Alterations of elastic architecture in human aortic dissecting aneurysm.

Elastin of the ascending aortic media of 10 cases with type A dissecting aneurysm, 14 hypertensive cases, and 30 control cases were prepared by the treatment of aortas with hot formic acid, and three-dimensional architecture was observed by scanning electron microscopy. In the control cases, elastin showed framework-like continuous structure consisting of elastic laminae, and interlaminar fibers that interconnected the laminae. In 6 of 10 cases of dissecting aneurysm, the interlaminar fibers were apparently irregular in arrangement and shape, and decreased in number, especially in the outer media. This architectural alteration resulted in a rarefaction of interconnection between the elastic laminae in the media, and possibly resulted in the local weakness against the dissecting force of the laminae. This medial weakness may be related to the mechanism of initiation and progression of dissecting aneurysm. The cystic medial necrosis (CMN) was found in 3 cases, but only 1 of them was accompanied by a mild decrease of the interlaminar fibers in the area outside of CMN, suggesting that the initiation of CMN did not directly relate to the decrease of the interlaminar fibers. The aortic media of hypertensives generally showed an increase of interlaminar fibers, but their focal decrease was encountered in the outer media of 3 cases. These findings suggest that the decrease of the interlaminar fibers of medial elastin seen in dissecting aneurysms were related to hypertension.