Bilateral investigation of the anatomical relationships of the external branch of the superior laryngeal nerve and superior thyroid artery, and also the recurrent laryngeal nerve and inferior thyroid artery

Relationship of Recurrent Laryngeal Nerve with Inferior Horn of Thyroid Cartilage, Berry's Ligament and Zuckerkandl's Tubercle

During neck surgery; Zuckerkandl's tubercle, Berry's ligament, the inferior horn of thyroid cartilages have become crucial anatomical landmarks in order to protect the integrity of the recurrent laryngeal nerve. Forty-two male postmortem human cadavers were used. The proximal part of the recurrent laryngeal nerve, before the inferior thyroid artery arises from its source has been observed in 87% inside the tracheoesophageal groove and in 13% running laterally to the trachea. The recurrent laryngeal nerve was encountered passing behind and through the branches of the inferior thyroid artery in 92% and 8% respectively. At all sides; the nerve was piercing the larynx 0.6 ± 0.1 mm below the inferior horn of thyroid cartilage, passing next to the inner-lower side of Berry's ligament and running under the lower middle part of Zuckerkandl's tubercle. These landmarks and their upper mentioned distances to the laryngeal nerve can be taken into consideration as important surgical guides.

The Anatomical and Clinical Significance of the Superior Laryngeal Nerve

OBJECTIVE

This study summarizes the anatomical features of the superior laryngeal nerve in Chinese to enable the rapid location of the superior laryngeal nerve during an operation.

STUDY DESIGN

Retrospective analysis of anatomical data.

SETTING

Hangzhou First People's Hospital Affiliated to Nanjing Medical University.

METHODS

A total of 71 embalmed human cadavers (132 heminecks) were examined over 3 months. The length and diameter of the internal and external branches of the superior laryngeal nerve and their relationships with different landmarks were recorded.

RESULTS

The total length of the internal branch of the superior laryngeal nerve was 23.4 ± 6.9 mm. The length of the external branch of the superior laryngeal nerve was 47.7 ± 11.0 mm. Considering the midpoint of the lower edge of the thyroid cartilage as the starting point and using that edge as a horizontal line, when the entry point is above that line, the external branch of the superior laryngeal nerve can be found within 41.1 mm and at an angle of 57.2°. When the entry point is below the lower edge of the thyroid cartilage, the external branch of the superior laryngeal nerve can be found within 34.0 mm and at an angle of 36.5°.

CONCLUSION

The superior laryngeal nerve in Chinese people has distinct anatomical characteristics. This article provides a new method of quickly locating the external branch of the superior laryngeal nerve during the operation, which can reduce the probability of damaging the external branch of the superior laryngeal nerve.

Surgical anatomy of the external branch of the superior laryngeal nerve: a systematic review and meta-analysis

PURPOSE

To provide a comprehensive evidence-based assessment of the anatomical characteristics of the external branch of the superior laryngeal nerve (EBSLN).

MATERIALS AND METHODS

A thorough systematic search was performed on the major electronic databases PubMed, EMBASE, Cochrane library, and ScienceDirect to identify eligible studies. Data were extracted and pooled into a meta-analysis. The primary outcomes were the EBSLN identification rate (total number of EBSLN identified divided by the total number of dissected hemilarynges) and the prevalence of various EBSLN types.

RESULTS

A total of 56 studies (n = 13,444 hemilarynges) were included. The overall pooled EBSLN identification rate was 89.24% (95% CI 85.49-92.49). This rate was higher for cadaveric (95.00%; 95% CI 89.73-99.35) compared to that reported in intraoperative studies (86.99%; 95% CI 82.37-91.01). Significantly higher identification rates were reported for studies in which intraoperative nerve monitoring was used (95.90%; 95% CI 94.30-97.25) compared to those which only relied on direct visual identification of the EBSLN (76.56%; 95% CI 69.34-83.08). Overall, Cernea type IIa (nerves crossing the superior thyroid artery less than 1 cm above the upper edge of the superior thyroid pole) and Friedman type 1 (nerves running their entire course superficial to the inferior pharyngeal constrictor) were the most prevalent (41.84%; 95% CI 33.28-48.08 and 50%; 95% CI 29.90-65.62, respectively). The combined prevalence of Cernea IIa and IIb (nerves crossing the superior thyroid artery below the upper edge of the superior thyroid pole) was higher in intraoperative studies compared to that in cadaveric studies (64.3% vs 49.4%). The EBSLN coursed medial to the superior thyroid artery in 70.98% (95% CI 55.14-84.68) of all cases.

