MORPHOMETRIC STUDY OF MYELINATED FIBERS IN HUMAN CERVICAL SPINAL-CORDWHITE-MATTER

Study Design. Using human autopsy spinal cord specimens, morphologic m easurements of myelinated nerve fibers were performed, focusing on the regions that include the main white matter conduction paths. The hemi lateral spinal cord morphology was also measured, and its relation wit h the component myelinated nerve fibers determined. Objectives. To det ermine the relation between spinal cord transverse area in the normal lower cervical spine, the site most vulnerable to chronic compressive myelopathy, and myelinated nerve fibers. Summary of Background Data. C onsiderable interindividual variation normally is observed in the morp hology of the spinal cord transverse area. The influence of this varia tion on the composition of the white matter myelinated nerve fibers is obscure. Methods. The C7 segments from seven cadavers were resected, and from magnified photographs of paraffin-embedded specimens, the hem ilateral spinal cord area and funicular area were measured. Nerve fibe r morphology was measured using Epon-embedded specimens. Three regions that included the main conduction paths were sampled, and magnified p hotographs obtained. The nerve fiber transverse morphology was measure d using the ellipse conversion method, and the myelinated nerve densit y and fiber area were determined. Results. Marked interindividual vari ations were found in both the hemilateral spinal cord transverse area and funicular area. A positive correlation was noted between the two, with the spinal cord transverse area large in the cases with a large f unicular area. For fiber density and area, histograms were constructed that showed characteristic distribution patterns in each region. By d ividing each region into two components (i.e., small- and large-diamet er fibers), it was found that the interindividual variation in large-d iameter fiber density was small, clarifying that the absolute number o f large-diameter fibers compared to fiber density is more strongly dep endent on the furicular area. Conclusions. The absolute number of targ e-diameter myelinated fibers is smaller in cross-sections of thin as c ompared to those of thick spinal cord. When elucidating the pathophysi ology of compressive myelopathy, it is necessary to study not only the circumstances surrounding the spinal cord, but this kind of factor in trinsic to the spinal cord itself.