Intraoperative Neurophysiologic Monitoring and Mapping in Children Undergoing Brainstem Surgery.

SUMMARY: Intraoperative neurophysiologic monitoring during surgery for brainstem lesions is a challenge for intraoperative neurophysiologists and surgeons. The brainstem is a small structure packed with vital neuroanatomic networks of long and short pathways passing through the brainstem or originating from it. Many central pattern generators exist within the brainstem for breathing, swallowing, chewing, cardiovascular regulation, and eye movement. During surgery around the brainstem, these generators need to be preserved to maintain their function postoperatively. This short review presents neurophysiologic and neurosurgical experiences of brainstem surgery in children.

Anticipating Facial Nerve Position Using Three-Dimensional Tractography During the Preoperative Assessment of Cerebellopontine Angle Tumors.

OBJECTIVE: We aim to evaluate the usefulness of preoperative facial nerve tractography in determining the facial nerve position in cerebellopontine angle tumor resection and its value in helping to preserve facial nerve function during surgery. METHODS: A prospective study was designed to include patients presenting with cerebellopontine angle tumors. Three-dimensional reconstruction of facial nerve tractography was performed and added to the usual preoperative testing in all patients. Facial nerve position was compared between tractography results and surgical findings. Moreover, facial nerve function was evaluated at baseline and during follow-up. RESULTS: Fifteen patients were included for analysis. Complete resection was obtained in 5 patients, near-total resection was achieved in 8 patients, and partial resection in 2 patients. We found a strong statistically significant concordance between the preoperative facial nerve tractography reconstruction and the intraoperative findings (complete concordance in 86.66% of all the cases; κ = 0.784; P < 0.0001). Facial nerve anatomic structure was preserved in all patients during surgery. At 6 months follow-up, 66.66% of patients had a facial nerve normal function or a mild dysfunction. CONCLUSIONS: Preoperative facial nerve tractography reconstruction showed a high correlation with intraoperative findings. Preoperative tractography information regarding facial nerve position and its cisternal course is valuable information and could help the surgeon in increasing the safety of the procedure during cerebellopontine angle tumor surgery.

Intraoperative monitoring of facial corticobulbar motor evoked potentials: Methodological improvement and analysis of 100 patients.

OBJECTIVE: A) To describe an improved methodology for continuously monitoring the functional integrity of facial nerve by eliciting facial corticobulbar motor-evoked potentials (FCoMEP) and B) To establish the prognosis of facial nerve function based on changes in FCoMEP during skull base surgery. METHODS: Intraoperative monitoring of FCoMEP performed in 100 patients. Previously published methodology has been improved upon by a) doing preoperative mapping of the facial nerve, b) facilitating the corticobulbar tract (CBT) by continuous transcranial electrical stimulation (TES) at 2 Hz repetition rate, c) recording from multiple facial nerve innervated muscles, and d) eliciting blink reflex (BR). We analyzed changes in FCoMEP, comparing them with the clinical facial nerve outcome scored with the House-Brackman (HB) scale. RESULTS: The monitorability rate was 100%. Out of 100 patients, nine presented a new facial deficit after surgery. Eight of these showed significant changes in FCoMEP. In four patients FCoMEPs were lost; they presented a complete facial paralysis from which they did not recover. To discriminate the prognosis of patients, ROC analysis identified a cut-off at 65% for FCoMEPs amplitude decrease with a sensitivity of 89% and specificity of 99%. In four patients FCoMEP showed a decrease in amplitude greater than 65%, and they presented mild/moderate facial paresis that was transient. One patient did not present changes in FCoMEP but had a mild facial paresis from which the patient recovered. CONCLUSIONS: The improved methodology allows the maximum rate of monitorability and minimizes false positive and false negative results. This study shows that prognosis of facial nerve may be reliably established based on FCoMEP parameters. SIGNIFICANCE: We improved the previously described methodology for continuously monitoring the functional integrity of the facial nerve by increasing the monitorability rate, and we describe the impact of FCoMEP intraoperative management of facial nerve. This method may permit establishing the short-term and long-term prognosis of facial nerve function in skull base surgery.

Monitoring cerebellopontine angle and skull base surgeries.