CONCLUSION

The use of intraoperative nerve monitoring improves EBSLN identification rates. In light of the highly variable anatomical patterns displayed by the EBSLN, thorough pre-operative knowledge of its anatomy can be crucial in minimizing incidences of its iatrogenic injury.

A systematic review of variations of the recurrent laryngeal nerve

With thyroid cancer fast becoming one of the most common endocrine cancers, the frequency of thyroid surgery has increased. A common and debilitating concern with thyroid surgery is recurrent laryngeal nerve (RLN) paralysis leading to glottal obstruction and airway compromise. A systematic review regarding the anatomical variation of the recurrent laryngeal nerve was performed to determine the position of anatomical variants of the RLN in relation to the inferior thyroid artery (ITA) as well as the prevalence of nonrecurrent laryngeal nerve (NRLN). MEDLINE, Web of Science, MEDITEXT, AMED, CINAHL, Cochrane, ProQuest, Pubmed, and ScienceDirect. Databases were searched using the search terms "inferior thyroid artery," "recurrent laryngeal nerve," "nonrecurrent laryngeal nerve," and "anatomical variation." The reference sections of the articles found were searched for additional reports. The references of all articles were searched to find articles missed in the database search. A total of 8,655 RLN sides were included in this study. One thousand eight hundred and thirteen (20.95%; 95% confidence interval (CI) 20.09, 2,182) showed a Type A configuration of RLN in relation to the ITA, 2,432 (28.10%; 95% CI 27.15, 29.06) showed a Type B configuration and 4,410 (50.95%; 95% CI 49.89, 52.01) showed a Type C configuration between the RLN and the ITA. The second search returned with 38,568 recurrent laryngeal sides and only 221 (0.57%; 95%CI 0.5, 0.65) NRLN documented. The RLN is most commonly found in the posterior position, relative to the ITA. The incidence of the NRLN is low, only occurring in 0.57% of people.

Recurrent laryngeal nerve landmarks revisited

BACKGROUND

The aim of this work was to evaluate, to prove their reliability, the different surgical landmarks previously proposed as a mean to locate the recurrent laryngeal nerve (RLN).

METHODS

The necks of 143 (68 male and 76 female) human adult embalmed cadavers were examined. RLN origin and length and its relationship to different landmarks were recorded and results compared with those previously reported. Statistical comparisons were performed using the chi-square test (significance, p ≤ .05).

RESULTS

Mostly, RLN is located anterior to the tracheoesophageal sulcus (41.6%), posterior to the inferior thyroid artery (35.8%), lateral to Berry's ligament (88.1%), below the inferior rim of the inferior constrictor muscle (90.4%), and entering the larynx before its terminal division (54.6%).

CONCLUSIONS

The position of the RLN in relation to those structures classically considered as landmarks is highly variable. The most reliable relationships are those with Berry's ligament or the inferior constrictor muscle.

Surgical anatomy of the internal branch of the superior laryngeal nerve

The internal branch of the superior laryngeal nerve (ibSLN) may be injured during anterior approaches to the cervical spine, resulting in loss of laryngeal cough reflex, and, in turn, the risk of aspiration pneumonia. Such a risk dictates the knowledge regarding anatomical details of this nerve. In this study, 24 ibSLN of 12 formaldehyde fixed adult male cadavers were used. Linear and angular parameters were measured using a Vernier caliper, with a sensitivity of 0.1 mm, and a 1 degrees goniometer. The diameter and the length of the ibSLN were measured as 2.1+/-0.2 mm and 57.2+/-7.7 mm, respectively. The ibSLN originates from the vagus nerve at the C1 level in 5 cases (20.83%), at the C2 level in 14 cases (58.34%), and at the C2-3 intervertebral disc level in 5 cases (20.83%) of the specimens. The distance between the origin of ibSLN and the bifurcation of carotid artery was 35.2+/-12.9 mm. The distance between the ibSLN and midline was 24.2+/-3.3 mm, 20.2+/-3.6 mm, and 15.9+/-4.3 mm at the level of C2-3, C3-4, and at the C4-5 intervertebral disc level, respectively. The angles of ibSLN were mean 19.6+/-2.6 degrees medially with sagittal plane, and 23.6+/-2.6 degrees anteriorly with coronal plane. At the area between the thyroid cartilage and the hyoid bone the ibSLN is the only nerve which traverses lateral to medial. It is accompanied by the superior laryngeal artery, a branch of the superior thyroid artery. The ibSLN is under the risk of injury as a result of cutting or compression of the blades of the retractor at this level. The morphometric data regarding the ibSLN, information regarding the distances between the nerve, and the other consistent structures may help us identify this nerve, and to avoid the nerve injury.