Multimodal Spinal Cord Mapping during Spinal Cord Stimulator Placement: Technical Note.

Spinal cord stimulation is used to treat patients with severe neuropathic pain and other forms of debilitating back pain. Spinal cord stimulators (SCS) can either be placed under sedation or general anesthesia (GA). This study evaluated the utility of neurogenic evoked potentials in enabling multimodal spinal cord mapping (MSCM) for the placement of SCSs under GA. The goal of our MSCM paradigm, which integrated recordings from multiple antidromic and orthodromic generators, was to enable the use of precise neuromonitoring techniques, typically used for localizing the midline of the dorsal spinal cord in intramedullary tumor cases, for the safe placement of SCSs. Two distinct modalities were incorporated - orthodromic responses from the somatosensory cortex (Cp3-Cp4 cancellation) and antidromic stimulation via the SCS which resulted in compound nerve action potentials of the extremities. In addition, two incidental findings were made. First, our results suggest that previous investigations may have incorrectly identified compound muscle action potentials as compound nerve action potentials. Additionally, anti D-wave responses, that are theorized to be the equivalent of a D-wave, were observed. This manuscript describes the first use of MSCM, which will ultimately provide neurophysiologists more information during SCS implantation, enabling them to confirm midline placement more confidently. MSCM also allows the application of techniques typically used in spinal cord tumors, allowing the neurophysiologist to maintain proficiency with these techniques on more common procedures. The parallel collection of several sources of data will allow for future studies that better define which mapping methods are the most accurate.

Multimodality intraoperative neurophysiological monitoring during Onyx embolization of cerebrovascular malformations.

General anesthesia prohibits neurological examination during embolization of cerebrovascular malformations when provocative testing prior to pedicle occlusion is needed. Intraoperative neurophysiological monitoring (IONM) has the potential to fill this gap but remains relatively unexplored. We conduct a retrospective review of consecutive patients with cerebrovascular malformations treated with Onyx (ethylene vinyl alcohol copolymer, dissolved in dimethyl sulfoxide) embolization under general anesthesia with IONM from 2009 to 2012. Somatosensory evoked potentials (SSEPs), transcranial motor evoked potentials (TcMEPs), visual evoked potential (VEPs), auditory brainstem response (ABR), and electroencephalography (EEG) were used selectively in all patients depending on the location of the malformation. Provocative testing combined with IONM was performed in 28 patients over 75 sessions. Three patients demonstrated changes in TcMEPs or ABR during provocative testing, which halted the planned embolization. Two patients demonstrated changes in baseline SSEPs after embolization, despite normal IONM during provocative testing, correlating with postprocedural contralateral weakness. Six patients developed visual deficits after arterial occlusion despite unchanged VEPs and occipital EEG during provocative testing and embolization. We therefore conclude that the sensitivity of TcMEPs and SSEPs is preferable to EEG, and we strongly caution against relying on occipital recorded VEPs to predict visual deficits.

Electroretinography during embolization of an ophthalmic arteriovenous fistula.

BACKGROUND: Intraoperative neuromonitoring (IONM) is used for real-time evaluation of neuronal tracts and reflexes in the anesthetized patient, when a neurologic exam is not possible. Changes in IONM signals forewarn of possible neurological deficit. This real-time feedback allows for immediate alterations in therapeutic technique by the treating physician. Transcranial visual evoked potentials are not reliable for evaluating the integrity of the prechiasmatic visual system. Electroretinography (ERG) has been used in animal models for monitoring retinal ischemia and can be used in humans as well to monitor for prechiasmatic ischemia of the retinae and optic nerves. CASE DESCRIPTION: We present a case where ERG signal amplitude and latency changed during ophthalmic arteriovenous fistula embolization, resulting in an intraprocedural decision to refrain from embolization of additional arterial pedicles to preserve vision. After awakening from general anesthesia, the patient had no deficits in visual acuity or field testing, but did complain of transient pain with eye movement that resolved the next day and worsened with episodes of blood pressure elevation. CONCLUSIONS: ERG may be helpful for detecting prechiasmatic ischemic changes during endovascular procedures and may provide early warning signs to the surgeon before the onset of permanent retinal damage. Further investigation is needed to assess the utility of ERG monitoring during the treatment of orbital and periorbital vascular lesions.

