Experimental studies of intracranial aneurysms (a preliminary report). Some biomechanical considerations on the wall structures of intracranial aneurysms and experimentally produced aneurysms (Japanese)

The authors investigated the mechanical properties and structures of the walls of cerebral aneurysms at autopsy and of experimental aneurysms produced in dogs by the authors' method. The results obtained showed that elastic fibers had high distensibility and collagen had little. The wall of cerebral aneurysm was occupied almost exclusively by collagen fibers and degenerative substances. Therefore, it was supposed that the aneurysmal wall had stiff property as a whole. Two types of aneurysm were produced in dogs experimentally. The 1st one was vein pouch aneurysm, which was produced at the side of the wall and at the bifurcations of the common carotid artery and abdominal aorta. The other type was fusiform aneurysm produced by segmental treatment with elastase from the intraluminal surface of the artery. The static mechanical properties of the experimentally produced aneurysms were examined. It was found that their distensibility was almost lost at the level of internal pressure of about 80 mm Hg. The area fractions occupied by each component in the cross section of the walls of cerebral aneurysm, of vein pouch aneurysm, and of common carotid artery as a control were examined. The density distribution profiles were obtained by scanning each negative film in a radial direction by a microphotometer. The area fractions of elastic fiber, collagen fiber and smooth muscle calculated from these density distribution profiles were, in order, 7.9, 41.3 and 2.1% in cerebral aneurysm, 7.2, 35 and 12.1% in vein pouch aneurysm, and 32.5, 22.9 and 35.6% in common carotid. These results suggest that both cerebral aneurysm and experimental aneurysms have common features in that both are rich in collagen and scanty in elastin and smooth muscle. The features correspond well to the mechanical properties mentioned above. The experimental aneurysms are similar to cerebral aneurysm and can be used for experimental studies concerning cerebral aneurysms.