The natural history of simple renal cysts: a preliminary study.

We examined the natural history of simple renal cysts in 59 patients followed periodically with renal ultrasonography. Using the parameters of cyst diameter and number we grouped the patients according to the differing natural history of the cystic lesions. The results indicate that simple cysts tend to progress in number rather than size. Furthermore, 3 patients had independent solid or complex lesions. The only patient explored had an adenocarcinoma of the kidney. Periodic reevaluation of patients with an ultrasonic diagnosis of simple renal cyst warrants serious consideration.