed homogenous contrast enhancement with non enhancing central hypodense radiating scar like area (AV +18 HU). Based on this typical feature, radiological diagnosis of oncocytoma was made which was confirmed after percutaneous needle biopsy.
Metastatic Disease of Kidney
A single case of metastatic disease of the kidney under study in our series was a 35 year old female patient with primary choriocarcinoma. She was subjected to spiral CT examination for the metastatic workup. The patient was otherwise asymptomatic. Retrospective USG examination revealed multiple small hypo to isoechoic areas in the left kidney.
Unenhanced CT scan showed multiple small 3-4 cm well defined hypo to isodense lesions in left kidney which showed homogenous contrast enhancement although it was less than the normal renal parenchymal enhancement.
Table 8 : Basis of final diagnosis of patient with renal neoplasm (n = 44).
Neoplasm Surgery & Percutaneous Classical Total
Histopathology Biopsy Imaging Cases
Finding Studied
RCC 14 10 1 25
Wilm's 2 1 1 4
Tumour
AML — 2 1 3
Metastasis — — — 1
Oncocytoma — 1 — 1
MCN 1 — — 1
TCC 1 — — 1
NB with WT — 1 — 1
Inflammatory — 2 4 6
Lesion
Polycystic — — 1 1
Disease
Of the 25 cases of RCC, surgery was done in only 14 cases, others were not operated because of either advanced disease/old age or other additional reasons like infiltration of adjacent organs and in few cases patients were unwilling to undergo surgery and further treatment.
Inflammatory Masses
Perinephric Abscess : Two cases of perinephric abscess under study in this series were young adult males who presented with complaint of high grade fever with rigor and chills, flank pain and difficulty in walking.
Contrast enhanced CT scan in one of the case showed a fairly normal sized left kidney which was pushed anteriorly and slight laterally by the thickened gerota fascia and the stranding in the posterior pararenal space. Multiple irregular hypodense areas (AV +28 to +32 HU) were seen on the posterior aspect of lower pole of left kidney along with few areas of predominently hypodense collection in posterior pararenal area with involvement of psoas muscle and the ipsilateral iliac fossa. The diagnosis was established by percutaneous aspiration of the abscess. The patient improved after drainage of pus and administration of culture sensitive antibiotic.
Pyonephrosis
Two cases of pyonephrosis in our series presented with complaints of dull flank pain, flank mass and malaise. In one of the cases, USG revealed an enlarged right kidney, with large homogenous hypoechoic mass with internal echoes in it. The normal renal cortex was reduced to a thin irregular rim around the mass. A large hyperechoic shadow with strong posterior shadowing suggestive of calculus (AV +560 HU) was also seen in right renal pelvis.
Contrast enhanced spiral CT scan demonstrated an enlarged right kidney, virtually replaced by a large homogenous hypodense mass (AV +56 to +60 HU) which was partially divided by thick enhancing walls and septae (AV +80 to +84 HU) with a thin irregular rind of renal parenchyma remaining and showing normal contrast enhancement. A large calculus was seen impacted in the right renal pelvis. No excretion of contrast material was seen on the affected side. USG guided percutaneous diagnostic aspiration was done along with placement of nephrostomy tube.
Emphysematous Pyelonephritis and Ureteritis with Bilateral Renal Calculi
A single case of emphysematous pyelonephritis and ureteritis with bilateral renal calculi in our study was a young 30 years non-diabetic male patient who presented with non-specific complaints of body aches with pain left flank, high grade fever and oliguria.
Contrast enhanced CT scan showed gas (AV -512 HU) in the parenchyma of left kidney and in the collecting system which had extended into the anterior subcapscular space and distally into the upper ureter. The left kidney was enlarged and exhibited multiple small hypodense areas (AV +32 to +38 HU) suggestive of enhancing necrotic abscesses surrounded by thick enhancing walls and septae. Left kidney also showed calcular shadows in the left renal pelvis and a small calculus was also seen in the right renal medulla in upper cuts. A radiological diagnosis of emphysematous pyelonephritis and ureteritis with renal calculi was given and accepted.
Xanthogranulomatous Pyelonephritis
One single case of xanthogranulomatous pyelonephritis in our study was a 60 year old male Gujjar patient who presented with complaint of pain in right flank with heaviness.
USG revealed a hyperechoic mass having strong echoes involving right kidney with only a thin rim of normal cortex remaining. Multiple calculi were seen impacted in the right renal pelvis.
Spiral CT revealed an enlarged and non-functioning right kidney showing a large staghorn calculus encased within non-dilated renal pelvis. The kidney was replaced by a large fluid density (AV +30 HU) pear-shaped mass showing rim enhancement.
Associated thickening of the perinephric space as well as ascitis was also seen. A radiological diagnosis of xanthogranulomatous pyelonephritis was offered which was confirmed histopathologically after nephrectomy.
Adult Polycystic Kidney Disease
One case of polycystic kidney disease under study was a 40 year old male who presented with complaints of painless hematuria and had history of hypertension. USG revealed bilateral enlarged kidneys studied with multiple small and large sized cystic area which were separated by echogenic septae. Few of the cysts were seen communicating with each other and showed internal echoes. The patient was further subjected to spiral CT scan.
Unenhanced CT scan showed bilateral subcapsular high density (AV +50 to +60 HU) cysts among many fluid density cysts (+15 to +20 HU). After intravenous contrast enhancement, high density cysts were also hypodense relative to enhanced residual renal parenchyma. Associated cysts were also seen in liver and spleen.
A tentative diagnosis of adult polycystic disease was offered and was accepted. The patient was managed conservatively.

DISCUSSION
With the explosion of technology in diagnostic radiology and awareness among physician and surgeons, more and more asymptomatic renal lesions are being detected at their early stage thereby increasing cure rate and patient survival.
Many more small RCC are now detected incidentally during the abdominal US and CT done for reasons other than the suspected renal pathology.
In the present study, 44 suspected renal neoplasm were investigated radiologically using spiral CT and in some of them US was also performed. Nearly all the patients were symptomatic for a renal mass lesion and in only 2 cases the renal mass was detected incidentally on USG performed for some non-related complaints.
