Retrospective study of surgery-related outcomes in patients with syringomyelia associated with Chiari I malformation: Clinical significance of changes in the size and localization of syrinx on pain relief

Object. Pain is one of the major symptoms in patients with syringomyelia; however, its origin is not fully understood, and postoperative improvement of pain is difficult to predict. The objectives of this study were to assess the surgery-related results obtained in patients who underwent treatment for syringomyelia associated with Chiari I malformation, particularly related to pain status, and to identify factors that may influence improvement in postoperative pain by comparing pre- and postoperative magnetic resonance (MR) imaging findings. Methods. The correlation between pre- and postoperative changes in the size and the location of the syrinx and pain improvement was investigated in 25 patients. The shapes of the syringes were classified into three types: central, enlarged, and deviated. In most cases in which the syrinx deviated toward the posterolateral aspect of the spinal cord at the level corresponding to dermatomal distribution of preoperative pain, the lesion remained at the same position postoperatively, and improvement in pain was poor. On the other hand, enlarged-type syringes were the most frequently observed prior to surgery, exhibited diverse changes postoperatively, and improvement in pain status was difficult to predict. When postoperative MR imaging revealed a transformation to the deviated type, poor pain improvement was noted. Conclusions. Neurons in the dorsal horn were thought to be involved in the development of pain as a result of the deafferentiation mechanism in cases of syringomyelia.