Indications
- •
Spinal dural arteriovenous fistulas (AVFs) are classified into two major categories. Lesions primarily associated with the nerve root are called radicular dural AVFs , and lesions primarily in the subarachnoid space are called perimedullary dural AVFs . Arteriovenous lesions that are located in the spinal cord—that is, involving the spinal pia and extending into the substance of the spinal cord—are called spinal arteriovenous malformations .
- •
Radicular dural AVFs are malformations that typically arise in the region of the dural nerve root sleeve. These lesions usually have a single arterial feeder that develops a connection or fistula to the spinal venous system. This fistula creates a high-flow, high-pressure venous drainage system that leads to venous hypertension and subsequent spinal cord hypoperfusion. Perimedullary dural AVFs are located in the subarachnoid space around the spinal cord but do not involve the pia and manifest with pathophysiology similar to radicular dural AVFs. These lesions may have more than one feeding artery.
- •
Symptoms of spinal dural AVFs often develop insidiously and progress over time and include weakness, sensory loss, and bowel or bladder incontinence. Dermatomal and myotomal symptoms may be distant from the actual level of the fistula. Surgery or embolization should be pursued in a timely manner to halt and potentially to reverse neurologic symptoms.
Contraindications
- •
A medically unstable condition and active infection are relative contraindications.
- •
Patients unable to tolerate either endovascular or surgical procedures should be followed closely for signs of neurologic deterioration. Therapy should be pursued when patients are medically stable.
Planning and positioning
- •
The initial assessment of a patient with a suspected spinal AVF begins with a detailed history and physical examination, including bladder, bowel, and sexual function. Patients with spinal dural AVFs typically have progressive upper and lower motor neuron involvement and dorsal column involvement with sensory paresthesias, and they may have loss of vibratory and position sense. A bruit over the spine has been reported in rare cases.
- •
Spinal computed tomography (CT) and magnetic resonance imaging (MRI) are typically the initial imaging studies. CT and MRI typically show only prominent subarachnoid veins. Spinal angiography is the critical study for preoperative planning. Angiography is essential for identifying the precise location of the AVF, the location of all arterial feeders, venous drainage patterns, and possible venous and arterial aneurysms. CT myelography is rarely used at the present time.
- •
Embolization can be used as definitive treatment for most spinal dural AVFs. Alternatively, embolization can serve as a preoperative adjunct for patients with AVF. Compared with cranial dural AVFs, spinal dural AVFs are generally more difficult to treat because of the smaller size of the feeding arteries, the low-flow nature of spinal AVFs, and the close proximity of crucial anterior and posterior spinal arteries.
- •
Intraoperative neurophysiologic monitoring with motor evoked potentials (MEPs) and somatosensory evoked potentials (SSEPs) is critical when operating on spinal AVFs. Because SSEPs and MEPs provide key neurologic information during surgery, the anesthetic regimen should be modified to maximize evoked potential monitoring.
Figure 88-1:
Preoperative MRI and angiography of a patient with a thoracic spinal dural AVF. MRI depicts signal abnormalities within the thoracic spinal canal on sagittal and axial T2-weighted images. Angiography shows AVF nidus within the left T8 nerve root sleeve. The left T8 intercostal artery fills a tortuous spinal vein early within the nerve root sleeve. These features are typical of spinal dural AVF.
