To understand AVMs, it is helpful to first discuss normal blood flow function within the body. In a healthy individual, blood normally flows from the heart through arteries to supply all organs including the brain. Four major arteries supply the brain including two carotid arteries in the front of the neck and two vertebral arteries in the back of the neck.
As blood flows from the heart into the large arteries, it is pumped at relatively high pressure and speed, both of which decrease as the blood flow reaches smaller and smaller arteries. Eventually the blood reaches the smallest vessels called capillaries, vessels smaller than the diameter of a human hair. As the blood flows slowly through these tiny conduits, it gives up oxygen and nutrients to the brain tissue and receives carbon dioxide and other waste products in return. The blood then enters tiny veins at very low pressure, eventually entering larger veins in its return to the heart and lungs. Thus, pressure and speed of blood flow in the veins (the vessels that return blood to the heart) are normally very low compared to that of the arteries (the vessels responsible to deliver or pump blood from the heart to the rest of the body). Because of this design, the walls of the veins are relatively thin and delicate compared to those of the arteries which must be thicker and more inflexible to handle higher pressure and speed.
AVMs occur when the relatively large arteries within the brain directly connect to veins without the capillary mesh that normally exists between them. Because of the abnormal “short circuit,” the blood is delivered at relatively higher pressure with more rapid flow directly into the veins. Because the veins are not designed for this condition, they expand, pushing against the neighboring areas of normal brain. The result may be damage to the normal brain tissue which can cause weakness, numbness, loss of vision, or seizures. Often the supplying arteries, the AVM itself, or the enlarged veins rupture, resulting in the most common presentation of an AVM, an intracranial hemorrhage which is a type of stroke.
AVMs are most often congenital (present at birth) and usually no specific cause for the AVM can be identified. In the vast majority of cases, AVMs are not inherited and other members of the family are not at increased risk for having an AVM.
Arterio-venous malformations (AVMs) are typically diagnosed by a CT scan or MRI upon presentation of symptoms that may include seizures, headache or stroke-like episodes. Once an AVM is confirmed, an angiogram or arteriogram is performed to identify the vessels involved in the malformation. Angiography is the only test currently available that provides sufficiently detailed information useful in planning and implementing therapy of most AVMs.
There are three major treatment methods that may be useful either alone or in combination to treat an AVM. The specific treatment for an individual is based on the patient’s history, symptoms, and anatomy of the AVM including its size, feeding arteries, draining veins, and location within the brain. Treatments include: endovascular embolization (closure of the AVM from within the blood vessels), open surgical removal of the AVM, or a combination of techniques.
Open surgical treatment involves removing a portion of the skull so that surgical instruments can be inserted to remove the AVM. Surgical treatment is often performed after embolization has closed portions of the AVM. The combination of embolization followed by surgical resection is frequently safer than surgical resection alone in treating an AVM.
Embolization is an endovascular technique (performed from within the blood vessels) to block the vessels of the AVM. In this procedure, a small catheter is threaded from the groin directly into the AVM vessels within the brain. Under X-ray guidance, material is injected through the catheter to permanently block and close off the vessels of the AVM. Materials used might include particles, small platinum coils, and/or liquid embolic agents similar to glue.
Embolization of an AVM is usually performed before treatment by either surgery. Embolization is often able to decrease the size of the AVM making the surgery much safer than would otherwise be the case. However, the blood flow from certain AVM’s may be totally blocked by embolization techniques, and no further therapy may be required.
Carotid-cavernous fistulae are abnormal connections between the carotid artery (or its branches) and a large vein (cavernous sinus) behind the eye. The cavernous sinus receives blood from the orbit, the pituitary gland, and the brain. A carotid-cavernous fistula may be either direct (high-flow) or spontaneous (indirect/low-flow).
Direct carotid-cavernous sinus fistulae generally are associated with trauma or surgical manipulation and are therefore commonly seen in young men. Indirect carotid-cavernous fistulae occur more commonly in middle-aged to elderly women.
Indirect (low-flow) fistulae can form as a result of trauma, clotting of the sinus with subsequent reopening, or rupture of an aneurysm (a weak spot in a vessel which causes the vessel wall to balloon out and eventually rupture) of the carotid artery where it passes through the sinus.
