Chronic changes in the walls of experimentally produced aneurysms in sheep.

Twenty-seven saccular aneurysms were fashioned on the common carotid arteries of sheep using the venous transplants with a side-to-side anastomosis. The vessels were examined at varying intervals up to eight months postoperatively. The venous sacs exhibited severe phlebosclerosis of rapid progression and gross loss of muscle, and elastica was most prominent at the fundus. Some aneurysms leaked, some contained mural thrombus and several exhibited minimal quantities of lipid. The histologic changes were similar to those in man and experimental models entailing severe hemodynamic stress and can be regarded as atherosclerotic in nature.