Hemodynamics of spinal dural arteriovenous fistulas. An intraoperative study

Local hemodynamics were investigated during nine operations for spinal dural arteriovenous (AV) fistulas. In eight cases, microvascular Doppler sonography was used to measure flow velocities and vasomotor reactivity to CO2 changes. Intravascular pressure recordings of the draining veins on the medullary surface were performed in nine cases. The flow velocities in dural AV fistula feeding vessels were not as high as has been shown in cerebral angioma feeders. The AV fistula feeders often showed low end-diastolic flow velocities as a sign of increased vascular resistance, even in the presence of a downstream AV fistula, thus proving disturbance of venous outflow from the spinal canal. After excision of the fistula, the circulation of the spinal cord vessels improved, with higher inflow and outflow velocities. In the veins formerly draining the fistula, no further flow could be recorded; however, they did not collapse, indicating that some pressure remained. The mean venous pressure in the dural AV fistulas was about 74% of the systemic arterial pressure. It increased concomitantly with the arterial pressure, which may explain the clinical deterioration that occurs during physical activity. Fistulas with a high shunt volume on angiography showed only moderately increased venous pressures and a more pronounced pressure drop compared to low-volume fistulas. The CO2 reactivity of vessels supplying the spinal cord could be demonstrated in all cases, and was normal before and after removal of the fistula.