The stress was on determining organ of origin, image morphology and characterisation of various neoplasms including the extent of the lesion and its staging.
The study included 44 patients ranged from 3 - 75 years of age (mean 46.5 years). The patients with RCC (n = 25) ranged from 21 to 75 years with mean age of 51 years. Among the 3 patients of AML (mean age 48 years) one was diagnosed as having AML at a slightly younger age of 25 years. Four patients of Wilm's tumour presented in the age group of 3 to 10 years (mean age 5 years). There was only one case of nephroblastomatosis with Wilm's tumour of 25 years age.
Another solitary male case of oncocytoma presented at the age of 45 years. The only case of transititional cell carcinoma was a male who presented in late sixties (68 years of age).
A single case each of MCN, a 44 year old male and a young female of 35 years of age which was a known case of primary choriocarcinoma referred from radiotherapy department for metastatic staging, showed solitary secondary deposit in the left kidney.
Renal Cell Carcinoma
RCC was the largest group among renal neoplasms in our series. Twenty-five among 44 cases evaluated in our study were confirmed to be of RCC. The age of presentation ranged between 21 years to 75 years with mean age of 51 years.
Maximum number of patients (49%, 12 out of 25) were seen in the age group of 41-60 years. This is in concordance with reports in the literature (Levine, 1995; Zegel et al., 1997; Belldegrun & Dekernjon, 1998). Wherein, it is described that maximum number of patients of RCC are seen in the 5th and 6th decades. The incidence of RCC is twice as common in men as among women (Levine, 1995; Zegel et al., 1997; Belldegrun & Dekernjon, 1998). In the present study male to female ratio was 1.27:1.
The usual presenting features of RCC are hematuria (38%), pain (41%), palpable mass (24%), weight loss (36%) and fever (18%) (Levine, 1995; Zegel et al., 1997; Belldegrun & Dekernjon, 1998).
Other presenting features may be recent development of varicocele or signs and symptoms of distant metastasis like lymphadenopathy, cutaneous nodules and paraneoplastic syndrome like hypertension (Levine, 1995; Zegel et al., 1997; Belldegrun & Dekernjon, 1998).
The classic triad of hematuria, pain and flank-mass is seen in 10% at presentation (Zegel et al., 1997; Belldegrun & Dekernjon, 1998). In our study, 48% (12/25) patients had hematuria, 72% (18/25) complained of pain abdomen and a palpable mass was seen in 56% (14/25). Anorexia, malaise and weight loss was seen in 32% each (8/25) and lymphadenopathy in 44% (11/25). Anemia was seen in 24% (6/25). Fever, nausea, vomiting and hypertension was seen in 8% (2/25) each. Raised blood urea and nitrogen was seen in 4% (1/25).
The classic triad of hematuria, pain and flank-mass was present in 6 patients (24%, 6/25) in our study.
In our study, hematuria was seen in slightly more number of cases as compared with reports in the literature probably because of larger size of lesion and late presentation of these cases.
One patient (4%, 1/25) was detected to have RCC incidentally on US, which was suspected as focal renal mass less than 1.5 cm on ultrasonography done for some other unrelated reason.
In the studies reported prior to 1980, RCC was detected as an incidental finding or a silent tumour in 4-23% of cases.
In last 22 years this percentage has dramatically grown. The incidence of incidentally detected RCC was 48.15% in a study done by Porena et al. (1992).
In our study, the diagnosis was confirmed histopathologically in 24 patients by post-operative biopsy in 14 patients and with FnAC in 10 cases. In one case the diagnosis was made on classical imaging features.
Out of 25 patients with RCC, all were having unilateral lesion. The right kidney was involved in 44% (11/25) while the left kidney was involved in 56% (14/25) with ratio of R:L of 1:1.4.
In literature, incidence of involvement of right and left kidney is 1:1 (McClenan &amp; Deyoe, 1994; Levine, 1995; Zegel et al., 1997; Belldegrun & Dekernjon, 1998). RCC of various dimensions were noted in our study with a range of 1.5 cm to more than 13 cm. Majority of the lesions were large (more than 4 cm) and only 12% (3/25) were less than 4 cm at the time of presentation. Among these, in one case the lesion was 1.5 cm in size. In a study done by Charboneau & Hattery (1983), 26% masses were less than 4 cm. 35% were 4-8 cm and 26% were greater than 8 cm. In our study, 44% (11 out of 25 cases) were larger than 8 cm.
Coleman et al. (1980) also reported that 4% lesion were less than 4 cm, 35% were 5 to 7 cm and 23% were more than 8 cm in size.
There were significantly more patients of larger size lesion in our study probably because of late presentation of patients.
One incidentally detected mass was 1.5 cm in size. Porena et al. (1992) also described that incidentally detected RCC are of smaller size.
In our study, all the portions of the kidney were equally involved. However, the lower pole involvement was seen in a little more number of patients. In a study done by Charboneau & Hattery (1983), 34% of the masses were seen in the upper pole, 37% in the lower pole and 24% in the middle portion of the kidney. In one out of 2 cases of cystic RCC almost whole of the kidney was replaced by the mass. Sonographically only 2 of the 25 cases (8%) of RCC were primarily cystic but also exhibited solid components harbouring the malignancy. In addition these had thick irregular walls and septations. According to the Bosniak classification, these two cystic lesions in our study were Type IV cysts suggestive of clearly malignant cysts. As in these two cases, the lesions appeared mainly cystic in nature, therefore the US, being a better modality to differentiate cystic and solid lesion, was performed to rule out benign cystic lesion. CT evaluation of renal mass begins with unenhanced scans. This helps in knowing the presence of any calcification which often remains undetected on plain X-ray abdomen or US and also helps in determining whether the tumour enhances and to what degree it enhances after the injection of contrast material.
The precontrast CT appearance of RCC vary considerably depending upon the gross pathological features. In our study, 21 out of 25 tumours (84%) appeared solid with necrotic areas. Two of the 25 cases (8%) appeared homogenously solid and two others (8%) were primarily cystic. Twenty-three out of 25 (92%) cases of RCC were having non-homogenous appearance on CECT. This inhomogenity has been described by Levine & Huntrakoon (1989) as due to changes in the internal composition of tumour secondary to haemorrhage and necrosis.
