A case of an incidental solid renal cell mass with multiple foci of intra-tumoral fat, which was shown to be a clear cell renal cell carcinoma (RCC) at nephrectomy.
A 53-year-old gentleman presented to clinic following an incidental finding of a right renal mass on abdominal ultrasound. Further investigation with CT revealed an exophytic irregular soft tissue mass emerging from the upper pole of the right kidney measuring 7.2cm in maximum diameter. No lymphadenopathy, renal vein involvement or invasion beyond Gerota's fascia was evident. Several foci of macroscopic fat were present within the tumour, which is considered a classic characteristic of an angiomyolipoma. Other imaging features raised suspicion for a renal cell carcinoma (RCC), including increased vascularity, large size, an irregular border, and focal areas of calcification. The patient proceeded to a laparoscopic radical right nephrectomy. Histopathology revealed the tumour to be a RCC confined within the renal capsule. Immunohistochemistry demonstrated clear-cell sub-type, nucleolar grade 3, with positive staining for vimentin and epithelial membrane antigen. Macroscopically, the tumour was composed of large areas of carcinoma separated by sclerotic fibrosis containing areas of calcification and ossification, with associated scattered nodular areas of fat up to 6mm in diameter. These foci were composed of mature adipocytes and represented fatty metaplasia.