METANEPHRIC ADENOMA DIAGNOSED PREOPERATIVELY AS RENAL CELL CARCINOMA: A REPORT OF TWO CASES

Metanephric adenoma is an extremely rare benign tumor. We report two cases of metanephric adenoma that were diagnosed preoperatively as renal cell carcinoma (RCC).Case 1 was a right renal tumor found by ultrasonography in a 57-year old woman who presented for a medical examination. Abdominal CT revealed a 26-mm mass that was enhanced weakly in the early phase and enhanced strongly in the late phase, in the right kidney. Based on a clinical diagnosis of RCC (cT1aN0M0), laparoscopic partial nephrectomy was performed. Case 2 was a left renal tumor incidentally found during an annual examination of a 79-year old woman with a past history of breast cancer. Abdominal CT revealed a 24-mm mass that was enhanced heterogeneously in the left kidney. Based on a clinical diagnosis of RCC (cT1aN0M0), laparoscopic radical nephrectomy was performed. The pathological diagnosis of both cases was metanephric adenoma.It is often difficult to distinguish metanephric adenoma from other malignant neoplasms preoperatively. When it is difficult to distinguish between renal cell carcinoma and metanephric adenoma, renal tumor biopsy and minimal surgery is required.