Biologic characterization of human bone tumors. VI. The aneurysmal bone cyst: an enzyme histochemical, electron microscopical, and immunohistological study.

The etiology of aneurysmal bone cyst is still unknown. Most theories of the histogenesis of this lesion assume a vascular origin and speculation has focused on the characteristic pseudoendothelial lining of the cyst walls. In the present study, this structure has been subjected to enzyme histochemical, electron microscopical, and immunohistochemical investigation. Of the enzymes tested only alkaline phosphatase was present in the cyst lining. Electron microscopy revealed fibroblast-like cells covering the walls of cystic cavities, but no genuine endothelium, basement membranes or pericytes were identified. For the immunohistochemical studies a panel of poly- and monoclonal antibodies against HLA-DR antigens, mature and immature macrophages/histiocytes, smooth muscle fibers and endothelial cells, as well as the lectin Ulex europaeus I agglutinin were used. None of these markers demonstrated the presupposed vascular characteristics in the cells constituting the pseudoendothelial lining of the cyst walls. Despite current theories to the contrary, it was concluded that aneurysmal bone cyst is unlikely to originate from the vascular system, and that a new concept of its pathogenesis must be sought.