A cerebral aneurysm is a dome or sac-like structure budding from weakened arterial walls in the brain. Cerebral aneurysms have no known specific cause currently. Considering the risks of surgery, when surgery should be performed on unruptured aneurysms is a very controversial issue. Some clinicians feel that an aneurysm should be surgically removed immediately upon discovery regardless of the size, if surgery is possible. While others feel that small aneurysms should be watched or treated with endovascular insertion of soft platinum coils, avoiding the risks associated with any brain surgery. To further study this question examination was done of specimens from surgical clip ligation of middle cerebral artery aneurysms and normal specimens.

Specimens of ruptured and unruptured aneurysm as well as normal artery removed from surgical patients were immediately preserved in cold 2.5% glutaraldehyde in 0.1 M PBS. The specimens were rinsed in PBS, post-fixed in 1% Osmium Tetroxide with 0.1% potassium ferricyanide,