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.
Arteriovenous malformations may involve more than one tissue type. In such cases there is likely to be a gene fault affecting the development of normal vascular beds in all these tissues. Such AVMs may involve the spinal cord, dura, vertebral bone, muscle and skin. In the embryo tissues develop segmentally- in a repeating pattern one block of tissue after another each with its own blood vessels arising from the main cetral vessel, the aorta. In the embryo these segments of tissue are termed metameres. Thee are 31 pairs of metameres and any may be involved in what has come to be termedSpinal Arteriovenous Metameric Syndrome or SAMS types 1-31. It is a non-hereditary genetic condition.
AVMs within the spinal cord have lower blood flow coursing through them compared to the larger volume lesions that may develop in the brain. Aneurysms develop less frequently on arteries feeding spinal cord AVMs than they do in the brain perhaps becuase of this relatively low blood flow. Aneurysms develop relatively frequently however in SAVMs within the context of SAMS.
When symptomatic there may be a case for pro-active treatment of intramedullary spinal cord AVMs although not all are amenable to definitive treatment. They may be compact lesions discrete from the nervous tissue or diffuse and intimately related to it. Endovascular embolisation is delployed to secure assosciated aneurysms and in selected cases to abolish the arteriovenous shunt definitively. In metameric AVMs only palliative management is usually possible with repeated embolisation usually the safest option.
With compact malformations it may be possible to microsurgically remove the AVM completely. In diffuse cases with a favorable angiogarchitectue a technique of in-situ disconnection may be deployed to effectively close the arteriovenous shunt without the need to physically remove the nidus of the AVM itself.
Stereotactic radiosurgery may be used to treat spinal cord AVM although their situation and the their movement in space as a result of breathing pose particularl challenges when directing the radiation beam. Robotic systems such as the Cyberknife may be utilised to compensate for this movement. Another issue is that the tolerance of the spinal cord for radiation is limited in such a small area meaning that sufficent energy to obliterate a lesion may cause injury.