Calcification was noted in 4 out of 25 cases (16%) on spiral CT. The calcification was in the form of amorphous sheet like or peripheral curvilinear plaques or specks.
In a study by Weymen et al. (1980), RCC is the most common adult tumour as well as the most frequently calcified lesion with an incidence of 8-18%. Previously, the pattern of calcification and its location within the mass was a reliable indicator of non-benignity of the lesion.
In a study of 111 calcified masses by Daniels et al. (1972) using Gold Standard of radiographic modalities, 87% of the non-peripheral lesion were found malignant. The peripherally calcified renal masses posed difficulty in evaluation of these lesions by the standard radiographic techniques. Weymen et al. (1980) described that cross-sectional spiral CT imaging for location of the calcification was much more accurate. They also noted that the presence of soft tissue mass extending beyond the calcification whether curvilinear or punctuate was the most reliable and specific indicator of the malignancy. Nine out of 10 RCC cases exhibited these features in their series.
In the present study, among 3 out of 4 cases of calcified RCC there was extension of soft tissue mass beyond the margin of calcification.
In another study by Levine (1995) the incidence of tumour calcification in RCC cases was 31% in the form of amorphous internal calcification or curvilinear calcification which may be central or peripheral. Zagoria & Wolfman (1990) stated that calcification may be found in as many as 31% of cases. In our study, fat was not seen in any RCC case. Strotzer & Lehner (1993) also found in their series that RCC rarely contain fat. Levine (1995) also found that RCC rarely contain small amount of fat because of osseous metaplasia of non-epithelial stromal part of the tumour.
Hyperdensity (AV +50 +60 HU) suggestive of haemorrhage was seen in 4 (16%) cases. On contrast enhanced spiral CT, the images were acquired in the nephrographic phase i.e. between 90 to 100 sec. after the start of intravenous injection. The vascular (solid) part of the RCC enhanced markedly but the cystic/necrotic areas enhanced slightly or not at all resulting in non-homogenous appearance. This was noted in 23 out of 25 patients (92%) in our series. This features which differentiates RCC from homogenous enhancement of benign renal neoplasm was noticed by Levine & Huntrakoon (1989).
The contrast enhancement of the renal neoplasm was less than that of normal renal parenchyma, accentuating the difference between the tumour and the surrounding normal kidney. This finding was also noticed by Pamilo & Suramo (1983), Fein et al. (1987) and Bosniak (1991).
There were 2 (8%) cases of cystic renal cell carcinoma in our series. These tumour appeared as well defined large hypodense cystic masses with internal septations and nodularity. There was evidence of calcification in one of the case. After the injection of contrast material there was enhancement of wall septation and the nodular areas. Pariently & Pradel (1985) also described the same features of malignancy in cystic renal cell carcinoma. In the present study, CT revealed inferior vena cava invasion in 2 (8%) cases. CT showed invasion of tumour thrombus in right renal vein in 4 (16%) cases and left renal vein in 2 (8%) cases. The tumour thrombus invasion of left renal vein and the IVC was seen in both the cases of left sided RCC on CT as seen on US. However, the CT was unable to show tumour thrombus in right renal vein in one case of right sided RCC with right RV involvement which was confirmed after surgery.
This difficulty has been observed by workers like Levine et al. (1979), who stated that CT is reliable in detecting gross tumour invasion in left renal vein but is less useful for detection of right renal vein thrombus presumably because of shorter and oblique course of right renal vein.
Thus the sensitivity and specificity of CT for detecting IVC thrombus is 100% and whereas it is 80-95% respectively for detecting renal vein thrombosis.
Madayog & Ambose (1979) stated that venacaval involvement is three times more common with right sided tumour than with left sided RCC possibly because of shorter length of right renal vein. In their study on inferior venacavography in staging of RCC they concluded that 9% RCC have venacaval involvement. In their series venacaval invasion was seen in 13% of 85 right sided RCC and 4.5% of 89 left sided RCC.
In our study, the incidence of IVC invasion with left side RCC was 14% whereas CT failed to demonstrate IVC invasion in one case of right side RCC.
Our findings did not correlate with observations made by Madayog & Ambose (1979) possibly because of lesser number of cases studied as well as late presentation of cases. Overall the incidence of IVC involvement in our series was 8% (2/25).
CT detected regional (renal hilar) lymph node involvement in 24% (6/25) and retroperitoneal lymph node involvement in 8% (2/25).
Spiral CT has the advantage over US in the detection of retroperitoneal and renal hilar lymph node involvement as the central intestinal gas often obscures central retroperitoneum on USG.
This advantage of CT has also been observed by other workers like Levine et al. (1979) and Weymen et al. (1980). According to Levine (1979), abdominal lymph node less than 1 cm can be identified on CT and are considered normal. Nodes in the range of 1-2 cm especially if numerous should be regarded with suspicion, but are considered indeterminate by size and criterion alone. It is the lymph node exceeding 2 cm in diameter which is almost always enlarged by the tumour. In our present study of RCC cases, interpretation of cross sectional imaging with spiral CT includes evaluation of tumour size and shape, parenchymal interphase, perinephric extension, type of enhancement and regional lymph node and major vascular involvement and local and distant metastatic spread.
Dynamic CT has proved to be the most sensitive, specific and accurate modality for staging of RCC. Problems in staging of RCC occurs when the tumour is extremely large or very small (< 1 cm).
The staging of RCC was done on the basis of Robson classification. In the present study, 7 (28%) tumour were confined within renal capsule i.e. Stage I. Five (20%) tumours showed invasion of perinephric fat, but within gerota fascia suggesting Stage II. Six (24%) patients showed tumour involvement of venous system including RV and/or IVC representing Stage IIIa. Six (24%) cases showed involvement of regional lymph nodes (Stage IIIb). Overall 11 (44%) patients constituted Stage IIIc.
There were only 4 (16%) cases which presented with adjacent organ involvement and distant metastasis in the form of involvement of liver, lung, ipsilateral psoas muscle and retroperitoneal lymph nodes (Stage IV). One patient had distant metastasis in the form of mediastinal lymph node enlargement possibly indicating lymphatic spread. As per literature in one study by McClenan & Deyoe (1994) more than one-third of patients presented in Stage I and another one-third in Stage IV. Patient with Stage III disease comprised approximately 25% and another 10% constituted Stage II. Whereas in our study more number of patients (44%, 11/25) were seen constituting Stage III disease possibly due to late presentation of cases as the state is mostly rural and hilly area.
