What are the health consequences of arteriovenous malformations (AVM)?


The greatest potential danger posed by AVMs is hemorrhage. Researchers believe that each year, two and four 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. However, massive, even fatal, bleeding episodes do occur. The present state of knowledge does not permit doctors to predict whether a particular patient of AVM will suffer an extensive hemorrhage. The lesions can remain stable or start growing suddenly. In some cases, they have also 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 larger ones. Impaired drainage by unusually narrow or deeply situated veins increases the chances of hemorrhage. Pregnancy also appears to increase the likelihood of clinically significant hemorrhage, mainly due to increased blood pressure and volume. Finally, AVMs that have hemorrhaged once are nine times more likely to bleed again during the first year, as compared to 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 causes more severe neurological damage than hemorrhage by lesions 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.

This answer from the National Institute of Neurological Disorders and Stroke has been reviewed and/or edited by Dr. William D. Knopf.