Clinical classification of recurrent laryngeal nerve palsy

Background

The application of intraoperative neurophysiological monitoring (IONM) has been accepted to avoid injury of a recurrent laryngeal nerve (RLN). Loss of the neuromonitoring signal indicates nerve injury and is subdivided into segmental type and global type nerve paralysis. This study aimed to determine the course of vocal cord function recovery after definitive loss of signal (LOS) types.

Methods

This retrospective study included 1,442 patients (with 2,752 nerves at risk) who had thyroidectomies between January 2018 and December 2021. Preoperative and postoperative vocal cord functions were evaluated by laryngoscopic examination.

Results

LOS occurred in 168 of 1,442 (11.7%) patients and 171 of 2,748 (6.2%) nerves at risk during surgery. Of LOS nerves of benign tumors, 74.2% showed global type. In cancer cases, segmental paralysis was more common, accounting for 51.3% of LOS nerves. Of nerves with segmental LOS in cancer patients, 55.3% needed partial layer resection for RLN invasion. Intraoperative recovery was seen in 9 of 62 nerves (14.5%) with segmental LOS and 32 of 109 (29.4%) nerves with global type LOS. The vocal cord palsy rate on postoperative days (PODs) 2-3 was lower after global type nerve paralysis (63.6%) than after segmental loss (84.9%). At 6 months postoperatively, the rate of vocal cord paralysis in benign tumors was not significantly different between segmental type and global type (P=0.586). However, cancer patients with segmental LOS significantly more often had vocal cord dysfunction than those with global LOS at 6 months postoperatively (rate of nerve palsy: segmental 40.0% vs. global 3.4%) (P<0.001).

Conclusions

The intraoperative recovery rate and early nerve recovery rate are significantly higher for patients with global LOS than for patients with segmental LOS. Cancer patients with segmental LOS significantly more often had vocal cord dysfunction than those with global LOS at 6 months postoperatively.

Cathodal Genesis of Ipsilateral Hand (Crossover) Motor Evoked Potentials: Evidence from a Patient with Previous Stroke

A case is described where baseline transcranial electrical motor evoked potentials (TcMEP) and somatosensory evoked potentials (SSEP) results were unilaterally absent in a patient with previous hemispheric stroke undergoing a right-sided carotid endarterectomy. SSEP data confirmed right cortical pathology and excluded a technical rationale for absent motor evoked responses. Attempts at generating left-hand (contralateral) TcMEP from right cortical anodal stimulation failed despite high stimulus intensities. However, TcMEP responses from anodal stimulation of the right cortex were recorded from the right-hand (ipsilateral) which were attributed to "crossover." Ipsilateral TcMEP onset latencies derived from the stimulus-response data supports the idea that crossover is a product of cathodal stimulation initially acting on pericortical motor pathways.

Confirming a C5 Palsy with a Motor Evoked Potential Trending Algorithm during Insertion of Cervical Facet Spacers: A Case Study

The use of cervical facet spacers has shown favorable clinical results in the treatment of cervical spondylotic disease; however, there are limited data regarding neurological complications associated with the procedure. This case report demonstrates the specificity of multi-myotomal motor evoked potentials (MEPs) in detecting acute postoperative C5 palsy following placement of facet spacers. A posterior cervical fusion with decompression and instrumentation involving DTRAX (Providence Medical Technology; Lafayette, CA) was used to treat a patient with cervical stenosis and myelopathy. Intraoperative neurophysiological monitoring (IONM) consisting of MEPs, somatosensory evoked potentials (SSEPs), and free-run electromyography (EMG), was used throughout the procedure. Immediately following the placement of the DTRAX spacers at C4-5, a decrease in amplitudes from the right deltoid and biceps MEP recordings (>65%) was detected. All other IONM modalities remained stable; it is noteworthy that there was an absence of mechanically elicited EMG. A novel post-alert regression analysis trending algorithm of MEP amplitudes confirmed the visual alert. This warning along with an intraoperative computed tomography (CT) scan of the cervical spine subsequently resulted in the decision to remove one of the facet spacers. Surgical intervention did not result in recovery of the aforementioned MEP recordings, which remained attenuated at the time of wound closure. Postoperatively, the patient exhibited an immediate right C5 palsy (2/5). A post-surgery application of the trending algorithm demonstrated that it correlated to the visual alert until the end of monitoring.

