Arteriovenous Malformations

Background

arly Stage squareAn arteriovenous malformation (AVM) is a complex tangle of abnormal arteries and veins. These can be found anywhere in the body but are most commonly located in the brain or spine.

The flow of oxygenated blood through the body normally progresses from large arteries to smaller capillaries where gas exchange (oxygen for carbon dioxide) occurs before deoxygenated blood is carried back to the heart. However, when an AVM exists, there is no capillary system, and the arteries are directly connected to the veins. This disrupts the normal blood flow and the ability to perform proper gas exchanges. Also, there is increased pressure in the veins, putting excessive stress on the thin-walled veins and raising the chance of hemorrhage, stroke or seizure.

Although AVMs are usually congenital and thought to arise during the fetal stage of development, their existence is often not apparent until the onset of symptoms. In about 50% of patients, the presentation is a sudden intracerebral hemorrhage. Other symptoms include headaches, aphasia, progressive weakness and vision loss. Symptoms can present at any time but are more likely between the ages of 10 and 40.

AVMs are more common in men than in women. According to the American Association of Neurological Surgeons, about 10-12,000 people per year are diagnosed with an AVM. There are currently 300,000 people in the United States with AVMs, and every year about 4% of these people will experience a hemorrhage. The hemorrhages carry a 15-20% risk of death or stroke.

Current Treatment

Many factors are considered when deciding on the best treatment option for AVM’s such as size and location, possibility of incomplete treatment, and risk of complications. In cases where the AVM is located in a sensitive area of the brain, doctors may forego an invasive surgical procedure in favor of monitoring the AVM and treating related symptoms with medication. The hope is that the AVM will remain stable and no further treatment will be required.

Endovascular embolization is a minimally invasive treatment that can cut off the blood supply to an AVM and reduce its size. The procedure involves inserting a catheter into the groin and threading it through arteries into the AVM. A substance is then injected into the artery to block it off. This procedure may need to be repeated depending on the AVM’s size. Endovascular embolization alone only cures AVMs about 20% of the time, and it is almost always used as a preliminary treatment.

Microsurgery is a relatively safe and effective treatment option for relatively simple AVMs. Although invasive, microsurgery, with the aid of high powered microscopes and image guided surgical navigation, can usually be done with minimal disruption to the rest of the brain. The surgery involves removing a piece of the skull bone (craniotomy) to gain access to and close off the AVM so that it can be removed.

Stereotactic Radiosurgery (Gamma Knife, proton beam) is a non-invasive treatment method indicated for more challenging AVMs. The procedure involves a single session of high dose radiation directed at the AVM which gradually occludes the vessels over of a period of 2 to 3 years. If the AVM has not been obliterated after 3 years, repeat radiosurgery may be performed.

Focused Ultrasound Research

Focused ultrasound is not currently an approved treatment for AVMs. In theory, focused ultrasound could be used as a non-invasive method to thermally ablate tissues and coagulate vessels to close off the AVM. This could be a superior treatment to radiotherapy as it would limit the potential short and long-term side effects. It could also be used to enhance the delivery of experimental drugs.

There has been a couple of isolated (lower extremity and uterine) case reports of treatment of an AVM, but further study is needed to help decide if this care is appropriate for general use in treatment of AVMs.

Notable Papers

Yan X, Zhao C, Tian C, Wen S, He X, Zhou Y. Ultrasound-guided high-intensity focused ultrasound ablation for treating uterine arteriovenous malformation. BJOG. 2017 Aug;124 Suppl 3:93-96. doi: 10.1111/1471-0528.14749.

van Breugel JM, Nijenhuis RJ, Ries MG, Toorop RJ, Vonken EJ, Wijlemans JW, van den Bosch MA. Non-invasive magnetic resonance-guided high intensity focused ultrasound ablation of a vascular malformation in the lower extremity: a case report. J Ther Ultrasound. 2015 Dec 30;3:23. doi: 10.1186/s40349-015-0042-7.

Hoerig CL1, Serrone JC1, Burgess MT1, Zuccarello M1, Mast TD1. Prediction and suppression of HIFU-induced vessel rupture using passive cavitation detection in an ex vivo model. J Ther Ultrasound. 2014 Sep 8;2:14. doi: 10.1186/2050-5736-2-14. eCollection 2014.