Intraoperative neurophysiology of the corticospinal tract of the spinal cord.
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Efferent Pathways↗
Biomedical subjects
Vedran Deletis
Publications and source records attributed to Vedran Deletis.
Motor evoked potential monitoring improves outcome after surgery for intramedullary spinal cord tumors: a historical control study.
OBJECTIVE: The value of intraoperative neurophysiological monitoring (INM) during intramedullary spinal cord tumor surgery remains debated. This historical control study tests the hypothesis that INM monitoring improves neurological outcome. METHODS: In 50 patients operated on after September 2000, we monitored somatosensory evoked potentials and transcranially elicited epidural (D-wave) and muscle motor evoked potentials (INM group). The historical control group consisted of 50 patients selected from among 301 patients who underwent intramedullary spinal cord tumor surgery, previously operated on by the same team without INM. Matching by preoperative neurological status (McCormick scale), histological findings, tumor location, and extent of removal were blind to outcome. A more than 50% somatosensory evoked potential amplitude decrement influenced only myelotomy. Muscle motor evoked potential disappearance modified surgery, but more than 50% D-wave amplitude decrement was the major indication to stop surgery. The postoperative to preoperative McCormick grade variation at discharge and at a follow-up of at least 3 months was compared between the two groups (Student's t tests). RESULTS: Follow-up McCormick grade variation in the INM group (mean, +0.28) was significantly better (P = 0.0016) than that of the historical control group (mean, -0.16). At discharge, there was a trend (P = 0.1224) toward better McCormick grade variation in the INM group (mean, -0.26) than in the historical control group (mean, -0.5). CONCLUSION: The applied motor evoked potential methods seem to improve long-term motor outcome significantly. Early motor outcome is similar because of transient motor deficits in the INM group, which can be predicted at the end of surgery by the neurophysiological profile of patients.
Adolescent↗
Motor evoked potential monitoring during cerebral aneurysm surgery: technical aspects and comparison of transcranial and direct cortical stimulation.
OBJECTIVE: This study evaluates technical aspects, handling, and safety of intraoperatively applied transcranial electrical stimulation (TES) and direct cortical stimulation (DCS) for eliciting muscle motor evoked potentials (mMEPs) during cerebral aneurysm surgery. METHODS: In 119 patients undergoing cerebral aneurysm surgery, mMEPs were evoked by a train of five stimuli with individual pulse duration of 0.5 milliseconds, a repetition rate of 2 Hz, and constant current anodal stimulation. The maximal stimulation intensity was 240 mA for transcranial and 33 mA for direct stimulation. mMEPs were recorded continuously from the abductor pollicis brevis, from tibial anterior muscles bilaterally, and from the biceps brachii and extensor digitorum communis muscles contralateral to the side operated on. RESULTS: In 118 (99%) of 119 patients, transcranially evoked mMEPs were monitorable for the vascular territory of interest. DCS was performed successfully in 95 (95%) of 100 patients. In 86 (99%) of 87 patients with internal carotid artery, middle cerebral artery, or posterior circulation aneurysms, mMEPs from upper-extremity muscles were obtained with DCS. In 11 (55%) of 20 patients with anterior communicating artery, anterior cerebral artery, or pericallosal aneurysms, mMEPs from the lower-extremity muscles could be recorded. The incidence of seizures was 0.84% for TES and 1% for DCS. Minor and inconsequential subdural bleeding after positioning of the strip electrode occurred in 2%. CONCLUSION: The cogent comprehensive combination of transcranial and direct cortical electrical stimulation allows for the continuous mMEP monitoring of the cerebral vascular territory of interest in 99% of the patients with cerebral aneurysms. Unwarranted effects of electrode placement and stimulation are rare and without clinical consequences.
Adolescent↗
The refractory period of fast conducting corticospinal tract axons in man and its implications for intraoperative monitoring of motor evoked potentials.
