A simple renal cyst invaded by infiltrating urothelial carcinoma mimicking a Bosniak Class IV renal cyst

We report a 79-year-old woman with a left side simple renal cyst invaded by infiltrating urothelial carcinoma mimicking a Bosniak Class IV renal cyst. Computerized tomography has high accuracy for the diagnosis of renal cysts and urothelail carcinoma. But, in this case it was still difficult to distinguish a simple renal cyst with infiltrating urothelial carcinoma invasion from a Bosniak Class IV renal cyst on CT scan. The management of a Bosniak Class IV renal cyst and urothelail carcinoma is totally different. Therefore, we performed a left side nephroureterectomy. This patient will have regular follow-up with cystoscopy every 3 months for the first 2 y, every 6 months for the next 2 y, and then annually thereafter.