Cystic renal cell carcinoma. Imaging findings with pathologic correlation.

Twenty-seven cystic renal cell carcinomas (RCC) in 23 patients were analyzed radiologically and histologically. They were classified into 4 histopathologic growth patterns: a) multilocular (n = 15, 9 with macrocystic and 6 with microcystic components); b) unilocular (n = 3); c) cystic necrosis (n = 9); and d) tumors originating in the wall of a simple cyst (n = 0). Macrocystic multilocular RCC showed multiloculated configuration on ultrasound and contrast enhanced CT. Angiography revealed neovascularity peripherally or within the tumor (7/9 tumors). Microcystic multilocular RCC did not fulfill the criterion for a cystic mass on ultrasound: they were irregularly hyperechoic. There was little enhancement on postcontrast CT and only slight neovascularity on angiography. Unilocular RCC showed a cystic mass with an irregular wall or mural nodules on ultrasound and contrast enhanced CT. Necrotic RCC showed various sonographic findings from anechoic to irregular echoic. The appearance on CT varied from cystic with mural nodules to a multiloculated or irregular architecture. Neovascularity was seen in the periphery in 8 of 9 tumors. Clinically, this type seemed to be the most aggressive.