A case of angiomyolipoma of the lower lip

Abstract Angiomyolipoma is a benign tumor that most commonly forms in the kidney, and rarely occurs in the oral region. Angiomyolipoma is composed of smooth muscle cells, blood vessels and mature fat cells. Because the three principal components in angiomyolipoma vary greatly in proportion and distribution, its heterogeneity may cause diagnostic confusions. We report a case of angiomyolipoma arising in the lower lip of man in his 50s. Histopathological analysis of the tumor revealed three mesenchymal components of smooth muscle, blood vessel and mature fat cells. Immunohistochemical examination showed that the tumor cells of the spindle cell were positive for alpha smooth muscle actin, desmin, and vimentin, but negative for S-100 protein and HMB-45. The endocapillary cells were positive for CD34. The adipose cells were positive for S-100 protein. Angiomyolipoma occurring in the head and neck do not express HMB-45, in contrast to the usual immunopositivity shown in angiomyolipomas from the kidney and liver, suggesting that there are differences among them. These histological and immunohistochemical analyses resulted in a final diagnosis of angiomyolipoma.