Renal cell carcinoma in a giant renal cyst

A case of renal carcinoma in a giant solitary renal cyst is reported. Ultrasonography and CT showed an apparently benign left renal cyst except for wall irregularity. Cytological examination and fat analysis of the cyst content were negative but the fluid was haemorrhagic in nature. Frozen section of the cyst wall revealed malignancy and further histopathologic examination indicated renal cell carcinoma.