Topographic anatomy of the internal laryngeal nerve: surgical considerations

The previously undescribed variant of the thyrohyoid muscle and its potential impact on surgical procedures

The thyrohyoid muscle belongs to the infrahyoid group located in the carotid triangle. It normally originates from thyroid cartilage and inserts into hyoid bone. Quite often, it is continuous with the sternohyoid muscle. Furthermore, there are variants that have their origin in the cricoid cartilage only, however, this occurs very rarely. During anatomical dissection, a two-headed variant of this muscle was found. One head had its origin in the cricoid cartilage and the other in the thyroid cartilage. This variant of thyrohyoid had not been previously described in the available literature. Therefore, we believe that it may be referred to as the cricothyrohyoid muscle. As the thyrohyoideus is often used as a landmark during surgical procedures in the prelaryngeal area and as a muscle graft, a thorough knowledge of its anatomy and variation is extremely important. We speculate that the two-headed version of this muscle may be problematic during surgical procedures in this region, however, it may also provide more options as a muscular graft.

Superior Laryngeal Nerve Block Response Rates in 54 Neurogenic Cough Patients

OBJECTIVE

Neurogenic cough related to hypersensitivity of the internal branch of the superior laryngeal nerve (SLN) is often treated with neuromodulating medications, which can cause considerable side effects. An alternative therapy is steroid and local anesthetic injection of the SLN ("SLN block"), initially proposed to benefit those with lateralizing symptoms (tenderness over the thyrohyoid membrane or unilateral cough source). Our objectives are to determine if SLN block produces subjective symptomatic improvements and if repeat injections further improve symptoms, and evaluate clinical factors potentially predictive of response.

METHODS

Retrospective chart review of 54 patients receiving SLN blocks at a tertiary medical academic center from January 2010 to June 2020. Medical history and anticipated predictors of positive response, including stigmata of laryngeal hypersensitivity, were recorded. Outcomes included symptomatic response, number of injections required, and side effects. Response was defined subjectively by asking patients whether the injection was beneficial and objectively by using CSI scores.

RESULTS

Fifty-four patients met the inclusion criteria. Thirty-eight patients (70.4%) endorsed improvement. No variables were identified as positive predictors of response. Thirty-two of the 38 (84.2%) endorsed improvement after one injection. Six of 15 (40%) patients who failed the first injection had positive response to the second. No significant side effects were reported.

CONCLUSION

No localizing symptoms, specific cough features, or aspects of the medical history helped predict response, suggesting that a broader range of patients may be offered the intervention. The majority of patients reported symptomatic improvement and repeat injections may benefit patients with initial nonresponse.

LEVEL OF EVIDENCE

4 Laryngoscope, 133:2647-2653, 2023.

Surgical landmarks for identification and preservation of the internal branch of the superior laryngeal nerve

OBJECTIVE

To determine the topographical anatomic features of the internal branch of the superior laryngeal nerve (ibSLN) at the thyrohyoid membrane entrance area in relation to certain consistent anatomical structures.

MATERIALS

METHODS: Twenty-two fresh adult head cadavers (9 male, 13 female; age range 52-95 years) with no signs of abnormality in the neck were dissected to determine the anatomic relationship of ibSLN and superior border of thyroid cartilage, thyroid notch, carotid bifurcation, hyoid corpus, and hyoid greater cornu.

RESULTS

The topographical relationship between ibSLN and superior border of thyroid cartilage, thyroid notch, carotid bifurcation, hyoid corpus, and hyoid greater cornu was identified bilaterally in all cadavers. According to the measures, danger zone and safe zone areas for surgical could be predicted and for surgical manipulations as well.

CONCLUSION

We provided the surgical anatomy and important landmarks for determining the internal branch of superior laryngeal nerve in the thyrohyoid membrane entrance region to avoid surgical damage during surgeries of this region.

In-Office Superior Laryngeal Nerve Block for Paralaryngeal Pain and Odynophonia

OBJECTIVES

Pain localized to the thyrohyoid region may be due to neuralgia of the superior laryngeal nerve (SLN), inflammation of the thyrohyoid complex, or a voice disorder. We present outcomes of treatment of paralaryngeal pain and odynophonia with SLN block.

STUDY DESIGN

Retrospective Review.

METHODS

A retrospective chart review of patients undergoing in-office SLN block for paralaryngeal pain between 2015 and 2018 at two tertiary care centers was conducted. Patient demographics, indications, and response to treatment were analyzed.

