A spinal vascular malformation is formed when there is an abnormal relationship between two parts of the body’s blood circulation system. Arteries are thick walled blood vessels designed to carry blood loaded with oxygen. Veins are thinner walled and are designed to carry blood away from the spinal cord once the oxygen has been delivered to the nerve cells that need it. The veins transport the blood back to the lungs so the red blood cells may collect more oxygen. The blood laden with oxygen is carried straight into he vein and not delivered to the nerve cells as intended. When there is a direct connection between the two blood vessels we call that an arteriovenous fistula (AVF). When a structure develops between the two made up of abnormal or immature blood vessels (a “nidus”) it is called an arteriovenous malformation (AVM). Together AVFs and AVMs make up the rare group of conditions that is spinal vascular malformations.
In many cases we simply do not know. The most common type of spinal AVF forms in the lining around the spinal cord (Spinal dural AVF or sDAVF). Most of these develop in adults and we suspect are caused as a result of blood clot forming in normal veins within the spinal cord. In other words we suspect these are acquired during life. Other, rarer types of SVM are probably present from before birth or develop in early childhood under the influence of a gene that is not working normally.
Extradural malformations- are distinguished from those developing within the dural lining of the spinal cord itself or within thespinal cord itself. Intradural vascular malformations may be classified according to the commonly used system shown below:
The most common SVM we treat (the Spinal Dural AVF) does not usually present because of bleeding. Damage is caused to the nerve cells of the spinal cord when they are deprived of oxygen. This happens because blood intended to carry oxygen to them is diverted away in the veins. The nerves begin to malfunction and eventually die. This is often a slow process and a patient or their doctor may not be aware something serious is amiss until significant harm has been done.
The rarer forms of spinal vascular malformation may sometimes cause bleeding and sudden severe damage to the nerves of the spinal cord a little similar to what happens when the brain suffers a stroke.
Most will be discovered on an MR scan of the spine. SVMs are sometimes easy to mistake for tumours or inflammation of the spinal cord. If one is suspected you will be referred to a specialist neurosurgeon.
In our unit we will usually begin by carrying out a special type of MR scan called a magnetic resonance angiogram. This can help reduce the radiation exposure and time needed for the next stage in investigation- a spinal angiogram.
Spinal angiograms may be carried out under local or general anaesthetic dependent of the needs of the patient. A needle is placed in a large artery usually at the top of the leg. Sometimes a blood vessel near the elbow is used instead. A thin wire is passed through the needle and then a tube over the wire is advanced into the blood vessels. X-rays are used to guide this tube into the individual arteries that carry oxygen to the spinal cord and a dye is injected into them. This provides a road map of the blood vessels making up the malformation and allows us to plan treatment.
For more details about angiograms see our leaflet about Cerebral and Spinal Angiography.
A specialist team experienced in the treatment of SVMs will review your angiogram. Together they will recommend how your SVM should be managed. Broadly speaking SVMs may be treated by one of the methods below or sometimes by a combination of treatments. There are occasions when no treatment is necessary or appropriate and in that case your specialist will discuss with you why this is the case.
This is carried out while the patient is asleep (general anaesthesia). A window is fashioned in the bone of the spinal canal to allow an opening to be made in the dura surrounding the nervous tissue in the spinal canal. The SVM is identified under a powerful microscope and the abnormal vessels disconnected from the healthy one to restore normal blood flow to the spinal cord. The exact procedure is determined by the results of the angiogram and will be discussed in detail with you by your surgeon. Risks too vary a great deal depending on the make up of the SVM and again will be discussed in detail by your Neurosurgeon as part of your consent process.
Endovascular treatment is carried out through a tiny tube placed within the SVM during a procedure similar to the spinal angiography described above. It will be carried out under a general anaesthetic. It aims to block the blood vessels carrying blood through the malformation by depositing a type of glue or tiny platinum metal coils within them. Again the exact procedure is determined by the results of the angiogram and will be discussed in detail by your Interventional Neuro-radiologist who will carry out the procedure. Risks too vary a great deal depending on the make up of the SVM and again will be discussed in detail by your surgeon as part of your consent process.
For rare SVMs untreatable by microsurgery or endovascular embolisation stereotactic radiosurgery offers another option. Highly focussed beams of radiation are aimed at the SVM and injure the blood vessels at a microscopic level. Over time- between three and five years in many cases- the vessels then become blocked by clot and the cells making up their walls are destroyed. Experience is still being accrued with what is a relatively new technique for treating very difficult SVMs but early results suggest about 50% may be obliterated in this way.