Utility of intraoperative neuromonitoring for decompression of Chiari type I malformation in 93 adult patients

Joseph SchaeferDepartment of Neurological Surgery, Thomas Jefferson University, Philadelphia, Pennsylvania

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Elias AtallahDepartment of Neurological Surgery, Thomas Jefferson University, Philadelphia, Pennsylvania

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Eric TecceDepartment of Neurological Surgery, Thomas Jefferson University, Philadelphia, Pennsylvania

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Sara ThalheimerDepartment of Neurological Surgery, Thomas Jefferson University, Philadelphia, Pennsylvania

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James HarropDepartment of Neurological Surgery, Thomas Jefferson University, Philadelphia, Pennsylvania

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Joshua E. HellerDepartment of Neurological Surgery, Thomas Jefferson University, Philadelphia, Pennsylvania

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OBJECTIVE

There is currently a lack of consensus on the utility of intraoperative neuromonitoring (IONM) for decompression of Chiari type I malformation (CM-I). Commonly used monitoring modalities include somatosensory evoked potentials (SSEPs), motor evoked potentials (MEPs), and brainstem auditory evoked potentials (BAEPs). The purpose of this study was to evaluate the utility of IONM in preventing neurological injury for CM-I decompression.

METHODS

The authors conducted a retrospective study of a population of adult patients (ages 17–76 years) diagnosed with CM-I between 2013 and 2021. IONM modalities included SSEPs, MEPs, and/or BAEPs. Prepositioning baseline signals and operative alerts of significant signal attenuation were recorded.

RESULTS

Ninety-three patients (average age 38.4 ± 14.6 years) underwent a suboccipital craniectomy for CM-I decompression. Eighty-two (88.2%) of 93 patients underwent C1 laminectomy, 8 (8.6%) underwent C1 and C2 laminectomy, and 4 (4.3%) underwent suboccipital craniectomy with concomitant cervical decompression and fusion in the setting of degenerative cervical spondylosis. Radiographically, the average cerebellar tonsillar ectopia/descent was 1.1 ± 0.5 cm and 53 (57.0%) of 93 patients presented with a syrinx. The average number of vertebral levels traversed by the syrinx was 5.3 ± 3.5, and the average maximum width of the syrinx was 5.8 ± 3.3 mm. There was one instance (1/93, 1.1%) of an MEP alert, which resolved spontaneously after 10 minutes in a patient who had concomitant stenosis due to pannus formation at C1–2. No patient developed a permanent neurological complication.

CONCLUSIONS

There were no permanent complications related to intraoperative neurological injury. Transient fluctuations in IONM signals can be detected without clinical significance. The authors suggest that CM-I suboccipital decompression surgery may be performed safely without IONM. The use of IONM in patients with additional occipitocervical pathology should be left as an option to the performing surgeon on a case-by-case basis.

ABBREVIATIONS

BAEP = brainstem auditory evoked potential; CCOS = Chicago Chiari Outcome Scale; CM-I = Chiari type I malformation; EEG = electroencephalography; EMG = electromyography; IONM = intraoperative neuromonitoring; MEP = motor evoked potential; SSEP = somatosensory evoked potential; TOF = train of four.
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Figure from Kim et al. (pp 1601–1609).

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