CT and ultrasound features of metanephric adenoma in adults with pathologic correlation

The purpose of this work was to correlate the CT, ultrasound, and pathologic features of metanephric adenoma, a rare benign renal tumor in adults. Retrospective review of medical records (1990-1997) revealed three adult female patients who had both preoperative imaging and nephrectomy with pathologic diagnosis of metanephric adenoma performed at our institution. CT (n = 3) and ultrasound (n = 2) features were reviewed in consensus by two radiologists and correlated with pathologic findings. In all three cases, the metanephric adenoma was of increased attenuation relative to adjacent renal parenchyma on unenhanced CT scans. No septa or calcifications were seen. Ultrasound images showed both tumors to be hyperechoic with enhanced through-transmission. The CT and ultrasound findings correlate with the pathologic features of a high nuclear-to-cytoplasmic ratio and psammomatous calcifications. In the adult population, it is unlikely that metanephric adenoma can be prospectively differentiated from renal cell carcinoma based on imaging features.