External Branch of the Superior Laryngeal Nerve : Anatomy and Operating Hurts

Purpose: Our purpose was to describe the anatomy of the external branch of the upper laryngeal nerve and to estimate the frequency of nerves at risk during the total thyroidectomies sub. Methodology: We realized in the CHU Point G in Bamako a forward-looking study over a period going from September 1st, 2016 till December 31st, 2017. All the patients operated by thyroidectomies subtotals for mild goiters were included to whom a systematic location of the external branch of the superior laryngeal nerve in the space avascular of Reeve was realized. Cancers and other thyroid pathologies were not included. Results: We counted and operated 120 cases of mild goiters. The external branch of the superior laryngeal nerve was seen and dissected in 80.8%; it was not seen in 19.2%. According to the classification of Cernea: the type 2 was found in 80.8% of the cases with him under typical 2b in 47.5% and under type 2a in 40 (33.3%). The global frequency of lesion of the external branch of the upper laryngeal nerve was 10.8% at 9 patients among whom 6 who presented a BENLS of Type Ni. Conclusion: The external branch of the upper laryngeal nerve of type 2 presents a risk of wound because the surgeon treats the upper pedicle at the level of the critical centimeter place over the upper pole of the thyroid. The identification of the nerve during the thyroid surgery is the solution of choice. How to cite this paper: Kanté, A., Ba, B., Sidibé, Y., Ouattara, D., Bengaly, B., Coulibaly, B., Traoré, D., Daou, M., Touré, T., Diallo, S., Coulibaly, A.D., Keita, M.A., Sanogo, S., Traoré, D., Magané, M.I., Touré, O.I., Tounkara, I., Diarra, A., Keita, B., Guidérè, T., Togola, B. and Ongoïba, N. (2018) External Branch of the Superior Laryngeal Nerve: Anatomy and Operating Hurts. International Journal of Otolaryngology and Head & Neck Surgery, 7, 388395. https://doi.org/10.4236/ijohns.2018.76039 Received: October 1, 2018 Accepted: October 31, 2018 Published: November 30, 2018 Copyright © 2018 by authors and Scientific Research Publishing Inc. This work is licensed under the Creative Commons Attribution International License (CC BY 4.0). http://creativecommons.org/licenses/by/4.0/ Open Access


Introduction
The subjective disorders of the voice are frequent after thyroid surgery without lesion of the recurring nerve [1] [2]. We incriminate the external branch of the upper laryngeal nerve (BENLS) or the external laryngeal nerve. The external laryngeal nerve innervates the crico-thyroid muscle which is a muscle tensor of vocal cords.
Consequently, the lesion of this nerve is responsible for a fatigability of the voice, for a modification of its tone which becomes graver as well as of disorders of the gulp.
He has an intimate and variable route with the upper thyroid pedicle what explains its vulnerability during the thyroid surgery [3]. It is necessary to know well the anatomical variations of its route to allow a careful dissection, so avoiding hurting it. Most of the surgeons prefer to avoid it rather than looking for it. But the latter run the inevitable risk of hurting nerves with low route which grind the upper thyroid pedicle.

Patients
We realized a forward-looking study from September 1st, 2016 till December 31st, 2017 in the service of surgery B of the university hospital G-spot of Bamako.
All the patients operated in the service for mild goiters were retained. Cancers and other thyroid pathologies were not included.
The diagnosis of mild goiter was paused by the histological examination realized on all the operating rooms.

Method
The group of hyperthyroid patients was handled medically with antithyroid ones of synthesis to have an eutthyroïdie before being scheduled for the surgical operation.
A complete clinical examination, an ultrasound, a dosage of free T3, T4, ultrasensitive TSH, preoperative biological balance sheet and cervical ultrasound were made at all the patients. The patients all had a consultation systematic ORL meadow and operating comment to study the mobility of vocal cords. For the operation, the sick person is installed in dorsal decubitus. The head is put in hyper extension by means of a block placed under the shoulders. The latter are lowered at the most to release well the neck. The way at first was a transverse cervicotomie type Kocher. Int. J. Otolaryngology and Head & Neck Surgery After section of the platysma muscle of the neck, the previous jugular veins are ligatured and split. An unsticking is made between the venous plan ventrally, the sterno-cleido-mastoid muscles dorsally and laterally, and the sterno-thyroid muscles dorsally and medially. The unsticking achieves crânialement the lower edge of the thyroid cartilage and caudally the upper edge of the manubrium sternal. A median vertical section is then realized up to the thyroid capsule. No muscle is cut in this way at first. The thyroid capsule is opened. Sterno-thyroid muscle were reclined to allow a better exhibition on the junction develop the muscle of lower constrictor, of crico-thyroid muscle. The lower laryngeal nerve was identified and dissected since the region rétrosternale until its penetration in the larynx to allow a better mobilization of the lower pole of the thyroid. Then we proceeded to a dissection of the face medial of the upper pole of the thyroid gland. Then we retracted laterally and caudally the thyroid gland to expose the crico-thyroid muscle. The nerve was identified in the space. The terminal segment of the BENLS is contained in the region of the triangle bounded crânialement sterno-thyro-laryngeal and ventrally by the sterno thyroid, caudally muscle by the upper pole of the thyroid gland and medially by the thyroid and cricoid cartilages .Il give nervous twigs for the thyroid gland and for the muscle lower constrictor of the pharynx, to end in the crico-thyroid muscle.
The BENLS crosses behind the upper thyroid pediclecranio-caudally and latero-medially. This level of crossing is for the origin of the classification of Cernea according to which we grouped the various found anatomical variants. Indeed Cernea and al [4] described a simple classification with aim to predict the hurts of the external laryngeal nerve during the ligature of the upper thyroid pedicle ( Figure 1).
The nerve which crosses the superior thyroid pedicle over 1 cm of the upper edge of the thyroid is classified typify 1. That passing below is classified type 2. Under type 2a corresponds to a crossing in the centimeter over the upper pole of the thyroid.
The subtype 2b takes place below the upper pole of the thyroid. And the latter represents a nerve to high risk of wound during the ligature of the pedicle. As for the type Ni, he corresponds to a nerve which was not identified in the triangle sterno-thyro-laryngeal. And it is generally a nerve branches of which distal penetrate into the muscle lower constrictor and walks below him. We defined by lesion of the BENLS any fatigability of the voice or the modification of its tone or disorders of the gulp appeared in operating comment, which persists one month, and which is not secondary in a lower laryngeal lesion of the nerve.
The data were seized and analyzed on the software Ear information (version 6). The test of X 2 and Student were used to compare our results with those of the literature. The threshold of meaning was fixed to 0.05.

