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Complete and precise knowledge of the neck anatomy and its eventual anomalies is crucial while performing a safe thyroid and parathyroid surgery. Embryo-genetic malformations of the IV branchial arch can lead to an uncommon anatomical alteration known as non-recurrent inferior laryngeal nerve. Its prevalence varies between 0.7% for the dextral branch and 0.04% for the sinistral. In these cases, the inferior laryngeal nerve branches originate directly from the cervical vagus nerve, entering the larynx without hooking, on the right side around the subclavian artery or on the left around the aortic arch. The presence of a non-recurrent laryngeal nerve is challenging, due to the increased risks of iatrogenic damage to the nerve, which results in hoarseness, dysphagia, glottal obstruction, vocal cords palsy, and serious airway impairment. We present the case of a 58-year-old woman. The patient was admitted to our department for a nodule classified as Bethesda IV in the right thyroid lobe. Through the use of intraoperative neuromonitoring (IONM), surgeons detected intraoperatively a non-recurrent laryngeal nerve. A subsequent computed tomography scan confirmed an anomalous right subclavian artery branching from the left aortic arch, the Lusoria Artery. Anatomical variants represent pitfalls in this case and an accurate knowledge of the neck region is imperative while performing thyroid surgery. Devices such as IONM are useful for detecting abnormalities that may lead to iatrogenic damages.

D-waves (also called direct waves) result from the direct activation of fast-conducting, thickly myelinated corticospinal tract (CST) fibres after a single electrical stimulus. During intraoperative neurophysiological monitoring, D-waves are used to assess the long-term motor outcomes of patients undergoing surgery for intramedullary spinal cord tumours, selected cases of intradural extramedullary tumours and surgery for syringomyelia. In the present manuscript, we discuss D-wave monitoring and its role as a tool for monitoring the CST during spinal cord surgery. We describe the neurophysiological background and provide some recommendations for recording and stimulation, as well as possible future perspectives. Further, we introduce the concept of anti D-wave and present an illustrative case with successful recordings.

OBJECTIVE: To develop and evaluate machine learning (ML) approaches for muscle identification using intraoperative motor evoked potentials (MEPs), and to compare their performance to human experts.
BACKGROUND: There is an unseized opportunity to apply ML analytic techniques to the world of intraoperative neuromonitoring (IOM). MEPs are the ideal candidates given the importance of their correct interpretation during a surgical operation to the brain or the spine. In this work, we develop and test a set of different ML models for muscle identification using intraoperative MEPs and compare their performance to human experts. In addition, we provide a review of the available literature on current ML applications to IOM data in neurosurgery.
METHODS: We trained and tested five different ML classifiers on a MEP database developed from six different muscles in patients who underwent brain or spinal cord surgery. MEPs were obtained by both transcranial (TES) and direct cortical stimulation (DCS) protocols. The models were evaluated within a single patient and on previously unseen patients, considering signals from TES and DCS both independently and mixed. Ten expert neurophysiologists classified a set of 50 randomly selected MEPs, and their performance was compared to the best performing model.
RESULTS: A total of 25.423 MEPs were included in the study. Random Forest proved to be the best performing model with 99 % accuracy in the single patient dataset task and a 78 %-94 % accuracy range on previously unseen patients. The model performance was maximized by representing MEPs as a set of features typically employed in signal processing compared to traditional neurophysiological parameters. The classification ability of the Random Forest model between six different muscles and across different MEP acquisition modalities (79 %) significantly exceeded that of human experts (mean 48 %).
CONCLUSIONS: Carefully selected ML models proved to have reliable capacity of extracting meaningful information to classify intraoperative MEPs using a limited number of features, proving robustness across patients and signal acquisition modalities, outperforming human experts, and with the potential to act as decision support systems to the IOM team. Such encouraging results lay the path to further explore the underlying nature of clinically important signals, with the aim to continue to produce useful applications to make surgeries safer and more efficient.

