Haemodynamically-induced intimal tears in experimental U-shaped arterial loops as seen by scanning electron microscopy.

Experimentally-induced U-shaped carotid loops, simulating arterial tortuosities and kinks were examined by scanning electron microscopy to seek flow-induced changes in the intimal surface. In 14 New Zealand white rabbits carotid arterial transplants were fashioned into U-shaped loops by microvascular surgery. The rabbits were sacrificed from 4 to 226 days post-operatively. Tears in the internal elastic lamina occurred in all loops from 5 days post-operatively and were predominantly transverse and localised about the greater curvature of the bends of each loop. Though initially denuded, all tears appeared endothelialised after 6 days, coalescing later as they increased in size and extent. In older animals only islands of wrinkled internal elastic lamina remained at those sites. Endothelial cells in the tears were small, numerous and polyhedral with raised nuclei. The lesser curvature of the three bends in the loops displayed some irregular wrinkling of the internal elastic lamina. In the three oldest animals a few longitudinal tears were observed on the lesser curvature of the main bend. The specific localization of intimal tears supports the concept that they were hemodynamically induced.