Subarachnoid–subarachnoid bypass: a new surgical technique for posttraumatic syringomyelia

Abstract

The origin of posttraumatic syringomyelia is not completely understood. With respect to posttraumatic syringomyelia, the optimum management strategy for patients with spinal cord injury has also not been established. The authors hypothesized that reconstruction of the subarachnoid channels would reestablish CSF flow, thereby addressing the underlying cause of the syrinx formation. The authors performed a new type of surgery, subarachnoid-subarachnoid bypass (S-S bypass), in which an attempt was made to reestablish normal CSF circulation around the spinal cord. The purpose of this study was to evaluate the effectiveness of S-S bypass for posttraumatic syringomyelia. Twenty consecutive patients with symptomatic posttraumatic syringomyelia who had progressive neurological symptoms and underwent S-S bypass were included in the study. The surgical procedure was as follows: a laminectomy was performed at the level of trauma, and a midline dural opening was made under a microscope. The arachnoid was exposed up to the area of normal arachnoid mater with normal CSF circulation. After dissection of the normal arachnoid mater at the cephalic and caudal sites, 1 or 2 tubes made of medical-grade silicone were inserted into the cephalic and caudal ends of the normal subarachnoid space. Bypass tubes were laid in the subdural space, and a watertight dural closure was accomplished using running sutures. The mean follow-up period was 48.2 months (range 12-93 months). The preoperative status and postoperative clinical course were assessed according to 3 grading systems: the Frankel grading system for global neurological status, the American Spinal Injury Association motor score for motor weakness, and the Klekamp system for bladder function. The major presenting symptoms or signs were assessed in terms of symptom improvement, stabilization, or deterioration. Preoperative and postoperative MRI was used to analyze the size and craniocaudal extension of the cavity. Twelve patients showed clinical improvement, 4 were stable, and 4 showed deterioration. The mean length of the syrinx observed on preoperative MRI was 9.9 spinal levels, and the mean Vaquero index was 62.3%. The mean length of the syrinx observed on postoperative MRI was 5.3 spinal levels, and the mean Vaquero index was 28.4%. These values were significantly lower than the preoperative values (p = 0.01 and p < 0.01, respectively). This study showed that interference with CSF flow was the major cause of syrinx development and that reconstruction of CSF flow is the most important treatment strategy based on the cause of the syrinx. Subarachnoid-subarachnoid bypass, which can be performed without myelotomy, was not only a safe and effective surgical technique, but may also be a more physiological way of treating posttraumatic syringomyelia.