Renal cell carcinoma presenting as a simple renal cyst: A case report.

Cases of renal cell carcinoma (RCC) presenting as a simple cyst are extremely rare. We herein report the case of a patient with RCC diagnosed as a simple renal cyst preoperatively. A 39-year-old female patient presented with abdominal pain for 3 months. Ultrasonography and contrast-enhanced computed tomography revealed a simple cyst in the left kidney. The patient underwent laparoscopic decortication of the renal cyst. Biochemical analysis of the cystic fluid revealed unusually low levels of potassium, sodium, calcium and glucose, and the histological examination of the floor of the cyst indicated malignancy. Laparoscopic nephrectomy was performed 20 days later and the pathological examination confirmed the diagnosis of RCC of the clear cell type. At the 2-year follow-up, the patient remained well and recurrence-free on imaging. The aim of the present study was to emphasize the importance of recognizing that RCC may occur in what appears to be a simple renal cyst based on imaging results. Biochemical analysis of the cystic fluid may help identify the presence of malignancy.