Metanephric adenoma: a rare differential diagnosis of renal tumor in children.

Metanephric adenoma is an extremely rare tumor of the kidney. The clinical and anatomic characteristics are not yet well defined, but it is currently considered to be a benign tumor with a good prognosis, although recently two metastatic cases have been reported. Around 50% of cases are incidental findings, and symptoms include polycythemia, abdominal pain, hematuria and palpable mass. The morphological characteristics are similar to those of Wilms' tumor, suggesting a common embryological precursor. We present here the youngest girl yet to be reported with a diagnosis of metanephric adenoma.