Intraoperative Neuromonitoring, Nerves at Risk and Staged Thyroidectomy, our Experience on 377 Consecutive Cases

PURPOSE

The aim of this study was firstly to report the experience of intermittent intraoperative neuromonitoring (I-IONM) and evaluate the impact of loss of signal (LOS) in staged thyroidectomy management.

METHODS

We retrospectively reviewed patients who underwent total thyroidectomy, performed by a single surgeon in two years. All patients have been subjected to I-IONM. In case of intraoperative loss of signal (LOS), planned total thyroidectomy was always aborted. Six-month follow-up was performed. Postoperative dysphonia was evaluated with VHI-10 score in 3 time settings T1, during hospital stay, T2 after 30 days, T3 after 6 months. Dysphonia has been compared to IONM results to evaluate sensitivity and specificity.

RESULTS

377 patients were included. Incidence of dysphonia was calculated based on the number of nerves at risk (NAR). We evaluated a total of 724 NAR. LOS encountered were 43 cases (5.9% of total NAR), of these 14 were LOS 1 while 29 were LOS 2. 27 patients (3.7% of NAR) presented early post-operative dysphonia with VHI-10 score > 13 (T1), among these 16 had presented LOS at IONM (true positives) while11 had no LOS (false negatives). In T2 and T3 we reported a decrease in true positive cases increasing false positives. Sensitivity at T3 reached 85.7% while specificity and odds ratio were respectively 94.8% and 110.

CONCLUSIONS

Given the high sensitivity and specificity, IONM should be considered a useful tool for thyroid surgery and its use should be suggested for patients undergoing planned total thyroidectomy. Its right application may cancel the risk of bilateral paralysis.

The value of intraoperative nerve monitoring against recurrent laryngeal nerve injury in thyroid reoperations

Reoperative thyroidectomy is challenging for surgeons because of the higher incidence of recurrent laryngeal nerve (RLN) palsy. RLN identification is the gold standard during thyroidectomy; however, it is sometimes difficult to perform thyroid reoperations. In recent years, intraoperative nerve monitoring (IONM) has gained increased acceptance, and the use of IONM can be a valuable adjunct to visual identification. The aim of this study was to evaluate the value of IONM during thyroid reoperation.A total of 109 patients who met our criteria at the Affiliated Hospital of Hangzhou Normal University from January 2010 to June 2020 were retrospectively analyzed and divided into the IONM group and the visualization-alone group (VA group) according to whether neuromonitoring was used during the operation. The patients' characteristics, perioperative data, and intraoperative information including the RLN identification, time of RLNs confirmation, operative time, intraoperative blood loss, and the rate of RLN injury were collected.Sixty-five procedures (94 RLNs at risk) were performed in the IONM group, whereas 44 (65 RLNs at risk) were in the VA group. The rate of RLN identification was 96.8% in the IONM group and 75.4% in the VA group (P < .05). The incidence of RLN injury was 5.3% in the IONM group and 13.8% in the VA group (P > .05). The incidence of surgeon-related RLN injury rate was 0% in the IONM group compared to 7.7% in the VA group (P < .05), but the tumor-related or scar-related RLN injury rate between the 2 groups were not significantly different (4.3% vs 3.1%, 1.1% vs 3.1%, P > .05).IONM in thyroid reoperation was helpful in improving the RLN identification rate and reducing the surgeon-related RLN injury rate, but was ineffective in reducing the tumor-related and scar-related RLN injury rate. In the future, multicenter prospective studies with large sample sizes may be needed to further assess the role of IONM in thyroid reoperations.

Sutureless Thyroidectomy With Intraoperative Neuromonitoring and Energy-Based Device Without Sternotomy for Symptomatic Substernal Goiter Harboring Thyroiditis of Gland Parenchyma

Since substernal goiter first being described by Haller in 1749, a consensus on the definition of this entity has not been ensured, yet. Despite substernal goiter or retrosternal goiter is delineated as an enlarged thyroid gland with a component extending into the mediastinum, at least 10 definitions have described being able to depict the most accurate definition for substernal goiter. Of note, no consensus still has been declared on the therapeutic management of asymptomatic substernal goiter. It should be pointed out that, the American Association of Endocrine Surgeons (AAES), Guidelines for the Definitive Surgical Management of Thyroid Disease in Adults reported approximately 9% to 13% of substernal goiters are being harbored thyroid malignancy. The following vignette case describes the clinical features of a symptomatic substernal goiter with chronic lymphocytic thyroiditis, her treatment by sutureless total thyroidectomy with intermittent-intraoperative neural monitoring (I-IONM), and the energy-based device without sternotomy, and the response of an adult who presented with a family history of malignant histopathology, differentiated thyroid carcinoma, which was exposed to the postoperative radioactive iodine ablation. We may recommend dividing the branches of superior thyroid arteries and the superior thyroid veins individually and exploring the fibrous Ligament of Berry, the true Ligament of Berry, with its safe interrelation to the inferior laryngeal nerve, finically, which may be regarded as different peas in a pod in a complete sutureless thyroidectomy for substernal goiter with thyroiditis in thyroidology.

