Cerebral arteriovenous malformation

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**Cerebral arteriovenous malformation**
*Classifications and external resources*
ICD-10	Q28.2
ICD-9	747.81
eMedicine	neuro/21

A cerebral arteriovenous malformation (AVM) is a congenital disorder of blood vessels within the brain, characterized by tangle(s) of veins and arteries. While an arteriovenous malformation can occur elsewhere in the body, this article discusses malformations found in the brain.

1 Symptoms
2 Diagnosis
3 Pathophysiology
4 Treatment
5 External links

[edit] Symptoms

The most frequently observed problems related to the mechanical and blood loss (ischemic) effects of an AVM are headache and seizure. Moreover, AVMs in certain critical locations may stop the circulation of the cerebrospinal fluid, causing accumulation of the fluid within the skull and giving rise to a clinical condition called hydrocephalus.

Symptoms of bleeding within the brain (intracranial hemorrhage) include loss of consciousness, sudden and severe headache, nausea, vomiting, incontinence, and blurred vision. A stiff neck can occur as the result of increased pressure within the skull and irritation of the meninges. Impairments caused by local brain tissue damage on the bleed site are possible, including seizure, hemiparesis, a loss of touch sensation on one side of the body, or deficits in language processing (aphasia). A variety of other symptoms can accompany this type of cerebrovascular accident.

Generally, intense headache, perhaps coincident with seizure or loss of bodily consciousness, is the first indication of a cerebral AVM. Estimates of the number of AVM-afflicted people in the United States range from 0.1% to 0.001% [1] [2] of the population.

[edit] Diagnosis

An AVM diagnosis is established by neuroimaging studies. A computed tomography scan of the head (head CT) is usually performed; this can reveal the site of the bleed. More detailed pictures of the tangle of blood vessels that compose an AVM can be obtained by using radioactive reagents injected into the blood stream, then observed using a fluoroscope or Magnetic Resonance Imaging (MRI). A spinal tap (lumbar puncture) can be used to examine spinal fluid for red blood cells; this condition is indicative of leakage of blood from the bleeding vessels into the subarachnoid space. The best images of an AVM are obtained through cerebral angiography. This procedure involves using a catheter, threaded through an artery up to the head, to deliver a contrast agent into the AVM. As the contrast agent flows through the AVM structure, a sequence of X-ray images can be obtained to ascertain the size, shape and extent of that structure.

[edit] Pathophysiology

While the cause of AVMs remains unknown, the main risk is intracranial hemorrhage. This risk is difficult to quantify. Approximately 70% of cases with cerebral AVM are discovered through symptoms caused by sudden bleeding due to the fragility of abnormally-structured blood vessels in the brain. However, some patients may remain asymptomatic or have minor complaints due to the local effects of the tangle of vessels. If a rupture or bleeding incident occurs, the blood may penetrate either into the brain tissue (cerebral hemorrhage) or into the subarachnoid space. This space is located between the sheaths (meninges) surrounding the brain (subarachnoid hemorrhage).

Once an AVM bleeds, the probability of rebleeding increases substantially.

AVMs that do not bleed may cause symptoms by either directly compressing the brain tissue or decreasing the blood flow to the neighbouring tissue (ischemia). Both mechanical and ischemic factors cause a permanent and continuous loss of nerve cells (neurons).

[edit] Treatment

The treatment in the case of sudden bleeding is focused on restoration of vital function. Anticonvulsant medications such as phenytoin are often used to control seizure; medications or procedures may be employed to relieve intracranial pressure. Eventually, curative treatment may be required to prevent recurrent hemorrhage.

Surgical removal of the blood vessels involved (craniotomy) is the preferred curative treatment for most types of AVM. While this surgery results in an immediate, complete removal of the AVM, risks exist.

Radiation treatment (radiosurgery) has been widely used on smaller AVMs with considerable success. The Gamma Knife, developed by Swedish physician Lars Leksell, is one apparatus used in radiosurgery to precisely apply a controlled radiation dosage to the volume of the brain occupied by the AVM. While this treatment is non-invasive, two to three years may pass before the complete effects are known. Complete occlusion of the AVM may or may not occur.

Embolization, that is, occlusion of blood vessels with coils or particles introduced by a radiographically guided catheter, is frequently used as an adjunct to either surgery or radiation treatment. However, embolization alone is rarely successful in completely blocking blood flow through the AVM.