Spinal = having to do with the spine
Arteriovenous = having to do with arteries and veins
Malformation = a congenital (present at birth) deformity
A spinal arteriovenous malformation (spinal AVM) is an abnormal tangle of blood vessels in the spinal cord.
The two types of major blood vessels in the body are arteries and veins. Arteries carry oxygen-rich blood to the body’s tissues, and veins bring oxygen-depleted blood back to the heart and lungs. Arteries are usually under high pressure, since the blood inside these vessels has recently been pumped forcefully from the heart. Veins are usually under lower pressure as the blood makes its way back to the heart.
Normally, arteries and veins are connected by tiny vessels called capillaries. Capillaries handle the transition from higher to lower pressure, and help the blood provide nutrients to surrounding tissues and absorb the tissues’ waste products. But in an AVM, the capillaries are missing. Arteries and veins are directly connected to each other.
This abnormal connection leads to a number of problems. For example, without capillaries, high-pressure arterial blood rushes directly into veins. This puts enormous pressure on the walls of the vessels, and weakens them over time. A bulge in a weakened vessel wall–an aneurysm–may develop, and put harmful pressure on spinal nerves. If an aneurysm ruptures, uncontrolled bleeding called a hemorrhage can occur, which also leads to swelling. In addition, without capillaries to handle nutrient exchange, the spinal cord tissue around the AVM can have difficulty receiving nutrients such as oxygen and glucose. The AVM can increase in size as the body attempts to supply nutrients to the surrounding area.
Any of these problems with blood flow, pressure, and nutrient delivery can injure the spinal cord tissues around the AVM. Tissue death in these areas can cause neurological dysfunction.
Spinal AVMs account for about four percent of abnormalities found in the spinal cord region.
For information about abnormal blood vessels in the lining of the spinal cord, see our page on SDAVFs (spinal dural arteriovenous fistulas).
The majority of spinal AVMs will cause neurological symptoms that worsen gradually over months or years. Such symptoms may include back pain, sensory loss, and leg weakness.
But about 10 to 20 percent of spinal AVMs will cause symptoms suddenly. These symptoms may include weakness, numbness, difficulty urinating, loss or reduction of bowel or bladder control, or paralysis. In these cases, a vessel may have burst, causing a hemorrhage (bleeding).
Causes and Risk Factors
Researchers do not yet understand what causes spinal arteriovenous malformations. Most AVMs develop in adults but some are present at birth, or develop later in childhood. There are no known risk factors for spinal AVMs, although they may rarely occur within families.
Tests and Diagnosis
Neurologists and neurosurgeons use magnetic resonance imaging (MRIs) to identify spinal AVMs. Spinal angiography (a test in which a tracer is injected to make the blood flow visible on an X-ray) may also be used to examine the structure of the malformation.
Our neurosurgeons consider a patient’s clinical history, symptoms, the physical examination, and the results of the spinal angiography in order to form a treatment plan.
Spinal AVMs are often treated with a procedure called endovascular embolization. This technique does not require surgery and involves passing a tiny catheter, or tube, into the vessels feeding into the AVM. Once in place, the catheter releases a glue-like material or tiny particles that can seal off sections, or in some cases all, of the malformation. However, for reasons that have to do with blood flow and vessel anatomy, this procedure may not be effective in every case.
Radiation therapy, also called stereotactic radiosurgery, is another nonsurgical option that may destroy the abnormal vessels of an AVM.
In some cases, surgery may be necessary. Using a surgical microscope and extremely fine instruments, neurosurgeons can microsurgically remove the malformation to restore the normal blood flow.
Spinal AVMs are complex lesions, and should be addressed at major centers with experts who are experienced in their treatment, like those at The Spine Hospital at The Neurological Institute of New York.