The usefulness of intraoperative neurophysiological monitoring in cervical spine surgery: a retrospective analysis of 200 consecutive patients.

The usefulness of intraoperative neurophysiological monitoring (IONM), including somatosensory-evoked potential (SSEP) and transcranial electrical motor-evoked potentials (TcMEPs) in cervical spine surgery still needs to be evaluated. We retrospectively reviewed 200 cervical spine surgery patients from 2008 to 2009 to determine the role of IONM in cervical spine surgery. Total intravenous anesthesia was used for all patients. IONM alerts were defined as a 50% decrease in amplitude, a 10% increase in latency, or a unilateral change for SSEP and an increase in stimulation threshold of more than 100 V for TcMEP. Three patients had SSEP alerts that were related to arm malposition (2 patients) and hypotension (1 patient). Five patients had TcMEP alerts: 4 alerts were caused by hypotension and 1 by bone graft compression of the spinal cord. All alerts were resolved when causative reasons were corrected. There was no postoperative iatrogenic neurological injury. The sensitivities of SSEP and TcMEP alerts for detecting impending neurological injury were 37.5% and 62.5%, respectively. The sensitivity of both SSEP and TcMEP used in combination was 100%. No false-positive and false-negative alerts were identified in either SSEP or TcMEP (100% specificity). The total intravenous anesthesia technique optimizes the detection of SSEP and TcMEP and therefore improves the sensitivity and specificity of IONM. SSEP is sensitive in detecting alerts in possible malposition-induced ischemia or brachial plexus nerve injury. TcMEP specifically detects hypotension-induced spinal functional compromises. Combination use of TcMEP and SSEP enhances the early detection of impeding neurological damage during cervical spine surgery.

Direct cortical stimulation but not transcranial electrical stimulation motor evoked potentials detect brain ischemia during brain tumor resection.

Motor evoked potentials (MEPs) elicited by both direct cortical stimulation (DCS) and transcranial electrical stimulation are used during brain tumor resection. Parallel use of direct cortical stimulation motor evoked potentials (DCS-MEPs) and transcranial electrical stimulation motor evoked potentials (TCeMEPs) has been practiced during brain tumor resection. We report that DCS-MEPs elicited by direct subdural grid stimulation, but not TCeMEPs, detected brain ischemia during brain tumor resection. Following resection of a brainstem high-grade glioma in a 21-year-old, the threshold of cortical motor-evoked-potentials (cMEPs) increased from 13 mA to 20 mA while amplitudes decreased. No changes were noted in transcranial motor evoked potentials (TCMEPs), somatosensory evoked potentials (SSEPs), auditory evoked potentials (AEPs), anesthetics, or hemodynamic parameters. Our case showed the loss of cMEPs and SSEPs, but not TCeMEPs. Permanent loss of DCS-MEPs and SSEPs was correlated with permanent left hemiplegia in our patient even when appropriate action was taken. Parallel use of DCS- and TCeMEPs with SSEPs improves sensitivity of intraoperative detection of motor impairment. DCS may be superior to TCeMEPs during brain tumor resection.

Transcranial motor evoked potential changes induced by provocative testing during embolization of cerebral arteriovenous malformations in patients under total intravenous anesthesia.

Cerebral motor evoked potential (MEP) monitoring during arteriovenous malformation (AVM) embolization is not well studied (Söderman et al. 2003). Alterations of cerebral blood flow (CBF) during cerebral embolization could cause ischemia/infarction to the cerebral cortex. Permanent loss of MEPs is correlated with a permanent motor deficit. We report a case of a patient undergoing AVM embolization during which transcranial electrical motor evoked potentials (TCeMEP) reliably predicted changes to CBF induced by selective methohexital testing. Our finding demonstrated that MEPs are a useful means of intraoperative monitoring of motor pathway integrity and predicting changes. The loss of MEP predicted and prevented severe postoperative motor deficits. Intraoperative neuromonitoring with SSEP, TCeMEP and continuous EEG revealed no changes until the posterior cerebral artery (PCA), but not the anterior cerebral artery (ACA), was injected. TCeMEP may be superior to somatosensory evoked potential (SSEP) and EEG monitoring in predicting motor impairment during AVM surgery.