a congenital disorder of the blood vessels in the brain where there is an abnormal connection between arteries and veins. cerebral aneurysms can sometimes occur with avms but are a separate entity.
Causes, incidence, and risk factors
Cerebral arteriovenous malformation (AVM) is a congenital disorder. The cause of abnormal blood vessel development in the brain is unknown.
Arteriovenous malformations vary greatly from person to person. The size varies, from massive lesions involving multiple vessels to lesions so small they are difficult to distinguish on testing. Large malformations may have enough blood flow through them to stress the pumping ability of the heart, especially in young patients.
There are often no symptoms until complications occur. In many cases, symptoms are related to bleeding from the abnormal vessels, which are often fragile and lack the normal supportive structure of arteries and veins. Up to 70% of people with AVM present with bleeding from the malformation at some point. The risk of bleeding is approximately 2-4% per year. While there is some controversy regarding this, in general, small lesions are more likely to bleed than large ones. If a lesion bleeds once, the risk is increased that it will bleed again in the future. Intracerebral or subarachnoid hemorrhages are the most common presentations of cerebral arteriovenous malformation.
Symptoms may also occur because of lack of blood flow to an area of the brain (ischemia), compression or distortion of brain tissue by large AVMs, or abnormal brain development in the area of the malformation. There may be a progressive loss of nerve cells in the brain caused by mechanical and ischemic factors. In some instances, hydrocephalus may develop, usually in the setting of hemorrhage. Cerebral arteriovenous malformations occur in approximately 3 out of 10,000 people. AVMs are slightly more common in males. Although the lesion is present at the time of birth, symptoms may occur at any time. Most often, symptoms develop before age 33 with about two-thirds presenting before the age of 40.
Signs and tests
Neurologic and muscular examination may indicate bleeding in the brain. There may be signs of increased intracranial pressure , focal neurologic deficits (loss of specific neurologic functions), or other abnormal findings. In some cases, a bruit (whooshing sound heard with the stethoscope) may be heard over the carotid arteries of the neck or over the eye or jaw. Tests that may be used to diagnose AVM include:
A head CT scan
A cerebral angiogram
A cranial MRI An EEG ( electroencephalogram ) may be performed if symptoms include seizures .
Treatment
Because symptoms do not usually appear until serious complications such as bleeding occur, arteriovenous malformation is often an emergency condition requiring immediate hospitalization and treatment. The goal of treatment is to prevent further complications. Treatment whether it be open surgery, endovascular treatment (also known as embolization) and/or radiosurgery is usually indicated for AVMs. Very large AVMs may allow enough short-circuit blood flow to cause cardiac decompensation (where the heart is unable to pump enough blood to compensate for bleeding in the brain). This condition is usually identified in infants and young children. Diagnosis of a cerebral AVM may be made prior to a catastrophic hemorrhage because of recurrent headaches . Early diagnosis is preferable to diagnosis following a catastrophic hemorrhage into the intracranial space. Surgical intervention is dependent upon accessibility of the lesion and status of the patient at the time of surgery. Other indications include increased intracranial pressure (pressure within the brain), and to prevent worsening of loss of brain functions (neurologic deficits). Surgical treatment usually consists of resecting the malformation. Embolization (occlusion of the blood vessel by injecting a substance into the vessel that acts like a clot to stop blood flow) may be an alternative if surgery is not feasible because of size, location, or other factors. Stereotactic radiosurgery may be another alternative treatment for inoperable arteriovenous malformations. Anticonvulsant medications such as phenytoin may be prescribed if seizures occur.
Expectations (prognosis)
The expected outcome varies. Approximately 10% of cases presenting with hemorrhage are fatal. Seizures and neurologic changes may be permanent or may resolve with treatment.
Calling your health care provider
Go to the emergency room or call the local emergency number (such as 911) if severe headache with vomiting , seizures , muscle weakness , numbness of parts of the body, or other symptoms of arteriovenous malformation occur.
Prevention
The cause, and prevention, is unknown.