Arteriovenous Malformations
(and
Other Vascular Lesions of the Central Nervous System)
What are arteriovenous malformations?
Arteriovenous malformations (AVMs) are defects of the circulatory system that
are generally believed to arise during embryonic or fetal development or soon
after birth. They are comprised of snarled tangles of arteries and veins.
Arteries carry oxygen-rich blood away from the heart to the body's cells; veins
return oxygen-depleted blood to the lungs and heart. The
presence of an AVM disrupts this vital cyclical process. Although AVMs can develop in many
different sites, those located in the brain or spinal cord-the two parts of the
central nervous system-can have especially widespread effects on the body.
AVMs of the brain or spinal cord (neurological AVMs) are believed to affect
approximately 300,000 Americans. They occur in males and females of all racial
or ethnic backgrounds at roughly equal rates.
What are the symptoms?
Most people with neurological AVMs experience few, if
any, significant symptoms, and the malformations tend to be discovered only
incidentally, usually either at autopsy or during treatment for an unrelated disorder. But for about
12 percent of the affected population (about 36,000 of the estimated 300,000
Americans with AVMs), these abnormalities cause symptoms that vary greatly in
severity. For a small fraction of the individuals within this group, such
symptoms are severe enough to become debilitating or even life-threatening. Each
year about 1 percent of those with AVMs will die as a direct result of the AVM.
Seizures and headaches are the most generalized symptoms
of AVMs, but no particular type of seizure or headache pattern has
been identified. Seizures can be partial or total, involving a loss of control
over movement, convulsions, or a change in a person's level of consciousness.
Headaches can vary greatly in frequency, duration, and intensity, sometimes
becoming as severe as migraines. Sometimes a headache consistently affecting one
side of the head may be closely linked to the site of an AVM. More frequently,
however, the location of the pain is not specific to the lesion and may encompass most of the head.
AVMs also can cause a wide range of more specific
neurological symptoms that vary from person to person, depending primarily upon
the location of the AVM. Such symptoms may include muscle weakness or paralysis in one part of the body;
a loss of coordination (ataxia) that can lead to such problems as gait
disturbances; apraxia, or difficulties carrying out tasks that require planning;
dizziness; visual disturbances such as a loss of part of the visual field; an
inability to control eye movement; papilledema (swelling
of a part of the optic nerve known as the optic disk); various problems using or understanding language
(aphasia); abnormal
sensations such as numbness, tingling, or spontaneous pain
(paresthesia or
dysesthesia); memory deficits; and mental confusion, hallucinations, or
dementia. Researchers have recently uncovered evidence that AVMs may also cause
subtle learning or behavioral disorders in some people during their childhood or adolescence, long before more obvious symptoms become
evident.
One of the more distinctive signs indicating the presence of an AVM is an
auditory phenomenon called a bruit, coined from the
French word meaning noise. (A sign is a physical effect observable by a
physician, but not by a patient.) Doctors use this term to describe the
rhythmic, whooshing sound caused by excessively rapid blood flow through the
arteries and veins of an AVM. The sound is similar to that made by a torrent of
water rushing through a narrow pipe. A bruit can sometimes become a symptom-that
is, an effect experienced by a patient-when it is especially severe. When
audible to patients, the bruit may compromise hearing, disturb sleep, or cause significant psychological distress.
Symptoms caused by AVMs can appear at any age, but because these
abnormalities tend to result from a slow buildup of neurological damage over
time they are most often noticed when people are in their twenties, thirties, or
forties. If AVMs do not become symptomatic by the
time people reach their late forties or early fifties, they tend to remain
stable and rarely produce symptoms. In women, pregnancy sometimes causes a
sudden onset or worsening of
symptoms, due to accompanying cardiovascular changes, especially increases in
blood volume and blood pressure.
In contrast to the vast majority of neurological AVMs,
one especially severe type causes symptoms to appear at, or very soon after,
birth. Called a vein of
Galen defect after the
major blood vessel involved, this lesion is located deep
inside the brain. It is frequently associated with hydrocephalus (an
accumulation of fluid within certain spaces in the brain, often with visible
enlargement of the head), swollen veins visible on the scalp, seizures, failure
to thrive, and congestive heart failure. Children born with this condition who
survive past infancy often remain developmentally impaired.
Next: How do arteriovenous malformations damage the brain and spinal cord? »
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