Arteriovenous Malformation (cont.)
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What Are the Health Consequences of AVMs?
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The greatest potential danger posed by AVMs is hemorrhage. Researchers believe that each year between 2 and 4 percent of all AVMs hemorrhage. Most episodes of bleeding remain undetected at the time they occur because they are not severe enough to cause significant neurological damage. But massive, even fatal, bleeding episodes do occur. The present state of knowledge does not permit doctors to predict whether or not any particular person with an AVM will suffer an extensive hemorrhage. The lesions can remain stable or can suddenly begin to grow. In a few cases, they have been observed to regress spontaneously. Whenever an AVM is detected, the individual should be carefully and consistently monitored for any signs of instability that may indicate an increased risk of hemorrhage.
A few physical characteristics appear to indicate a greater-than-usual likelihood of clinically significant hemorrhage. Smaller AVMs have a greater likelihood of bleeding than do larger ones. Impaired drainage by unusually narrow or deeply situated veins also increases the chances of hemorrhage. Pregnancy also appears to increase the likelihood of clinically significant hemorrhage, mainly because of increases in blood pressure and blood volume. Finally, AVMs that have hemorrhaged once are about nine times more likely to bleed again during the first year after the initial hemorrhage than are lesions that have never bled.
The damaging effects of a hemorrhage are related to lesion location. Bleeding from AVMs located deep inside the interior tissues, or parenchyma, of the brain typically causes more severe neurological damage than does hemorrhage by lesions that have formed in the dural or pial membranes or on the surface of the brain or spinal cord. (Deeply located bleeding is usually referred to as an intracerebral or parenchymal hemorrhage; bleeding within the membranes or on the surface of the brain is known as subdural or subarachnoid hemorrhage.) Thus, location is an important factor to consider when weighing the relative risks of surgical versus non-surgical treatment of AVMs.
Medically Reviewed by a Doctor on 2/4/2013
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