Wilm's Tumour
Wilm's tumour is the most common renal tumour of childhood (Beckwith & Kiviat, 1990). Peak incidence is between 30 months and 3 years of age with a range of 1 to 10 years, occasional cases are also encountered in adult life. Bilateral Wilm's tumour is seen in 5% of patients and are present at younger age than unilateral Wilm's tumour and is commonly associated with nephroblastomatosis. Histologically the tumour is composed of epithelial and connective tissue elements arising from embryonic nephrogenic tissue.
The most common symptom is enlarging abdominal mass (Beckwith &amp; Kiviat, 1990; Beckwith, 1993). Less frequently the presenting symptoms include abdominal pain, fever and microscopic or gross hematuria (Beckwith & Kiviat, 1990; Beckwith, 1993). The lung is the most frequent site of metastatic disease, liver is less frequently involved.
In our study, all the 4 patients were male. Beckwith & Kiviat (1990) has also stated that Wilm's tumour is more common in male child, though females are also involved. In our series, 3 out of 4 cases were less than 4 years of age. This is in accordance with reports in literature, while a single case in the present study presented at a little higher spectrum of age incidence.
All the cases were unilateral heterogenous masses with large cystic/necrotic areas having a pseudocapsule which showed enhancement though less than the residual renal parenchyma which was displaced. Reiman & Siegel (1986) also described that CT is able to detect necrosis and pseudocapsule correctly in 90% and 60% of cases respectively.
None of the cases demonstrated calcification in unilateral Wilm's tumour in our series. In literature, the incidence of tumour calcification is reported in about 13% (Fishman, 1983). A large lobulated and exophytically growing mass crossing the midline and causing encasement of right renal vein showed the typical appearance of Wilm's tumour described in literature (Fishman, 1983).
Non-functioning of the affected kidney with tumour thrombus in the RV and the IVC were noted in one case (25%). In literature, absence or poor function because of either venous tumour extension, compression of collecting system or extensive tumour infiltration is seen in 10% of cases. High incidence in our series is due to less number of cases studied.
Reiman & Siegel (1986) has also stated that tumour thrombus involvement of RV and the IVC is better shown by CT particularly after rapid dynamic bolus injection of contrast material. In his series, CT alone was able to correctly diagnose the extent of tumour involvement in 77% of patients contrary to 23% of accuracy shown by ultrasound scanning. Perinephric extension, lymphadenopathy, metastatic organ involvement and presence of contralateral tumour was significantly better shown by CT.
Transitional Cell Carcinoma
Primary tumours of renal pelvis and collecting system are relatively uncommon constituting 5-10% of all renal neoplasm (Latham & Kay, 1974). TCC accounts for 90% of all cancers of renal pelvis while squamous cell carcinoma and adenocarcinoma comprise 9% and 1%, respectively. Papillary type is the most common (85%) variety among transitional cell carcinoma (Latham & Kay, 1974) and usually present as exophytic polypoid lesions that are attached by a stalk to the mucosa. They behave in a low grade malignant fashion and are slow to infiltrate, late to metastasize and follow a relatively benign course.
In our study, the only case of TCC was of papillary variety proven on histopathology. As per literature, the average age of the patient with TCC at the time of presentation is 65 years and approximately 70% of patients are older than 60 years at the time of diagnosis with a range of 32-88 years and male to female ratio of 4:1 (Latham & Kay, 1974).
The patient of TCC in our study was a 68 year old male who presented with complaints of intermittent hematuria and pain abdomen. Rubenstein & Waltz (1978) stated that most common symptom in patient with TCC is hematuria being seen in 75% of cases in his study.
Other symptoms may be flank pain (25%), weight loss (10%) etc. Incidental detection is very uncommon (< 5%). The classical findings of TCC on CT scan are described by Leder & Dunnick (1990). According to the literature, TCC can be detected as a mass of density greater than that of urine, but less than that of renal parenchyma with minimal enhancement, central location and centrifugal expansion without distortion of the shape of kidney. The centrifugal expansion of the TCC can result in CT findings of compression, displacement, disappearance of renal sinus fat, trapping of contrast material in the narrowed and compressed caleceal spaces or obstructed and slightly dilated calices or thining of surrounding renal parenchyma with focal enlargement of the kidney with uneven centrifugal invasion of renal parenchyma or any combination of these findings may occur on CT. The proximal ureter may be dilated and/or thickened by invasion of the tumour.
In our patient the mass was central in location (left renal pelvis) with density greater than that of urine and less than that of renal parenchyma and showing minimal enhancement after contrast administration.
The mass showed irregular centrifugal expansion within the renal sinus fat with invasion of renal parenchyma cranially and upper ureter caudally. The mass did not cause distortion of the shape of kidney and no evidence of any calcification was seen.
Dinsmore et al. (1988) has also stated that prevalence of calcification in TCC ranges from less than 1% to 17%. No evidence of regional lymphadenopathy, renal vein invasion or distant metastasis was seen. Geiger et al. (1986) also described that invasion of TCC into renal vein is an uncommon late finding.
Angiomyolipoma
Angiomyolipoma is a benign renal tumour comprising of variable amount of smooth muscle, mature adipose tissue and blood vessels in a jumbled architecture. Seventy-five percent of these tumour occurs as solitary renal mass without evidence of tuberous sclerosis and are usually found incidentally in middle aged female. About 20% of angiomyolipoma patient will have tuberous sclerosis and in these cases tumours are usually multiple and often bilateral. The remaining 5% will have multiple bilateral angiomyolipoma but without the evidence of tuberous sclerosis.
In our study, a total of 3 patients, 2 females and one male were studied. Of these one male patient had bilateral angiomyolipoma but none of these patients had obvious stigmata of tuberous sclerosis like cutaneous nodules or periventricular calcification etc. The female to male ratio was 2:1 in our series whereas the female to male ratio ranges from 2.3:1 to 25:2 in literature (Hajdu & Foote, 1969).