Mapping of the Language Cortex

Awake craniotomy with intraoperative neurophysiological language mapping (INLM) is an established procedure for patients undergoing surgery to resection tumors in the language cortex area. INLM and continuous neurophysiological monitoring allow assessment of the language function, which is not possible under general anesthesia. INLM of the brain areas provides a helpful tool to the operating surgeon in reducing the risks associated with tumor resection in the motor and language cortex. We present a literature review and the technical method used for INLM by utilizing direct electrical cortical stimulation. We also report the usefulness of INLM for evaluation of the language function during resection of cortical tumors, epilepsy foci, and arteriovenous malformations (AVMs) located near language areas. First, the central sulcus is identified by sensory mapping, followed by the motor cortex's identification by direct electrical cortical stimulation (DECS). Neurological assessment of the patient is done by auditory and visual feedback. The patient is asked to repeat numbers, days, words, sentences, read words, and name pictures during cortical stimulation. DECS may cause a slurring or speech arrest. Electrocorticography (ECoG) is also performed during cortical stimulation to identify any after-discharges. Examination of the patient occurs immediately after surgery, and then 24 hours, one week, six months, and 12 months postoperatively. Bipolar DECS for motor mapping with ECoG can safely and reliably be utilized to identify essential language areas with minimizing permanent language deficits and maximizing the extent of tumor resection.

Mapping of the Motor Cortex

The resection of brain tumors located within or near the eloquent tissue has a higher risk of postoperative neurological deficits. The primary concerns include loss of sensory and motor functions in the contralateral face, upper and lower extremities, as well as speech deficits. Intraoperative neurophysiological monitoring (IONM) techniques are performed routinely for the identification and preservation of the functional integrity of the eloquent brain areas during neurosurgical procedures. The IONM modalities involve sensory, motor, and language mapping, which helps in the identification of the boundaries of these areas during surgical resection. Cortical motor Mapping (CmM) technique is considered as a gold-standard technique for mapping of the brain. We present the intraoperative CmM technique, including anesthesia recommendations, types of electrodes, as well as stimulation and recording parameters for successful monitoring.

Intraoperative Neurophysiological Monitoring During Trigeminal Schwannoma Surgery

Surgical manipulation during skull base surgeries places various cranial nerves (CN) at risk, including the nerves innervating the extraocular muscles. It could be very challenging for the surgeon to identify these cranial nerves due to the distortion of the normal anatomy by the tumors. Despite the recent advancement in technology, surgeries involving the third, fourth, fifth, and sixth cranial nerves still carry a risk of temporary or permanent paralysis of the muscles supplied by these cranial nerves. Intraoperative Neurophysiological Monitoring (IONM) with spontaneous and triggered electromyography (EMG) can help in guiding the surgeon in locating the nerves and avoiding any injury to them during the resection. IONM for extraocular cranial nerves requires highly skilled personnel with knowledge of anatomy and expertise in the placement of the electrodes. Benign tumors of the nerve sheath that arise from the perineural Schwann cells are known as schwannomas. Various cranial nerves might be involved in schwannomas of the head and neck. Trigeminal schwannomas are rare tumors. In this report, we describe the setup and stimulation technique and parameters as well as the benefits of utilizing IONM during the aggressive resection of a trigeminal schwannoma. The main purpose of utilizing IONM during these high-risk surgical procedures is to minimize any intraoperative damage to the neural structures involved.

Mapping of the Somatosensory Cortex

Intraoperative sensory cortical mapping is a reliable and safe method for the functional localization of the central sulcus (CS). It is utilized during neurosurgical procedures performed near eloquent brain tissue. It helps in identifying the somatosensory cortex and CS, hence preventing any postoperative neurological deficits. When executed properly, this method can identify the somatosensory cortex for both the upper and lower limbs by locating the CS. This technical report outlines the benefits of cortical sensory mapping (CsM) and detailed methodology. With the help of a properly trained intraoperative neuromonitoring staff who can accurately interpret the signals being monitored, CsM can help in injury prevention during brain surgeries.

