Bilateral patterns and motor function of the extralaryngeal branching of the recurrent laryngeal nerve

Electrophysiological monitoring of the nonrecurrent inferior laryngeal nerve and radiological evaluation of concurrent vascular anomalies

Purpose

The objective of this study was to characterize the electrophysiological characteristics of nonrecurrent inferior laryngeal nerves (NRILNs) that were dissected via intraoperative neuromonitoring (IONM) and concomitant vascular anomalies in patients with NRILNs.

Methods

A retrospective analysis was conducted on 7865 patients who underwent thyroidectomy with IONM at three tertiary referral centers. The study included 42 patients in whom an NRILN was detected. IONM data and postoperative vocal cord (VC) examinations were recorded for all patients. The absence of an initial vagal EMG response and/or a short (<3.5 ms) latency period during the initial vagal stimulation or the inability to identify the RLN within the Beahrs triangle was considered highly suspicious for the presence of an NRILN. Postoperative cross-sectional imaging was performed in 36 out of 42 patients to assess any concurrent vascular anomalies.

Results

The prevalence of NRILN was 0.53%. An NRILN was suspected due to EMG findings in 32 (76%) patients and the inability to identify the RLN within the Beahrs triangle in the remaining 10 (24%) patients. The mean right VN latency period was 3.05 ± 0.15 ms. The V1 latency period of the right VN was shorter than 3.5 ms in 39 (93%) and longer than 3.5 ms in 3 (7%) patients. One of these three patients with latency>3.5ms had a large mediastinal goiter. Transient VC paralysis occurred in one (2.4%) patient. Of the 36 patients with postoperative imaging data, 33 (91.4%) had vascular anomalies. All 33 patients had aberrant right subclavian arteries, and 13 (39.4%) also had accompanying additional vascular anomalies.

Conclusion

The NRILN is an anatomical variation that increases the risk of nerve injury. Observation of an absent EMG response and/or a short latency period during the initial vagal stimulation facilitates the detection of an NRILN at an early stage of thyroidectomy in the majority of patients.

Pre- and Postoperative High-Speed Videolaryngoscopy Findings in Adductor Spasmodic Dysphonia Following Transoral CO2 LASER-Guided Thyroarytenoid Myoneurectomy

INTRODUCTION

Vocal cord vibration after transoral CO₂ LASER-guided thyroarytenoid (TA) myoneurectomy in adductor spasmodic dysphonia (AdSD) patients is unclear to date. The precise vibratory patterns in AdSD patients are difficult to evaluate with routine videolaryngostroboscopy. High-speed videolaryngoscopy (HSV) is an ideal choice to evaluate such patients. This study was performed to compare pre- and postoperative, after 6 months, vocal fold vibratory onset delay (VFVOD) and closed phase glottal cycle (CPGC) in AdSD patients following transoral CO₂ LASER-guided TA myoneurectomy using the HSV.

MATERIALS AND METHODS

Retrospective study, conducted from January, 2016 to January, 2019, of the AdSD patients who underwent transoral CO₂ LASER-guided TA myoneurectomy using the HSV. Patient data were acquired from the hospital database to evaluate VFVOD and CPGC from HSV recordings of the patients. VFVOD was calculated as sum of prephonatory delay (PPD) and steady-state delay (SSD). The PPD and SSD were evaluated and compared separately for each patient. The MedCal Version 19.2.6 was used for data analysis. Paired sample t test was performed to compute the significance of the difference between the mean of the dataset. A P value less than 0.05 was considered significant.

RESULTS

A total of nine patients were included in the study, out of which three were females and six were males. The average age was 45.5 ± 6.9 years. The mean of postoperative PPD (166.8 ± 22.1), SSD (76.5 ± 8.6), and CPGC (62.6 ± 4.8) were significantly less than mean of preoperative PPD (222.6 ± 22.1), SSD (97.7 ± 9.5), and CPGC (71.6 ± 5 %), with P values of 0.0007, 0.0001, and 0.0001, respectively.

CONCLUSIONS

There was a significant decrease in VFVOD and CPGC posttransoral CO₂ LASER-guided TA myoneurectomy in AdSD patients after 6 months follow-up. This study also establishes efficiency of the HSV to measure the vocal cord vibration in the patients with AdSD. The primary limitations of the study were the small sample size and its retrospective nature. Future prospective studies with increased sample size can further substantiate the findings of the work performed here.

Anatomy and motor function of extra-laryngeal branching patterns of the recurrent laryngeal nerve; an electrophysiological study of 1001 nerves at risk

INTRODUCTION

Safe thyroid surgery depends on a deep knowledge of human neck anatomy, including the recurrent laryngeal nerve (RLN). Anatomic variations such as extra-laryngeal terminal branching (ETB) are common.

PATIENTS AND METHODS

We studied the ETB pattern of 1001 RLNs at risk in 596 patients. We identified and exposed the location of division points on the cervical part of bifid RLN. The function of nerve branches was assessed through intraoperative nerve monitoring (IONM).

RESULTS

Bifid RLNs was identified in 39.6% of patients. The nerve-based prevalence of ETB was 28.5%. The prevalence of ETB for the right and left RLN was 21.8% and 35.5%, respectively (p < 0.001). The location of the division point was found in the middle, distal, and proximal segments in 48.8%, 33.3%, and 18% of bifid RLNs, respectively. Electrophysiological monitoring revealed motor functions in all anterior and in 7% of posterior branches. The rate of injury was 0.4%, and 1.1% in single trunk and bifid nerves, respectively (p = 0.360), and 3.9% in nerves with proximal branching (p = 0.084).

