Spinal Arteriovenous Malformations

Detailed Description of Spinal AVMs

An arteriovenous malformation (AVM) is an abnormal tangle of blood vessels. Normally, oxygen-rich blood flows to the spinal cord through arteries, which branch into smaller arterioles until the blood reaches the capillaries, the smallest blood vessels. While the blood is in the capillaries, oxygen is removed and used by the spinal cord, and then the unoxygenated blood passes into small venules and into larger veins that drain it out of the spinal cord and back to the heart and lungs. In an AVM, the capillaries are missing, and arteries dump blood directly into veins through an abnormal passageway (fistula).

The problem is that the spinal cord cannot absorb oxygen from the blood. Spinal tissues are starved of normal amounts of oxygen, and the cells that make up these tissues begin to deteriorate or die. It also pressures the thin-walled veins since there are no capillaries to "slow down" the blood flow. Over time, the veins or the abnormal group of blood vessels (AVM) may rupture and cause a spinal hemorrhage. In addition, the AVM may become larger and compress or displace parts of the spinal cord.

Spinal AVMs are classified several ways; most are based on their location in the spinal cord. Two broad categories include spinal arteriovenous fistulas (AVFs), most often found in the dura (the tough membrane that covers the spinal cord), and spinal intradural (inside the dura) AVMs.

Arteriovenous fistulas develop near the base of a spinal nerve and are the most common spinal AVM in adults. These fistulas are usually found in the lower half of the spinal cord and occur most often in men older than 40. The symptoms they cause increase over a period of months to years. Generally, these do not exert as much pressure on the blood vessels as other AVMs, and the chance of hemorrhage is less. Scientists believe arteriovenous fistulas may develop as a result of events such as back trauma or prior surgery.

Spinal intradural AVMs occur anywhere along the spinal cord and develop inside the protective dura close to, on or within the spinal cord. They are believed to be congenital (present at birth), caused by mistakes that occur during embryonic or fetal development. A few blood vessel malformations are hereditary, based in genetics.

Symptoms from spinal AVMs may develop quickler and are more pronounced. The pressure on the blood vessels is usually high, resulting in a higher risk of hemorrhaging. Spinal AVMs are found most often in people under 30.