Spinal Vascular Malformations (Spinal Dural AV Fistula)
What is it?
There are a few types of spinal vascular abnormalities. One are arteriovenous malformations, or ‘AVMS’ – these are covered in the “Brain & Spine AV” page. The other are called spinal ‘fistulas’. A fistula is an abnormal connection between two different parts of the body. The most common type of fistula in the blood vessels around the spine is called a dural arteriovenous fistula, or dAVF. This is a fistula that occurs in the dura (the layers around the spinal cord) that connects the arteries to the veins. An artery carries high-pressure blood to the spinal cord, and a vein drains the spinal cord and has low-pressure blood in it. Sometimes, an abnormal connection (or fistula) occurs between the two. When this happens, high-pressure blood from the artery drains directly into the vein, which is normally used to low-pressure blood. This can cause problems with the spinal cord itself, which can get swollen as it does not drain properly. In this way, a spinal dAVF can cause symptoms such as weakness in the legs or difficulty walking. There are other rarer types of fistulas in the spine, but a dAVF is the most common.
How did I get it?
There is no single cause of a spinal dAVF. Some patients may have had surgery before, or a history of trauma or injury to that area. They usually occur in older patients. In most cases, however, we do not know the cause.
How would I know I have an aneurysm?
The fistula can be completely asymptomatic – a patient might never know they have one, and it might be found during an MRI scan performed for something else. In other cases, a patient might have symptoms related to the part of the spine that is swollen because it is not being drained properly. These symptoms can range from mild problems with leg weakness, to back pain or leg pain. Sometimes they can cause problems with bladder or bowel function. In more serious cases, the spinal cord can be so badly affected that it can cause paralysis.
How is a spinal fistula diagnosed?
Once a spinal fistula is suspected, the first step is an MRI scan of the spine if this has not been already performed. This helps us look at the spinal cord itself, to see if it is swollen or enlarged which might point us toward a possible fistula. We will often to a special type of MRI called an MR Angiogram, which lets us look at the blood vessels in the spine. This gives us a better look at the blood vessels, to try and see if there is a fistula, and what level it is at.
If we see a fistula, the next step is to do an angiogram of the spine. This is the best test to look at blood vessels. It is done with the patient under general anaesthetic, and involves placing a catheter (or tiny tube) into the blood vessels of the spine, by going in through the femoral artery, a blood vessel in the groin. By injecting the spinal vessels with x-ray contrast (or dye) one by one, we can then see where the fistula is. It also gives us a better look at the anatomy of the fistula, and the other blood vessels in the area.
Does it need to be treated?
We will discuss this with you at the time of referral, but in brief, the majority of these fistulas tend to get worse over time. Furthermore, if left for a long time the damage to the spinal cord – and the symptoms – can become irreversible. For these reasons, we usually recommend treatment with this lesions.
How can a spinal fistula be treated?
There are two main ways to treat a spinal fistula. The whole point of treatment is to close off the fistula – the abnormal connection between the artery and the vein.
The first way is by embolization – this means to close off the blood vessels from the inside. We do this during the angiogram – by using the catheters in the same way we do with the angiogram, we can place tiny catheters inside the blood vessels beside the fistula. By injection certain materials in the blood vessel we can then close off the hole between the artery and the vein.
Sometimes, it is not possible to safely embolise the fistula. This can be because it is too difficult to get the catheter to the point of the fistula, or it can be because there are other important blood vessels which supply the spine in the same area as the fistula.
The second way we can treat these fistulas then is by surgery. We can usually go in and identify the connection between the artery and the vein and close it off. The vast majority of spinal fistulas can be treated in one way or the other.
What happens after treatment?
This depends a lot on how well the spinal cord is draining after treatment, and for how long the cord was not draining well. Sometimes the symptoms can go away completely, and quite quickly. Other patients make a good recovery, but this can happen over weeks to months. Some patients make a partial recovery, while others may have long-term damage to the cord, and their symptoms might not improve.