Benington & Beckwith (1975) described that patients of symptomatic angiomyolipoma have flank pain (75%), flank mass (41%), hematuria (30%) and hypotension. In patients with tuberous sclerosis about 2% develop renal insufficiency later on. In our study, 2 (66%) out of 3 patients were symptomatic of angiomyolipoma while one case (33%) was discovered incidentally.
The size of the angiomyolipoma ranges from several centimetre to more than 20 cm with a mean diameter of 9.4 cm in a study conducted by (Hajdu & Foote, 1969). In our study size ranged from 2.5 cm to 12 cm with mean diameter of 7.25 cm.
On US, 2 (50%) out of 4 lesions were diffusely hyperechoic and another 2 (50%) lesions were heterogenous in echotexture. Different types of US appearance of angiomyolipoma has been described in literature. Of the diffusely hyperechoic lesion, none of the lesion showed a peripheral hypoechoic halo or intratumoral cyst which are considered characteristic of RCC. This finding which differentiates renal cell carcinoma from angiomyolipoma has been described by Yamashita & Ueno (1993) and Siegel et al. (1996). Presence of posterior shadowing in diffusely hyperechoic lesion of AML unlike RCC is also described in literature (Siegel et al., 1996) and was also observed in our study.
On unenhanced CT scan the fat was well demonstrated in all the 4 lesions, 2 lesions were well defined, solid and heterogenous in attenuation with mild inhomogenous contrast enhancement. This classical CT appearance is characteristic of AML and has been described in literature (Sherman et al., 1981; Yuh & Cohan, 1997). Remaining 2 lesions of AML were well defined, small (2.5 cm and 3.4 cm), homogenously low attenuation areas on CT which did not show any appreciable contrast enhancement on CECT.
Raghavendra et al. (1983) also stated that when the lesion is smaller than 2 cm determination of attenuation value may be unreliable because of partial volume averaging. In our study none of the lesion suffered from this problem as the smallest lesion was 2.5 cm. Hyperdensity suggestive of haemorrhage within the lesion which increases the CT. Number of lesion as described in literature (Hartman et al., 1991) was also not seen in our study. None of the lesion demonstrated perinephric extension or invasion of the renal vein IVC or regional lymph node or distant metastasis.
Multilocular Cystic Nephroma (MCN)
This is an uncommon renal mass consisting of multiple noncommunicating cystic areas confined within a capsule. It is described by various names in the literature as renal multilocular cyst, cystic nephroblastoma, benign cystic adenoma, cystic adenoma and cystic Wilm's tumour.
There is also confusion regarding the true nature of this entity (Banner & Pollack, 1981) and various theories for pathogenesis of the lesion have been proposed including dysplasia hamartoma and neoplasia (Carlson et al., 1978). However, the current prevailing opinion is that it is more likely a benign neoplasm of the kidney.
A single case studied in our series was a 44 years old female. Madewell et al. (1983) had stated that this rare tumour has an age spectrum ranging from 3 months to 71 years with two peaks — one in first 2 years of life and other in adulthood usually from 5th to 8th decade. Mean age for early group is 17 months and for later is 60 years (Epstein et al., 1978).
Epstein et al. (1978) and Madewell et al. (1983) stated that in toddlers sex ratio is equal, whereas in adults it is more common among females. MCN usually presents as an asymptomatic mass in children but pain hematuria and occasionally hypertension may be present (Madewell et al., 1983). In adults, however, the common presenting features are abdominal pain, hematuria, non-painful abdominal mass, urinary tract infection and hypertension in order of decreasing frequency. Our patient presented with pain in the left hypochondrium.
The size of the mass in our patient was 6×8.5 cm. In a study conducted by Madewell et al. (1983) the mean size of the mass was 9.8×11.7 cm in patients who were older than four years of age.
In the present case, routine US examination revealed a well defined mass with multiple cysts separated by echogenic septae. This type of US picture has been described by Carlson et al. (1978), wherein it is described that MCN can present on US as solid tumour or as a mass with multiple cysts depending upon the size of the cysts. If the cysts are too small, US and CT both show a predominantly solid tumour making preoperative diagnosis difficult. In our case the mass was cystic as is common observed.
On NCCT the tumour appeared as well defined cystic mass with septae and trabeculation. ON CECT mild to moderate enhancement of capsule and septae is seen. According to Pariently et al. (1981), this type of appearance is suggestive of MCN but not specific to warrant cancellation of surgery. However, they suggested that CT may provide such valuable information which may help limit the surgery.
Our preoperative radiological diagnosis was cystic RCC which later on turned out to be multilocular cystic nephroma on post-operative histopathology. Christ (1967) has also suggested that these lesions although are benign, malignant transformation can occur so surgical intervention is a must once diagnosed. Other workers like Beckwith & Kiviat (1990) stated that even when typical findings are present radiologically suggesting a diagnosis of MCN, the presence of co-existing malignancy cannot be excluded entirely. Malignancy like RCC or Wilm's tumour occurs in association with MCN or develops from pre-existing multilocular cysts making surgery essential in all these cases.
Powell & Shakman (1951) has laid down precise histological criteria for the identification of MCN. These are, the mass must be unilateral, solitary, multilocular without communication with renal pelvis or with one another and lined by epithelium. No renal elements should be present within the cyst. Remaining kidney tissue should be normal except for pressure atrophy. Our single case satisfied all these histopathological criteria of MCN.
Nephroblastomatosis with Wilm's Tumour (NB with WT)
Nephroblastoma, an embryonal renal tumour is presumed to originate from abnormalities of renal histiogensis. Abnormal foci composed of persistent embryonal cells called nephrogenic rests (NR) are considered precursor lesions of this tumour. They may occur in unifocal, multifocal or diffuse pattern of distribution and are associated with 99% of multicenteric or bilateral Wilm's tumour (WT) (Beckwith & Kiviat, 1990). Nephroblastomatosis is defined as presence of multiple or diffuse NR. NR are associated with unilateral WT in 41% with synchronous bilateral WT in 99% and with metachronous bilateral WT in 94% of cases. Therefore the presence of nephroblastomatosis in a patient with unilateral WT indicated a higher risk for WT formation in the remaining kidney (Beckwith, 1993).
