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Eric M. Jackson, Daniel M. Schwartz, Anthony K. Sestokas, Deborah M. Zarnow, N. Scott Adzick, Mark P. Johnson, Gregory G. Heuer, and Leslie N. Sutton

Object

Fetal myelomeningocele closure has been shown to be advantageous in a number of areas. In this study, the authors report on neural function in patients who had previously undergone fetal myelomeningocele repair and returned to the authors' institution for further surgery that included intraoperative neurophysiological monitoring.

Methods

The authors retrospectively reviewed data obtained in 6 cases involving patients who underwent fetal myelomeningocele repair and later returned to their institution for spinal cord untethering. (In 4 of the 6 cases, the patients also underwent removal of a dermoid cyst [3 cases] or removal of an epidermoid cyst [1 case] during the untethering procedure.) Records and imaging studies were reviewed to identify the anatomical level of the myelomeningocele as well as the functional status of each patient. Stimulated electromyography (EMG) and transcranial motor evoked potential (tcMEP) recordings obtained during surgery were reviewed to assess the functional integrity of the nerve roots and spinal cord.

Results

During reexploration, all patients had reproducible signals at or below their anatomical level on stimulated EMG and tcMEP recordings. Corresponding to these findings, prior to tethering, all patients had antigravity muscle function below their anatomical level.

Conclusions

All 6 patients had lower-extremity function and neurophysiological monitoring recording signals at or below their anatomical level. These cases provide direct evidence of spinal cord and nerve root conductivity and functionality below the anatomical level of the myelomeningocele, further supporting that neurological status improves with fetal repair.

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Vidya M. Bhalodia, Daniel M. Schwartz, Anthony K. Sestokas, Gary Bloomgarden, Thomas Arkins, Patrick Tomak, Judith Gorelick, Shirvinda Wijesekera, John Beiner, and Isaac Goodrich

Object

Deltoid muscle weakness due to C-5 nerve root injury following cervical spine surgery is an uncommon but potentially debilitating complication. Symptoms can manifest upon emergence from anesthesia or days to weeks following surgery. There is conflicting evidence regarding the efficacy of spontaneous electromyography (spEMG) monitoring in detecting evolving C-5 nerve root compromise. By contrast, transcranial electrical stimulation–induced motor evoked potential (tceMEP) monitoring has been shown to be highly sensitive and specific in identifying impending C-5 injury. In this study the authors sought to 1) determine the frequency of immediate versus delayed-onset C-5 nerve root injury following cervical spine surgery, 2) identify risk factors associated with the development of C-5 palsies, and 3) determine whether tceMEP and spEMG neuromonitoring can help to identify acutely evolving C-5 injury as well as predict delayed-onset deltoid muscle paresis.

Methods

The authors retrospectively reviewed the neuromonitoring and surgical records of all patients who had undergone cervical spine surgery involving the C-4 and/or C-5 level in the period from 2006 to 2008. Real-time tceMEP and spEMG monitoring from the deltoid muscle was performed as part of a multimodal neuromonitoring protocol during all surgeries. Charts were reviewed to identify patients who had experienced significant changes in tceMEPs and/or episodes of neurotonic spEMG activity during surgery, as well as those who had shown new-onset deltoid weakness either immediately upon emergence from the anesthesia or in a delayed fashion.

Results

Two hundred twenty-nine patients undergoing 235 cervical spine surgeries involving the C4–5 level served as the study cohort. The overall incidence of perioperative C-5 nerve root injury was 5.1%. The incidence was greatest (50%) in cases with dual corpectomies at the C-4 and C-5 spinal levels. All patients who emerged from anesthesia with deltoid weakness had significant and unresolved changes in tceMEPs during surgery, whereas only 1 had remarkable spEMG activity. Sensitivity and specificity of tceMEP monitoring for identifying acute-onset deltoid weakness were 100% and 99%, respectively. By contrast, sensitivity and specificity for spEMG were only 20% and 92%, respectively. Neither modality was effective in identifying patients who demonstrated delayed-onset deltoid weakness.

Conclusions

The risk of new-onset deltoid muscle weakness following cervical spine surgery is greatest for patients undergoing 2-level corpectomies involving C-4 and C-5. Transcranial electrical stimulation–induced MEP monitoring is a highly sensitive and specific technique for detecting C-5 radiculopathy that manifests immediately upon waking from anesthesia. While the absence of sustained spEMG activity does not rule out nerve root irritation, the presence of excessive neurotonic discharges serves both to alert the surgeon of such potentially injurious events and to prompt neuromonitoring personnel about the need for additional tceMEP testing. Delayed-onset C-5 nerve root injury cannot be predicted by intraoperative neuromonitoring via either modality.

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Bikash Bose, Anthony K. Sestokas, and Daniel M. Schwartz

Object

The incidence of postoperative C-5 spinal nerve root palsy following decompressive cervical spinal surgery has been reported to be as high as 12% for anterior procedures and 30% for posterior procedures. The present study was conducted to document the prevalence of iatrogenic C-5 nerve root deficit during anterior cervical spinal surgery, as well as to evaluate the sensitivity and specificity of intraoperative transcranial electrical stimulation (TES)–induced motor evoked potentials (MEPs) and spontaneous electromyographic (EMG) activity for identifying evolving C-5 nerve root impairment.

Methods

The authors conducted a retrospective study of 238 consecutive anterior cervical spinal procedures performed by a single surgeon at Christiana Care Hospital within a 48-month period. Techniques used to monitor spinal nerve root function included TES-induced MEPs and spontaneous EMG activity from deltoid, biceps, triceps, wrist extensor, and hand intrinsic muscles innervated by the C5–T1 spinal nerve roots. Spinal cord function was monitored by recording TES-induced MEPs from upper- and lower-extremity muscles as well as somatosensory evoked potentials from stimulation of the ulnar and posterior tibial nerves.

Conclusions

Transcranial electrical stimulation–induced MEPs and spontaneous EMG activity offer complementary information about evolving iatrogenic C-5 spinal nerve root impairment during anterior cervical spinal surgery. The TES-induced MEPs provide prognostic information and show increased sensitivity to C-5 deficit compared with spontaneous EMG activity alone. Monitoring of spinal nerve root function using only EMG activity carries a risk of false-negative findings; without timely warning of impending neurological impairment, timely intervention to prevent permanent deficit cannot occur.