Cerebellopontine angle (CPA) surgery represents a challenge for neurosurgeons due to the high risk of iatrogenic injury of vital neurological structures. Therefore, important efforts in improving the surgical techniques and intraoperative neurophysiology have been made in the last decades. We present a description and review of the available methodologies for intraoperative neuromonitoring and mapping during CPA surgeries. There are three main groups of techniques to assess the functional integrity of the nervous structures in danger during these surgical procedures: (1) Electrical identification or mapping of motor cranial nerves (CNs), which is essential in order to locate the nerve in their different parts during the tumor resection; (2) Monitoring, which provides real-time information about functional integrity of the nervous tissue; and (3) Brainstem reflexes including blink reflex, masseteric reflex, and laryngeal adductor reflex. All these methods facilitate the removal of lesions and contribute to notable improvement in functional outcome and permit on the investigation of their physiopathology in certain neurosurgically treated diseases. Such is the case of hemifacial spasm (HFS). We describe the methodology to evaluate the efficacy of microvascular decompression for HFS treatment at the end of this chapter.

Surgery and intraoperative neurophysiologic monitoring for aneurysm clipping.

This chapter describes the feasibility, utilization, and value of intraoperative neurophysiologic monitoring (IONM) in cerebrovascular cases. Practical advice on the integration of these adjunct methods into the modern neurosurgical operating room is based on our own neurophysiologic and neurosurgical experience. Most IONM is done for anterior circulation aneurysms. Somatosensory and motor evoked potentials are the modalities of choice covering vascular territories of the internal, anterior, and middle cerebral arteries. While monitoring both hemispheres with the unoperated side as control, monitoring focus is laid upon those territories at risk and bearing the aneurysm. The specificity of IONM is close to 1, and sensitivity ranges from 0.2 to 1, depending on the categorization of transient changes. The overall likelihood of worsened neurologic outcome after any intraoperative signal deterioration (transient or permanent) is 0.4.

Correction to: Is the new ASNM intraoperative neuromonitoring supervision "guideline" a trustworthy guideline? A commentary.

The article Is the new ASNM intraoperative neuromonitoring supervision "guideline" a trustworthy guideline? A commentary, written by Stanley A. Skinner, Elif Ilgaz Aydinlar, Lawrence F. Borges, Bob S. Carter, Bradford L. Currier, Vedran Deletis, Charles Dong, John Paul Dormans, Gea Drost, Isabel Fernandez­Conejero, E. Matthew Hoffman, Robert N. Holdefer, Paulo Andre Teixeira Kimaid, Antoun Koht, Karl F. Kothbauer, David B. MacDonald, John J. McAuliffe III, David E. Morledge, Susan H. Morris, Jonathan Norton, Klaus Novak, Kyung Seok Park, Joseph H. Perra, Julian Prell, David M. Rippe, Francesco Sala, Daniel M. Schwartz, Martín J. Segura, Kathleen Seidel, Christoph Seubert, Mirela V. Simon, Francisco Soto, Jeffrey A. Strommen, Andrea Szelenyi, Armando Tello, Sedat Ulkatan, Javier Urriza and Marshall Wilkinson, was originally published electronically on the publisher's internet portal (currently SpringerLink) on 05 January 2019 without open access. With the author(s)' decision to opt for Open Choice the copyright of the article changed on 30 January 2019 to © The Author(s) 2019 and the article is forthwith distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits use, duplication, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license and indicate if changes were made. The original article has been corrected.

Treatment of cavernous malformations in supratentorial eloquent areas: experience after 10 years of patient-tailored surgical protocol.

BACKGROUND: Eloquent area surgery has become safer with the development of intraoperative neurophysiological monitoring and brain mapping techniques. However, the usefulness of intraoperative electric brain stimulation techniques applied to the management and surgical treatment of cavernous malformations in supratentorial eloquent areas is still not proven. With this study, we aim to describe our experience with the use of a tailored functional approach to treat cavernous malformations in supratentorial eloquent areas. METHODS: Twenty patients harboring cavernous malformations located in supratentorial eloquent areas were surgically treated. Individualized functional approach, using intraoperative brain mapping and/or neurophysiological monitoring, was utilized in each case. Eleven patients underwent surgery under awake conditions; meanwhile, nine patients underwent asleep surgery. RESULTS: Total resection was achieved in 19 cases (95%). In one patient, the resection was not possible due to high motor functional parenchyma surrounding the lesion tested by direct cortical stimulation. Ten (50%) patients presented transient neurological worsening. All of them achieved total neurological recovery within the first year of follow-up. Among the patients who presented seizures, 85% achieved seizure-free status during follow-up. No major complications occurred. CONCLUSIONS: Intraoperative electric brain stimulation techniques applied by a trained multidisciplinary team provide a valuable aid for the treatment of certain cavernous malformations. Our results suggest that tailored functional approach could help surgeons in adapting surgical strategies to prevent patients' permanent neurological damage.

Evaluation of the High-Frequency Monopolar Stimulation Technique for Mapping and Monitoring the Corticospinal Tract in Patients With Supratentorial Gliomas. A Proposal for Intraoperative Management Based on Neurophysiological Data Analysis in a Series of 92 Patients.

