Vascular and neural pathology of lumbosacral spinal stenosis

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✓ During a study of the intrinsic vasculature of the lumbosacral spinal nerve roots in cadavers, a typical case of spinal stenosis was encountered. A review of the antemortem anamnesis revealed that this patient had had an intermittent claudication of the cauda equina. Investigation of the concomitant vascular and histopathological alterations of the affected nerve roots suggested that the claudication may have resulted from ectopic nerve impulse discharges elicited by rapid changes in the blood supply following exertion. The unexpectedly slight apparent neural deficit relative to observed root damage may be attributed to a neuronal plasticity within the spinal cord that permitted functional compensations to develop during the slow acquisition of the chronic nerve root pathology.

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Address reprint requests to: Wesley W. Parke, Ph.D., Department of Anatomy, University of South Dakota School of Medicine, Vermillion, South Dakota 57069.

© AANS, except where prohibited by US copyright law.

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    A: Lateral radiogram of the lumbar spine of an 83-year-old anatomic cadaver showing L4–5 spondylolisthesis in excess of 25% (arrows). The vertebral displacement plus facet joint hypertrophy produced a marked spinal stenosis. No neural arch components are seen here, as they were removed to expose the cord prior to discovery of the condition. B: Photograph of the extirpated cord showing the extent of the external constriction of the dura between the thecal extensions of the L-4 and L-5 nerve roots. C: The ventrally slit dura shows considerable constriction of all lumbosacral nerve roots inferior to L-4. The anterior spinal artery had been injected at the T-10 level and latex-India ink medium can be seen in the radicular arteries.

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    A: Isolated right L-5 dorsal and ventral roots showing hypertrophy of the pia-arachnoid (PA) in the region of the constrictive lesion (between arrows). The roots in the area of stenosis were bound to each other and the dura by an adhesive arachnoiditis. B: The isolated right S-1 dorsal root has been cleaned of redundant pia-arachnoid to show the extent of irreversible chronic root compression. Note that the diameter has been reduced to less than 25% of the original root dimensions. Measure in centimeters. C: Photograph of the cleared and transilluminated specimen shown in B (above). Surprisingly, most of the longitudinal radicular arteries maintained their continuity during the slowly developing compression. The pronounced compensatory coils (CC) are more exaggerated adjacent to the lesion. This is believed to compensate for the immobilization of the root at the point of the lesion which would produce extra tension during flexionextension of the lumbar vertebrae. D: A section of the right S-1 dorsal root proximal to the lesion that has been treated with hydrogen peroxide to inflate the veins (V). Note the large-bore arteriovenous anastomoses (AVA) that permitted the medium to pass from the injected radicular arteries (RA) to the veins. The interradicular branches (IRB) of the vasculature that passed between adjacent roots are shown.

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    A: Photomicrograph of a paraffin-embedded section of the right S-1 dorsal root about 1 mm proximal to the narrowest part of the lesion. There is a complete lack of large myelinated fibers, but degenerating/regenerating small fibers are present. The interstices between the fascicles appear edematous, and the large vein (V) was congested. Masson's trichrome, bar = µm. B: Photomicrograph of a paraffinembedded section of normal lumbar dorsal root for comparative reference to the pathological section shown in A (above). Note the number of large myelinated fibers and the profusion of normal small fibers of various degrees of myelination. Masson's trichrome, bar = 20 µm.

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    A: Scanning electron micrograph of a cut end of the compressed right S-1 dorsal root near the region of maximum constriction. The major longitudinal arteries are easily identified by the solidified latex medium within their lumina. Few veins (V) showed any continuity through the lesioned area as they are more readily collapsed by the chronic compression. Demyelination, nerve fiber degeneration, and interstitial fibrosis give the area a solidified amorphous appearance. Erythrocytes appear as small spherules on the cut surface and, being consistently 7 µm in diameter, provide a comparative size scale. Note the hypertrophic pia-arachnoid around the larger superficial arteries (A). B: Scanning electron micrograph of a sectioned end of normal human lumbosacral dorsal nerve root showing the typical arrangement of myelinated nerve fibers and their relationship to healthy capillaries (C) and connective tissue.

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