Aneurysm Overview An aneurysm is an abnormal, outward swelling of an artery caused by weakness in the arterial wall. According to the American Stroke Association, cerebral (brain) aneurysms may be congenital, or associated with other medical conditions including hypertension, vessel wall defects, flow dynamics, smoking, atherosclerosis, and defective vessel repair mechanisms. Aneurysms are more prevalent among women (60%), and 20% of patients have two or more aneurysms. The average age of aneurysm patients is between 40 and 60 years. Most cerebral aneurysms (85%) occur in the front (anterior) part of the brain. The other 15% are found in the back (posterior) part of the brain. The Cerebral aneurysms are categorized primarily by shape and size. Shape: Saccular, outpouching from the arterial wall, with a definable neck. Improved healing at the aneurysm neck. Fusiform, swelling of the entire circumference of the arterial wall, with no definable neck. Size: Small, up to 10 mm. Large, 10-25 mm Giant, larger than 25 mm These factors are important in determining therapy for the aneurysm and durability of the treatment. Cerebral aneurysms can rupture and cause a serious stroke or death; or compress surrounding brain tissue or cranial nerves. Most individuals are asymptomatic until the aneurysm ruptures. In 40% of cases, though, there may be some warning signs that an aneurysm is present, including pain above and behind the eye, localized headache, neck or upper back pain, nausea, and vomiting. In the United States, some 30,000 people a year present with acute hemorrhage due to rupture of a cerebral aneurysm. Rupture of a cerebral aneurysm is considered a medical emergency, and 25% of patients suffering a ruptured aneurysm will die before reaching a hospital.