[Metanephric renal adenoma].

Objective: To describe a case of metanephric adenoma, a rare and little known tumor with no potential to malignancy. This tumor type can occasionally coexist with Wilms' tumor, with which it is histogenically related.

Methods/results: A 54-year-old female patient was referred to the Urology Service for a small mass in the left kidney that had been incidentally detected during an ultrasound evaluation. Patient evaluation disclosed a solid, circumscribed, unencapsulated mass of 2.3 cm in its largest segment. It was mainly localized in the medulla of the kidney, although it was extensively in contact with the renal cortex. Histologically, it was comprised of small epithelial cells in a tubular or papillary arrangement, without atypia, mitosis, necrosis or invasion of adjacent renal parenchyma or vascular structures, and with abundant psammoma-like calcifications. The histological findings were characteristic of metanephric adenoma.

Conclusion: Metanephric adenoma is an uncommon, morphologically distinct tumor type, with characteristic histopathological features. Despite its size, it is benign and should be distinguished from renal cell carcinoma or Wilms' tumor.