NR show two types of distribution — the diffiuse type and the multifocal type. In multifocal type, NR typically resembles the normal renal cortex with regard to their echogenicity and density on US and CT respectively. After contrast medium administration they become markedly hypodense on CT due to poor uptake of contrast in comparison with brightly enhancing renal cortex. But the most characteristic feature of NR is their overall homogenicity on pre- as well as post-contrast examination which is seen with all the latest imaging modalities i.e. CT and MRI.
In comparison, WT is generally heterogenous and the heterogenicity increases after contrast administration. Histopathologically homogenicity of NR is because of avascular stroma whereas inhomogenicity of WT is due to areas of necrosis or haemorrhage within the variably vascularised tumour (Brantley & Simon, 1976).
A single case of bilateral multifocal nephroblastomatosis with Wilm's tumour in right kidney was a male of 25 years age who exhibited the classical radiological features of multiple small foci of NB in both the kidneys and a large (7.8 cm) Wilm's tumour in right kidney on both US and pre- and post-contrast spiral CT imaging which was confirmed after percutaneous biopsy of the larger lesion.
Oncocytoma
A relatively uncommon benign tumour of kidney oncocytoma is usually seen in middle and old age and constitutes 3-6% of all renal tumours. Male to female ratio is 1.7:1 (Liber & Tobera, 1981). A 45 year old male was a single case of oncocytoma who exhibited classical features of this entity on CT and US. The patient presented with pain abdomen and heaviness right flank although most of these lesions are detected incidentally (Liber & Tobera, 1981). Renal oncocytoma are usually single tumour. Although they may also be multiple, they are rarely bilateral (Quinn & Hartman, 1984). In our study, the lesion was solitary present in the right kidney.
Levine & Huntrakoon (1983) has described that CT and US are effective technique for evaluating and characterising the internal architecture of renal mass and they also reveal gross morphological features which differentiates most oncocytoma from renal cell carcinoma. Quinn & Hartman (1984) described that presence of central scar in an otherwise homogenous solid tumour on CT and US appears to be quite characteristic feature of oncocytoma. On CT it is recognised as well defined stellate area of low density, and a small discrete branching anechoic area within an otherwise homogenous mass on sonographic examination.
In our single case, the mass was well defined and homogenous in echotexture with central echogenic stellate scar and central calcification. Wasserman & Ewing (1983) and Quinn & Hartman (1984) has also described that calcification is not commonly seen in oncocytoma.
One CT the mass was well defined lobulated homogenous with central hypodense radiating stellate scar and calcification showing homogenous marked enhancement on CECT. No evidence of metastatic spread is seen. Quinn & Hartman (1984) has also suggested that if mass appears homogenous but no central scar is present, angiography should be performed. Oncocytoma is suggested on angiography if a spoke wheel configuration and homogenous blush are seen. But in patient with equivocal findings a preoperative investigation with FnA for cytology may be indicated.
Metastasis
The findings of secondary renal neoplastic involvement especially from epithelial tumours is a frequent occurrence at autopsy ranging from 7% to 20%. (Abrams et al., 1950). In descending order of frequency, the most common site of origin of primary malignancies are lung, breast, stomach, pancreas, colon, kidney and oesophagus. The route of spread is generally hematogenous resulting in preferential cortical involvement.
In our study, a single case of metastatic disease of kidney was a 35 year old female who was a known case of primary choriocarcinoma. She was subjected to spiral CT examination for metastatic workup. She was otherwise asymptomatic. Choyke & White (1987) has also described that most of the renal metastasis are asymptomatic. On CT scan there were multiple small, less than 3 cm lesions which were hypodense and non-enhancing on CECT.
Honda & Coffman (1992) has also described the same features of metastasis as hypoechoic on US and hypodense with minimal or no contrast enhancement after contrast administration on CT.
Choyke & White (1987) also stated that a new renal lesion in a patient with advanced non-curable cancer is more likely metastatic than primary and that biopsy in this condition is unlikely to be of any help.
No other organ invasion or involvement of renal vein or IVC was seen in our patient. Our single patient thus conformed to the observations made in the previous studies in literature that renal metastatic lesion are classically multiple and bilateral, though unilateral also and small in size, well defined showing only mild enhancement on CECT.
Inflammatory Masses
Six renal masses in our present study, out of total 43 cases investigated as per selection criteria laid down, turned out to be of benign nature as per typical spiral CT findings and FnAC reports.
Two cases among these six benign masses were that of perinephric abscess. These were young adult males who at the onset of presentation had high grade fever, rigors, chills and flank pain with palpable left kidney.
On contrast enhanced spiral CT, findings in one of the case showed a predominantly hypodense collection (AV +28 to +32 HU) in posterior pararenal areas with displacement of left kidney anterolaterally by the thickened gerota fascia and stranding in the posterior pararenal space. Gold & McClenan (1983) has described that a perinephric abscess may ultimately result if the infection extends through the renal capsule.
Hypodense collection (AV +32 HU) in the posterior pararenal area with involvement of ipsilateral psoas muscle and iliac fossa was also seen. Levine (1989) has also described that focal thickening of adjacent renal fascia and stranding in the adjacent perinephric fat are common CT findings. Soulen (1989) has also described that renal abscesses usually have AV of about +30 HU since their contents do not enhance and this distinguishes them from fluid density renal cyst.
Percutaneous needle aspiration confirmed thick purulent material confirming spiral CT diagnosis based on typical findings. The patient showed response to the antibiotics.
Another two cases in our series among six cases turned out to be of pyonephrosis, who presented with dull flank pain and palpable mass on the affected side.
In one of the case, US examination performed before the CT scan showed enlarged right kidney with large hypoechoic mass involving the right kidney with internal echoes in it. Normal renal cortex seen posteromedially was reduced in thickness and irregular especially against the mass. There was strong acoustic with posterior shadowing from a calculus in the renal pelvis.
Contrast enhanced spiral CT demonstrated enlarged right kidney which was replaced by homogenous hypodense mass measuring 6.5×6.1 cm and AV +28 HU with thick septae in-between (AV +80 to +84 HU) surrounded by thin irregular enhancing rim of renal parenchyma. A large hyperdense calculus was also seen in right renal pelvis. The hypodense areas within the mass were dilated calyces with thick pus in the calyceal system. These typical findings have been described by Levine (1989).
