Metanephric adenoma of the kidney

A case of a rare renal tumor showing characteristic histologic features is presented. The patient was a 54 year old female, whose renal tumor was incidentally detected on abdominal ultrasound (US) examination. Ultrasound, computed tomography and angiography findings were consistent with a diagnosis of renal cell carcinoma of the hypovascular type. Left nephrectomy was performed. The tumor, which measured 2.6 x 2.6 x 2.5 cm, was located in the left renal cortex, and had a uniformly whitish-yellow cut surface and well-defined margin. Histologically, the tumor was characterized by its monomorphous growth pattern and was composed of uniformly small cells arranged in a tubular or rosette-like pattern. The tumor cells had scant cytoplasm and the nuclei were small, round and regular. These histologic features resembled the epithelial elements of a metanephric hamartoma in the nephroblastomatosis complex in infants. However, there was no mitosis and cellular atypia was minimal, suggesting benignity. According to these histologic features, the diagnosis of metanephric adenoma was made. Its clinicopathologic features are discussed.