Renal cell carcinoma (RCC) is a malignancy of the renal tubular epithelium; with almost 50% of cases being incidentally discovered. RCC comprises about 2-3% of all malignancies and about 85% of all solid renal tumors. 2% of RCC cases are bilateral and 16-25% of cases are multicentric (in the same kidney). The usual age of presentation is 50 to 70 years with a male to female ratio of 2:1. Lesions usually arise in the renal poles (upper more than lower) and they appear as exophytic mass(es) that alter the renal contour. Most lesions are solid and of soft tissue density that is hyperdense, isodense or hypodense to renal tissue, yet may show hemorrhage, necrosis, fatty or cystic changes. It rarely calcifies (less than 10%) but the combination of fat and calcification suggests RCC rather than an angiomyolipoma.

The histopathological types of RCCs are: (1) Clear cell 70-80%, (2) Chromophil cell (papillary) 10-15%, (3) Granular cell 7%, (4) Chromophobe cell 5%, and (5) Spindle cell (sarcomatoid) 1-1.5%. Metastases may affect the lungs, liver, bone, adrenal glands, other kidney and brain. It has some association with von Hippel-Lindau disease and tuberous sclerosis. An RCC is asymptomatic in many cases and presentation with the classic triad of frank hematuria, flank pain and palpable mass appears in <10% of cases ^1,2.

Multiphasic CT is the best imaging tool to depict RCCs. This includes a precontrast phase, arterial phase (15 s), corticomedullary phase (60 s), nephrographic phase (>80 s) and excretory or pyelographic phase (2 to 5 minutes). RCC appears as an enhancing lesion (increase of more than 20 HU cf. precontrast density) being hyperdense to renal parenchyma in both nephrographic and pyelographic phases ^1,2. Seldomly the lesion is hypovascular (usually papillary cell type) which may be mistaken for a cyst on all imaging modalities ¹.

Lesions may infiltrate the renal vein or the calyces (where it may be mistaken for transitional cell carcinoma) and they may infiltrate surrounding muscles, diaphragm, colon as well as the IVC, liver, or right atrium in right sided lesions and pancreas or spleen (in left sided lesions) ^1,2.

Although radical nephrectomy was considered for years the optimal treatment option, the results of numerous studies have demonstrated almost equivalent survival rates for patients who underwent radical nephrectomy vs. partial nephrectomy (or nephron-sparing surgery) for small renal neoplasms. Thus elective partial nephrectomy is now a valid treatment approach ^1,2,4. Partial nephrectomy or ablation (either by cryotherapy, radiofrequency or microwaves) may be considered in lesions of small size and no extrarenal spread ^1,2. There is a limited role of chemotherapy and radiotherapy ¹. Now, partial nephrectomy and radical nephrectomy can be carried out either by open or laparoscopic approaches ².

Vermooten in 1950 was the first to suggest that localized RCC could successfully be excised while leaving a surrounding area of normal renal parenchyma ⁶.

Common imaging findings after surgery are: kidney displacement (posterior more than anterior), perinephric fat stranding, parenchymal defect, non-fat-containing postoperative collection. Fat stranding is seen more with an open than laparoscopic route. Collections are seen more in laparoscopic rather than open route, yet they resolve more rapidly with the open route. Occurrence and resolution of collection are not affected by age, sex, preoperative lesion size or location ³.

Changes like posterior kidney displacement and perinephric fat strands (when seen in imaging) may provide evidence of previous renal surgery. Fatty packing done by the surgeon into the renal cortical defect post partial nephrectomy may be mistaken later for angiomyolipoma, and other hemostatic materials used in operation may show gas bubbles and be mistaken for abscess ⁴.