OBJECTIVE: To determine the absolute and relative refractory period (RRP) of fast conducting axons of the corticospinal tract in response to paired high intensity (HI or supramaximal) and moderate intensity (MI or submaximal) electrical stimuli. The importance of the refractory period of fast conducting corticospinal tract axons has to be considered if repetitive transcranial electrical stimulation (TES) is to be effective for eliciting motor evoked potentials (MEPs) intraoperatively. METHODS: Direct (D) waves were recorded from the epidural space of the spinal cord in 14 patients, undergoing surgical correction of spinal deformities. To assess the absolute and RRPs of the corticospinal tract, paired transcranial electrical stimuli at interstimulus intervals (ISI) from 0.7 to 4.1 ms were applied. Recovery of conditioned D wave at short (2 ms) and long (4 ms) ISI was correlated with muscle MEP threshold. The refractory period for peripheral nerve was tested in comparison to that for the corticospinal tract. In four healthy subjects sensory nerve action potentials of the median nerve were studied after stimulation with paired stimuli. RESULTS: HI TES revealed a mean duration of 0.82 ms for the absolute refractory period of the corticospinal tract, while MI stimulation resulted in a mean refractory period duration of 1.47 ms. Stimuli of HI produced faster recovery of D wave amplitude during the RRP. Furthermore, short trains of transcranial electrical stimuli did not elicit MEPs when D wave showed incomplete recovery. A similar influence of stimulus intensity on recovery time was found for the refractory period of peripheral nerve. CONCLUSIONS: The recovery of D wave amplitude is dependent upon stimulus intensity. High intensity produces fast recovery. This is an important factor for the generation of MEPs. When HI TES is used to elicit MEPs, short and long ISIs are equally effective. When MI TES is used to elicit MEPs, only a long ISI of 4 ms is effective.
Action Potentials↗
Neurophysiologic monitoring and pharmacologic provocative testing for embolization of spinal cord arteriovenous malformations.
BACKGROUND AND PURPOSE: Embolization of a spinal cord arteriovenous malformation (SCAVM) is still considered risky. We evaluated the efficacy and reliability of pharmacologic provocative testing with neurophysiologic monitoring in the embolization of SCAVMs. METHODS: We retrospectively analyzed results of 60 provocative tests during 84 angiographic procedures (in 52 patients) with intended endovascular embolization. Tests included 47 sodium amytal and 56 lidocaine injections. All procedures were performed with general anesthesia and monitoring of cortical somatosensory evoked potentials (SEPs) and transcranial motor evoked potentials (MEPs). For provocative testing, 50 mg of amytal and 40 mg of lidocaine were consecutively injected through a microcatheter placed at the position of intended embolization. If SEPs and MEPs did not change, embolization was performed with N-butyl-cyanoacrylate (NBCA). If SEPs or MEPs changed, NBCA embolization was not performed from that catheter position. RESULTS: One false-negative result occurred, with an increase in spasticity after embolization. Nineteen positive results occurred: four after amytal injection and 15 after lidocaine injections. Seven injections in a posterior spinal artery feeder resulted in loss of SEPs or MEPs. Eleven injections in the anterior spinal artery feeder and one in the posterior inferior cerebellar artery feeder resulted in loss of MEPs. CONCLUSION: Provocative testing with amytal and lidocaine combined with neurophysiologic monitoring had a high negative predictive value and was a useful adjunct for SCAVM embolization. Both amytal and lidocaine should be used as provocative agents, and both SEPs and MEPs should be monitored.
Adult↗
Transient paraplegia revealed by intraoperative neurophysiological monitoring: was it caused by the epidural anesthetic or an epidural hematoma?
IMPLICATIONS: Our case report describes the electrophysiological features associated with the development of a spinal epidural hematoma during surgery of the lumbar spine. It stresses the importance of the evaluation of nonsurgical factors, which can potentially affect intraoperative evoked potentials; in this case, epidural local anesthetic or epidural hematoma.
Adult↗
Neurophysiological criteria for intraoperative prediction of pure motor hemiplegia during aneurysm surgery. Case report.
The value of motor evoked potentials (MEPs) as an intraoperative neurophysiological monitoring tool for detecting selective subcortical ischemia of the motor pathways during intracerebral aneurysm repair is described and the use of such measures to predict postoperative motor status is discussed. The authors present the case of a 64-year-old woman in whom there was an incidental finding of two right middle cerebral artery (MCA) aneurysms. During the aneurysm clipping procedure, an intraoperative MEP loss in the left abductor pollicis brevis and tibial anterior muscles occurred during an attempt at permanent clip placement. There were no concurrent changes in somatosensory evoked potentials. Postoperatively, the patient demonstrated a left hemiplegia with intact sensation. A computerized tomography scan revealed an infarct in the anterior division of the MCA territory, including the posterior limb of the internal capsule. In this patient, intraoperative neurophysiological monitoring with MEPs has been shown to be a sensitive tool for indicating subcortical ischemia affecting selective motor pathways in the internal capsule. Therefore, intraoperative loss of MEPs can be used to predict postoperative motor deficits.
