Cytologic and cytogenetic analysis of metanephric adenoma of the kidney: a report of two cases.

Metanephric adenoma is a recently described renal neoplasm. Because follow-up to date has been benign, accurate diagnosis on fine-needle aspiration material may be important for appropriate clinical management. A retrospective analysis of fine-needle aspiration material from two metanephric adenomas was performed. The aspirates were cellular and composed of many small to large tightly packed clusters of cells and short papillae. Occasional tubules, rosettes, and glomeruloid-like structures were seen. The tumor cells had very scant cytoplasm; small, oval to round, uniform, overlapping nuclei with fine delicate chromatin; and minute or absent nucleoli. Rare psammoma bodies were noted. Atypia, pleomorphism, necrosis, and mitoses were absent. Cytogenetic analysis showed normal karyotypes in both cases. The cytologic differential diagnosis included Wilms' tumor, renal-cortical adenoma, papillary renal cell carcinoma, and neuroendocrin, and metastatic tumors. We conclude that metanephric adenoma has unique cytologic features that may allow distinction from other renal neoplasms on fine-needle aspiration material. In difficult cases, ancillary studies may be helpful.