Anatomical variations of the external branch of the superior laryngeal nerve in relation to the inferior constrictor muscle: cadaveric dissection study

Patnaik, Uma; Nilakantan, Ajith; Shrivastava, Tripti

doi:10.1017/s0022215112001454

Cited by 13 publications

(7 citation statements)

References 19 publications

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“…The current study reports an overall pooled EBSLN identification rate of 82%. Several studies reported similar identification rates [ 28 – 31 ], while others reported EBSLN identification rates ranging from 20% [ 32 ] to 100% [ 33 , 34 ]. This heterogeneity in EBSLN identification rates could be attributed to topographical variations of the nerve, type of study (intraoperative or cadaveric), or the technique of nerve identification used (visual identification alone or with the aid of neuromonitoring devices).…”

Section: Discussionmentioning

confidence: 99%

Is identification and dissection of the external laryngeal nerve necessary during thyroidectomy? A prospective study

Bourabaa,

Settaf

2024

BMC Surg

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Background Compared to the recurrent laryngeal nerve, the EBSLN (or external laryngeal nerve) is less studied in terms of its course and relationship with the thyroid gland. This is a prospective intraoperative study designed to identify the anatomical variations of the EBSLN in relation to the IPC, the superior thyroid pedicle, and the point where the nerve crosses the STA. Additionally, the study aims to propose a technical procedure for its preservation. Methods We conducted a prospective study of 50 patients (total of 100 nerves) undergoing total thyroidectomy at the Department of Surgery ‘B’ in Ibn Sina Hospital, Rabat. Intraoperatively, the EBSLN was visually identified and preserved before ligating the superior thyroid vessels. Each nerve was categorized using established classification systems. Results The overall pooled EBSLN identification rate was 82%. Cernea type IIa (nerves crossing the STA less than 1 cm above the upper edge of the superior thyroid pole) and Friedman type II (nerves piercing the lower fibers of the IPC) were the most prevalent (64% and 44%, respectively). Kierner type IV (nerves crossing the branches of the STA immediately above the upper pole of the thyroid gland) was represented in 27% of cases. Conclusion A better understanding of surgical anatomy of the neck allows for better results of thyroidectomy by preserving the external and recurrent laryngeal nerves.

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Section: Discussionmentioning

confidence: 99%

Is identification and dissection of the external laryngeal nerve necessary during thyroidectomy? A prospective study

Bourabaa,

Settaf

2024

BMC Surg

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“…In our study, 2.7% of EBSLNs were neither visually nor functionally identified. Patnaik et al [ 26 ] studied the courses of the EBSLN in relation to the inferior constrictor muscle in 29 fresh cadavers. They reported that 16% of nerve branches had Friedman’s type 3 courses and concluded that the EBSLN would not be encountered in a certain percentage of individuals since it lies under the inferior constrictor.…”

Section: Discussionmentioning

confidence: 99%

Motor Interconnections Between Superior and Inferior Laryngeal Nerves

Gürleyik

2018

Cureus

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IntroductionAnatomical 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).MethodsIONM 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.ResultsEighty (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.ConclusionRecordable 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.

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“…The fundamental principle of any surgery is the identification of a structure to avoid injuring it (21). Although nearly all RLNs can be visually identified, approximately 20% of the EBSLNs can not be visually identified due to their subfascial/ intramuscular course into inferior constrictor muscle, which makes it necessary to conduct a microdissection for the identification of the nerve (22).…”

Section: Discussionmentioning

confidence: 99%

Contribution of intraoperative neuromonitoring to the identification of the external branch of superior laryngeal nerve

2017

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Objective:We evaluated the contribution of intraoperative neuromonitoring to the visual and functional identification of the external branch of the superior laryngeal nerve. Material and Methods:The prospectively collected data of patients who underwent thyroid surgery with intraoperative neuromonitoring for external branch of the superior laryngeal nerve exploration were assessed retrospectively. The surface endotracheal tube-based Medtronic NIM3 intraoperative neuromonitoring device was used. The external branch of the superior laryngeal nerve function was evaluated by the cricothyroid muscle twitch. In addition, contribution of external branch of the superior laryngeal nerve to the vocal cord adduction was evaluated using electromyographic records. Results:The study included data of 126 (female, 103; male, 23) patients undergoing thyroid surgery, with a mean age of 46.2±12.2 years (range, 18-75 years), and 215 neck sides were assessed. Two hundred and one (93.5%) of 215 external branch of the superior laryngeal nerves were identified, of which 60 (27.9%) were identified visually before being stimulated with a monopolar stimulator probe. Eighty-nine (41.4%) external branch of the superior laryngeal nerves were identified visually after being identified with a probe. Although 52 (24.1%) external branch of the superior laryngeal nerves were identified with a probe, they were not visualized. Intraoperative neuromonitoring provided a significant contribution to visual (p<0.001) and functional (p<0.001) identification of external branch of the superior laryngeal nerves. Additionally, positive electromyographic responses were recorded from 160 external branch of the superior laryngeal nerves (74.4%). Conclusion:Intraoperative neuromonitoring provides an important contribution to visual and functional identification of external branch of the superior laryngeal nerves. We believe that it can not be predicted whether the external branch of the superior laryngeal nerve is at risk or not and the nerve is often invisible; thus, intraoperative neuromonitoring may routinely be used in superior pole dissection. Glottic electromyography response obtained via external branch of the superior laryngeal nerve stimulation provides quantifiable information in addition to the simple visualization of the cricothyroid muscle twitch.

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Anatomical variations of the external branch of the superior laryngeal nerve in relation to the inferior constrictor muscle: cadaveric dissection study

Cited by 13 publications

References 19 publications

Is identification and dissection of the external laryngeal nerve necessary during thyroidectomy? A prospective study

Is identification and dissection of the external laryngeal nerve necessary during thyroidectomy? A prospective study

Motor Interconnections Between Superior and Inferior Laryngeal Nerves

Contribution of intraoperative neuromonitoring to the identification of the external branch of superior laryngeal nerve

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