An AVM (arterio-vascular malformation) is a tangled bundle of abnormal arteries and veins that are directly connected to each other. Under normal circumstances an artery gives rise to tiny capillaries which are interposed within the tissue of the brain. Nutrients and oxygen leave the capillaries to nourish the adjacent brain cells. The capillaries then give rise to a vein which drains blood back to the heart. In an AVM, however, blood is shunted from an artery directly into a vein without having nourished brain tissue. In fact, brain tissue is entirely displaced to the outskirts of the malformed tangle of vessels of an AVM.
An AVM may be located on the surface of the brain or deep within the brain. An AVM is supplied by one or more feeding arteries, and blood exits via one or more draining vein. Most AVMs are congenital malformations, meaning that they were present at birth. Dural AVMs are a special type of malformation which can develop in childhood or adult life. AVMs are rare; bleeding from an AVM accounts for only 1% of all strokes. Because of their rarity and complexity, AVMs should only be treated by experienced specialists.
What problems can result from having an AVM?
AVMs are usually detected when the patient develops symptoms. If no symptoms develop, it may be possible to live one's entire life with an AVM and never know it. The following represents symptoms associated with an AVM.
Bleeding. About 40-50% patients present with bleeding (or hemorrhage), which is the most feared complication of an AVM. This usually occurs in patients between ages 30 to 50. If an AVM is deep in the brain, blood is released into the brain tissue; this occurs about 2/3 of the time and is called an intracerebral hemorrhage. If an AVM is on the brain surface bleeding is released into the CSF, which is called subarachnoid hemorrhage.
Seizures (or convulsions). In 33% of patients, AVMs are diagnosed when the patient develops seizures. Patients presenting with seizures as an initial symptom are usually younger than those presenting with hemorrhage. Because of where the malformations are usually located, patients may report non convulsive seizures (episodes of odd sensations or visual hallucinations).
Headaches. In about 15% of patients the first symptom occurs as a headache. Like seizures, headaches usually first present in patients during adolescence. Typically patients have throbbing headaches which always occur in the same location.
Focal neurologic deficits. AVMs may occasionally manifest as weakness on one side of the body, sensory loss, or a speech or visual disturbance. This can result from either local brain compression, or less commonly from ischemia in adjacent brain regions if the AVM "steals" blood flow intended for that area.
How is an AVM treated in a neuro-ICU?
The primary role of the neuro-ICU in AVM patients is for treating the complications of hemorrhage. This may include reduction of blood pressure (to prevent rebleeding and limit brain swelling), prevention of seizures, and treatment of brain swelling (cerebral edema) and increased intracranial pressure. Once a ruptured AVM is stabilized, it can be treated by surgery, focal beam irradiation, or endovascular therapy aimed at blocking off the feeding arteries. Research is being done into treating AVM patients with glue which is injected into an appropriate feeding artery. The intention is to have the embolus become lodged in the feeding artery, in order to prevent blood from entering the malformation. This type of treatment generally requires monitoring in a neuro-ICU.