Arteriovenous malformation (AVM)
A cerebral arteriovenous malformation is an abnormal connection that usually forms before birth between the arteries and veins in the brain. The cause of AVMs is unknown. The condition occurs when arteries in the brain connect directly to nearby veins without having the normal vessels (capillaries) between them.
Arteriovenous malformations vary in size and location in the brain. An AVM rupture occurs because of pressure and damage to brain tissue, as well as a lack of blood flow to the brain. Symptoms also can occur when large AVMs that have not bled press on the brain tissue.
AVMs occur in less than 1 percent of people. Although the condition is present at birth, symptoms can occur at any age. Hemorrhages occur most often in people ages 15-20, but also can occur later in life. Some patients with an AVM also have cerebral aneurysms.
There often are no symptoms until the AVM ruptures. This results in sudden bleeding in the brain (hemorrhagic stroke)In more than half of patients with AVM, hemorrhage is the first symptom. Symptoms of AVM hemorrhage are the same as those of other intracerebral hemorrhage.
Physical and neurological exams are needed, but they could be completely normal. Tests that might be used to diagnose an AVM include:
- Cerebral angiogram.
- Cranial MRI.
- Electroencephalogram (EEG).
- Head CT scan.
- Magnetic resonance angiography (MRA).
A bleeding AVM is a medical emergency. The goal of treatment is to prevent further complications by controlling the bleeding and seizures and, if possible, removing the AVM.
- Open brain surgery.
- Endovascular treatment.
Some treatment options are used together.
- Open brain surgery removes the malformation through an opening made in the skull.
- Embolization (endovascular treatment). The injection of a glue-like substance into the abnormal vessels to stop blood flow in the AVM and reduce the risk of bleeding. This may be the first choice for some kinds of AVMs, or if surgery cannot be done.
- Stereotactic radiosurgery. This procedure delivers radiation directly to the area of the AVM to cause scarring and shrinkage. The procedure can control bleeding and other symptoms and is particularly useful for small, deep AVMs that are difficult to remove by surgery.
Dural AV fistulas (DAVF)
A dural arteriovenous fistula is a site of abnormal connectivity between arteries and veins, where the abnormal connection, or fistula, lies in the covering of the brain or spinal cord known as the dura.
Unlike AVMs, which are thought to be present from birth, cranial DAVF often develop later in life following blockage or thrombosis of a cranial dural venous sinus. When a venous sinus blocks off, the brain can try to compensate by moving venous blood across other collateral pathways. In this process, however, a fistula might form, representing an abnormal collateral pathway to drain blood away from the brain. This could occur due to chronic central nervous system infection, brain trauma, or a patient with a tendency to experience thrombosis.
DAVF can occur in the brain (cranial DAVF), or in the spinal cord (spinal DAVF).
- A cranial DAVF is supplied by branches of the carotid artery and possibly also by branches of the vertebral artery before these arteries penetrate the dura. The fistula usually resides in the dura overlying the brain hemisphere, or in the dura between the forebrain and hindbrain.
- A spinal DAVF is supplied by dural arterial branches arising from the aorta's spinal arteries. The fistula itself is in the spinal nerve root dural sleeve. Typically, a spinal DAVF occurs somewhere in the lower half of the spine.
Cranial DAVF are more commonly diagnosed in women over the age of 40, while spinal DAVF are more commonly diagnosed in men over the age of 40.
Depending on the location of the fistula:
- Symptoms of a cranial DAVF may be a "whooshing sound" heard by the patient, or abnormal eye bulging and pulsation, and impairment of vision and/or eye movement. Isolated but persistent headaches, or symptoms of a brain hemorrhage including a sudden severe headache, neurological impairment and/or collapse are also common.
- Symptoms of a spinal DAVF may be slow but progressive loss of function in the limbs (more often the legs than the arms), bowel and bladder dysfunction including incontinence, and progressive erectile dysfunction in males.
Any of the above symptoms and signs may lead to investigation by your specialist. Unfortunately, in the case of spinal DAVF, the diagnosis may be missed or delayed because such lesions occur so rarely, and when they do occur, their symptoms and signs may be mistaken for disk disease or spinal cord inflammation.
For a cranial DAVF, regular CT scanning is not very helpful in diagnosing a fistula, but it might show a hemorrhage from a fistula. CT angiography, which is CT arteriography plus CT venography, is helpful in defining a cranial fistula, as are MRI techniques. However, the standard for detection and characterization of a DAVF is cerebral angiography.
For a spinal DAVF, the standard is selective spinal angiography. In this process, a catheter is used to inject multiple spinal segmental arteries arising from the aorta, one-by-one, until the fistula is found and characterized.
The two main ways of treating a DAVF are through open surgery or endovascular surgery.
- Open surgery. The goal of surgery is to physically disconnect the fistula in the dura, with particular attention to obliterating the draining vein. Open surgery for a DAVF typically has a very high success rate.
- Endovascular surgery. This involves a catheter-based technique of squirting "glue" into the arteries feeding the DAVF, or directly into the vein draining the DAVF. This process is known as embolization. Sometimes, embolization is used alone to obliterate the fistula, or it may be used as an additional option prior to open surgery to help shut down as much of the fistula as possible.