Risk Assessment of Incidentally Detected Complex Renal Cysts in Children: Potential Role for a Modification of the Bosniak Classification

Purpose: Incidentally detected complex renal cysts in children are a rare but worrisome occurrence due to the perceived potential risk of malignancy. We examined the natural history of such cysts in a cohort of children. Materials and Methods: We obtained access to a database containing all radiology reports generated at a single institution from 1996 to 2004. We used key words to limit our search, subsequently reviewing charts and images to confirm the diagnosis of a complex renal cyst and to collect clinical data. Cases were categorized according to a modification of the Bosniak classification, using ultrasound in most patients and computerized tomography or magnetic resonance imaging when available. Results: Complex renal cysts were identified in 39 children. Mean patient age at presentation was 7 years. Mean cyst size was 1.6 cm. A total of 18 cases diagnosed by ultrasound only were observed with serial imaging. Additional contrast enhanced computerized tomography or magnetic resonance imaging was performed in 21 of 39 patients (54%). Surgical resection was performed in 5 patients and pathological evaluation revealed benign cyst in 3 (modified Bosniak class II in 2 patients and class III in 1) and renal cell carcinoma in 2 (III in 1 and IV in 1). All other patients had modified Bosniak class II cysts, which remained essentially unchanged during a mean followup of 26.8 months (range 9 to 70). Conclusions: While not validated in children, our data suggest the modified Bosniak classification appears useful as a guideline to direct the management of complex renal cysts in the pediatric population.