Pathology of spinal cord lesions caused by ossification of the posterior longitudinal ligament.

The pathologic changes in the spinal cord of three autopsied cases associated with ossification of the posterior longitudinal ligament ( OPLL ) are reported. Compression of the spinal cord was marked at the level of the intervertebral disc, and the spinal cord was strikingly flattened antero-posteriorly. Intensive damage was seen in the gray matter as compared to the white matter. The white matter showed demyelination and axon loss with status spongiosus, which was more marked in the postero-lateral than in the anterior columns. The most seriously damaged parts of the spinal cord showed tissue necrosis and cavity formation which extended from the central parts of the gray matter to the ventral parts of the posterior columns. Adventitial fibrous thickening of the vein, hyaline degeneration of the walls of the arterioles, and compression of the anterior spinal vein were observed in the damaged regions. It was evident that secondary circulatory disturbance due to the compression produced by the ossification was of significance in the pathogenesis of the spinal cord damage. A tangle of peripheral nerves, ectopic and reactive, with Schwann cell proliferation was present in the posterior median fissure and the postero-lateral columns in one case. The spinal nerve roots that showed marked demyelination and axon loss were damaged by ossification at the places where the anterior nerve roots emerged from the spinal cord and where the roots penetrate the dura. There was ossification of the dura mater in all cases examined.