RESULTS

Thirty-eight patients underwent blockade of the internal branch of the SLN for paralaryngeal pain, with 10 excluded for incomplete medical records. Eighty-two percent (23/28) reported an improvement in their symptoms. Patients underwent an average of 2.5 blocks (SD = 1.88, range 1-8), with 10 patients (36%) undergoing a single procedure. Of the 18 patients who underwent multiple blocks, nine had eventual cessation of symptoms (50%) compared to resolution in 6/10 undergoing a single injection. Eleven patients (39%) noted odynophonia related to vocal effort, and all of these patients had improvement in or resolution of their symptoms and were more likely to improve compared to those without odynophonia (P = .006). Of the four patients who had a vocal process granuloma (VPG) at presentation, three had complete resolution of the lesion at follow-up.

CONCLUSION

In-office SLN block is effective in the treatment of paralaryngeal pain. It may be used as an adjunct in the treatment of vocal process granulomas, as well as voice disorders where odynophonia is a prominent symptom.

LEVEL OF EVIDENCE

4 Laryngoscope, 2021.

The Superior Laryngeal Nerve and Its Vulnerability in Surgeries of the Neck

Anatomical considerations of the superior laryngeal nerve (SLN), a branch of the vagus, provides information to minimize the potential for iatrogenic intraoperative injury, thereby preventing motor and sensory dysfunctions of the larynx. The present study aims to assess the variation of the SLN and its relationship to the superior thyroid artery (STA) and superior laryngeal artery (SLA). The study was done on 35 formalin-fixed cadavers at Oakland University in 2018-2019. In our study, we found that out of 21 cadavers, 52.4% of the external laryngeal branches (ebSLN) are related posteromedial to the STA, while 47.6% are related anteromedial to it. Out of 14 cadavers, 64.3% of the internal laryngeal branches (ibSLN) are related superoposterior to the SLA, while 35.7% are inferoposterior to it. In most cases, the SLA crosses above the ebSLN while traveling to pierce the thyrohyoid membrane to reach the larynx. The data demonstrate that both the ebSLN and ibSLN display variation in their relationship with the STA and the SLA, respectively. Awareness of these variable relationships is critical for identification and isolation of these structures in order to prevent consequences of nerve injury, primarily a reduction in the highest attainable frequency of the voice and aspiration pneumonia.

Distinct modulation of tracheal and laryngopharyngeal cough via superior laryngeal nerve in cat

Unilateral and bilateral cooling and bilateral transsection of the superior laryngeal nerve (SLN) were employed to modulate mechanically induced tracheobronchial (TB) and laryngopharyngeal (LPh) cough in 12 anesthetized cats. There was little effect of SLN block or cut on TB. Bilateral SLN cooling reduced the number of LPh (<50 %, p < 0.05), amplitudes of diaphragm EMG activity (<55 %, p < 0.05), and cough expiratory efforts (<40 %, p < 0.01) during LPh. Effects after unilateral SLN cooling were less pronounced. Temporal analysis of LPh showed only shortening of diaphragm and abdominal muscles burst overlap in the inspiratory-expiratory transition after unilateral SLN cooling. Bilateral cooling reduced both expiratory phase and total cough cycle duration. There was no significant difference in the average effects of cooling left or right SLN on LPh or TB as well as no differences in contralateral and ipsilateral diaphragm and abdominal EMG amplitudes. Our results show that reduced afferent drive in the SLN markedly attenuates LPh with virtually no effect on TB.

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.

Unmapped landmarks around branches of the Superior Laryngeal Nerve: An exploratory cadaveric study

Objectives

Preserving the External Branch of Superior Laryngeal Nerve (EBSLN) and Internal Branch of Superior Laryngeal Nerve (IBSLN) is essential during thyroidectomy. However, due to potential distortions caused by large goitres, the present anatomical landmarks used to identify these nerves are flawed. Although under such circumstances, bony landmarks may offer more stable reference points, not much has been explored in this regard. This study measures the distance between the most vulnerable points of the EBSLN and IBSLN and their relatively unexplored bony landmarks, such as the hyoid bone and thyroid notch as well as soft-tissue landmarks like the origin of the Superior Thyroid Artery (STA) and carotid bifurcation.

Methods

An exploratory cadaveric study was conducted in a medical school affiliated with a tertiary care hospital. The detailed analysis included 13 sides from 8 cadavers.

