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Vascular Malformations of the Spinal Cord

The spinal cord emerges like a tail from the brain and travels down the centre of the body protected by the bony part of the spine (The spinal column) and a leathery covering that also protects the brain called the Dura. Almost All the nerves travelling between the brain and the various organs of the body travel in the spinal cord. This section contains information for patients affectd by a rare group of conditions called Spinal Vascular Malformations

 

What is a Spinal vascular Malformation (SVM)?

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.

 

What causes 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.

 

What are the different types of SVM?

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:

  • Spinal dural arteriovenous fistulaType I- Spinal Dural Arteriovenous Fistula: Spinal dural arteriovenous fistulae comprise the commonest sub-type of spinal vascular malformation. unlike most other vascular malformations of the nervous system it is believed that they are acquired during life as a result of some vascular event of the spinal cord. They cause symptoms most often during the seventh and eighth decades of life. Usually a single fistulous vessel pierces the dural covering of the spinal cord close to here a nerve root is exiting. This then joins anomalously to the venous plexus which normally drains blood away from the spinal cord. The resultant congestion of the cords venous system prevents the efficient transfer of oxygen to the cells of the cord and the neurones begin to die. The symptoms are often insidious ad this can lead to delays in diagnosis. Patients experience loss of sensation in the legs and difficulty walking or balancing. They may experience difficulties with control of the bladder- at first an urge to micturate frequently or a sense of urgency. This may progress to frank incontinence. Because these symptoms often develop and progress slowly the diagnosis may take some time to make. MRI scan is the most appropriate test and the appearances of a spinal cord affected by a spinal dural fistula are very characteristic with swelling evident within the cord itself and dilated veins on its surface.The diagnosis is confirmed with a spinal angiogram and treatment is possible by either microsurgical division of the fistula or endovascular occlusion. The quality of recovery however is determined by how much harm has already been done to the cells of the spinal cord. In our experience most patients have significant symptomatic improvement making the prompt diagnosis and treatment of spinal dural arteriovenous fistulae very important.
  • Type II- Glomus Arteriovenous Malformation: These are true arteriovenous malformations similar to those encountered within the brain. They may present with haemorrhage or with symptoms caused by reduction in blood flow to the spinal cord. They are very rare lesions ad tend to affect younger people that Type I fistulae including very young children. The diagnosis will usually be made again by MRI and confirmed with a spinal angiogram. Treatment can be complex and this will be determined by the results of thorough investigation. A combination of therapies may be suggested including microsurgery, endovascular embolisation and stereotactic radiosurgery.
  • Type III- Spinal Arteriovenous Metameric Syndomre(SAMS): These were formerly known as Juvenile or Metameric AVMs. The human embryo can be thought of as developing in discrete segments and the organisation of tissues (muscle, bone, blood vessel etc.) repeats between segments. Where one or more segments giving rise to the spinal coloumn is affected an AVM which may invlolve not only the spinal cord and its covering but also of the surrounding bone and muscle. These are extemely rare and difficult lesions to manage.
  • Type IV- Direct (Perimedullary) Arteriovenous Fistula: Similar in terms of architecture to type 1 fistulae but the abnormal connectionbetween vein and artery forms on the surgace of the spinal cord itself, usually form on of the spinal arteries. These can be large and polyfistulous giving some difficulty distinguishing from a glomus AVM. They may be treated by endovascular or microsurgical means in most cases.

 

How do they cause problems?

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.

 

What tests do I need if a Spinal Vascular Malformation is suspected?

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.

 

How may SVMS be treated?

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.

Microsurgery.
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 embolisation:
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.

Stereotactic Radiosurgery:
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.