Misconceptions in IONM Part III: Stimulation Repetition Rate Effects on Intraoperative Somatosensory Evoked Potential Amplitude and Latency

The rate at which stimulation is applied to peripheral nerves is critical to generating high-quality intraoperative somatosensory evoked potentials (SSEPs) in a timely manner. Guidelines based on a limited study and anecdotal evidence present differing, incorrect, or incomplete stimulation rate recommendations. We examined the effect stimulating the ulnar and tibial nerves at 1.05, 2.79, 5.69, and 8.44 Hz had on cortical, subcortical, and peripheral response amplitude and latency in 10 subjects with neuromuscular blockade (NMB) and 10 without NMB in the operating room under general anesthesia. As the stimulation repetition rate increased, the amplitude of upper and lower extremity cortical responses decreased equally in both groups. The ulnar nerve N20 cortical response amplitude decreased 27.9% at 2.79 Hz, 48.8% at 5.69 Hz, and 53.8% at 8.44 Hz. The tibial nerve P37 cortical response amplitude decreased 30.3% at 2.79 Hz, 53.8% at 5.69 Hz, and 56.8% at 8.44 Hz. Neither upper or lower extremity peripheral or subcortical amplitudes nor upper and lower extremity subcortical or peripheral latencies were affected by increasing repetition rate in either group. Low SSEP stimulation repetition rates ensure the highest quality cortical responses.

Management of Extramedullary Intradural Spinal Tumors: The Impact of Clinical Status, Intraoperative Neurophysiological Monitoring and Surgical Approach on Outcomes in a 12-Year Double-Center Experience

Objective: Intradural Extramedullary (IDEM) tumors are usually treated with surgical excision. The aim of this study was to investigate the impact on clinical outcomes of pre-surgical clinical conditions, intraoperative neurophysiological monitoring (IONM), surgical access to the spinal canal, histology, degree of resection and intra/postoperative complications.

Methods: This is a retrospective observational study analyzing data of patients suffering from IDEM tumors who underwent surgical treatment over a 12 year period in a double-center experience. Data were extracted from a prospectively maintained database and included: sex, age at diagnosis, clinical status according to the modified McCormick Scale (Grades I-V) at admission, discharge, and follow-up, tumor histology, type of surgical access to the spinal canal (bilateral laminectomy vs. monolateral laminectomy vs. laminoplasty), degree of surgical removal, use and type of IONM, occurrence and type of intraoperative complications, use of Ultrasonic Aspirator (CUSA), radiological follow-up.

Results: A total number of 249 patients was included with a mean follow-up of 48.3 months. Gross total resection was achieved in 210 patients (84.3%) mostly in Schwannomas (45.2%) and Meningiomas (40.4%). IONM was performed in 162 procedures (65%) and D-wave was recorded in 64.2% of all cervical and thoracic locations (99 patients). The linear regression diagram for McCormick grades before and after surgery (follow-up) showed a correlation between preoperative and postoperative clinical status. A statistically significant correlation was found between absence of worsening of clinical condition at follow-up and use of IONM at follow-up (p = 0.01) but not at discharge. No associations were found between the choice of surgical approach and the extent of resection (p = 0.79), the presence of recurrence or residual tumor (p = 0.14) or CSF leakage (p = 0.25). The extent of resection was not associated with the use of IONM (p = 0.91) or CUSA (p = 0.19).

Conclusion: A reliable prediction of clinical improvement could be made based on pre-operative clinical status. The use of IONM resulted in better clinical outcomes at follow-up (not at discharge), but no associations were found with the extent of resection. The use of minimally invasive approaches such as monolateral laminectomy showed to be effective and not associated with worse outcomes or increased complications.

Intraoperative Neurophysiological Monitoring of the Laryngeal Nerves During Anterior Neck Surgery: A Review

Contributions to the literature on intraoperative neuro monitoring (IONM) during endocrine and head and neck surgery have increased over recent years. Organizational support for neural monitoring during surgery is becoming evident and is increasingly recognized as an adjunct to visual nerve identification. A comprehensive understanding of the role of IONM for prevention of nerve injuries is critical to maximize safety during surgery of the anterior compartment of the neck. This review will explore the potential advantages of IONM to improve the outcomes among patients undergoing anterior neck surgery.