Urothelial carcinoma mimicking Bosniak IV cystic mass: A case report.

Urothelial carcinoma is the primary malignancy of the urothelium that has varying radiographic features based on the location of the tumor. Differentiating urothelial carcinoma from renal cell carcinoma is critical as interventions and management methods differ. We present a case of urothelial carcinoma within the calyceal diverticula that was initially suspected to represent Bosniak IV cyst due to cystic renal cell carcinoma. A 71-year-old male with a history of gross hematuria and a previously identified Bosniak II renal cyst underwent further imaging, revealing a Bosniak IV cystic mass with enhancing nodules. Subsequent nephrectomy unveiled noninvasive low-grade papillary urothelial carcinoma within a calyceal diverticulum. This case highlights the complexity of diagnosing urothelial carcinoma within the calyceal diverticula, emphasizing the need for a high index of suspicion. The study contributes to understanding the limitations of imaging modalities, especially in cases involving calcification or stone evaluation. The coexistence of urothelial carcinoma and calyceal diverticula is rare but crucial for accurate diagnosis and treatment. Documenting cases like these is vital for recognizing urothelial carcinoma mimics and ensuring appropriate patient management. The study underscores the significance of distinguishing features of calyceal diverticula and advocates for comprehensive imaging approaches in renal cystic lesions.