[Metanephric adenoma. 11 case reports and detection of collagen spherules in one tumor]

Eleven cases of metanephric adenoma are reported. The tumors were selected out of 6500 tumorous and pseudotumorous lesions of the kidney in our registry. Female to male ratio was 1:1.2. The average age of the patients was 48.3 years, with a range of 13-79 years. The mean size of the tumors was 7.2 cm. The tumors were spherical in shape, whitish to yellowish in colour. Histologically, they were arranged in a mainly tubular pattern with short pseudopapillae. The tumorous cells were deeply eosinophilic to basophilic with predominantly round nuclei. Psammomatous bodies were numerous. Immunohistochemically, they reacted positively with antibodies against cytokeratins, vimentin, and WT1. Ultrastructurally, the cytoplasm contained mitochondria, RER, and ribosomes. A collagenous spherulosis, identical with those in salivary gland and mammary tumors, was revealed in one case. The spherules were located mainly inside tubular structures. Ultrastructurally, they were composed of basement membrane-like material, which was surrounded by epithelial cells. Follow-up all of our patients was negative (if known) for 10 months to 4 years.