Angiomyolipoma: Immunohistochemical and ultrastructural study of 14 cases

Angiomyolipoma (AML) is a mesenchymal neoplasm of unclear histogenesis. In addition to varying amounts of smooth muscle, adipose tissue, and blood ves sels, it contains a population of clear or pale eosinophilic epithelioid ce lls often arranged around blood vessels. Various phenotypes of AML have bee n described: leiomyoma-like, lipoma-like, epithelioid, and atypical. AMLs s how consistent immunopositivity for HMB-45. This has been associated with t he ultrastructural observation of melanosome-like structures in rare instan ces. In the present study, 14 AM is from 13 patients were analyzed by elect ron microscopy and immunohistochemistry to determine the appearance and nat ure of cells composing AMLs. Overlap between cell types (spindle smooth mus cle cells, epithelioid cells, and adipocytes) was found by both electron mi croscopy and immunohistochemistry. Melanosomes were found in 7 tumors. The cell of origin remains mysterious. Nevertheless, the study demonstrates tha t the AML is likely derived from a single cell that shares homology with th e pericyte.