Chiari I Malformation: Potential Role for Intraoperative Electrophysiologic Monitoring

Abstract

Intraoperative electrophysiologic monitoring can diminish the risk of neurologic injury by enabling the detection of injury at a time when it can be reversed or minimized. Although it is clear that in patients with cervical spine disease monitoring during surgery reduces the incidence of neurologic injury, almost no data are available regarding its utility in patients undergoing suboccipital decompression for Chiari I malformation. Patients with Chiari I malformation have caudal displacement of the cerebellar tonsils below the skull base, thereby creating a tight foramen magnum and cervical canal. Although the majority of pediatric neurosurgeons perform a bony decompression with duraplasty for symptomatic patients, there is much controversy regarding the amount of bony decompression required for clinical improvement and whether a duraplasty is essential. The authors therefore conducted a prospective, observational study using intraoperative brainstem auditory evoked potentials (BAEPs) and somatosensory evoked potentials in pediatric patients undergoing suboccipital decompressions for Chiari I malformations to determine whether there were consistent changes in intraoperative BAEPs that could help the operating surgeon decide how extensive a decompression was needed in these patients, and whether changes in BAEPs or somatosensory evoked potentials occurred during operative positioning that could be modified to reduce the risk of neurologic injury.

Outcomes after suboccipital decompression without dural opening in children with Chiari malformation Type I

“…6,26,28,33,36,47,48 Although pediatric neurosurgeons have a great deal of experience with PFD and duraplasty, both case series and intraoperative electrophysiological studies have demonstrated that in many patients physiological decompression can be achieved without opening of the dura. 3,4,8,18,33,48 …”

Cervical Spine Motion Generated With Manual Versus Jackson Table Turning Methods in a Cadaveric C1–C2 Global Instability Model

“…9 -12 In addition to instrumentation and deformity correction, surgical positioning is a key point in the perioperative process, which puts the spinal cord at risk. 9,10,12,13 Two previous studies have shown that that the "Jackson table turn" (Jackson) technique generated significantly less motion compared to the log-roll technique in the unstable cervical spine during supine to prone transfers onto the OR table using a C5-C6 instability model. This was true whether or not a cervical collar was used.…”

Delayed resolution of syrinx after posterior fossa decompression without dural opening in children with Chiari malformation Type I

“…4,11,25,26,32,35,42 High rates of radiographic syrinx improvement have been reported after PFD with dural opening in pediatric CM-I, with symptom resolution often occurring prior to syrinx resolution and scoliosis improvement often occurring after. [1][2][3][4][5][6][7][8][10][11][12][15][16][17]20,26,27,[29][30][31][32][33][34][35]42,44 In part because syrinx improvement has been noted to occur in the majority of 17,19,36,39 At the 2006 American Society of Pediatric Neurosurgeons meeting, for example, a survey of 50% of the membership demonstrated that for children with a symptomatic CM-I and syrinx, only 4% would perform nondural opening surgery and another 4% would use ultrasound to guide whether to add duraplasty, with the vast majority opting for duraplasty with or without tonsillar resection. 36 However, controversy exists over whether the dura must be opened for successful surgery for pediatric CM-I with or without a syrinx, with good clinical outcomes being reported for a variety of methods.…”

“…This rate is similar to previous studies that have reported the proportion of syrinx improvement after PFD with dural opening between 55% and 100%. [1][2][3]5,6,11,20,26,35,44 In the largest series of patients undergoing PFD with dural opening for pediatric CM-I, 80% radiographic syrinx improvement was reported. 42 In the 2 largest series of patients with PFD and mixed dural opening and non-dural opening surgeries, the radiographic syrinx improvement rate was 62% in one study and 29% in the other, with no difference detected between the 2 procedure types.…”

“…13,14,26,32 Although pediatric neurosurgeons have a great deal of experience with PFD with duraplasty, both case series as well as intraoperative electrophysiological studies have demonstrated that many patients can experience physiological decompression without opening of the dura. 2,3,8,15,32,49 As a result, it is controversial whether the dura must be opened for adequate decompression.…”