The symptoms include pulsating bulging of the eye, redness and swelling of the whites of the eyes, increased pressure in the eye (glaucoma), loss of vision in the eye (occurs in 20-30% of patients with indirect carotid-cavernous sinus fistulae), double vision, and pain.
Because of their location, carotid-cavernous fistulae are difficult to treat surgically. Instead, endovascular treatments may be employed by placing a catheter into the blood vessels and injecting materials to block off the fistula and/or the vein. Sometimes, the same method is utilized so that the carotid artery itself may be blocked off to close the fistula. If this is necessary, tests are performed first to make sure that there is enough blood flow to the brain from the other arteries.
Dural arteriovenous fistulae are abnormal connections between arteries in the head and the large veins that are found in the covering of the brain (dural sinuses) which are responsible for draining the brain. With this particular condition, there is a direct connection between the arteries and the sinus without any normal capillary mesh between the two.
These fistulae can result from trauma, infections (such as sinus infections or mastoiditis), or from clotting of the vein. In the latter case, the fistula forms when the body tries to reopen the vein. The most dangerous complication of a fistula is rupture of the vein, resulting in hemorrhage in or around the brain.
The symptoms of a fistula can vary. An unusual sound may be heard in one ear (pulsating or humming). If the fistula increases the pressure in the veins responsible for draining the brain, neurological symptoms and headaches may be present.
The treatment for a dural fistula depends on the vessels involved. Surgery or radiation therapy may be recommended. Often, these fistulae are treated through endovascular methods by placing a catheter into the blood vessels and injecting materials to block off the vessels, a procedure called embolization. Blockage of arteries, vein (sinus), or both may be needed. Multiple treatments may be needed to close the fistula.
Treatment of an AVM is directed toward preventing brain injury that could result from bleeding or re-bleeding. No treatment currently exists which can repair damage already done to the brain by the AVM. For example, seizures might continue after embolization or even complete removal of the AVM. Patients with neurological deficits resulting from AVM hemorrhage would likely still experience the same deficits after treatment of the AVM, although improvement may occur.
Vascular malformations are an abnormal vessel or vessels that form a direct connection between arteries and veins without the normal capillary mesh between them to facilitate blood flow. In the spine, vascular malformations can involve: the spinal cord, the tissues around the spinal cord within the spinal canal, the bones of the spine, the tissues around the spine, or a combination of these. Including all types of malformations, the incidence in the general population is approximately 3-7%.
Spinal vascular malformations can pose serious medical issues to physicians and patients. Malformations in particular areas can result in weakness and in severe cases, paralysis, of some or all limbs.
Some malformations in the spine are present at birth while others develop later in life. Symptoms can be caused by decreased blood supply to the spine and nerves, by pressure from the abnormal vessels, or by rupture of the vessels resulting in hemorrhage.
Vascular malformations are an abnormal vessel or vessels forming a direct connection between arteries and veins without the normal capillary mesh between them to facilitate bloodflow. These malformations can occur in the tissues of the face and neck (extracranial) or surrounding the spine (paraspinal).
Extracranial/paraspinal vascular malformations can have serious consequences for the patient as they can cause congestive heart failure if the flow through the abnormal vessels is of a high volume and speed. This condition is most often seen in infants.
Symptoms are caused when increased blood flow through the malformations enlarge the vessels, putting pressure on surrounding structures and causing deformity of the face (often tongue, lip, eyelid). Excess pressure on the nerves can cause difficulties with functions such as eyesight or swallowing. These lesions are often congenital (present at birth) and can change greatly as a child grows. Most often, they disappear as the child grows. Certain “birth marks” are in fact vascular malformations.
When vascular malformations do not disappear, or, cause symptoms, grow with age, or appear during adult life, a variety of treatment options may be considered. Some may be surgically removed, while others are treated with laser therapy. In other cases, vascular malformations are treated through endovascular methods by placing a catheter into the blood vessels supplying the malformation and injecting various materials to block off the blood supply to the abnormal vessels. This procedure is called embolization.
Another treatment option utilized by doctors involves placing a needle directly through the skin into the malformation and injecting material to block off the malformation.