We do not have enough knowledge concerning the process from the non-ruptured aneurysm to the ruptured aneurysm. Hemodynamic stress is one of the important factors that influence the growth and rupture of cerebral aneurysm. The hemodynamic stress affects vascular endothelium inside of the aneurysm. We investigated the morphology of the vascular endothelial cells of 5 ruptured aneurysms. These aneurysms were surgically obtained in the acute stage, and the specimens were processed for the scanning electron microscope. The inner surface of the aneurysmal sac was examined.
In one patient, the endothelial cell layers were relatively preserved. However, the gap between endothelial cells was enlarged where leukocytes adhered. We found defects of endothelium where the extracellular matrix of the wall became exposed, and blood cells invaded into the aneursmal wall in 2 patients. In those 2 patients, there were relatively well preserved endothelium in other areas.
Blood cells also adhered to the enlarged gap between endothelial cells. There was no layer of the endothelial cells within the specimen obtained from the other 2 patients. We found damage of the endothelial cell layer inside the aneurysm and blood cells invasion into the aneurysmal wall in the ruptured aneurysm. One possible explanation is that increases in hemodynamic stress injure the endothelium inside of the aneurysm, and then, leukocytes, platelets, and blood plasma invade the aneurysm wall before the rupture. These processes can cause the destruction and rupture of the aneurysmal wall.
Acom, anterior communicating artery; ICA, internal carotid artery; MCA, middle cerebral artery; SAH, subarachnoid hemorrhage.