BACKGROUND: Surgical resection is the preferred treatment in most conus medullaris and cauda equina tumor (CMCET) cases. However, total resection is usually challenging to obtain and has a strong possibility of causing various complications if forcibly attempted. Intraoperative neurophysiological monitoring (IONM) has become a necessary adjunctive tool for CMCET resection.
OBJECTIVE: The current study aimed to evaluate the application value of bulbocavernosus reflex (BCR) monitoring in CMCET surgery.
METHODS: A retrospective clinical study.
METHODS: The medical records of patients who underwent CMCET resection by the same neurosurgical team at our hospital from September 2020 to June 2022 were retrospectively reviewed. IONM was conducted in all surgeries. According to inclusion criteria and exclusion criteria, ultimately, 105 patients were enrolled in the study.
METHODS: The voiding function was assessed before surgery, 1 month after, and 6 months after surgery using the Neurogenic Bladder Symptom Score (NBSS). If the NBSS obtained 1 month after surgery exceeds 9 points than that before surgery, it can be considered that the patient suffered new-onset postoperative voiding dysfunctions (PVDs). Moreover, if the NBSS could restored (less than 9 points higher than before the surgery) at 6 months after surgery, it was defined as a short-term PVD. Otherwise, it was defined as a long-term PVD.
METHODS: The amplitude reduction ratios (ARRs) of bilateral BCR waveforms were calculated and compared between patients with PVDs and those without. The receiver operating characteristic curve analysis was subsequently applied to determine the cut-off value of the maximal and minimal ARRs for predicting PVDs.
RESULTS: The maximal and minimal ARRs were significantly correlated with short-term and long-term PVDs (p<.001 for all comparisons, Mann-Whitney U test). The threshold values of maximal ARR for predicting short-term and long-term PVD were 68.80% (AUC=0.996, p<.001) and 72.10% (AUC=0.996, p<.001), respectively. While those of minimal ARR were 50.20% (AUC=0.976, p<.001) and 53.70% AUC=0.999, p<.001).
CONCLUSIONS: The amplitude reduction of intraoperative bilateral BCR waveforms showed high predictive value for PVDs.

OBJECTIVE: Increasing importance has been attributed in recent years to the preservation of the pelvic autonomic nerves during rectal resection to achieve better functional results. In addition to improved surgical techniques, intraoperative neuromonitoring may be useful.
METHODS: This single-arm prospective study included 30 patients who underwent rectal resection performed with intraoperative neuromonitoring by recording the change in the tissue impedance of the urinary bladder and rectum after stimulation of the pelvic autonomic nerves. The International Prostate Symptom Score, the post-void residual urine volume and the Low Anterior Resection Syndrome Score (LARS score) were assessed during the 12-month follow-up period.
RESULTS: A stimulation-induced change in tissue impedance was observed in 28/30 patients (93.3%). In the presence of risk factors such as low anastomosis, neoadjuvant radiotherapy and a deviation stoma, an average increase of the LARS score by 9 points was observed 12 months after surgery (p = 0,04). The function of the urinary bladder remained unaffected in the first week (p = 0,7) as well as 12 months after the procedure (p = 0,93).
CONCLUSIONS: The clinical feasibility of the new method for pelvic intraoperative neuromonitoring could be verified. The benefits of intraoperative pelvic neuromonitoring were particularly evident in difficult intraoperative situations with challenging visualization of the pelvic nerves.

BACKGROUND: The aim of this study is to describe the management and associated follow-up strategies adopted by thyroid surgeons with different surgical volumes when loss of signal (LOS) occurred on the first side of planned bilateral thyroid surgery, and to further define the consensus on intraoperative neuromonitoring (IONM) applications.
METHODS: The International Neural Monitoring Study Group (INMSG) web-based survey was sent to 950 thyroid surgeons worldwide. The survey included information on the participants, IONM team/equipment/procedure, intraoperative/postoperative management of LOS, and management of LOS on the first side of thyroidectomy for benign and malignant disease.
RESULTS: Out of 950, 318 (33.5%) respondents completed the survey. Subgroup analyses were performed based on thyroid surgery volume: <50 cases/year (n = 108, 34%); 50 to 100 cases/year (n = 69, 22%); and >100 cases/year (n = 141, 44.3%). High-volume surgeons were significantly (P < .05) more likely to perform the standard procedures (L1-V1-R1-S1-S2-R2-V2-L2), to differentiate true/false LOS, and to verify the LOS lesion/injury type. When LOS occurs, most surgeons arrange otolaryngologists or speech consultation. When first-side LOS occurs, not all respondents decided to perform stage contralateral surgery, especially for malignant patients with severe disease (eg, extrathyroid invasion and poorly differentiated thyroid cancer).
CONCLUSIONS: Respondents felt that IONM was optimized when conducted under a collaborative team-based approach, and completed IONM standard procedures and management algorithm for LOS, especially those with high volume. In cases of first-site LOS, surgeons can determine the optimal management of disease-related, patient-related, and surgical factors. Surgeons need additional education on LOS management standards and guidelines to master their decision-making process involving the application of IONM.

