Histological Evaluation for the Mechanism of Syrinx Formation in the Rat Experimental Model with Injury and Secondary Adhesive Arachnoiditis

Summary

To elucidate the mechanism of cavity formation, histological findings of the spinal cord of the rat experimental model with injury and secondary adhesive arachnoiditis were examined. Twenty-two Wistar rat spinal cords were injured by epidural clipping at the level of T8 (model 1). Among these 22 specimens, 11 rats were injected with kaolin solution into the subarachnoid space of the lower lumbar spine (model 2). Rats were killed 2–16 days after injury. The spine and spinal cord were removed en bloc and sectioned transversely. Both models showed a high rate of syrinx formation (10/12 in model 1; 8/10 in model 2) in the gray matter to the posterior column with no relation to the central canal. In the early stage, parenchymal bleeding occurred, and an intramedullary cavity with surrounding reactive cells was then formed in the later stage. Venous dilatation and occlusion of subarachnoid space were more prominent in model 2. The size of the cavity enlarged chronologically. Syrinx formation in these experimental models indicated that the intramedullary cavity was initially caused by mechanical stress and was enhanced by circulatory disturbance with or without arachnoiditis. We conclude that syringomyelia caused by injury is the result of intramedullary degeneration in association with arachnoiditis, which makes it difficult to treat.