Renal epithelioid angiomyolipoma--a close mimic of renal cell carcinoma. Report of a case and review of the literature

The epithelioid variant of angiomyolipoma (EAML) is a rare tumor of unpredictable behavior that is composed of epithelioid, spindle, and giant cells and contains no or only a minimal amount of lipomatous tissue. The picture can lead to an erroneous diagnosis of renal cell carcinoma or sarcoma. We report on a case of EAML in the kidney of a 47-year-old female without any signs of tuberous sclerosis and review the literature. Grossly, a well-demarcated, spheroid, largely hemorrhagic tumor measuring 4.2 cm in diameter occupied the central third of the kidney. Histologically, it was solid, highly cellular, with occasional microcysts, composed of medium to large epithelioid cells with clear or oxyphilic cytoplasm, short spindle cells, and numerous giant multinucleated cells. After extensive sampling, adult-appearing fat tissue was found to present as rare foci of microscopic dimensions. Immunohistochemically, the tumor cells showed positive reactions with antibodies against HMB-45, melan A, CD-68, muscle-specific actin, and, rarely, smooth muscle actin. Cytokeratins and epithelial membrane antigen were negative. The EAML is a variant growing in a carcinoma-like pattern that can lead to an erroneous diagnosis of renal cell carcinoma. An extensive sampling and HMB-45 and CD-68 positivity combined with cytokeratin negativity are of paramount importance for the correct diagnosis. As a sporadic renal tumor it followed a benign course in most of the reported cases.