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| Arteriovenous malformations (AVM) |
| Overview |
 | Definition:
 | Complex tangle of abnormal arteries and veins linked by one or more
fistulas. |
| Small arteries have a deficient muscularis. |
| The fistulas allow high-flow, rapid shunting, can induce arterial
hypotension in adjacent areas of the brain. |
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| Learning disorders have been documented in 66 % of adults. |
| May be caused by developmental derangements, or other mechanisms, such as
trauma, occlusion of the venous sinus with the formation of neovascular collaterals,
or occlusion of branch arteries with the formation of arterial collaterals. |
| 10 to 58 percent of patients have classic aneurysms. |
| Usually present before the age of 40 |
| Affect both sexes in nearly equal proportions |
| 0.1 percent of the population (300,000 persons) in the US may have an
AVM. |
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| Symptoms |
| Rupture accounts for 2 percent of all strokes. |
| Autopsy data suggest that as few as 12 percent of AVM are symptomatic
during life. |
| Annual rate of hemorrhage: 2 to 4 percent
| Occurrence of a first hemorrhage is associated with an increased risk of
subsequent hemorrhage, annual rate of rehemorrhage was 18 percent. |
| Risk of rehemorrhage is highest in the first year. |
| Among those with no history of bleeding: bleeding rate 2 percent per
year. |
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| Presenting Symptoms:
| Intracranial hemorrhage: most common |
| Seizures that are not caused by hemorrhage: 16 to 53 percent |
| Headache: 7 to 48 percent of patients, with no distinctive features |
| Focal neurologic deficits without signs of hemorrhage: 1 to 40 percent of
patients. The range in this rate reflects the nonuniformity of definitions of such
deficits. |
| Progressive neurologic deficits: 4 to 8 percent |
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| Potential risks of treatment |
| Persistent neurologic deficits and mortality rates with different forms
of treatment:
| Surgery: 8 percent |
| Endovascular embolization: morbidity of 13 percent and mortality of 2
percent. |
| Staged embolization followed by surgical resection: cumulative rate of
persistent deficits of 9 percent and a mortality rate of 4 percent. |
| Radiotherapy: 2 to 4 percent
 | cannot be readily compared |
| the rate of success of is inversely related to the size of the
arteriovenous malformation. |
| Lesions with diameters > 3 cm are difficult to eradicate. |
| 20% or more of small AVM and up to 80% of the larger AVM may not be
obliterated by radiotherapy. |
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| Spetzler-Martin five-point scale: Score of 4 or 5 points, higher risk of
persistent neuro deficit after surgery.
| Size of lesion (maximal diameter):
| <3 cm: 1 point |
| 3-6 cm: 2 points |
| >6 cm: 3 points |
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| Location:
| Noneloquent: 0 point |
| Sensorimotor, language visual cortex, hypothalamus, internal capsule,
brainstem, cerebellar peduncle, cerebellar nuclei: 1 point |
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| Pattern of venous drainage:
| superficial: 0 point |
| deep: 1 point |
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| Recommendation for treatment |
| After a hemorrhage, patients whose neurologic condition is good and who
have a small arteriovenous malformation located on the cerebral convexity commonly undergo
treatment to obliterate or remove the malformation |
| Asymptomatic patients and those without a history of hemorrhage, the
approach to treatment is less well defined. |
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| References & Further Reading |
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