Experimentally induced cerebral aneurysms in rats: VII. Scanning electron microscope study.

The luminal surfaces of experimentally induced cerebral aneurysms and the branching sites in the circle of Willis in rats were investigated by scanning electron microscopy. Gap formation at the junctions of the endothelial cells was one of the most obvious changes on the endothelial surface of the aneurysms. Many leukocytes were observed adhering to these gaps. Regressive changes of endothelial cells, such as balloonlike protrusions and craterlike depressions, were also found in the aneurysms. At the branching site, where cerebral aneurysms often develop, endothelial cells were disarranged, rounded, and varied in size. A deep groove was also found adjacent to the apex. The role of endothelial cells and leukocytes in the development of cerebral aneurysms is discussed.