Last updated: 11/24/2009

Cerebral aneurysms become apparent in two general ways: from rupture followed by bleeding within the brain, or from enlargement and compression on surrounding critical brain structures, which leads to symptoms. The most life-threatening presentation...

is bleeding and is often described clinically as subarachnoid hemorrhage (SAH), a term derived from the anatomic area of the brain that becomes contaminated with blood when an aneurysm ruptures. The surface of the brain is covered by three thin membranous layers, or meninges, called the dura mater, the pia mater, and the arachnoid. The dura mater adheres to the skull, while the pia mater adheres to the brain. The arachnoid lies between the other two meninges. The space between the pia mater and the arachnoid is known as the subarachnoid space and is normally filled with cerebrospinal fluid. SAH occurs when blood leaks into this space, contaminating the cerebrospinal fluid. About half of all SAH result from a ruptured cerebral aneurysm.

Clinically, the rupture causes the sudden explosive onset of a very severe headache that patients describe as the worst headache of their life. Other symptoms can include short-term loss of consciousness, neck stiffness, back pain, nausea or vomiting, and an inability to tolerate bright light. Sometimes a seizure can occur. About 40% of patients have symptoms and signs prior to the actual rupture, including minor headaches or dizziness, which are thought to result from swelling of the aneurysm or minor bleeding that occurs prior to the full rupture. Unfortunately, many of these events go undetected.

Rupture of a cerebral aneurysm is an emergency situation. About 10% of people with SAH die within the first day, and without treatment, 25% succumb within the next three months. More than half of those who survive have significant neurological damage. Partial paralysis, weakness, or numbness may linger or be permanent, as may vision and speech problems.

When SAH is suspected, a computerized tomography (CT) scan is performed to confirm the diagnosis by visualizing the bleeding. The aneurysm itself is only rarely seen using this test. CT scanning is positive (detects the bleeding) in more than 90% of patients within the first 24 hours after the event, and for more than 50% within the first week. As time goes on, however, the bleeding becomes harder and harder to detect using this imaging method. If no bleeding is detected, a second test that could be performed is a lumbar puncture (LP), which involves drawing cerebrospinal fluid through a needle from the lower back of the patient. If SAH has occurred, the collected cerebrospinal fluid will contain blood and could be discolored yellow, caused by the presence of breakdown products of the blood cells. Other more sophisticated tests can also be performed to confirm the presence of blood and its breakdown products in the sample.

The definitive test for a cerebral aneurysm is a fluoroscopic angiogram, as it can often directly document the aneurysm, particularly its location and size. This procedure involves the placement of fluorescent material into the vein or artery of concern that increases the contrast between vessels and surrounding tissue so that their path can be clearly seen. The vessel is accessed through the insertion of a catheter in the femoral (leg) artery and threading it through the heart and into the blood vessels of the brain. A microcatheter is threaded through the larger one and used to deliver the contrast material to the precise location of the suspected aneurysm. Digital subtraction removes the bony structures from the image and leaves only the vessels. Generally, when SAH is suspected, a full cerebral angiogram that studies all four of the major cerebral arteries is performed. Modern angiograms are able to identify 85% of all cerebral aneurysms, with another 10% visible upon a second test seven to 10 days later. If this test is negative, magnetic resonance imagining (MRI), which is in some ways a more sensitive test, is often recommended.

If an aneurysm presents without rupture, some symptoms include seizures, double vision, progressive blindness in one eye, numbness on one side of the face, difficulty speaking, or, occasionally, hydrocephalus (accumulation of cerebrospinal fluid in the brain). Because of the sensitivity of available scanning techniques (particularly MRI), many aneurysms are discovered even before symptoms develop. This raises the issue of whether non-ruptured, asymptomatic aneurysms should be surgically treated.

Many health professionals view an unruptured aneurysm as a potential time bomb. In general, there is a 3% per year cumulative risk of rupture once an aneurysm is identified, or stated another way, about 0.5–0.75% of all aneurysms rupture each year. Each rupture brings with it the very high probability of serious neurological damage or even death. Furthermore, there are certain aneurysms that rupture more commonly than others, and environmental factors such as smoking and high blood pressure contribute to these events. However, all other things being equal, research indicates that by 10 years after diagnosis, there is an approximately 30% chance the aneurysm will rupture. Yet, the surgery itself carries significant risk. Whether or not to treat an unruptured aneurysm is a difficult decision and should be made only after careful consideration of the many influencing factors.

After diagnosis with a cerebral aneurysm, a patient will be put on strict bed rest and receive medication to avoid complications, keep blood pressure under control, and for pain relief.