Arteriovenous Malformations (AVMs) and AV Fistulas

Arteriovenous malformations (AVMs) are abnormal tangles of arteries and veins. While many AVMs remain asyptomatic for life, they can cause serious problems when they occur inside the brain as a cerebral AVM, or in the brain’s covering (the dura) as a dural AVM, or in the spinal cord as a spinal AVM.

AV fistulas are an abnormal connection between arteries and veins. This condition can occur in the brain, the covering of the brain (dura) and the spinal cord. They can cause symptoms by affecting the surrounding brain or spinal cord, and in some cases from bleeding.

In both conditions, the capillaries that normally exchange blood between the arteries and the veins don’t develop in a certain area, and as a result, the arteries dump blood directly into the veins. Unlike arteries, the veins do not have strong walls. Over time, because of the high blood pressure of arterial blood flow, these veins dilate and become engorged, creating the risk of rupture and hemorrhage, as well as seizures, headaches and other symptoms. These symptoms typically develop between the second and fourth decade of life. Half of all brain AVMs present with a brain hemorrhage, while the rest typically present as a seizure (25%), a headache (usually one sided and migraine-like), or a neurological deficit. Studies indicate that untreated AVMs carry a high long-term risk of hemorrhage, stroke or death.

Associated Conditions

The primary goal of AVM treatment is to prevent hemorrhage, control seizures, and arrest or reverse the neurologic deficits, while minimizing the risk related to the treatment.

Incidental Asymptomatic AVMs

Because of the prevalence of brain scanning, a small number of asymptomatic AVMs are incidentally discovered. Because the long-term natural history of these lesions has not been clearly defined, we recommend a comprehensive discussion of all treatment options including observation. In addition, we recommend a cerebral angiogram to identify any associated aneurysm or vein stenosis that might require urgent treatment. The ARUBA clinical study attempted to compare observation to treatment for AVMs without brain hemorrhage. The study was terminated early without long term follow-up data, as patients who were simply observed had less side effects in the short term than those who underwent different forms of treatment. However one of the primary goals in the care of any AVM patient is long-term elimination or reduction in the risk of brain hemorrhage (stroke). We believe that every patient must be considered as an individual and the specific short and long-term benefits and risks discussed in detail. Every patient and every AVM is different.

Aneurysms Associated with AVMs

15% of AVMs are associated with brain aneurysms. Since the rupture of an aneurysm carries a high mortality rate, we usually recommend treating these aneurysms.

Recent Hemorrhage from an AVM

An AVM that has recently hemorrhaged is at a greater risk of another bleed. The re-bleed rate over the first year following a hemorrhage is approximately 10%. In these cases, we usually initiate treatment whenever the patient is stable. In life-threatening hemorrhages, urgent treatment might be needed.

AVM and Epilepsy

Seizures are frequently associated with AVMs. While most of these can be well controlled with medications, surgical treatment of the AVM may also be done to reduce or eliminate the seizures, especially if they are of recent onset.

Treating AVMs

AVMs should be treated once they declare themselves and become symptomatic, whether the symptoms involve a hemorrhage, a seizure, a headache, or a neurologic deficit.

The patient's age, the location of the AVM, and its angiographic picture play a major role in the evaluation and treatment of these lesions. Cerebral angiography remains the gold standard for evaluating AVMs and identifying any associated aneurysms. MRI and MRA scans can also be useful for providing three-dimensional details about the AVM, while CT scans are useful in evaluating past and current bleeding of the AVM. 

The goal of treatment is to completely eliminate the AVM. Incomplete or partial treatment, in which a residual amount of the AVM remains, has actually been associated with a higher complication rate than of leaving an AVM untreated. Microsurgery, stereotactic radiosurgery and endovascular embolization, used alone or in combination, are the mainstays of AVM treatment. Our cerebrovascular surgeons have extensive expertise in all three approaches. Treatment options are recommended based on an individual assessment of each patient.

Microsurgical Resection

Surgical resection is the preferred method of treatment for brain AVMs. Advances in microscopic visualization, computer-assisted stereotactic guidance, intraoperative angiography and electrophysiologic monitoring have significantly improved outcomes of this approach, and today it provides immediate and permanent elimination of the risk of hemorrhage, improvement in neurologic function, and a decrease in the incidence of seizures. The only disadvantage is that it requires an open-skull operation.

Stereotactic Radiosurgery

Non-invasive stereotactic radiosurgery treatment of AVMs avoids the need for an open craniotomy and general anesthesia. While less effective than direct surgery in terms of eliminating and curing AVMs, it allows treatment of AVMs in deep inaccessible locations with a relatively low complication rate. Lesion obliteration occurs over a two- to three-year period. To be eligible for this treatment, the AVM must be less than 3 cm in diameter.

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Endovascular AVM Embolization

embolization

In this approach, usually done under general anesthesia (though sedation is also an option), a catheter is used to place a special glue inside the AVM to produce an immediate reduction of blood flow to the AVM. This approach is usually used as an adjunct to surgery or stereotactic radiation, rather than as a primary treatment modality. Endovascular embolization makes microsurgery safer, and can also reduce the size of an AVM making it smaller and thus amenable to radiosurgery.