Ultrasound guided percutaneous aspiration showed pus in the dilated calyces and nephrostomy tube was also put for drainage. The patient also responded to the antibiotics and his clinical symptoms subsided. These CT findings are consistent with literature by Levine (1989) and Soulen (1989) that in obstructed cases pyonephrosis develops secondary to calcular hydronephrosis.
Emphysematous Pyelonephritis
There was a single case of emphysematous pyelonephritis among the six benign cases of infective origin.
This case of emphysematous pyelonephritis and ureteritis with bilateral renal calculi presented with generalised body aches and pain in left flank with high grade fever and oliguria and palpable renal mass.
Spiral CT showed gas shadows within renal parenchyma having AV of -512 HU involving left kidney especially in the collecting system which has extended into the subcapsular space and also distally into the upper ureter on left side. Gold & McClenan (1983) has described that CT is the most sensitive method for establishing the diagnosis in these cases and can distinguish among gas in the collecting system, parenchymal gas and gas in the perinephric tissues. He has also emphasized that gas in the renal pelvis and calyces alone does not qualify as emphysematous pyelonephritis. The findings in our case was typical of the emphysematous pyelonephritis.
Left kidney was enlarged and showed multiple small hypodense areas in it which showed some contrast uptake peripherally suggestive of necrotic abscesses with enhancing septae and walls.
A hyperdense shadow suggestive of calculus (AV +1012 HU) was also seen in left renal pelvic region. A small hyperdense shadow (calculus) was also seen in the right renal cortex in the superior, upper pole cuts.
As per literature, emphysematous pyelonephritis is a severe gas forming infection of renal parenchyma, usually a complication of acute pyelonephritis and is typically seen in diabetic patient. Our patient was a young adult non-diabetic male.
In mild cases, percutaneous nephrostomy tube drainage is treatment of choice. Whereas, in case of severe infective and nonfunctioning unilateral kidney, nephrectomy is advisable.
Xanthogranulomatous Pyelonephritis (XGP)
A 60-year old male Gujjar patient was a single case of XGP in our study who presented with complaints of pain right flank with heaviness. Ultrasound examination revealed a hyperechoic mass with strong acoustics involving the right kidney with only a thin irregular rim of renal cortex remaining on the periphery. Multiple calculi were also seen impacted in the renal pelvis.
Spiral CT revealed an enlarged non-functioning right kidney with a large hyperdense Staghorn calculus impacted in the undilated renal pelvis. The kidney was replaced by one large and multiple small fluid density cysts (AV +8 to +28 HU). The largest pear-shaped cyst measured 10.8×6.0 cm in size and had attenuation value of +28 HU. The cysts showed irregular and patchy rim enhancement. There were also multiple areas of low AV (-20 HU) and of high AV (+512 HU) suggestive of fat and calculus, respectively in the right renal area.
Goldman (1984) has described the usual CT features of XGP as a globally enlarged or less often an atrophic, non-functioning kidney showing replacement lipomatosis of the walls of the fluid filled cortices representing either dilated calyx or focal area of parenchymal destruction with pus and/or debris. Perinephric extension of the inflammatory process is common (14%) and was also seen in our case as thickening and stranding of the perinephric space. Associated calculus was also seen in our case as described in the literature.
The patient was subjected to nephrectomy as the affected kidney was non-functional and diagnosis was confirmed histopathologically.
Adult Polycystic Kidney Disease (ADPKD)
One case of polycystic kidney disease in our series was a 40-year old hypertensive male who presented with hematuria. USG revealed bilateral enlarged kidneys which were studied with multiple small and large sized cystic areas separated by echogenic septae. A few of the cyst were seen communicating with each other and had internal echoes.
Unenhanced CT showed bilateral subcapsular and centrally located high density (AV +50 to +60 HU) cysts interspersed among many fluid density cyst (AV +15 to +20 HU) and the normal compressed renal parenchyma. The high density cysts were homogenously hyperdense with smooth contour and clear interface with each other and the renal parenchyma. After I/V contrast administration the cysts were hypodense relative to the briskly enhancing residual normal renal parenchyma with no change in the attenuation value. No evidence of cyst calcification or wall enhancement was seen.
Levine & Grantham (1985) has also described the typical CT findings in a case of ADPKD. In his series the percentage of high density, occasional high density and no high density cyst is 42.9%, 25.7% and 31.4%, respectively. According to him, these high density cysts were usually subcapsular in location and more frequently seen in enlarged kidney. Pathologically high density cyst were found to contain haemorrhagic fluid which may occur as a natural history of the disease or because of trauma to the enlarged kidney. Renal carcinomas occur rarely in ADPKD and may occasionally be hyperdense. However, high density can usually be distinguished from renal cell carcinoma on CT by their smooth contour, sharp interface with renal parenchyma and lack of contrast enhancement.
Based on the above findings alongwith associated clinical history of hypertension we were able to make a diagnosis of adult polycystic kidney disease. The patient responded with the conservative management.

SUMMARY AND CONCLUSION
The present study was undertaken to evaluate the role of spiral CT in the detection and characterisation of renal mass with special emphasis on the organ of origin, nature and extent of the lesion and to coorelate the imaging findings with the operative and histopathological findings. In some of the cases, US examination was also performed, both retrospectively as well as prospectively.
A total of 44 patients (28 males and 16 females) were studied. These included renal cell carcinoma (n - 25), Wilm's tumour (n = 4), angiomyolipoma (n = 3), nephroblastomatosis with Wilm's tumour (n = 1), oncocytoma (n = 1), transitional cell carcinoma (n = 1), renal metastasis (n = 1), multilocular cystic nephroma (n = 1), masses of inflammatory origin (n = 6) and adult polycystic kidney disease (n = 1).
The age group of patients ranged from 3 to 75 years with mean age of 46.5 years. Among the neoplastic masses, the presenting complaints were flank pain (n = 26), flank mass (n = 18), hematuria (n = 17), lymphadenopathy (n = 11), anorexia and malaise (n = 9), weight loss (n = 8), anemia (n = 6), fever (n = 4), hypertension (n = 2), nausea and vomiting (n = 4) and raised blood urea nitrogen (n = 1).
