Fine needle aspiration cytology of renal and retroperitoneal angiomyolipoma. Report of two cases with cytologic findings and clinicopathologic pitfalls in diagnosis.

BACKGROUND: Angiomyolipoma is a benign soft tissue neoplasm that usually arises in the kidney, although rare extrarenal examples have been documented.

CASES: Two cases of the neoplasm occurred in which fine needle aspiration (FNA) biopsies were performed. The first patient was a 73-year-old female with a history of breast carcinoma who presented with a large retroperitoneal mass. Transabdominal FNA biopsy revealed multiple fragments of spindle-shaped mesenchymal cells, a few of which showed marked cellular atypia with occasional cells containing fat vacuoles, producing a lipoblastlike appearance. However, the atypical spindle cells were immunohistochemically reactive for actin, raising the possibility of a smooth muscle tumor rather than a liposarcoma. The surgically resected specimen revealed an extrarenal, retroperitoneal angiomyolipoma. The second patient was a 71-year-old female who presented with a right renal mass and hepatomegaly. Computed tomography showed a mass in the upper pole of the kidney and multiple enhancing lesions in the liver. FNA biopsy was diagnostic of angiomyolipoma, which was confirmed histologically.

CONCLUSION: Angiomyolipoma should be considered in aspirates of both renal and extrarenal masses when an admixture of blood vessels, fat and smooth muscle cells is encountered. Pitfalls leading to an incorrect diagnosis include aspiration at unusual sites for angiomyolipoma and/or the presence of atypical spindle cells and lipoblastlike cells, which can be mistaken for leiomyosarcoma or liposarcoma cells. Ancillary studies, such as immunocytochemistry for smooth muscle markers, may be helpful in making the correct diagnosis.