BACKGROUND: Intraoperative identification and preservation of the corticospinal tract is often necessary for glioma resection. OBJECTIVE: To make a proposal for intraoperative management with the high-frequency monopolar stimulation technique for monitoring the corticospinal tract. METHODS: Ninety-two patients operated on with the assistance of the high-frequency monopolar stimulation. Clinical and neurophysiological data have been related with the motor status at 3 months to establish prognostic factors of motor deterioration. RESULTS: Twenty-one patients (22.8%) presented intraoperative alterations in motor-evoked potentials (MEPs). Twelve (13%) presented an increment in the MEP threshold ≥5 mA (no deficit at 3 months). Two (2.2%) presented an MEP amplitude reduction >50% (100% deficit at 3 months). Seven (7.6%) had an intraoperative MEP loss (80% deficit at 3 months). Subcortical stimulation was positive in 75 patients (81.5%). Eighty-five patients were available for the analysis at 3 months. Fourteen presented new deficits (16.5%). Among them, 5 presented a deficit in nonmonitored muscles (5.9%) and 1 presented a new deficit not detected intraoperatively. The combination of patients with preoperative motor deficits, MEP deterioration, or loss and intensity of subcortical stimulation ≤3 mA showed the highest sensitivity and specificity in the prediction of new deficits. CONCLUSIONS: Persistent MEP loss or deterioration is associated with a high probability of new deficits. It seems recommendable to stop the subcortical resection before obtaining a subcortical MEP threshold at 3 mA especially in patients with preoperative motor deficits. A careful selection of muscles for the registration of MEPs is mandatory to avoid deficits in nonmonitored muscles.

Functional approach using intraoperative brain mapping and neurophysiological monitoring for the surgical treatment of brain metastases in the central region.

OBJECTIVE Brain metastases are the most frequent intracranial malignant tumor in adults. Surgical intervention for metastases in eloquent areas remains controversial and challenging. Even when metastases are not infiltrating intra-parenchymal tumors, eloquent areas can be affected. Therefore, this study aimed to describe the role of a functional guided approach for the resection of brain metastases in the central region. METHODS Thirty-three patients (19 men and 14 women) with perirolandic metastases who were treated at the authors' institution were reviewed. All participants underwent resection using a functional guided approach, which consisted of using intraoperative brain mapping and/or neurophysiological monitoring to aid in the resection, depending on the functionality of the brain parenchyma surrounding each metastasis. Motor and sensory functions were monitored in all patients, and supplementary motor and language area functions were assessed in 5 and 4 patients, respectively. Clinical data were analyzed at presentation, discharge, and the 6-month follow-up. RESULTS The most frequent presenting symptom was seizure, followed by paresis. Gross-total removal of the metastasis was achieved in 31 patients (93.9%). There were 6 deaths during the follow-up period. After the removal of the metastasis, 6 patients (18.2%) presented with transient neurological worsening, of whom 4 had worsening of motor function impairment and 2 had acquired new sensory disturbances. Total recovery was achieved before the 3rd month of follow-up in all cases. Excluding those patients who died due to the progression of systemic illness, 88.9% of patients had a Karnofsky Performance Scale score greater than 80% at the 6-month follow-up. The mean survival time was 24.4 months after surgery. CONCLUSIONS The implementation of intraoperative electrical brain stimulation techniques in the resection of central region metastases may improve surgical planning and resection and may spare eloquent areas. This approach also facilitates maximal resection in these and other critical functional areas, thereby helping to avoid new postoperative neurological deficits. Avoiding permanent neurological deficits is critical for a good quality of life, especially in patients with a life expectancy of over a year.

Intraoperative Monitoring and Mapping of the Functional Integrity of the Brainstem.

The risk of iatrogenic damage is very high in surgical interventions in or around the brainstem. However, surgical techniques and intraoperative neuromonitoring (ION) have evolved sufficiently to increase the likelihood of successful functional outcomes in many patients. We present a critical review of the methodologies available for intraoperative monitoring and mapping of the brainstem. There are three main groups of techniques that can be used to assess the functional integrity of the brainstem: 1) mapping, which provides rapid anatomical identification of neural structures using electrical stimulation with a hand-held probe, 2) monitoring, which provides real-time information about the functional integrity of the nervous tissue, and 3) techniques involving the examination of brainstem reflexes in the operating room, which allows for the evaluation of the reflex responses that are known to be crucial for most brainstem functions. These include the blink reflex, which is already in use, and other brainstem reflexes that are being explored, such as the masseter H-reflex. This is still under development but is likely to have important functional consequences. Today an abundant armory of ION methods is available for the monitoring and mapping of the functional integrity of the brainstem during surgery. ION methods are essential in surgery either in or around the brainstem; they facilitate the removal of lesions and contribute to notable improvements in the functional outcomes of patients.

