Scanning electron-microscopic study of the inner surface of experimental aneurysms in rabbits.

A scanning electron-microscopic study of the inner surface of experimental saccular aneurysms in rabbits was conducted to demonstrate the effects of haemodynamics on the aneurysmal wall. Animals with aneurysms were killed from 2 to 83 weeks postoperatively, and the controls from 7 to 51 weeks. In both series, re-endothelialization was complete in approximately 2 weeks. In control tissue endothelium was normal, and sutures caused mild distortion of the luminal surface. In the aneurysms, there were tracts of spindle-shaped cells, often arranged in whorl-like patterns and interspersed with regions of polyhedral cells with thickened intercellular borders, prominent stomata and numerous microvilli. In some areas, long filamentous intercellular processes were prominent. The few jet lesions seen were covered with polyhedral cells and were less complex than those in arteriovenous fistulae. Ridges, caused by elevated subendothelial connective tissues were crescentic or circular, outlining depressions and craters, as if delineating vortices. The carotid artery opposite the aneurysm exhibited endothelium similar to normal tissue, except in older aneurysms where corrugations caused by the internal elastic lamina were completely or partially absent. The experiments demonstrate the effect of intra-aneurysmal haemodynamics on the topography of the endothelium and subendothelial tissues of the sac wall, and support the concept that endothelial topography in the vascular system under physiological conditions is haemodynamically determined.