A cerebral arteriovenous malformation is an abnormal connection between the
arteries and veins in the brain. Signs and symptoms
The most frequently observed problems, related to an AVM, are headaches and
seizures, backaches, neckaches and eventual nausea, as the coagulated blood
makes its way down to be dissolved in the individual's spinal fluid. It is
supposed that 15% of the population, at detection, have no symptoms at all.
Other common symptoms are a pulsing noise in the head, progressive weakness
and numbness and vision changes as well as debilitating, excruciating pain.
In serious cases, the blood vessels rupture and there is bleeding within the
brain. 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, a loss of
touch sensation on one side of the body and deficits in language processing.
Minor bleeding can occur with no noticeable symptoms. Following the
bleed's cessation, most AVM victims return to normal, after the blood vessel
has had time to repair itself. 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.
Diagnosis 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, magnetic resonance imaging, 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 conjunctiangiogram, 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. Grading
A common method of grading cerebral AVMs is the Spetzler-Martin grade. This
system was designed to assess the patient's risk of neurological deficit
after open surgical resection, based on characteristics of the AVM itself. Based
on this system, AVMs may be classified as grades 1 - 5. This system was not
intended to characterize risk of hemorrhage.
"Eloquent cortex" is a name used by neurologists for areas of cortex that,
if removed will result in loss of sensory processing or linguistic
ability, minor paralysis, or paralysis. The risk of post-surgical neurological
deficit increases with increasing Spetzler-Martin grade.
Pathophysiology AVMs are an abnormal connection between
the arteries and veins in the human brain. Arteriovenous malformations are
most commonly of prenatal origin. The cause of AVMs remains unknown. In a
normal brain oxygen enriched blood from the heart travels in sequence through
smaller blood vessels going from arteries, to arterioles and then
capillaries. Oxygen is removed in the latter vessel to be used by the brain.
After the oxygen is removed blood reaches venules and later veins which
will take it back to the heart and lungs. On the other hand when there is
an AVM blood goes directly from arteries to veins through the abnormal vessels
disrupting the normal circulation of blood.
Prognosis The main risk is intracranial
hemorrhage. This risk is difficult to quantify since many patients with
asymptomatic AVMs will never come to medical attention. Small AVMs tend to
bleed more often than do larger ones, the opposite of cerebral aneurysms. If a
rupture or bleeding incident occurs, the blood may penetrate either into the
brain tissue or into the subarachnoid space, which is located between the
sheaths surrounding the brain. Bleeding may also extend into the ventricular
system. Cerebral hemorrhage appears to be most common. One long-term study of
over 150 symptomatic AVMs found the risk of cerebral hemorrhage to be
approximately 4% per year, slightly higher than the 2-3% seen in other
studies. A simple, rough approximation of a patient's lifetime bleeding risk is
105 -. This equation assumes a 3% yearly bleeding risk. For example, a healthy
30-year-old patient would have approximately a 75% lifetime risk of at
least one bleeding event. Treatment
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. Preventive treatment of as yet
unruptured brain AVMs has been controversial, as several studies
suggested favorable long-term outcome for unruptured AVM patients not
undergoing intervention. The NIH-funded longitudinal ARUBA study compares the
risk of stroke and death in patients with preventive AVM eradication versus
those followed without intervention. Interim results suggest that fewer
strokes occur as long as patients with unruptured AVM do not undergo
intervention. Because of the higher than expected event rate in the
interventional arm of the ARUBA study, NIH/NINDS has stopped patient enrollment
in April 2013, while continuing to follow all participants to determine
whether the difference in stroke and death in the two arms changes over time.
Surgical elimination of the blood vessels involved is the preferred
curative treatment for many types of AVM. Surgery is performed by a
neurosurgeon who temporarily removes part of the skull, separates the AVM
from surrounding brain tissue, and resects the abnormal vessels. While
surgery can result in an immediate, complete removal of the AVM, risks exist
depending on the size and the location of the malformation. The preferred
treatment of Spetzler-Martin grade 1 and 2 AVMs in young, healthy patients is
surgical resection due to the relatively small risk of neurological damage
compared to the high lifetime risk of hemorrhage. Grade 3 AVMs may or may not
be amenable to surgery. Grade 4 and 5 AVMs are not usually surgically treated.
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 does not require an incision and craniotomy, three or more years may
pass before the complete effects are known, during which time patients are at
risk of bleeding. Complete obliteration of the AVM may or may not occur after
several years, and repeat treatment may be needed. Radiosurgery is itself not
without risk. In one large study, nine percent of patients had transient
neurological symptoms, including headache, after radiosurgery for AVM.
However, most symptoms resolved, and the long-term rate of neurological symptoms
was 3.8%. 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 obliterate some AVMs. In high flow
intranidal fistula we can use balloon to reduce the flow so that embolization can
be done safely. Epidemiology
The annual new detection rate incidence of AVMs is approximately 1 per 100,000 a
year. The point prevalence in adults is approximately 18 per 100,000. AVMs are
more common in males than females, although in females pregnancy may start
or worsen symptoms due the increase in blood flow and volume it usually brings.
Research directions No randomized, controlled clinical trial
has established a survival benefit for treating patients with AVMs that have
not yet bled. References
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External links The Aneurysm and AVM Foundation