Ultrastructure of aneurysms.

The fine structure of five cerebral aneurysms, four early aneurysmal changes, and three arteriovenous aneurysms (two cerebral and one spinal) were investigated from surgical and autopsy specimens. Each lesion was characterized by thickening, lamination, redundancy, and separation of basement membranes, abundant cellular debris, and a paucity or absence of elastica. In several instances, extracellular lipid and lipophages were present. These vascular lesions were remarkably similar to one another and also to the degenerative changes in experimental arteriovenous aneurysms, thus substantiating the concept that they, too, are essentially degenerative in nature.