Conservative treatment of metanephric adenoma. A case report and review of the literature.

Metanephric adenoma (MA) is a rare kidney tumor, especially in children, with an excellent prognosis and frequent association with polycythemia. We report the case of a 4-year-old girl presenting a MA revealed by polycythemia. Any secondary polycythemia requires checking for a possible kidney tumor even when the erythropoietin level is not elevated. MA is an exclusively epithelial tumor that can be similar to nephroblastoma or papillary renal cell carcinoma; therefore, it requires strict histopathological analysis. There are few radiological characteristics of MA: well circumscribed tumor, slightly enhanced after the injection of an intravenous contrast medium on computed tomography scan or magnetic resonance imaging. Diagnosis can be supported by core-needle kidney biopsy after hemostasis check, following two published cases of associated acquired von Willebrand disease. Chemotherapy can then be avoided and first-line conservative surgical treatment by partial nephrectomy can be considered, as in our patient's case. However, the marginal resection raised the question of frozen sections analysis of the margins. We recommend thorough follow-up visits, combining clinical examination, ultrasonography and, in the case of polycythemia, biological assays.