A brain arteriovenous malformation (AVM) is a complex, abnormal network of blood vessels in the brain. In a healthy brain, blood circulates from arteries to veins via tiny vessels called capillaries. The capillaries allow for the exchange of oxygen and nutrients from the blood to the brain tissue, and the removal of waste products. However, in a brain AVM, direct connections form between the arteries and veins, bypassing these capillaries. This abnormality can disrupt normal blood flow and oxygen circulation.
Whilst AVMs may lead to health problems, many do not cause any problems and can be left alone without treatment.
The most frequently observed problems related to a cerebral AVM are headaches and seizures. These headaches can vary in intensity and frequency, potentially mimicking migraines in some instances. Seizures may manifest in various ways, ranging from changes in a person’s behavior or consciousness to involuntary movements or loss of control over movement. In serious cases, the abnormal blood vessels in an AVM may rupture, causing bleeding within the brain (intracranial haemorrhage). Bleeding from a ruptured AVM can cause a sudden, severe headache, nausea, vomiting, incontinence, blurred vision, and even loss of consciousness. Depending on the location of the bleed, impairments caused by local brain tissue damage are also possible, including seizure, weakness on one side of the body (hemiparesis), a loss of touch sensation on one side of the body, and deficits in language processing (aphasia).
Cause
The exact cause of brain AVMs is not fully understood, but they are most commonly believed to originate before birth. They may grow over time or remain static in size.
Epidemiology of Brain AVMs
Brain AVMs are relatively rare, with an estimated annual detection rate of around 1 per 100,000 people. The prevalence in adults is approximately 18 per 100,000.
AVMs seem to occur more often in males than females. However, symptoms may start or worsen in females during pregnancy due to the increased blood flow and volume. There is also a significant occurrence (15-20%) of AVMs in patients with hereditary hemorrhagic telangiectasia, also known as Osler-Weber-Rendu syndrome, which is a genetic disorder that leads to abnormal blood vessel formation.
Prognosis of Brain AVMs
The main risk associated with brain arteriovenous malformations (AVMs) is intracranial hemorrhage, which is bleeding inside the skull. This risk varies among patients and is difficult to measure because many patients with AVMs don’t show symptoms and therefore never seek medical attention.
The earlier in life an AVM appears, the greater the likelihood of experiencing a haemorrhage over one’s lifetime. Ruptured AVMs can lead to serious health complications. Ruptures may cause loss of life or permanent disability.