Fine needle aspiration biopsy of metanephric adenoma: a case report.

BACKGROUND

Metanephric adenoma (MA) is a rare, benign renal neoplasm. Only 3 previous case reports describe the fine needle aspiration biopsy (FNAB) cytologic features of MA. Regarding treatment, radioflrequency ablation (RFA) is an emerging alternative to surgical resection of renal neoplasms in appropriately selected patients.

CASE

A 49-year-old woman had a 3.3-cm cortical mass in the left kidney. Computed tomography-guided FNAB was performed, followed by RFA of the lesion. The aspirate smears displayed multiple aggregates of benign-appearing, tightly packed and overlapping nuclei surrounded by basement membrane- type material. The cohesive aggregates were arranged in tubular or tubulopapillary structures without fibrovascular cores. No atypia, mitotic figures or necrosis were present. Immunohistochemical (IHC) stains performed displayed positive staining for WT-1, CD57 and cytokeratin AE1/AE3 and equivocal staining for CD56. The AMACR, CK7 and EMA immunostains were negative. Although the differential diagnosis included adult Wilms' tumor and papillary renal cell carcinoma, the bland morphology and IHC staining pattern strongly favored a neoplasm consistent with MA.

CONCLUSION

FNAB can be used to diagnose most renal neoplasms. A diagnosis of MA can be suggested on FNAB in the context of appropriate cytomorphology, IHC staining and cytogenetic analysis.