Results
We dissected 120 nerves during thyroidectomies subtotals. Photo 1 shows a type 2b of the external branch of the superior laryngeal nerve.

Anatomo-Pathological Data
The histological examination was made at all the sick, we found a goiter colloid in 77%. At 64 sick a micro-follicular goiter, 32 macrofollicular goiters and 24 microcomputing-macrofolliculaires. The goiter was hyperplasique hyperfunc-

Rate of Identification of the External Laryngeal Nerve According to the Surgical Technique
The BENLS was 120 times looked for; it was seen and dissected in 97 cases (80.8%); it was not seen in 23 cases (19.2%).
So we classified nerves identified according to the classification of Cernea: we did not find a nerve of type 1. On the other hand the type 2 was found in 97 cases with him under type 2b in 57 cases (47.5%) and typical money 2a in 40 cases (33.3%) (Figure 2).

Complications Operating and Typical Comment of the External laryngeal Nerve
The global frequency of lesion of the BENLS according to our definition was 9 cases (10.8%).
Consequently, the morbidity was 10.8% (9 cases): it was about subjective disorders of the voice to type of fatigability in 7.2% (6 cases) and of disorders of the gulp in 3.6% (53 cases). Among the sick having presented a complication operating comment 6 were classified type Nor. The mortality was nil (Figure 3).

Age and Sex
The goiter is pathology of the young adult. The average age of our sick was of 37 years with extremes of 22 years and 69 years. This young age is brought reported by other African authors [5] [9] who found respectively 35 ± 13.5 years and 32 years.
According to several studies [5] [6] [7], the female genital organ is more represented in the thyroid pathologies. We counted 7 women for a man. This is in compliance with the data of the literature. In the USA, Friedman [14] [15] Dissected 2357 nerves by the technique of identification distal at the level of the junction develop the muscle of lower constrictor and of crico-thyroid muscle and followed the nerve in a reactionary way.

Rate of Identification of the External Laryngeal Nerve According to the Surgical Technique
His Rate of success was 85.1% of the cases.
Fu-Jie in china [16] dissected 86 anatomical subjects by using as the lower horn of the thyroid cartilage spots and located the penetration of the BENLS in the crico-thyroid muscle has 1.5 cm medially of the horn inferior.
All these techniques were assisted by a nervous monitoring. Aina [10] showed that thanks to the monitoring the rate of detection of the nerves of type 1 passed from 14.8% to 30%.

Estimation of the Risk
Cernea [4] estimated the risk of lesion of the BENLS at 0% if we proceeded to his identification, against 12% if the sick person is operated by a senior without trying to identify the BENLS and 28% if the sick person is operated by a resident.
Janson [17] estimated the risk at 58% if we do not try to identify the BENLS before the ligature of the superior thyroid artery.
On 120 cases of thyroidectomiessubtotals, we found 9 hurts (10.8%) at the sick presenting a nerve of type 2b and Nor. This frequency is comparable to that brought reported by Benyounes [18] who found 10% (n = 10) of lesion at the sick with a type 2b.

Conclusion
The BENLS of type 2 presents a risk of wound because the surgeon treats the upper pedicle at the level of the critical centimeter places over the pole cranial of the thyroid. That is why the systematic identification of the nerve during the thyroid surgery is the solution of choice; requiring knowledge of the anatomical variations of this nerve. And she is helped by the location of the space avascular.

Conflicts of Interest
We, authors of this article declare that there is no conflict of interests.