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An arteriovenous
malformation (AVM) is an entanglement of blood vessels that forms
as a result of the failure of embryonic vessels to separate into
arteries and veins. These malformations are exceptionally thin and
without the normal characteristics of arteries or veins. The thinness
of the vessels and the pressure of large amounts of blood flowing
through them make AVM blood vessels susceptible to rupture, causing
bleeding within the brain (Cavernous Malformations/AOVMs
are often confused with AVMs. However, AOVMs symptoms and effects
are different.)
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Also, the increased supply of blood flowing through the AVM causes
a decrease in the blood supply to other parts of the brain. This
rerouting of the blood supply deprives critical tissue of sufficient
blood supply. This deficiency causes damage to tissue within and
around the AVM.
Although some arteriovenous malformations do not cause symptoms,
many become symptomatic in patients between the ages of 10 and
30 years old. Some of the symptoms include:
- Hemorrhage - Bleeding is one of the most
frequent initial symptoms of an AVM and can be either within
the brain or beneath the membrane (meninges) that covers it.
- Seizure - Another frequent initial symptom,
may be preceded by unusual sensory events such as a disagreeable
odor, bitter or metallic taste, ringing or hissing sound,
a sense of familiarity with an unfamiliar environment, or
a sense of unfamiliarity with familiar environment. Seizures
usually include loss of consciousness and uncontrolled shaking
of the body, but some seizures may not be associated with
loss of consciousness.
- Migraine-like Headache - These may be
sudden and severe or they may be more chronic. The combination
of seizure activity and headache should prompt careful consideration
of the presence of an arteriovenous malformation.
- Bruit - (pronounced brew-ee) This is a
noise or murmur caused by the abnormal blood flow to the AVM,
which is heard in rhythm with the heartbeat.
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