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, possibly the result of venous thrombosis in the epidural vessels. Symptoms typically develop 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 spinal cords venous drainage prevents the efficient transfer of oxygen to the cells of the cord and the neurones begin to die.
The symptoms are often insidious and this may lead to delays in diagnosis. Patients experience loss of sensation in the legs with resultant 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 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.
Successsful treatment of the arteirovenous fistula may not completely refelct the effects of prolonged lack of oxygen on the nerve cells but is usually effective in arresting the neurological deterioration. Most patients report partial improvement in sensation, co-ordination or limb strength. Problems with bladder and bowel control are those least likely to improve. However input from specialists can improve the quality of life bby managing these problems more effectively after treatments of the fistula.
Treatment of Spinal Dural Arteriovenous Fistula
Microsurgical division of a spinal dural arteriovenous fistula will usually be considered as first-line therapy. The procedural risk is the same or superior to published outcomes for endovascular treatment and the result is durable.
The surgery is carried out under general anaesthesia and the location of the small incision depends on the level the fistula is formed. The draining vein is identified as it enters through the dura and disconnected with electrocautery. Indocyanine-green videoangiography is used at out unit to confirm that the arteriovenous shunt has been normalised.
Endovascular embolisation of the fistulous vein may also be feasible if liquid embolic agent can be pushed sufficently far in. Some centres rely on this as first line therapy reserving surgical division if it is unsuccessful. It is less likely to successfully close the fistula than surgery and more recurrences are somewhat more frequent. Taking account of the procedural orbidity assosciated with each treatment our multidisciplinary team currently favors microsurgical treatment for SDAVF.