SPINAL-CORD MORPHOLOGY AND PATHOLOGY IN OSSIFICATION OF THE POSTERIORLONGITUDINAL LIGAMENT

We analysed nine autopsy cases of ossification of the posterior longit udinal ligament (OPLL) to elucidate the relationship between morpholog y and pathology of the spinal cord. The cross-sectional shape of the s pinal cord at the most severely affected segment was classified into t wo categories: boomerang (convex lateral surfaces and concave anterior surface) and triangular (angular lateral surfaces and flat anterior s urface). In the cases with a boomerang shape, even when the compressio n was severe, major pathological changes were restricted to the grey m atter and the white matter was relatively well preserved. No secondary descending degeneration of the lateral columns was seen, and ascendin g degeneration of the posterior column was restricted to the fasciculu s cuneatus whose fibres were derived from the affected segments. In th e cases with a triangular shape, pathological changes were more severe , both white matter and grey matter were involved and only the anterio r columns were free of pathological changes. There were severe patholo gical changes over more than one segment, and both descending degenera tion of the lateral pyramidal tracts and ascending degeneration of the posterior column, including the fasciculus gracilis, were observed. T he transverse area of the spinal cord was >60% of normal in most of th e cases with a boomerang shape, but it was reduced to <60% of normal i n more than one segment in the cases with a triangular shape. The comp ression. ratio of the spinal cord (sagittal diameter/transverse diamet erX100%) was not related to pathological changes. In conclusion, a tri angular-shaped spinal cord with transverse area of <60% of normal in m ore than one segment appeared to be associated with severe and irrever sible pathological changes in cases of OPLL.