Spinal = having to do with the spine
Dural = having to do with the dura, the outer lining of the brain and spinal cord
Arteriovenous = having to do with arteries and veins
Fistula = an abnormal connection or passageway
A spinal dural arteriovenous fistula (SDAVF) is an abnormal connection between arteries and veins in the dura, the outer lining of the spinal cord.
Arteries and veins are the two types of major blood vessels in the body. 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.
Normally, arteries and veins are connected by tiny vessels called capillaries. Capillaries handle the transition from higher to lower pressure, help supply nutrients from the blood to surrounding tissues, and help move waste products from the tissues to the blood. But in an SDAVF, the capillaries are missing. Arteries and veins are directly connected to each other. The direct connection between artery and vein is called a fistula.
This abnormal connection leads to a number of problems. For example, without capillaries, high-pressure arterial blood rushes directly into veins. Veins are not equipped to handle this influx. They can swell and bloat, and blood flow through them can become congested. This leads to swelling, which places harmful pressure on the spinal cord. In addition, without capillaries to handle nutrient exchange, the tissue around the SDAVF can have difficulty receiving nutrients like oxygen and glucose.
Any of these problems with blood flow, pressure, and nutrient delivery can cause injury to the tissues around the SDAVF. Tissue death in these areas can cause neurological dysfunction.
For information about abnormal tangles of blood vessels inside the spinal cord, see our page on spinal arteriovenous malformations (spinal AVMs).
Symptoms of SDAVF are generally nonspecific, meaning they are similar to symptoms of many other problems that affect the spinal cord. These symptoms may include back pain, numbness, weakness, or “pins and needles” in the legs, clumsiness, difficulty walking or climbing stairs, impairment in bladder or bowel function, and sexual dysfunction. Symptoms may develop slowly and steadily, or they may progress and then stay the same for a while before progressing again.
Many patients have symptoms for a year or more before the SDAVF is diagnosed.
Causes and Risk Factors
The cause of SDAVF is not yet known. SDAVFs are more common in men than in women, and most common in older adults.
SDAVFs usually occur in the mid- to lower spine (the thoracic and lumbar spine).
Tests and Diagnosis
SDAVFs are usually identified by a MR (magnetic resonance) imaging scan. This procedure uses large magnets, radiofrequencies, and a computer to produce detailed images of the spinal cord. However, even an MR image does not reveal the location of the SDAVF itself, just effects on the spinal cord–like swelling and enlarged blood vessels–that imply a SDAVF may be present.
Once a diagnosis of SDAVF has been suggested by MR imaging, an angiogram will make it possible to identify the exact location of the fistula itself. In an angiogram, a radiologist injects a dye into the blood vessels. X-ray or MRI scans will then be taken to show the specifics of the blood flow. Because of the complexity of SDAVF and of the problems it may cause, several injections and scans may be necessary.
Most patients do quite well with treatment. Left untreated, however, patients may experience progressive spinal cord dysfunction and ultimately paralysis. Therefore, in the overwhelming majority of cases, treatment is recommended.
SDAVFs 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 fistula. Once in place, the catheter releases a glue-like material or tiny particles that can seal off the fistula. However, for reasons that have to do with blood flow and vessel anatomy, this procedure may not be effective in every case.
In some cases, surgery may be necessary. Using a surgical microscope and extremely fine instruments, neurosurgeons can microsurgically remove the malformation and restore the normal blood flow to the spinal cord.
Spinal dural arteriovenous malformations are complex problems. They should be addressed at major medical centers by professionals–like those at The Spine Hospital at The Neurological Institute of New York–who are experienced in their treatment.