Helen Gao: Since 1986, the Bosniak classification system has been used to stratify the malignant potential of complex renal cysts. To date, long-term oncologic outcomes have been incompletely characterized, particularly for patients undergoing active surveillance. 106 adult patients diagnosed with Bosniak II through IV renal cysts between 2010 and 2024 were included. We reviewed their clinical, demographic, imaging data management strategy, cyst progression, and if surgery was performed final pathology. To quantify surveillance burden, we calculated cumulative radiation exposure in millisieverts and estimated annual imaging cost based on Medicare reimbursement rates.

Primary outcomes included malignancy rate, cancer-specific survival, and operative intervention. 92% of patients were managed with active surveillance. Median follow-up was 4.1 years with a range of two to six years. Nine patients underwent surgical exploration. Intervention rates increased with each Bosniak category, 2.6%, 5.3%, 14%, and 25% for Bosniak II, IIF, III, and IV patients. Eight low-grade renal cell cancers were identified. No patient developed a metastatic lesion. There were no cancer-specific deaths.

Radiation exposure increased with cyst complexity from 11.6 to 25.1 millisieverts per year. Median annual imaging cost also increased with cyst complexity, from $410 for Bosniak II cysts to $800 for Bosniak III and IV cysts. With a median follow-up of four years, the majority of complex Bosniak renal cysts were effectively and safely managed with active surveillance.