Electron microscopic study of the arterial wall in the cerebral aneurysms.

The ultrastructural modifications were observed in electron microscopy of the congenital aneurysm of the internal carotid artery with subarachnoid hemorrhage. The tunica intima very enlarged contains in the endothelial cells numerous microvesicles of pinocytosis, and rare cell organelles. The internal elastic lamina presented ruptured or absence zones. The luminal face of the cells appeared irregular with large evaginations and deep and narrow invaginations. Under the endothelial lining, large masses of extracellular matrix with different degrees of edema, and fragmented collagen fibrils realize a metabolic barrier between the tunica intima and media. The muscle fibers of the tunica media and the myofilaments in each myocyte are in reduced number.