Suprasegmental neurophysiological monitoring with H reflex and TcMEP in spinal surgery. Transient loss due to hypotension. A case report.

OBJECTIVE: H-reflex is a well known neurophysiological test used to evaluate sensory afferent and motor efferent impulses of S1 root. Despite its simplicity and feasibility, it is not used very often in the operating room. METHODS: We report the case of a 16-year-old male patient who undergoes a surgical correction for a severe paralytic scoliosis (160°). On account of previous deficits, intraoperative neurophysiological monitoring was achieved through TcMEP and H-reflex. RESULTS: Intraoperative neurophysiological monitoring (IONM) showed a transient and simultaneous loss of bilateral TcMEP and H-reflex, coinciding with an abrupt hypotension during pedicle screw placement. After having dismissed mechanical injury and after increasing blood pressure, TcMEP and H-reflex were equivalent to those at baseline. CONCLUSIONS: The H-reflex is a classic neurophysiological test not used very frequently in the operating room. It is a feasible and reliable technique that can be helpful during spine surgery IONM, especially in patients with preexisting neurological deficits. Although simultaneous TcMEP and H-reflex monitoring has been previously described, to our knowledge, this is the first recorded case of a decline in both associated with abrupt hypotension.

Neurophysiologic markers in laryngeal muscles indicate functional anatomy of laryngeal primary motor cortex and premotor cortex in the caudal opercular part of inferior frontal gyrus.

OBJECTIVE: The aim of this study was to identify neurophysiologic markers generated by primary motor and premotor cortex for laryngeal muscles, recorded from laryngeal muscle. METHODS: Ten right-handed healthy subjects underwent navigated transcranial magnetic stimulation (nTMS) and 18 patients underwent direct cortical stimulation (DCS) over the left hemisphere, while recording neurophysiologic markers, short latency response (SLR) and long latency response (LLR) from cricothyroid muscle. Both healthy subjects and patients were engaged in the visual object-naming task. In healthy subjects, the stimulation was time-locked at 10-300 ms after picture presentation while in the patients it was at zero time. RESULTS: The latency of SLR in healthy subjects was 12.66 ± 1.09 ms and in patients 12.67 ± 1.23 ms. The latency of LLR in healthy subjects was 58.5 ± 5.9 ms, while in patients 54.25 ± 3.69 ms. SLR elicited by the stimulation of M1 for laryngeal muscles corresponded to induced dysarthria, while LLR elicited by stimulation of the premotor cortex in the caudal opercular part of inferior frontal gyrus, recorded from laryngeal muscle, corresponded to speech arrest in patients and speech arrest and/or language disturbances in healthy subjects. CONCLUSION: In both groups, SLR indicated location of M1 for laryngeal muscles, and LLR location of premotor cortex in the caudal opercular part of inferior frontal gyrus, recorded from laryngeal muscle, while stimulation of these areas in the dominant hemisphere induced transient speech disruptions. SIGNIFICANCE: Described methodology can be used in preoperative mapping, and it is expected to facilitate surgical planning and intraoperative mapping, preserving these areas from injuries.

Inducing transient language disruptions by mapping of Broca's area with modified patterned repetitive transcranial magnetic stimulation protocol.

OBJECT: Until now there has been no reliable stimulation protocol for inducing transient language disruptions while mapping Broca's area. Despite the promising data of only a few studies in which speech arrest and language disturbances have been induced, certain concerns have been raised. The purpose of this study was to map Broca's area by using event-related navigated transcranial magnetic stimulation (nTMS) to generate a modified patterned nTMS protocol. METHODS: Eleven right-handed subjects underwent nTMS to Broca's area while engaged in a visual object-naming task. Navigated TMS was triggered 300 msec after picture presentation. The modified patterned nTMS protocol consists of 4 stimuli with an interstimulus interval of 6 msec; 8 or 16 of those bursts were repeated with a burst repetition rate of 12 Hz. Prior to mapping of Broca's area, the primary motor cortices (M1) for hand and laryngeal muscles were mapped. The Euclidian distance on MRI was measured between cortical points eliciting transient language disruptions and M1 for the laryngeal muscle. RESULTS: On stimulating Broca's area, transient language disruptions were induced in all subjects. The mean Euclidian distance between cortical spots inducing transient language disruptions and M1 for the laryngeal muscle was 17.23 ± 4.73 mm. CONCLUSIONS: The stimulation paradigm with the modified patterned nTMS protocol was shown to be promising and might gain more widespread use in speech localization in clinical and research applications.