Scanning electron microscopic study of hemodynamically induced tears in the internal elastic lamina of rabbit...

A scanning electron microscopic investigation of tears in the internal elastic lamina of the afferent artery of experimental arteriovenous fistulae was undertaken to determine their site of initiation and to elucidate their nature. Carotid-jugular arteriovenous fistulae and contralateral common carotid arteriotomies were performed in rabbits sacrificed from two to 63 days post-operatively. Following de-endothelialization, scanning electron microscopy of the internal elastic lamina revealed predominantly transverse straight tears with sharp margins. Even in chronic fistulae the tears retained their sharp margins despite their propagation. No evidence of repair was observed. The tears commenced by rupture of the elastic trabeculae traversing the fenestrae. Enzymatic digestion of the internal elastic lamina did not resemble the hemodynamically induced tears and no evidence of elastolytic enzyme activity was detected. The tears suggest that the abnormally stressed elastic tissue has undergone some structural alteration leading to a reduction in its tensile strength.