Bulbocavernosus Reflex Monitoring During Intramedullary Conus Tumor Surgery

A T10 to L2 spinal cord tumor exploration and biopsy was performed with intraoperative neurophysiological monitoring (IONM) on a 75-year-old male diagnosed with an intradural intramedullary appearing spinal cord lesion with no other lesions in the central nervous system, chest, abdomen or pelvis.

Intraoperative neurophysiology consisted of transcranial electrical motor evoked potentials (TCeMEPs), somatosensory evoked potentials (SSEPs), triggered and spontaneous electromyography (S-EMG, T-EMG), bulbocavernosus reflex (BCR) and train of four (TOF) monitoring. Loss of BCR responses during conus exposure and identification were resolved with multiple small pauses in manipulation throughout the procedure. T-EMG mapping aided in identification and avoiding the removal of nervous tissue.

Postoperatively the patient experienced some mild weakness in his left foot and leg that correlated with a significant amplitude drop in the left abductor hallucis TCeMEP. By the following day, the patient was almost back to preoperative baseline. The patient’s bowel and bladder function were preserved, consistent with final BCR recordings. The patient was discharged to rehabilitation postoperatively. Pathology results indicated glioblastoma.

This case study demonstrates the utility of a multimodality approach with bulbocavernosus reflex and urethral sphincter monitoring to optimize intraoperative data to the surgeon during conus tumor surgeries.

Intraoperative Triggered Electromyography Recordings from the External Urethral Sphincter Muscles During Spine Surgeries

Introduction: Bowel and bladder function are at risk during tumor resection and other surgeries of the conus, cauda equina, and nerve roots. This study demonstrates the ability to acquire triggered electromyography (t-EMG) from the external urethral sphincter (EUS) muscles by utilizing a urethral catheter with an electrode attached.

Methods: A retrospective analysis of neurophysiological monitoring data from two medical centers was performed. Seven intradural tumors and three tethered cord release surgeries that used urethral sphincter electrodes to record t-EMG were included in the analysis. The patients consisted of five females and five males with ages ranging from eight months to 67 years (median: 49 years). Our neuromonitoring paradigm included upper and lower extremity somatosensory evoked potentials (SSEPs) and transcranial electrical motor evoked potentials (TCeMEPs), as well as spontaneous and triggered electromyography (EMG) from the external anal sphincter (EAS), EUS muscles and lower extremity muscles bilaterally. A catheter with urethral electrodes attached was used for recording spontaneous electromyography (s-EMG), t-EMG, and TCeMEPs from the skeletal muscle of the EUS. Train of four (TOF) was also recorded from the abductor hallucis muscle as well for monitoring the level of muscle relaxant.

Results: We were able to successfully record t-EMG responses from the EUS muscles in all patients (100%). It is worthy to note that only one patient presented preoperatively with bladder incontinence, urgency, and frequency. Almost immediately in the postoperative phase, the patient’s frequency and urgency improved, and the bladder function normalized within two weeks of having the tumor removed.

Conclusions: In this small series, we were able to acquire t-EMG in 100% of patients when recorded from the EUS using a urethral catheter with electrodes built into it. T-EMGs can be attempted in surgeries that put the function of the pelvic floor at risk. More study is needed to establish better statistical methods, better modality efficacy, and a better understanding of intraoperative countermeasures that may be employed when an alert is encountered to prevent impending neurological sequelae.

Multimodality Intraoperative Neurophysiological Monitoring (IONM) in Anterior Hip Arthroscopic Repair Surgeries

Arthroscopic hip surgery is performed routinely for the treatment of various hip disorders. Leg traction during labral tear repair, femoroplasty, and acetabuloplasty for hip stabilization can stretch the peripheral nerves. This may cause temporary or permanent nerve injury. This study illustrates the benefit of utilizing multimodality Intraoperative Neurophysiological Monitoring (IONM) during hip surgical procedures.

We performed a retrospective review of 10 arthroscopic hip surgeries with neurophysiological monitoring at one medical center. The patients consisted of six females and four males (mean age: 48.9 years). The procedures were equally divided into left and right-sided procedures. IONM setup included posterior tibial, peroneal, and femoral or saphenous nerve somatosensory evoked potentials (SSEPs), transcranial electrical motor evoked potentials (TCeMEP), train of four (TOF), and electromyography (EMG) from the lower extremities.

