Arteriovenous Malformation
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What is an AVM?
A cerebral arteriovenous malformation (AVM) is an abnormal connection between the arteries and veins in the brain.
What are the symptoms?
The most frequently observed problems related to an AVM are headaches and seizures while at least 15% of the population at detection has no symptoms at all.
Other common symptoms are a pulsing noise in the head, progressive weakness and numbness and vision changes. In serious cases, the blood vessels rupture and there is bleeding within the brain (intracranial hemorrhage). Nevertheless in more than half of patients with AVM, hemorrhage is the first symptom. Symptoms due to bleeding include loss of consciousness, sudden and severe headache, nausea, vomiting, incontinence, and blurred vision, amongst others. Impairments caused by local brain tissue damage on the bleed site are also possible, including seizure, one-sided weakness (hemiparesis), a loss of touch sensation on one side of the body and deficits in language processing (aphasia). Minor bleeding can occur with no noticeable symptoms.
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. A stiff neck can occur as the result of increased pressure within the skull and irritation of the meninges.
How is it diagnosed?
An AVM diagnosis is established by neuroimaging studies after a complete neurological and physical examination. Three main techniques are used to visualize the brain and search for AVM: computed tomography (CT), magnetic resonance imaging (MRI), and cerebral angiography. A CT scan of the head is usually performed first when the subject is symptomatic. It can suggest the approximate site of the bleed.
MRI is more sensitive than CT in the diagnosis of AVMs and provides better information about the exact location of the malformation. More detailed pictures of the tangle of blood vessels that compose an AVM can be obtained by using radioactive agents injected into the blood stream. If a CT is used in conjunction of dye this is called a computerized tomography angiogram while if MRI is used it is called magnetic resonance angiogram. 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 are obtained.
Treatments for AVMs?
Treatment depends on the location and size of the AVM and whether there is bleeding or not. 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. However, any type of intervention may also carry a risk of creating a neurological deficit.
Surgical elimination of the blood vessels involved is the preferred curative treatment for many types of AVM. It is performed by a neurosurgeon who temporarily removes part of the skull (craniotomy) and separates the AVM from surrounding brain tissue. While this surgery results in an immediate, complete removal of the AVM, risks exist depending on the size and the location of the malformation and in some cases other methods would be preferred.
Radiosurgery has been widely used on small AVMs with considerable success. The Gamma Knife, is an apparatus used 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, and 8%-10% of patients develop long-term neurological symptoms after radiation.
Embolization is the occlusion of blood vessels most commonly with a glue-like substance introduced by a radiographically guided catheter. Such glue blocks the vessel and reduces blood flow into the AVM. Embolization is frequently used as an adjunct to either surgery or radiation treatment. Before other treatments it reduces the size of the AVM while during surgery it reduces the risk of bleeding. However, embolization alone may completely block the blood flow through the AVM in 30- 60 % of AVM's. This has the advantage of being minimally invasive technique with much faster recovery than with conventional surgical techniques.