Spinal Dural Arteriovenous Fistula

Spinal dural arteriovenous fistula is an abnormal connection between a radicular artery and a radiculomedullary vein within the dura of a nerve root sleeve, causing venous hypertension and congestive myelopathy of the spinal cord. It is the commonest spinal vascular malformation.

It accounts for about 70% of spinal vascular malformations. It affects men in 80 to 90%, usually aged 50 to 70 years, with thoracolumbar location in most.

Pathophysiology. Arterialised pressure is transmitted to the coronal venous plexus, which reduces the arteriovenous pressure gradient and causes chronic spinal cord oedema and ischaemia. The cause is unknown and the lesion is acquired.

Presentation is slowly progressive leg weakness and stiffness, sensory disturbance, back pain, and bladder, bowel and sexual dysfunction, with a stepwise or fluctuating course. Symptoms often worsen with exercise, prolonged standing or hot baths (neurogenic claudication pattern). Examination shows mixed upper and lower motor neuron signs. Diagnosis is often delayed by 1 to 3 years.

Red flags.

• Subacute progressive paraparesis in an older man.
• Deterioration after corticosteroid treatment.
• Acute worsening after exertion.

MRI of the spine shows long segment T2 hyperintensity in the central cord, often with patchy enhancement, and dilated perimedullary flow voids on the dorsal surface. MR angiography may localise the fistula. Spinal digital subtraction angiography is the definitive test and shows the level and feeding artery. CSF may show raised protein.

Differential diagnosis.

• Transverse myelitis, multiple sclerosis and neuromyelitis optica spectrum disorder.
• Spinal cord tumour, cord infarction and compressive myelopathy.
• Motor neuron disease, vitamin B12 deficiency myelopathy and hereditary spastic paraplegia.

Treat early, since delay worsens disability.

Occlusion of the fistula.

• Endovascular embolisation with liquid embolic agent (n-butyl cyanoacrylate) when the feeding artery does not supply the spinal cord. Recurrence occurs in 10 to 30%.
• Surgical disconnection (laminectomy and coagulation and division of the draining vein) is durable and has a low recurrence of under 5%.

Avoid. High dose corticosteroids, which can cause rapid deterioration, and unnecessary lumbar puncture. Avoid hypotension.

Venous thromboembolism prophylaxis. Enoxaparin 40 mg SC daily (20 mg if creatinine clearance is under 30 mL/min) when immobile, timed with the procedure.

Rehabilitation. Physiotherapy, bladder and bowel care, spasticity treatment (baclofen 5 mg three times daily, increased to a maximum of 80 mg daily) and pain management.

Outcome. Gait often improves by one or more grades, and bladder and sexual symptoms recover least.

Monitoring. Follow up MRI at 3 to 6 months, and angiography if symptoms recur.

Referral and escalation. Refer urgently to neurosurgery and neuroradiology.

Special groups. In older adults and patients on anticoagulants, plan the procedure with haematology.