Characterization of smooth muscle components in renal angiomyolipomas: Histological and immunohistochemical comparison with renal capsular leiomyomas

The smooth muscle components of angiomyolipoma (AML) of the kidney have a wide histological and immunohistochemical spectrum. In the present study, 50 cases of AML and seven cases of renal capsular leiomyoma (RCL) were reviewed histologically and immunohistochemically, and the results compared with those of leiomyomas of soft parts. The AML cases were subclassified into 34 cases of common, 12 of leiomyomatous and four of lipomatous type. Even the common-type AML tissues showed a variety of histologic features, including lymphangiomyoma. The cytoplasm of leiomyomatous cells in AML was usually plump and eosinophilic, but sometimes clear with abundant glycogen, and an ovoid or irregular cleaved nucleus. AML cells, irrespective of whether they were epithelioid or leiomyomatous, stained positively for HMB45, S100 protein, and alpha-smooth muscle actin. RCL cells had histologic features identical to those of the leiomyomatous cells in AML. Moreover, the immunohistochemical profiles of the RCL cells were also identical to those of AML. These morphologic and immunohistochemical findings are different from those of smooth muscle tumors in soft parts and confirm that AML and RCL are closely related proliferative entities.