Hepatic angiomyolipoma - A clinicopathologic study of 30 cases and delineation of unusual morphologic variants

Hepatic angiomyolipoma (AML) is frequently misdiagnosed. HMB-45 is a promis ing immunomarker for this tumor that leads to recognition of some AMLs with unusual morphology. The purpose of this collaborative study is to better d efine the morphologic variations of AML. Thirty AMLs were examined, includi ng four biopsy specimens and two fine-needle aspirates. The diagnosis was c onfirmed by the presence of HMB-45-positive myoid cells. Almost half the ca ses were originally misdiagnosed as carcinomas or sarcomas. There was marke d female predominance (25:5), and the mean age was 48.7 years (range 29-68) . Three patients (10%) had evidence of tuberous sclerosis and all had renal AML. According to the line of differentiation and predominance of tissue c omponents, the tumors was subcategorized into mixed, lipomatous (greater th an or equal to 70% fat), myomatous (less than or equal to 10% fat), and ang iomatous type. The mixed type was the most common (11 resected cases), comp rising sheets of epithelioid muscle cells admired with islands of adipocyte s, abnormal vessels, and frequently, hematopoietic cells. Six tumors (inclu ding three from biopsy specimens) were heavily fatty and showed predominant ly adipocytes with epithelioid and short spindle myoid cells webbed between fat cells. Of 10 myomatous AMLs, five tumors showed a pure sinusoidal trab ecular pattern and comprised mainly epithelioid cells. Typically, mature ad ipocytes were absent or scanty, but fat was seen as fine droplets within cy toplasm or as occasional large globules in sinusoids. Pelioid and inflammat ory pseudotumor-like patterns were identified focally. Regarding cellular f eatures of the myoid cells, most of the epithelioid cells were either eosin ophilic or clear with spiderweb cell morphology. Three AMLs showed an almos t purely oncocytic appearance with scanty fat. Large pleomorphic epithelioi d cells existed as small foci. Spindle cells arranged in long fascicles wer e uncommon. D-PAS-positive globules were common around pelioid areas. Brown pigments with staining characteristics of hemosiderin and/or melanin were noted. In conclusion, we propose HMB-45-positive myoid cells as the definin g criterion of hepatic AML, which is a tumor capable of dual myomatous and lipomatous differentiation and melanogenesis. Because of its protean morpho logic appearance, recognition of the various variant patterns and cell type s is important for a correct diagnosis, assisted by immunohistochemical con firmation with HMB-45. Trabecular and oncocytic cell tumors appear to stand out as distinctive subtypes.