An AVM is an abnormal tangle of blood vessels in the brain or spine. Some AVMs have no specific symptoms and pose little or no risk to a person’s life or overall health, while others cause severe and devastating effects if they bleed and result in an intracerebral hemorrhage (ICH).
Normally, large arteries carry blood from the heart to all areas of the body. As arteries branch, they become smaller, eventually becoming capillaries. The capillary bed is where the blood exchanges oxygen and nutrients and picks up waste. The blood travels from the capillary bed back to the heart through veins. In an AVM, arteries connect directly to veins without a capillary bed in between, creating a condition known as a high-pressure shunt or fistula. Because the veins cannot handle the pressure of blood coming directly from the arteries, they stretch and enlarge and the weakened blood vessels can rupture and bleed. The surrounding normal tissues also may be damaged as the AVM “steals” blood from those areas.
Signs and Symptoms
Signs and symptoms of an AVM vary depending on its location in brain. Stroke-like symptoms such as confusion, loss of consciousness, headache, vision changes, numbness/tingling sensation in arm or leg, slurred or garbled speech and/or facial droop are common if the AVM results in an ICH. Sudden onset of seizures is another common symptom of brain AVMs whereas spinal AVMs can cause severe sudden back pain, weakness or paralysis in the arms or legs.
AVM treatment options include surgical removal, radiosurgery and/or endovascular treatments. Often, multiple treatments are utilized to fully cure the AVM.
In some cases, a surgical opening is made in the skull (craniotomy) so the brain can be gently retracted to locate the AVM. Using a variety of techniques such as laser and electrocautery, the AVM is shrunken and dissected from normal brain tissue.
In endovascular treatment, small catheters are inserted through the groin and threaded up into the blood vessels of the brain to deliver materials to occlude the abnormal vessels of the AVM in a process called embolization. The materials allow for blood to no longer flows through the malformation thus decreasing the likelihood of rupture and bleeding into the brain. These procedures are performed in the angiography suites of the Radiology Department by a Neuro Interventionalist. Many times a patient may undergo embolization of their AVM prior to surgery in an effort to assist the surgeon to safely remove the abnormal vessels.
Radiosurgery aims a precisely focused beam of radiation at the abnormal vessels. After six months to two years, the vessels gradually close off and are replaced by scar tissue. This treatment is best suited for smaller AVMs and may take a long time to show effect (during which time risk of hemorrhage exists). However, radiosurgery is a quick, painless, non-invasive out-patient procedure that requires no incision.
Related Condition of AVMs
A cavernous malformation, also called cavernous hemangioma, is a cluster of abnormal blood vessels. Viewed under a microscope, a cavernous malformation appears to be a blood-filled cavern in the brain. These blood vessel malformations can also occur in brain stem, the spinal cord, the covering of the brain (dura), or the nerves of the skull. The lesion may be compact, and there is typically no brain tissue located within its walls. Cavernomas can cause small hemorrhages or leaks within the enclosed cluster of vessels. Typically this blood does not leak out into the rest of the brain tissue. Frequently patients diagnosed with a cavernoma will have multiple cavernomas in various places in the brain.
Cavernomas are usually detected when the cavernoma bleeds, leading to signs and symptoms such as: headaches, seizures, and other neurological deficits like vision changes, weakness in an arm or leg, or changes in speech. Many times patients will describe multiple episodes of headaches that will go away and then come back. These headaches occur in response to leakage of blood or multiple small bleeds from the cavernoma.
Cavernoma treatment includes observation, surgical excision, or stereotactic radiosurgery.
If the cavernoma is surgically accessible and the patient is experiencing neurological symptoms and/or seizures, surgical treatment is an option. Current microsurgical techniques involve specialized approaches and sophisticated intra-operative neurological monitoring.
If a cavernoma is located in the brain stem, the patient will need specialized monitoring in the operating room and possible placement of an external pacemaker to control vital functions such as heart rate and breathing, since many of those functions are located in the brainstem.
Stereotactic radiosurgery treatment for symptomatic brainstem cavernomas may be used if the risk of surgery is high or when lesions are surgically inaccessible.