The role of intraoperative neuromonitoring in adults with Chiari I malformation

• INM during Chiari-I-Malformation surgery does not demonstrate significant changes.
• Syringomyelia was present in 85% of patients with Chiari malformation.
• Patients can improve their SSEP and MEP during surgery.
• Changes in INM during surgery do not reflect clinical changes.

ObjectSuboccipital decompression and duraplasty is considered the treatment of choice for Chiari-I-malformation. Several studies have shown improvement of neurophysiological parameters during decompressive surgery in pediatric patients. However, there is no evidence of the beneficial role of intraoperative neuromonitoring in adults.MethodsA total of 39 consecutive patients (25 female, age 41.1 ± 14.5 years [mean ± SD]) underwent suboccipital decompression for the treatment of symptomatic Chiari-I-malformation senior neurosurgeon and his team. Continuous intraoperative monitoring of somatosensory-evoked potentials of the median nerve (m-SSEPs) and the posterior tibial nerve (t-SSEPs) and motor-evoked potentials to the hand (APB-MEPs) and foot (TA-MEPs) were applied to all patients, alone or in combination. The m-SSEP-N20, t-SSEP-P40, APB-MEP and TA-MEP amplitudes and latencies were recorded at the beginning of the surgery (baseline) and after dura closure. Neurological assessments of the patient were performed prior to surgery, after surgery and during each follow-up visit (3, 6 and 12 months).ResultsThere was no significant change in m-SSEP-N20, t-SSEP-P40 or APB-MEP and TA-MEP amplitudes or latencies between the baseline and final measurements (p > 0.05, Student’s t-test). The average time between both recordings was 125 ± 48 min (mean ± SD). Postoperatively, none of the patients presented new neurological deficits. During the mean follow-up period of 22.4 ± 20.3 months, 92.6% of the symptoms improved or remained stable. Three patients (8.1%) exhibited a relapse of symptoms after 25.7 ± 7.6 months, and only one patient (2.5%) needed secondary decompression after 24 months.ConclusionIntraoperative neuromonitoring (INM) during the primary treatment of Chiari-I-malformation shows only subtle non-significant changes in SSEPs/MEPs without clinical correlation during suboccipital decompression. INM is not considered a prerequisite for a safe suboccipital decompression when operated by an experienced surgical team.