Cerebral aneurysms are pathologic focal dilatations of the cerebrovasculature that are prone to rupture. These vascular abnormalities are classified by presumed pathogenesis. Saccular, berry, or congenital aneurysms constitute 90% of all cerebral aneurysms and are located at the major branch points of large arteries.
Saccular aneurysms are situated in the anterior circulation in 85-95% of cases, whereas dolichoectatic aneurysms affect predominantly the vertebrobasilar system. The location of saccular aneurysms at specific arterial segments varies in frequency because of differences in reported study populations. Multiple saccular aneurysms are noted in 20-30% of patients with cerebral aneurysms.
Saccular aneurysms frequently rupture into the subarachnoid space, accounting for 70-80% of spontaneous subarachnoid hemorrhages (SAH). Aneurysmal rupture also may result in intraparenchymal, intraventricular, or subdural hemorrhage. Giant saccular aneurysms, defined as greater than 25 mm in diameter, represent 3-5% of all intracranial aneurysms. Although giant aneurysms may cause SAH, these lesions frequently produce mass effects and result in distal thromboembolism.
Aneurysmal SAH is a catastrophic condition, affecting 30,000 individuals in the United States every year. Most of these individuals (60%) either die or suffer permanent disability; 50% of survivors with favorable outcomes experience considerable neuropsychological dysfunction. Cerebral vasospasm (i.e., narrowing of proximal arterial segments) complicates 20-50% of cases and is the major cause of death and disability associated with aneurysmal SAH.
- Family History. People who have a family history of brain aneurysms are more likely to have an aneurysm than those who don’t.
- Previous Aneurysm. People who have had a brain aneurysm are more likely to have another.
- Gender. Women are more likely to develop a brain aneurysm or to suffer a subarachnoid hemorrhage.
- Race. African Americans are more likely than whites to have a subarachnoid hemorrhage.
- Hypertension. The risk of subarachnoid hemorrhage is greater in people with a history of high blood pressure (hypertension).
- Smoking. In addition to being a cause of hypertension, the use of cigarettes may greatly increase the chances of a brain aneurysm rupturing.
Symptoms of a ruptured brain aneurysm often come on suddenly.
A sudden, severe headache that is different from past headaches.
- Neck pain.
- Nausea and vomiting.
- Sensitivity to light.
- Fainting or loss of consciousness.
Microsurgical techniques focus on exclusion of the aneurysm from the cerebral circulation and reduction of mass effects on adjacent structures. Various approaches have been developed and tailored to the anatomy and location of the aneurysm. A surgical clip usually is placed across the aneurysm neck with preservation of the parent vessel, eliminating any aneurysmal rests that may redevelop subsequently. Alternative surgical techniques involve proximal or Hunterian ligation, wrapping of the aneurysm, or trapping (i.e., a combination of proximal and distal vessel occlusion).
The other potential and effective microsurgical technique is endovascular coiling. The goal of endovascular coiling is to isolate an aneurysm from the normal circulation without blocking off any small arteries nearby or narrowing the main vessel. Endovascular describes the minimally invasive technique of accessing the aneurysm from within the bloodstream, specifically during angiography (see Angiogram). The bloodstream is entered through the large femoral artery in the upper leg (groin area). A flexible catheter is advanced from the femoral artery to one of four arteries in the neck that lead to the brain. While viewing an x-ray monitor, called a fluoroscope, the doctor steers the catheter through the blood vessels. A special dye injected into the bloodstream makes the blood vessels visible on the monitor. The result is a kind of roadmap of the arteries.
Once the catheter reaches the aneurysm, a very thin platinum wire is inserted. The wire coils up as it enters the aneurysm and is then detached. Multiple coils are packed inside the dome to block normal blood flow from entering. Over time, a clot forms inside the aneurysm, effectively removing the risk of aneurysm rupture. Coils remain inside the aneurysm permanently.
Coils are made of platinum and other materials, and come in a variety of shapes, sizes, and coatings that promote clotting. Wide-neck aneurysms may be more difficult to occlude with these devices. Other materials, such as balloons or glue, also may be used. Complications include vessel perforation, hemorrhage, or distal thromboembolism.