A progressively enlarging cystic renal mass in a previously healthy 48-year-old woman.

A 48-year-old previously healthy woman was referred for evaluation of a cystic right renal mass. The mass was first noted in 1991 when an abdominal computed tomography (CT) scan revealed a 6 × 6-cm cystic mass with internal septations located in the mid right kidney. CT-guided aspiration was performed and cytologic evaluation of the specimen revealed no evidence of malignancy. Over the next seven years, periodic renal ultrasounds demonstrated enlargement of the mass. A second CTguided cyst aspiration in 1995 again showed no evidence of malignancy on cytologic evaluation. An image from an abdominal CT scan performed in 1998 is shown in the Figure. The scan demonstrates a complex, nonenhancing, 14-cm cystic renal mass with multiple internal septations. The mass displaces the right psoas muscle and right kidney, and it splays the right renal collecting system anteromedially. Based on its appearance, the lesion was categorized as a Bosniak class III cystic renal mass.1 The left kidney and both ureters appeared normal. The patient had been without complaint since 1991 except for some mild abdominal discomfort in the weeks prior to referral.