Cerebral Aneurysm

Cerebral aneurysms are defined as dilations that occur at weak points along the arterial circulation within the brain. They can vary in size (small less than 0.5 mm, medium 6 to 25 mm, and large greater than 25 mm). Most are saccular (berry), which is associated with a thin or absent tunica media, and an absent or severely fragmented internal elastic lamina. However, fusiform (circumferential) and mycotic (infectious) aneurysms are present in a small percentage of cases. The majority of cerebral aneurysms are silent and may be found incidentally on neuroimaging or upon autopsy. Approximately 85% of aneurysms are located in the anterior circulation, predominately at junctions or bifurcations along the circle of Willis (see ACom aneurysm, MCA Bifurcation Aneurysm). Subarachnoid hemorrhage (SAH) usually occurs with rupture and is associated with a high rate of morbidity and mortality.