Intraoperative neurophysiological monitoring during surgery for Chiari malformations

Reports on the use of intraoperative neurophysiological monitoring (INM) techniques during surgery for Chiari malformations are anecdotal. There are almost no data on significant intraoperative worsening in either somatosensory-evoked potentials (SEPs) or brainstem auditory-evoked potentials (BAEPs) during surgery that would have alerted the surgeon to modify the surgical strategy. Yet, a few reports suggest that INM may play a role in preventing spinal cord injury during positioning of the patient. Overall, the use of INM in this type of surgery can be considered only as an option. More speculatively, INM adds information to the ongoing discussion on the most appropriate surgical technique for posterior fossa decompression in Chiari malformations. This debate applies especially to children where a more conservative approach is advisable to reduce the complications. Studies on the conduction time of BAEPs provide some evidence that, from a merely neurophysiological perspective, most of the improvement occurs after bony decompression and removal of the dural band at the level of the atlanto-occipital membrane, not after duraplasty.