Cerebral arteriovenous malformation (AVM) is a disorder of the blood vessels consisting of an abnormal connection between the arteries and the veins in the brain. It’s a congenital disorder commonly resulting in tangled masses of thin-walled, dilated blood vessels between arteries and veins that aren’t connected by capillaries. AVM primarily occurs in the posterior portion of the cerebral hemispheres. Adequate perfusion of brain tissue is prevented due to abnormal channels between the arterial and venous systems that allow mixing of oxygenated and unoxygenated blood. AVMs range in size from a few millimeters to large malformations that extend from the cerebral cortex to the ventricles. Patients typically present with multiple AVMs.
Complications of AVM include development of aneurysm and subsequent rupture, hemorrhage (intracerebral, subarachnoid, or subdural, depending on the location of the AVM), and hydrocephalus.
Although some AVMs occur as a result of penetrating injuries such as trauma, most are present at birth. However, symptoms typically don’t occur until between the ages 10 and 20. Very large AVMs may short-circuit blood flow enough to cause cardiac decompensation, in which the heart can’t pump enough blood to compensate for bleeding in the brain. This typically occurs in infants and young children.
The vessels of an AVM are very thin and one or more arteries feed into it, causing it to appear dilated and tortuous. Typically, high-pressured arterial flow moves into the venous system through the connecting channels to increase venous pressure, engorging and dilating the venous structures. If the AVM is large enough, the shunting can deprive the surrounding tissue of adequate blood flow. Thin-walled vessels may ooze small amounts of blood — they may even rupture — causing hemorrhage into the brain or subarachnoid space.
Cerebral arteriovenous malformations occur in approximately 3 out of 10,000 people. Although the lesion is present at birth, symptoms may occur at any time. Two-thirds of cases occur before age 40. Evidence suggests that AVMs run in families. Males and females are affected equally.
An AVM may be asymptomatic until complications occur; these may include rupture and a resulting sudden bleed in the brain, known as a hemorrhagic stroke. Arteriovenous malformations vary in size and location within the brain. Systolic bruit may be auscultated over the carotid artery, mastoid process, or orbit on examination.
Symptoms that occur prior to an AVM rupture are related to smaller and slower bleeding from the abnormal vessels, which are usually fragile because their structure is abnormal.
In more than half of patients with AVM, hemorrhage from the malformation is the first symptom. Depending on the location and the severity of the bleed, the hemorrhage can be profoundly disabling or fatal. The risk of bleeding from an AVM is approximately 2% to 4% per year.
The first symptoms often include headache, seizure, or other sudden neurological problems, such as vision problems, weakness, inability to move a limb or a side of the body, lack of sensation in part of the body, or abnormal sensations, such as ringing and numbness. Symptoms are the same as for stroke. The individual with an AVM may complain of chronic mild headache, a sudden and severe headache, or a localized or general headache. The headache may resemble migraine and vomiting may occur. Seizures may result from focal neurologic deficits (depending on the location of the AVM) resulting from compression and diminished perfusion. Symptoms of intracranial (intracerebral, subarachnoid, or subdural) hemorrhage result. Muscle weakness and decreased sensation can occur in any part of the body. Mental status change can occur where the individual appears sleepy, stuporous, lethargic, confused, disoriented, or irritable. Additional symptoms may include stiff neck, speech or sense of smell impairment, dysfunctional movement, fainting, facial paralysis, eyelid drooping, tinnitus, dizziness, and decreased level of consciousness (LOC).
If an AVM bleeds once, the risk is greater that it will bleed again in the future. Intracerebral or subarachnoid hemorrhages are the most common first symptoms of cerebral arteriovenous malformation. In some cases, symptoms may also occur due to 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. Progressive loss of nerve cells in the brain may occur, caused by mechanical (pressure) and ischemic (lack of blood supply) factors.
Tests used to diagnose AVM include head computed tomography scan, cranial magnetic resonance imaging, and magnetic resonance angiography. An EEG may be performed if symptoms include seizures, but this test isn’t diagnostic of the specific area of the lesion.
Cerebral arteriogram confirms the presence of AVMs and evaluates blood flow. Doppler ultrasonography of cerebrovascular system indicates abnormal, turbulent blood flow.
General support measures include aneurysm precautions to prevent possible rupture. This involves placing the patient on bed rest or with limited activity and maintaining a quiet atmosphere. Analgesics may be given for headache, and sedatives may be given to help calm the patient and prevent rupture. Stool softeners may be given to prevent straining at stool, which increases intracranial pressure.
A bleeding AVM is a medical emergency requiring immediate hospitalization. The goal of treatment is to prevent further complications by limiting bleeding, controlling seizures and, if possible, removing the AVM. Surgery for correction may include block dissection, laser, or ligation to repair the communicating channels and remove the feeding vessels. Embolization or radiation therapy may be done, if surgery isn’t possible, to close the communicating channels and feeder vessels, thereby reducing blood flow to the AVM. Open brain surgery, endovascular treatment, and radiosurgery may be used separately or in any combination, depending upon the physician and the patient’s individual situation. Surgery is dependent upon the accessibility and size of the lesion and the patient’s status. Open brain surgery involves the actual removal of the malformation in the brain through an opening made in the skull. This surgery is particularly risky because the surgery itself may cause the AVM to bleed uncontrollably.
Embolization (injecting a gluelike substance into the abnormal vessels to stop aberrant blood flow into the AVM) may be an alternative if surgery isn’t feasible due to the size or location of the lesion. Stereotactic radiosurgery may also be an alternative for patients with inoperable arteriovenous malformations. It’s particularly useful for small, deep lesions, which are difficult to remove by surgery.
Anticonvulsant medications such as phenytoin are usually prescribed if seizures occur.
❑Monitor vital signs and titrate medications to control hypertension
❑Monitor neurologic status.
❑Monitor for seizure activity and institute seizure precautions.
❑Maintain a quiet atmosphere and provide relaxation techniques.
❑Discuss the importance of reporting any signs of intracranial bleeding immediately (sudden severe headache, vision changes, decreased movement in extremities, and change in LOC).
❑Refer to social service for support services if neurological deficits have occurred from a ruptured AVM.
Review other book chapters online related to Arteriovenous Malformation:
Copyright notice for book excerpts: Copyright © 2008 Lippincott Williams & Wilkins. All rights reserved.
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More About This Book:
Title: Professional Guide to Diseases (Eighth Edition) Authors: Springhouse Publisher: Lippincott Williams & Wilkins Copyright: 2005 ISBN: 1-58255-370-X 
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