ANGIOMYOLIPOMA MIMICKING TRUE LIPOMA OF THE LIVER - REPORT OF 2 CASES

Hepatic angiomyolipoma (AML) is very rare and only about 80 cases have been reported. The tumor is fundamentally heterogeneously composed of the three tissue components of blood vessels, smooth muscle cells (SM C), and fat cells. Two cases of hepatic AML are reported here, both of which are histologically composed predominantly of a fat cell element and resembled true lipoma (lipomatous AML). However, careful examinat ion of both tumors revealed the presence of a small amount of epitheli oid SMC, especially around blood vessels. Immunohistochemical study us ing monoclonal antibody for melanoma (HMB-45) clearly revealed a small amount of HMB-45-positive SMC around the blood vessels and scattered in the diffuse fat cell growth in both tumors. Since no liver tissue c omponents or primary liver tumors are reactive with HMB-45 except AML cells, the presence of HMB-45-positive cells within the tumor clearly established the diagnosis of hepatic AML. Any fatty tumor or focal fat ty lesion of the liver that superficially resemble true lipomas should be tested for the presence of HMB-45-positive SMC in the tumor to dif ferentiate it from AML.