Spinal Dural Fistulas and Arteriovenous Malformations

Symptoms typically develop gradually after age 40 and progress slowly. They consist of some combination of back or radicular pain, weakness, sensory disturbances, and impaired sphincter function. Neurogenic claudication may be present. Examination commonly reveals mixed upper and lower motor neuron deficits, sensory abnormalities, and reflex changes in the legs. Without treatment, the gait becomes progressively more impaired until the patient is chair-bound. A discrete or vague sensory level is sometimes present. A bruit may be audible over the spine.

Intradural AVMs may occur at any level but are more common in the cervical region. There may be one or multiple feeding vessels, which arise from a radiculomedullary vessel supplying the anterior spinal artery or from one of the branches to the spinal cord. The nidus may be intramedullary, in the pia (i.e., extramedullary), or both intramedullary and extramedullary. These are high-volume, high-pressure shunts with rapid blood flow, from which spontaneous intraparenchymal or subarachnoid hemorrhage may occur. Symptoms develop usually during early adult life. Patients present with sudden back pain and a neurologic deficit in the limbs, perhaps accompanied by impaired consciousness when hemorrhage has occurred, or with a progressive myelopathy. When the lesion is located cervically, both upper and lower extremities may be affected. Recurrent hemorrhages leads to clinical deterioration.

Cavernous angiomas or malformations are rare, isolated, or multiple lesions that can spontaneously hemorrhage and are best shown by magnetic resonance imaging. Spinal arteriography is normal.

In patients with spinal dural fistulas, MRI demonstrates serpentine filling defects of reduced signal in the subarachnoid space, corresponding to blood flow in the dilated, tortuous coronal venous plexus. Sometimes cord signal is increased from edema or venous congestion. Low cord signal may reflect an intradural nidus. Computed tomography (CT) myelography may demonstrate serpentine linear defects, but its use has largely been supplanted by MRI. Selective spinal arteriography defines the precise site of the nidus, its arterial feeders, and the normal blood supply to the spinal cord. Endovascular occlusion of feeding vessels is often undertaken during the procedure and may obliterate the lesion or, at least, reduce its size so that it is easier to remove surgically. Intramedullary lesions may be inoperable, but embolization can occlude feeding vessels and the nidus, reducing flow and allowing lesion thrombosis. It is important to maintain the vascular supply to the spinal cord to prevent damage from subsequent ischemia. After nonoperative obliterative procedures, feeding vessels may recanalize or new feeders can open up, requiring further treatment.

Early detection and treatment can improve gait disturbances, and sometimes bladder or bowel dysfunction, and a previously progressive course can be arrested.

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