A cerebral or brain aneurysm is a cerebrovascular disorder in which weakness in the wall of a cerebral artery or vein causes a localized dilation or ballooning of the blood vessel.

Locations

A common location of cerebral aneurysms is on the arteries at the base of the brain, known as the Circle of Willis. Approximately 85% of cerebral aneurysms develop in the anterior part of the Circle of Willis, and involve the internal carotid arteries and their major branches that supply the anterior and middle sections of the brain. The most common sites include the anterior communicating artery (30-35%), the bifurcation of the internal carotid and posterior communicating artery (30-35%), the bifurcation of the middle cerebral artery (20%), the bifurcation of the basilar artery, and the remaining posterior circulation arteries (5%).

Causes of Cerebral Aneurysms

Aneurysms may result from congenital defects, preexisting conditions such as high blood pressure and atherosclerosis (the buildup of fatty deposits in the arteries), or head trauma. Cerebral aneurysms occur more commonly in adults than in children and are slightly more common in women than in men, but they may occur at any age.

Classification of Cerebral Aneurysms

Cerebral aneurysms are classified both by size and shape. Small aneurysms have a diameter of less than 15 mm. Larger aneurysms include those classified as large (15 to 25 mm), giant (25 to 50 mm), and super giant (over 50 mm.) Saccular aneurysm are those with a saccular outpouching and are the most common form of cerebral aneurysm. Berry aneurysms are saccular aneurysms with necks or stems resembling a berry. Fusiform aneurysms are aneurysms without stems.

Symptoms of Aneurysms

A small, unchanging aneurysm will produce no symptoms. Before a larger aneurysm ruptures, the individual may experience such symptoms as a sudden and usually severe headache, nausea, vision impairment, vomiting, and loss of consciousness, or the individual may be asymptomatic, experiencing no symptoms at all. Onset is usually sudden and without warning. Rupture of a cerebral aneurysm is dangerous and usually results in bleeding into the meninges or the brain itself, leading to a subarachnoid hemorrhage (SAH) or intracranial hematoma (ICH), either of which constitutes a stroke. Rebleeding, hydrocephalus (the excessive accumulation of cerebrospinal fluid), vasospasm (spasm of the blood vessels), or multiple aneurysms may also occur. The risk of rupture from an unruptured cerebral aneurysm varies according to the size of an aneurysm, with the risk rising as the aneurysm size increases. The overall rate of aneurysm rupture is estimated at 1.3% per year. The risk of short term re-rupture increases dramatically after an aneurysm has bled, though after approximately 6 weeks the risk returns to baseline.

Classification of Ruptured Aneurysm Severity

In outlining symptoms of ruptured cerebral aneurysm, it is useful to make use of the Hunt and Hess scale of subarachnoid hemorrhage severity:

• Grade 1: Asymptomatic; or minimal headache and slight nuchal rigidity. Approximate survival rate 70%.
• Grade 2: Moderate to severe headache; nuchal rigidity; no neurologic deficit except cranial nerve palsy. 60%.
• Grade 3: Drowsy; minimal neurologic deficit. 50%.
• Grade 4: Stuporous; moderate to severe hemiparesis; possibly early decerebrate rigidity and vegetative disturbances. 20%.
• Grade 5: Deep coma; decerebrate rigidity; moribund. 10%.

The Fischer Grade classifies the appearance of subarachnoid hemorrhage on CT scan:

• Grade 1= No hemorrhage evident
• Grade 2= Subarachnoid hemorrhage less than 1 mm thick
• Grade 3= Subarachnoid hemorrhage more than 1 mm thick
• Grade 4= Subarachnoid hemorrhage of any thickness with intra-ventricular hemorrhage (IVH) or parenchymal extension

The Fischer Grade is most useful to communicate the description of SAH. It is less useful prognostically than the Hunt-Hess Scale.

Vasospasm

One complication of aneurysmal subarachnoid hemorrhage is the development of vasospasm. Approximately 1 to 2 weeks following the initial hemorrhage, patients may experience 'spasm' of the cerebral arteries, which can result in stroke. The etiology of vasospasm is thought to be secondary to an inflammatory process that occurs as the blood in the subarachnoid space is resorbed.

Vasospasm is monitored in a variety of ways. Non-invasive methods include transcranial Doppler, which is a method of measuring the velocity of blood in the cerebral arteries using ultrasound. As the vessels narrow due to vasospasm, the velocity of blood increases. The amount of blood reaching the brain can also be measured by CT or MRI or nuclear perfusion scanning.

The definitive, but invasive method of detecting vasospasm is cerebral angiography. Vasospasm can be treated medically by a variety of methods, including bed rest, drug therapy, or 'Triple H' (hypertensive-hypervolemic-hemodilution therapy (which elevates blood pressure, increases blood volume, and thins the blood) to drive blood flow through and around blocked arteries. Alternatively, narrowed arteries in the brain can be treated by balloon angioplasty to widen the arteries and increase blood flow to the brain. The effectiveness of all these treatments are still being evaluated, and new treatments are in continual evolution.

Treatment

Emergency treatment for individuals with a ruptured cerebral aneurysm generally includes restoring deteriorating respiration and reducing intracranial pressure. Surgery is usually performed within the first three days to clip the ruptured aneurysm and reduce the risk of rebleeding. When aneurysms are discovered before rupture occurs, microcoil thrombosis or balloon embolization may be performed on patients for whom surgery is considered too risky. During these procedures, a thin, hollow tube (catheter) is inserted through an artery to travel up to the brain. Once the catheter reaches the aneurysm, tiny balloons or coils are used to block blood flow through the aneurysm.

Prognosis

The prognosis for a patient with a ruptured cerebral aneurysm depends on the extent and location of the aneurysm, the person's age, general health, and neurological condition. Some individuals with a ruptured cerebral aneurysm die from the initial bleeding. Other individuals with cerebral aneurysm recover with little or no neurological deficit. However, estimates are, that of the 30,000 people per year in the United States who suffer a ruptured aneurysm, only 20% will be alive and well in one year's time. 20% will be alive but disabled, and 60% will have died.

See also

• Stroke
• International Subarachnoid Aneurysm Trial
• Neil Young, a famous recipient of a coil embolization for a brain aneurysm. Laura Branigan and Quincy Jones are among the notable musicians who have suffered ruptured brain aneurysms; Branigan's was fatal.

External links

• Aneurysm - Cerebral
• Brain Aneurysm & Cerebrovascular Resource
• http://www.brainaneurysm.com/
• Brain Aneurysm-Brain Surgery Patient Help Site

Neurology | Neurosurgery | Radiology

脳動脈瘤 | Aneurisma cerebral