UNASSIGNED: Dexmedetomidine is often used as an adjunct to total intravenous anesthesia (TIVA) for procedures requiring intraoperative neurophysiologic monitoring (IONM). However, it has been reported that dexmedetomidine might mask the warning of a neurological deficit on intraoperative monitoring.
UNASSIGNED: We reviewed the intraoperative neurophysiological monitoring data of 47 patients who underwent surgery and IONM from March 2019 to March 2021 at the Department of Neurosurgery, Renmin Hospital of Wuhan University. Pre- and postoperative motor function scores were recorded and analyzed. Dexmedetomidine was administered intravenously at 0.5 μg/kg/h 40 min after anesthesia and discontinued after 1 h in the dexmedetomidine group.
UNASSIGNED: We found that the amplitude of transcranial motor-evoked potentials (Tce-MEPs) was significantly lower in the dexmedetomidine group than in the negative control group (P < 0.0001). There was no statistically significant difference in the somatosensory-evoked potentials (SSEPs) amplitude or the Tce-MEPs or SSEPs latency. There was no significant decrease in postoperative motor function in the dexmedetomidine group compared with the preoperative group, suggesting that there is no evidence that dexmedetomidine affects patient prognosis. In addition, we noticed a synchronized bilateral decrease in the Tce-MEPs amplitude in the dexmedetomidine group and a mostly unilateral decrease on the side of the brain injury in the positive control group (P = 0.001).
UNASSIGNED: Although dexmedetomidine does not affect the prognosis of patients undergoing craniotomy, the potential risks and benefits of applying it as an adjunctive medication during craniotomy should be carefully evaluated. When dexmedetomidine is administered, Tce-MEPs should be monitored. When a decrease in the Tce-MEPs amplitude is detected, the cause of the decrease in the MEPs amplitude can be indirectly determined by whether the decrease is bilateral.

OBJECTIVE: Target localization for deep brain stimulation (DBS) is a crucial step that influences the clinical benefit of the DBS procedure together with the reduction of side effects. In this work, we address the feasibility of DBS target localization in the globus pallidus internus (GPi) aided by intraoperative motor evoked potentials (MEP) with emphasis on the reduction of capsular side effects.
METHODS: Micro-macroelectrode recordings were performed intraoperatively on 20 patients that underwent DBS treatment of the GPi (GPi-DBS). MEP were elicited intraoperatively by microelectrode stimulation during stereotactic DBS surgery. We studied the relationship between MEP thresholds and the internal capsule (IC) proximity.
RESULTS: We found a significant correlation between intraoperative MEP thresholds and IC proximity.
CONCLUSIONS: We provide further evidence of the role of MEPs for DBS target localization in the GPi, which extends and confirms the usefulness of MEPs as previously reported by DBS target localization studies dealing with the subthalamic and thalamic nuclei. Our approach is advantageous in that it provides criteria to determine the DBS target without the need to rely on a patient\'s response while avoiding capsular effects.

The use of microelectrode recording (MER) during deep brain stimulation (DBS) for Parkinson Disease is controversial. Furthermore, in asleep DBS anesthesia can impair the ability to record single-cell electric activity.The purpose of this study was to describe our surgical and anesthesiologic protocol for MER assessment during asleep subthalamic nucleus (STN) DBS and to put our findings in the context of a systematic review of the literature. Sixty-three STN electrodes were implanted in 32 patients under general anesthesia. A frameless technique using O-Arm scanning was adopted in all cases. Total intravenous anesthesia, monitored with bispectral index, was administered using a target controlled infusion of both propofol and remifentanil. A systematic review of the literature with metanalysis on MER in asleep vs awake STN DBS for Parkinson Disease was performed. In our series, MER could be reliably recorded in all cases, impacting profoundly on electrode positioning: the final position was located within 2 mm from the planned target only in 42.9% cases. Depth modification > 2 mm was necessary in 21 cases (33.3%), while in 15 cases (23.8%) a different track was used. At 1-year follow-up we observed a significant reduction in LEDD, UPDRS Part III score off-medications, and UPDRS Part III score on medications, as compared to baseline. The systematic review of the literature yielded 23 papers; adding the cases here reported, overall 1258 asleep DBS cases using MER are described. This technique was safe and effective: metanalysis showed similar, if not better, outcome of asleep vs awake patients operated using MER. MER are a useful and reliable tool during asleep STN DBS, leading to a fine tuning of electrode position in the majority of cases. Collaboration between neurosurgeon, neurophysiologist and neuroanesthesiologist is crucial, since slight modifications of sedation level can impact profoundly on MER reliability.