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.
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.
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.
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