Stroke & Cerebrovascular Care : Vascular Malformations

What are vascular malformations?

Blood normally flows from the heart through arteries and into smaller and smaller vessels called capillaries. The blood drains back to the heart by low pressure vessels called veins. Vascular malformations exist in different forms, many of which are benign and require no treatment. 

Vascular malformations include:

• Capillary telangiectasias
• Developmental venous anomalies
• Cavernous malformations
• Arteriovenous malformations
• Arteriovenous fistulae

An arteriovenous malformation (AVM) is an abnormal tangle of arteries and veins with no capillaries in between. This causes shunting of pressurized blood from arteries directly into veins, exposing the veins to high pressure. AVM’s are rare, occurring in about .14 percent of the population (140 cases per 100,000 people).

An arteriovenous fistula (AVF) also is rare and is very similar to AVM. An AVF is an abnormal connection between arteries and veins. There are many types of AVF’s. The most common types are a dural arteriovenous fistula (dAVF) and a carotid-cavernous fistula (CCF).

A dAVF is an abnormal connection between arteries and veins in the covering of the brain, known as the dura. It is characterized by a direct connection between the arteries and the sinus (vein) without any vessels between. This condition is usually acquired and can occur after trauma, infection or clotting off of the veins. Symptoms include headaches, bleeding into the brain and abnormal noises in the head due to increased blood flow.

A CCF is specific kind of dural fistula that involves the carotid artery (or its branches) and a large vein (cavernous sinus) behind the eye. It can result from trauma, a ruptured aneurysm in the carotid artery or an unidentifiable cause. Symptoms can include eye pain, swelling and redness of the eye, double vision or loss of vision if untreated.
  

What causes vascular malformations?

Most AVMs are thought to be congenital. However, many vascular malformations may be acquired from trauma, infection or thrombosis (closing off) of a vein.

How do vascular malformations present?

AVMs are commonly asymptomatic and usually are found incidentally. Depending on the location, AVMs may cause headaches, weakness, numbness or seizures. More commonly, they present after rupturing, causing a hemorrhagic stroke. Knowledge of AVMs is evolving. It is thought that AVMs rupture at a rate of 2 to 10 percent per year, however the morbidity (permanent neurological deficits) and mortality (death) from rupture is between 10 and 30 percent. AVFs usually present because of hemorrhage, headache, numbness, weakness, vision changes or tinnitus (ringing in the ears).

How are vascular malformations diagnosed?

AVMs and AVFs are usually diagnosed with CT or MR imaging, which can show the abnormal tangle of vessels with in the brain. However, an angiogram is usually needed to fully identify the anatomy of the malformation. An angiogram is an invasive procedure during which a neuro-interventional surgeon guides a flexible tube (catheter) through an artery over the hip to the vessels of the brain. A liquid dye or contrast agent is injected into the vessel, and pictures are taken with a fluoroscope. An angiogram gives the highest detailed pictures of the location, feeding vessels, nidus and drainage pattern of the malformation. All of this information is taken together to formulate the best treatment for each lesion.

How are vascular malformations treated?

AVM embolization with Onyx liquid embolic agent

There are four main treatments, often used in combination with one another. Treatment can include careful observation, radiosurgery, open surgical resection and endovascular embolization.

Sometimes careful watching of an AVM or AVF is the best treatment because procedures may be too risky.

Radiosurgery, or radiation therapy, focuses a beam of radiation on the abnormal vessels, which close off over time, usually in six months to two years. Radiosurgery often is used to treat small AVMs that are difficult to approach surgically or endovascularly.

Surgical resection requires creating a small opening, or window, in the skull through which the neurosurgeon delicately removes the AVM and disconnects the vessels supplying it. An AVF may be treated similarly by disconnecting the draining veins.  On the other hand, a CCF is usually not treated surgically because of its location.

Endovascular embolization is performed as an extension of the angiogram. Tiny microcatheters are positioned in the vessels supplying the AVM or AVF and liquid embolic agents are injected to seal off the lesion and the vessels supplying it so that blood no longer flows through it. Endovascular embolization is commonly performed prior to open surgical resection to help reduce blood loss during the operation. It can also be performed prior to radiosurgery to reduce the size the malformation. In select cases embolization maybe curative.