ANGIOMYOLIPOMA PREDOMINANTLY COMPOSED OF SMOOTH-MUSCLE CELLS - PROBLEMS IN HISTOLOGICAL DIAGNOSIS

Aims: Five cases of angiomyolipoma (AML) composed exclusively or predo minantly of smooth muscle cells (SMC) are presented to emphasize the h istological diversity and to caution against errors in histological di agnosis. Methods and results: Four tumours were located in the liver a nd one in the renal capsule. Three patients were female and two were m ale, ranging from 36 to 76 years of age with a mean age of 50 years. O ne patient with a renal capsular tumour was associated with tuberous s clerosis. Two tumours were composed predominantly of a spindle-shaped SMC component, whereas three others were composed predominantly of epi thelioid SMC elements. AMLs composed exclusively or predominantly of s pindle-shaped smooth muscle cells (SMCs) simulated leiomyoma, whereas AMLs composed exclusively or predominantly of epithelioid SMCs resembl ed epithelioid leiomyoma or leiomyosarcoma or other sarcoma when cellu lar atypia was present. However, both spindle and epithelioid SMCs wer e characteristically positive for HMB-45 melanoma-specific antibody; n o other tissue components in either the liver or kidney were reactive to HMB-45. Conclusions: AML is often composed predominantly of SMC ele ments, and morphological features of the SMC elements are quite variab le. Therefore, careful attention must be given to histological assessm ent of AML, Whenever a pathologist encounters an unfamiliar hepatic or renal tumour, the possibility of AML should be considered. Reactivity for HMB-45, however, confirmed the diagnosis of AML.