Diseases And Conditions

Cerebral aneurysm

An unruptured aneurysm is an outpouching or blister that forms on the wall of cerebral blood vessels. Unruptured aneurysms are relatively common, occurring in up to 6% of the population. Most aneurysms are asymptomatic and are never detected. The minority are detected incidentally, usually while obtaining brain imaging for an unrelated condition. Some aneurysms are detected only after a subarachnoid hemorrhage (SAH).

SAH is a devastating brain hemorrhage caused by a bleeding aneurysm. SAH results in death in approximately 50% of cases. Up to 20% of SAH survivors are dependent due to disability. Overall, 2 out of every 3 patients with SAH are either dead or disabled. Bleeding rates from unruptured aneurysms are not known exactly and this is a subject of some controversy. Some investigators have reported a 1% to 2% per year risk of bleeding. Subsequent studies have reported that the bleeding rate is dependent on the aneurysm size and location. Small aneurysms in the anterior circulation are reported to have an almost zero risk of bleeding, while small aneurysms in the posterior circulation, (including the posterior communicating artery-a common sight of aneurysm occurrence), are reported to have up to a 2.5% risk of bleeding over 5 years. Larger aneurysms and aneurysms in patients with a personal history of SAH have a higher risk of bleeding. In actuality, bleeding risk from an unruptured aneurysm is multifactorial. Risk factors for SAH include female sex, smoking history, history of previous SAH, posterior circulation location, high blood pressure, aneurysm appearance, (presence of a teat or wind-sock configuration), aneurysm size and whether or not the aneurysm is causing any symptoms. In determining what the likelihood of bleeding maybe, it is important to take all of these factors into account and understand that a true determination of bleeding risk may be very elusive.

The reason why risk of bleeding, though elusive, is important to determine in patients harboring aneurysms is because it must be balanced with the risks of treatment. If the aneurysm is felt to be benign, long term monitoring will be advised. If the aneurysm is felt to be at risk of bleeding, then treatment may be recommended. Treatment options for unruptured aneurysms include surgery and endovascular treatment. Surgical treatment involves opening the skull and placing a clip on the aneurysm, closing it off. In endovascular therapy, the surgeon navigates a tiny tube from an artery in the leg to the brain. The tube is navigated to the aneurysm and one of a number of therapies can be administered. Endovascular treatment involves either intracranial embolization or intracranial stenting. Embolization involves the implantation of either coils or glue into the aneurysm, blocking it from the inside. In stenting, a wire mesh tube, called a stent, is implanted across the aneurysm orifice. This serves to divert flow from the aneurysm or support coils in the aneurysm.

While the incidence of aneurysm rupture may be lower than previously thought, the results are devastating. Evolving technologies may lower the threshold for treating small unruptured aneurysms if complication rates can be kept very low.