Fine-needle aspiration cytology of renal angiomyolipoma: report of a case with immunocytochemical and electron microscopic findings.

A case is presented in which the diagnosis of renal angiomyolipoma was made by computed tomography (CT)-guided, fine-needle aspiration cytology and the examination of a cell block. The tumor was characterized by epithelioid smooth muscle cells, blood vessels and fat in the cytologic material. The cytodiagnosis was further substantiated by positive staining of the epithelioid muscle cells for markers of muscle-specific actin, HMB45, and trace positivity for vimentin but not with S100 protein, desmin, or cytokeratin. Further studies for the recently described crystalloids were also performed by using the periodic-acid Schiff stain with and without diastase treatment and electron microscopy on the cytologic material. However, no such crystalloids were found. A preoperative cytologic diagnosis of renal angiomyolipoma was considered to be of value due to the difference in management between angiomyolipoma and a renal carcinoma, both of which can present as a renal mass on imaging.