[Two Cases of Metanephric Adenoma Operated on for Preoperative Diagnosis of Renal Malignancy].

Metanephric adenoma is an extremely rare disease. We describe two cases of metanephric adenoma. Case 1 : A 17-year-old male adolescent developed gross hematuria, and urinalysis revealed positive protein and occult blood. He was referred to our department for further evaluation and likely tumor removal. Contrast-enhanced computed tomography (CT) showed a neoplasm (23 mm) with poor contrast effect during the early as well as the late contrast phase. Case 2 : A 61-year-old woman presented with an incidentally detected tumor in the lower pole of the right kidney ; contrast-enhanced CT revealed a large neoplasm (10 mm) with poor contrast effect during the early as well as late contrast phase. Both patients underwent robot-assisted partial nephrectomy (RAPN) under the preoperative diagnosis of papillary renal cell carcinoma. Metanephric adenoma is histopathologically indistinguishable from papillary renal cell carcinoma preoperatively, and histopathology and immunostaining are neceaasry for accurate diasnosis.