All patients exhibited changes in IONM data during the surgical procedure. Changes in the latency and amplitude or loss of the lower SSEPs on the surgical side occurred in 36% of the monitorable SSEPs. The surgeon instructed the team to reduce the leg lengthening by removing traction when changes were observed. The SSEPs exhibited a full recovery in 75% of the affected lower extremity SSEPs. In the two instances of nonrecovery, the SSEP responses remained increased in latency or decreased in amplitude at closing, but the waveform was intact. There were five instances of complete loss of the waveform (four in the ipsilateral leg, and one in the contralateral leg) with recovery after traction was reduced. TCeMEP changes occurred in 53% of the ipsilateral lower muscles monitored. Many of the TCeMEP changes were attributed to ischemia of the feet and could not be resolved intraoperatively.

Multimodality IONM can be a beneficial and protective tool during surgical procedures involving hip and acetabular areas. Early identification of changes in evoked potentials during hip arthroscopy surgeries can minimize post-operative neurological deficits due to peripheral nerve injury and leg ischemia.

Motor Interconnections Between Superior and Inferior Laryngeal Nerves

Introduction Anatomical studies on human cadavers have established anastomoses between laryngeal nerves. However, we need to functionally identify motor communication via these anastomoses between the recurrent laryngeal nerve (RLN) and the external branch of the superior laryngeal nerve (EBSLN) in living bodies. We aim to establish motor interconnections using intraoperative nerve monitoring (IONM). Methods IONM of 112 EBSLNs and RLNs in 62 thyroidectomy cases was used to establish motor functions of laryngeal nerves. Electrophysiological parameters were recorded, and cricothyroid muscle (CTM) contraction was observed after stimulation of laryngeal nerves. Results Eighty (71.4%) EBSLNs were visually identified, and 109 (97.3%) EBSLNs were functionally identified with CTM contraction. Stimulation of 74 (67.9%) EBSLNs induced contraction of laryngeal muscles and generated wave amplitude from intrinsic laryngeal musculature. The stimulation of the RLN induced CTM contraction in 65 (58%) of the 112 muscles. The mean conductivity powers of the EBSLN and of the RLN to intrinsic laryngeal musculature were calculated as 231.3 µV and 1354.5 µV, respectively. Conclusion Recordable waveform amplitude with EBSLN stimulation yielded motor relations between laryngeal nerves. CTM contraction after stimulation of the RLN confirmed these relations. These results of IONM established motor interconnections between superior and inferior laryngeal nerves in the majority of patients. The EBSLN may have an effect on motor innervations for intrinsic laryngeal muscles via motor interconnections.

Vertebral Column Resection for Kyphoscoliosis in a Patient with Ehlers-Danlos Syndrome: An Intraoperative Neurophysiological Monitoring Alert

A 16-year-old male patient with Ehler-Danlos syndrome (EDS) and a back deformity since birth presented with severe kyphoscoliosis. The patient was neurologically intact but had respiratory and cardiac insufficiencies. A two-stage vertebral column resection (VCR) at T9-T10 with multiple level fusion with multimodality intraoperative neurophysiological monitoring (IONM) was planned. 

During the first stage, pedicle screws were placed at multiple spinal levels above and below the VCR level. Upper and lower somatosensory evoked potentials (SSEP), transcranial electrical motor evoked potentials (TCeMEP), and electromyography were monitored continuously and showed no significant changes. The second stage was performed one week later. Baseline SSEP and TCeMEP responses were present in all extremities. The surgeon was informed of a sudden 70% amplitude drop in TCeMEP in the lower limbs with stable SSEP after ligating one of the left nerves/vessels fully stretching the spinal cord. The surgeon removed the ligation, and an improvement in motor responses followed. Surgery proceeded with the highest levels of caution. Later, there was a sudden loss of TCeMEP and SSEP in the lower limbs bilaterally. The correction was released, mean arterial pressure was increased, and intravenous dexamethasone was administered. The surgical correction was aborted, and the decision was made to close the site. Lower SSEP and TCeMEP responses remained absent until closing, while upper SSEP and TCeMEP responses remained stable.

A wake-up test was done after closing. The patient moved his upper limbs but was unable to move his lower limbs bilaterally. The patient was sent for a magnetic resonance imaging scan while intubated and then sent to the intensive care unit. At 24 hours and 36 hours post-operation, the patient had no sensory and motor function below the T8 level. Forty-eight hours post-operation, the patient started to feel sensory stimuli at the T10 level. At one week post-operation, the patient regained sphincter functions, and at four weeks postoperatively, the patient’s hip flexors started to recover.

VCR in patients with EDS has a very high risk of damaging the spinal cord due to the fragile vasculature of the spinal cord. Real-time IONM is useful in the early identification of spinal cord injury in cases of this nature.