Aneurysm↗
Neurophysiological evaluation of the corticospinal tract by D-wave recordings in young children.
OBJECTIVE: The objective was to neurophysiologically evaluate corticospinal tract (CT) maturation in children younger than 36 months by recording D-waves. METHODS: In 19 children, D-wave recordings were attempted during resection of intramedullary spinal cord tumors (imSCTs). D-waves were elicited by transcranial electrical stimulation (TES; single pulse, anodal stimulation) and recorded from a catheter-electrode inserted into the epidural space caudal to the imSCTs. The presence of the D-wave was analyzed in respect of the patients' age. RESULTS: A D-wave was present in 7 children (21-36 months) and absent in the remaining 12 children (8-31 months). In the youngest child (21 months) the D-wave was recorded from the lower thoracic spinal cord. CONCLUSION: These D-wave recordings indicate that in the immature CT a synchronized descending volley via fast conducting fibers is evoked by TES and can be recorded as a D-wave from the lower thoracic spinal cord at 21 months. As all D-waves have been recorded caudal to the imSCTs, it is difficult to distinguish the contributing factor affecting the D-wave recordings in children older than 21 months: the prolonged CT maturation for the lower extremities, the individual variability of CT maturation or the influence of the imSCT.
Cerebral Cortex↗
Intraoperative neurophysiological monitoring in pediatric neurosurgery: why, when, how?
INTRODUCTION: This review is primarily based on peer-reviewed scientific publications and on the authors' experience in the field of intraoperative neurophysiology. The purpose is a critical analysis of the role of intraoperative neurophysiological monitoring (INM) during various neurosurgical procedures, emphasizing the aspects that mainly concern the pediatric population. Original papers related to the field of intraoperative neurophysiology were collected using medline. INM consists in monitoring (continuous "on-line" assessment of the functional integrity of neural pathways) and mapping (functional identification and preservation of anatomically ambiguous nervous tissue) techniques. We attempted to delineate indications for intraoperative neurophysiological techniques according to their feasibility and reliability (specificity and sensitivity). DISCUSSION AND CONCLUSIONS: In compiling this review, controversies about indications, methodologies and the usefulness of some INM techniques have surfaced. These discrepancies are often due to lack of familiarity with new techniques in groups from around the globe. Accordingly, internationally accepted guidelines for INM are still far from being established. Nevertheless, the studies reviewed provide sufficient evidence to enable us to make the following recommendations. (1) INM is mandatory whenever neurological complications are expected on the basis of a known pathophysiological mechanism. INM becomes optional when its role is limited to predicting postoperative outcome or it is used for purely research purposes. (2) INM should always be performed when any of the following are involved: supratentorial lesions in the central region and language-related cortex; brain stem tumors; intramedullary spinal cord tumors; conus-cauda equina tumors; rhizotomy for relief of spasticity; spina bifida with tethered cord. (3) Monitoring of motor evoked potentials (MEPs) is now a feasible and reliable technique that can be used under general anesthesia. MEP monitoring is the most appropriate technique to assess the functional integrity of descending motor pathways in the brain, the brain stem and, especially, the spinal cord. (4) Somatosensory evoked potential (SEP) monitoring is of value in assessment of the functional integrity of sensory pathways leading from the peripheral nerve, through the dorsal column and to the sensory cortex. SEPs cannot provide reliable information on the functional integrity of the motor system (for which MEPs should be used). (5) Monitoring of brain stem auditory evoked potentials remains a standard technique during surgery in the brain stem, the cerebellopontine angle, and the posterior fossa. (6) Mapping techniques (such as the phase reversal and the direct cortical/subcortical stimulation techniques) are invaluable and strongly recommended for brain surgery in eloquent cortex or along subcortical motor pathways. (7) Mapping of the motor nuclei of the VIIth, IXth-Xth and XIIth cranial nerves on the floor of the fourth ventricle is of great value in identification of "safe entry zones" into the brain stem. Techniques for mapping cranial nerves in the cerebellopontine angle and cauda equina have also been standardized. Other techniques, although safe and feasible, still lack a strong validation in terms of prognostic value and correlation with the postoperative neurological outcome. These techniques include monitoring of the bulbocavernosus reflex, monitoring of the corticobulbar tracts, and mapping of the dorsal columns. These techniques, however, are expected to open up new perspectives in the near future.
Brain Mapping↗