Epithelioid angiomyolipoma of the kidney: case report

Renal angiomyolipoma is a benign tumour histologically characterized by a mixture of adipose tissue, smooth muscle cells and thick walled blood vessels. Long-believed to be a benign hamartoma, angiomyolipoma is now considered to arise from perivascular epithelioid cells. Epithelioid angiomyolipoma is a rare type of angiomyolipoma, composed partially or completely of epithelioid cells, with a potentially aggressive behaviour. Histologically it can mimic renal cell carcinoma. Positivity for HMB45, Melan A, CD68 and CD117 are useful for diagnosis. Herein, we report the clinicopathologic and immunohistochemical features of a renal tumour composed of large epithelioid mononucleated or multinucleated cells with abundant acidophilic cytoplasm and prominent nucleoli. Despite the morphologic resemblance of this tumour to renal cell carcinoma, its phenotype (HMB45, Melan A and CD68 positivity and keratin negativity) parallels the phenotypic profile of angiomyolipoma. Therefore, immunohistochemistry should be considered when diagnosing this variant of angiomyolipoma.