All the suspected patients were evaluated on spiral CT. The imaging findings on spiral CT were correlated with both operative and histopathological findings in 20 patients, while in 15 cases the diagnosis was confirmed by percutaneous biopsy. In 8 patients the final diagnosis was made on classical imaging features.
Renal Cell Carcinoma
Most of the RCC cases presented in the 5th and 6th decade (49%) with a mean age of 54 years and male to female ratio of 2 : 1.
The most common presenting feature of RCC was flank pain (72%), followed by flank mass (56%), hematuria (48%), LAP, anorexia, malaise, weight loss, anemia, fever, hypertension and raised blood urea nitrogen in descending order of frequency. In one patient, the diagnosis was made incidentally. All the patients were having unilateral tumour, out of which right kidney was involved in 44% (11/25), while left kidney's involvement was seen in 56% (14/25).
Most of the lesion (88%) were larger than 4 cm. More number of larger size lesion and higher incidence of hematuria in the patients studied signifies late presentation of cases with advanced disease because of the remote and hilly areas, as well as low literacy rate.
On CT most of the lesions of RCC were heterogenous in attenuation with inhomogenous contrast enhancement which was less than that of normal renal parenchyma. Calcification was observed in 16%, necrosis in 92% and haemorrhage in 16% of the lesion of RCC. There were 2 (8%) lesions of RCC which appeared primarily cystic but also exhibited solid element, thick irregular walls and internal septations with contrast enhancement of these structures. Most common site of distant metastasis from RCC in our study was liver, followed by lung, ipsilateral psoas muscle and mediastinal lymph nodes.
The tumour staging of RCC was fairly correctly done by CT, however most of the difficulties occurred in differentiating Stage I lesion from Stage II and Stage IIIa. US had clear advantage over the CT in the detection of solid/cystic nature of lesion especially in the complex masses and in the evaluation of renal vein invasion by the lesion whereas the CT was more sensitive in the evaluation of size of lesion as well as calcification, haemorrhage and necrosis within the lesion.
Perinephric extension, adjacent organ involvement and regional lymphadenopathy was also clearly shown by CT. In the detection of venous system invasion both US and CT were equally sensitive, however, the US had an edge over the CT in the detection of cranial extent of tumour thrombus.
Wilm's Tumour
A total of 4 cases of Wilm's tumour studied in our series were all male. Three patients were less than 4 years of age while the fourth case was 10 years old.
All the lesions were unilateral with mean age of presentation of 5 years. Main presenting symptoms were palpable abdominal lump, hematuria, flank pain and fever.
On CT, the most common appearance of Wilm's tumour was a large spherical heterogenous mass with multiple cystic/necrotic areas having a pseudocapsule of compressed renal parenchyma which showed enhancement, though less than the normal residual renal parenchyma. Metastasis to liver with regional lymphnode involvement alongwith non-functioning of the affected kidney, because of tumour thrombus in renal vein and IVC constituting Stage IV was seen in one case, whereas displacement of ipsilateral RV and the IVC was seen in another case because of a large lobulated heterogenous mass crossing the midline. No evidence of calcification was seen in any case.
Transitional Cell Carcinoma
A 68 year old male was a single case of transitional cell carcinoma in our series who presented with complaints of pain abdomen and intermittent hematuria.
On CT a central soft tissue mass having attenuation value of +30 +32 HU was seen located in the renal pelvis causing obliteration of renal sinus fat. Typically, the mass was having AV less than that of renal parenchyma and more than that of urine and showed mild contrast enhancement with centrifugal expansion and invasion of renal parenchyma. The imaging findings were characteristic of TCC and the diagnosis was confirmed histopathologically.
Angiomyolipoma
Three cases of this benign entity (2 females and 1 male) were studied in our series. Of these, one male patient of 67 years of age was having bilateral angiomyolipomas, but without the clinical stigmata of tuberous sclerosis.
The mean age at presentation was 54.3 years with female to male ratio of 2:1 in our series.
Two patients presented with pain and hematuria in right flank and with intermittent hematuria in one case while the third case was diagnosed incidentally on USG performed for non-related complaint.
On CT the most common appearance of angiomyolipoma was a well defined heterogenous expanding mass lesion showing areas of internal fat density attenuation lying in the iso- to slightly hyperdense stroma of the tumour. The lesion showed minimal inhomogenous contrast enhancement.
Multilocular Cystic Nephroma
The only patient of MCN was a 44 year old female who presented with complaint of pain in the left hypochondrium CT showed a largely hypodense but well marginated mass with multiple cysts separated by trabeculation and septae. Some internal calcification and mild to moderate enhancement of the mass was also seen. Although the imaging findings were classical as described in literature the final diagnosis could be made only by histopathology.
Nephroblastomatosis with Wilm's Tumour
A 25 year old male who presented with complaints of heaviness in both Flanks and hematuria was the single case of NB with WT in our series. On CT the patient had bilateral multiple lesion. all the lesions except the one were small, cortical in location and homogenously hypodense, showing no contrast enhancement. The single large lesion of Wilm's tumour was heterogenous in appearance. The final diagnosis was established by the percutaneous biopsy of larger lesion.
Oncocytoma
The only patient of oncocytoma in our study was a 45 year male who presented with pain abdomen and heaviness in right flank. CT showed a well defined lobulated homogenous mass with a central hypodense area with some calcification in it. The mass showed homogenous contrast uptake with the central non-enhancing radiating scar like area. A preoperative diagnosis of oncocytoma was made, based on the presence of central stellate scar which although characteristic, is seen in only 50% cases was confirmed by histopathology.
Metastatic Kidney Disease
A single case of metastatic kidney disease was evaluated in our series. The patient was a known case of chariocarcinoma. Multiple, small, well-defined hypo- to isodense lesions were detected in the renal parenchyma which showed homogenous contrast enhancement though it was than the normal renal parenchyma.

CONCLUSION
It is possible to characterisse most of the renal neoplasms on CT giving emphasis on the image morphology.
It is recommended that US should be the initial screening modality in a patient suspected of having a renal neoplasm and CT should be used for further characterisation of the lesion as well as the staging of the malignant lesion.

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