CONCLUSIONS

The ETB prevalence is high and showing division points in different cervical segments of the RLN. All anterior branches and some posterior branches contain motor fibers. Knowledge and awareness of these anatomic and functional variations are mandatory for every thyroid surgeon to avoid misidentification and misinterpretation of human RLN anatomy.

The Most Common Anatomical Variation of Recurrent Laryngeal Nerve: Extralaryngeal Branching

Objective:

Extralaryngeal branching of recurrent laryngeal nerve (RLN) is frequent. In various studies, detection rate of extralaryngeal nerve branching was increased by intraoperative neuromonitorization (IONM). Our aim was evaluation of the relationship between the features of extralaryngeal branching of RLN and other anatomic variations in thyroidectomy patients under the guidance of IONM.

Methods:

Patients underwent thyroidectomy using IONM between January 2016 and December 2019 and whose RLNs were fully explored till the nerve’s entry point to the larynx, were enrolled to the study. Extralaryngeal branching of RLN was accepted as branching of the nerve at a ≥5 mm distance from its laryngeal entry point and having its all branches entering the larynx. Entrapment of RLN at the region of ligament of Berry (BL) by a vascular structure or posterior BL and relationship between RLN and inferior thyroid artery (ITA) was evaluated.

Results:

Out of 696 patients meeting the inclusion criteria, 1127 neck sides (536F and 160M) were evaluated. Mean age was 49.1±13.4 (range; 18–89). Nerve branching ratio was 35.3% and was higher in females than males (38.2%vs.25.8%, p<0.0001, respectively). Extralaryngeal branching of RLN was detected in 398 (35.3%) out of 1127 nerves. A total of 368 (92.5%) RLNs had two, 27 (6.8%) nerves had three, and 3 (0.7%) had multiple branches. RLN crossed anterior to and between branches of ITA more frequently in branching nerves than non-branching nerves (47.7 vs. 44.4% and 12.8% vs. 7.6%, respectively) but crossed posterior to ITA less frequently in branching nerves (38.5% vs. 48%, respectively, p=0.001). Entrapment of RLN at the region of BL was higher in branched nerves (25.9% vs. 17.5%, respectively, p=0.001). Entrapment of RLN wasmore frequent at the right side than left side both in branching (31.5% vs.19.4%, respectively, p=0.008) and non-branching nerves (20.6% vs. 14.4%, respectively).

Conclusion:

Extralaryngeal branching of RLN is not rare and mostly divided into two branches. Branching ratio is higher in females than males. In branching nerves, rate of crossing anterior to and between branches of ITA was higher, in non-branching nerves, rate of crossing posterior to ITA was higher. In branching nerves, possibility of entrapment of RLN at the region of BL was higher. Both in branching and non-branching nerves, entrapment of RLN at the region of BL was higher at the right side. Extralaryngeal branching, relationship between RLN and ITA, and entrapment of RLN at the region of BL are frequently seen and variable anatomic variations and cannot be foreseen preoperatively. Most of the extralaryngeal branches and their relationship with other variations can be detected by finding RLN at the level of ITA and following RLN until its entry point to the larynx.

Prophylactic Central Neck Dissection in Well-differentiated Thyroid Cancer

Well-differentiated cancers, both papillary and follicular, account for 90% of all diagnosed thyroid cancers. They have an indolent disease course with a 20-year disease-specific survival over 90%. According to current guidelines, the therapy of choice for well-differentiated thyroid carcinoma is total thyroidectomy or lobectomy. The indication for prophylactic central neck dissection is still a controversial issue and the subject of unfinished and ongoing debate. There is no indication for prophylactic central neck dissection in follicular thyroid carcinomas, which primarily metastasize hematogenously. In small solitary papillary thyroid carcinomas (T1 and T2), prophylactic central neck dissection is not indicated as it does not bring benefits in terms of improved patient survival and at the same time significantly increases the risk of temporary and permanent postoperative complications. Prophylactic central neck dissection is indicated in advanced papillary thyroid cancers (T3 and T4) and all other high-risk well-differentiated thyroid cancer, as well as in the presence of metastatic lymph nodes in the lateral neck.

Use of intraoperative neural monitoring for prognostication of recovery of vocal mobility and reduction of permanent vocal paralysis after thyroidectomy

INTRODUCTION

The benefits of intraoperative neural monitoring (IONM) of recurrent laryngeal nerve (RLN) on post-thyroidectomy vocal cord palsy (VCP) rates are contentious. We wished to study impact of IONM on permanent VCP after thyroidectomy.

METHODS

Retrospective review of prospective series of 1011 (1539 nerves-at-risk) patients undergoing thyroidectomy without (418, group 1) and with (583, group 2) IONM.

RESULTS

There were three recognized nerve injuries in group 1, vs one in group 2 (P = .3). There were no differences in overall VCP rates. However, patients in group 2 with immediate postoperative VCP had higher likelihood of full recovery than patients in group 1 (55 of 56 vs 23 of 29 patients, P = .01), and lower incidence of total permanent VCP (2 of 917 vs 9 of 647 patients, P = .01).

CONCLUSION

Among patients with immediate postoperative VCP after thyroidectomy, IONM is associated with a higher likelihood of regaining normal vocal function. This may be related to better identification of RLN branching in IONM cases.