SPINAL-CORD AND NERVE ROOT BLOOD-FLOW IN ACUTE DOUBLE LEVEL SPINAL STENOSIS

Study Design. Twenty-four pigs were randomized into three groups of ei ght pigs; a control group with 0% stenosis, a 25% stenosis group, and a 50% stenosis group. A fourth 75% stenosis group was added when resul ts of the randomized experiment had been analyzed. Blood flow of the s pinal cord and nerve roots and spinal evoked potentials were determine d before and 1 hour after induction of the spinal stenoses. Objectives . To study and acute effects of different degrees of spinal stenosis o n neural tissue blood flow and spinal evoked potentials. Summary and B ackground Data. Spinal cord dysfunction may be caused by vascular impa irment or mechanical injury to neural tissue. Experimental double leve l compression of the cauda equina causes reversible nerve root edema, stasis, blood flow decrease, and compromised neural function. The vasc ular pathophysiology after spinal cord trauma was studied previously, and both increased and decreased neural tissue blood flow have been re ported. Methods. Two level spinal stenosis was introduced by placement of stenosing bands around the dural sac at L4 and L6. Neurologic func tion was monitored by sensory and motor evoked potentials. Regional bl ood flow (RBF) was measured in the stenotic segments between the bands and other regions of neural tissue by radioactive microspheres before and after induction of stenosis. Results. Regional blood flow increas ed in the stenotic segments after 0% sham stenosis. Analysis of varian ce revealed no differences in RBF between the three randomized groups under comparable conditions of 0% stenosis. However, the RBF level of the added 75% group was lower than that of the other three groups. By comparison of RBF within groups before and after stenosis, no decrease in RBF was found between the stenosing bands in any of the groups. Fi fty percent stenosis changed the amplitude of evoked potentials in hal f of the animals. Seventy-five percent stenosis caused severe changes in evoked potentials in 7 of 8 animals. Conclusions. Blood supply of t he spinal cord and nerve roots in the segments between two central ste nosis is preserved immediately after stenosis introduction by way of t he segmental nerve pathway, even if nerve conduction is impaired.