Histological and ultrastructural study of intracranial saccular aneurysmal wall.

The material studied consists of 10 cases of intracranial saccular aneurysms. Four came from autopsies, and in each of the other six aneurysmal wall was obtained at surgery after clipping of the aneurysm. The most significant findings from this pathological study are the almost complete disappearance of the internal elastic lamina at the level of the aneurysmal neck, sclerosis of the muscle coat, and in satellite vessels and vasa vasorum disruption of the internal elastic lamina and partial luminal occlusion. The importance of ischaemic changes in the aneurysmal wall is discussed. Rupture of the aneurysm at the distal extremity of the sac depends probably on the progressive brittleness of its wall which becomes sclerotic and less resistant to the blood pressure within. Splitting or rupture of the aneurysm appears to be dependent on degenerative ischaemic alterations in its wall.