Pathological report and prognostic meaning of Bosniak IV cysts: results from a contemporary cohort

INTRODUCTION: Surgery is the recommended treatment for Bosniak IV renal cysts. We performed a retrospective analysis of Bosniak IV lesions surgically removed to increase evidence on their prognostic meaning. MATERIAL AND METHODS: Patients with a Bosniak IV cyst were considered. A contrast-enhanced computed tomography (CT) scan or magnetic resonance imaging (MRI) detected a solid component with contrast enhancement. In no case a percutaneous biopsy was performed. A radical (9, 21.4%) or partial (33, 78.6%) nephrectomy was performed with laparoscopic (14, 33.3%) or robot-assisted (28, 66.7%) approach. Analysis of the final pathology was performed, and recurrence rate was assessed. RESULTS: 42 patients were included. Median lesion size was 54.7 mm (IQR 20.0–81.2). A solid tumour was detected in 40 patients (95.2%), whereas in 2 cases (4.8%) a benign cyst without neoplastic component was diagnosed. Final pathology revealed a low-grade clear cell renal cell carcinoma (ccRCC) in 16 cases (38.0%), a multilocular cystic renal neoplasm of low malignant potential in 6 cases (14.3%), a low-grade papillary RCC (pRCC) type I in 4 cases (9.5%), a clear cell papillary RCC (ccpRCC) in 10 cases (23.8%) and an oncocytoma in 2 cases (4.8%). A high-grade ccRCC was detected in 2 cases (4.8%), whereas no patients had a pRCC type II. In all cases surgical margins were negative. Median follow-up was 24 months and no recurrence occurred. CONCLUSIONS: Our results increase evidence on the favourable pathology and good prognosis of Bosniak IV renal cysts, supporting the role of surgery as a definitive treatment and suggesting the need for a low-intensity follow-up.