Results

The average distance from the EBSLN piercing site to the greater cornua of the hyoid bone, thyroid cartilage prominence, origin of the STA, and carotid bifurcation was 35.1(±7.2) mm, 33.3(±3.8) mm, 25.7(±6.3) mm, and 31.5(±5.0) mm, respectively and from the IBSLN piercing site was 15.9(±5.9) mm, 32.9(±4.7) mm, 16.3(±4.2) mm, and 20.7(±5.9) mm, respectively. For most cadavers, the distal EBSLN had Cernea type 2a-like relationship with the STA. Certain variations were also observed in the way these nerves branched with respect to the origin of the STA.

Conclusions

This study provides metric information (linear measurements) regarding the distance between the branches of SLN and certain unique landmarks. This could potentially aid in minimising intraoperative trauma to these branches.

Ex vivo study of vagal branches at risk for iatrogenic injury during laryngoplasty in horses

OBJECTIVE

To localize vagal branches within the surgical field of laryngoplasty and identify potentially hazardous surgical steps.

STUDY DESIGN

Observational cadaveric study.

SAMPLE POPULATION

Five equine head-neck specimens and four entire equine cadavers.

METHODS

Dissection of the pharyngeal region from a surgical perspective. Neuronal structures were considered at risk if touched or if the distance to instruments was less than 5 mm.

RESULTS

The branches of the pharyngeal plexus (PP) supplying the cricopharyngeal muscle (PPcr), the thyropharyngeal muscle (PPth), and the esophagus (PPes) were identified in the surgical field in nine of nine, five of nine, and one of nine specimens, respectively. The internal branch of the cranial laryngeal nerve (ibCLN) was identified within the carotid sheath in six of nine specimens. The external branch of the cranial laryngeal nerve (ebCLN) was identified close to the septum of the caudal constrictors in nine of nine specimens. The blade of the tissue retractor compressed the ibCLN in six of six, the ebCLN in four of six, the PPcr in six of six, the PPth in two of three, and the PPes in two of two specimens in which the respective nerves were identified after further dissection. Surgical exploration of the dorsolateral aspect of the pharynx and the incision of the septum of the caudal constrictors harmed the ebCLN in nine of nine, PPcr in seven of nine, and PPth in four of eight specimens.

CONCLUSION

Several vagal branches were located in the surgical field and must be considered at risk because of their location.

CLINICAL SIGNIFICANCE

Use of the tissue retractor, dissection over the pharynx, and dissection of the septum of the caudal constrictors involve a risk to damage vagal branches.

Topographic anatomy of the ınternal branch of the superior laryngeal nerve

PURPOSE

The aim of this study was to investigate the surgical and topographical anatomy of the internal branch of the superior laryngeal nerve (ibSLN) in laryngectomy patients.

METHODS

Patients aged 36-90 years old who underwent a total laryngectomy operation with a diagnosis of laryngeal carcinoma participated in the study. Fifteen patients who underwent a total laryngectomy operation between June 2015 and November 2016 were included in the study. A total of 29 superior laryngeal nerves (SLN) of 15 patients were studied. The position of the nerve was photographed before the thyrohyoid membrane (THM) was passed during dissection. The relationship and course of the ibSLN with respect to the superior laryngeal artery (SLA) were observed. The distance to adjacent formations and branching variants were examined along the course of the nerve.

RESULTS

Of the total 29 ibSLN, 17 were divided into three branches and 12 into two branches. In all cases except for one, the ibSLN course after piercing the THM was determined. The ibSLN penetrated the THM at a mean of 12.0 ± 2.61 mm (6-16 mm) from the superior border of the thyroid cartilage. The ibSLN penetrated the THM with a mean distance of 9.34 ± 1.65 (6-12) mm from the inferior border of the hyoid bone.

CONCLUSION

Our study demonstrated the surgical and topographical features of the ibSLN with respect to the THM, and provided a more precise knowledge of its anatomy in laryngectomy patients. It thus may help head and neck surgeons identify this nerve.

Superior Laryngeal Nerve Neuralgia: Case Series and Review of Anterior Neck Pain Syndromes

Superior laryngeal nerve neuralgia (SLNN) is an anterior neck pain syndrome that is underrecognized and, as a result, is often misdiagnosed. We present a series of patients who were diagnosed with and subsequently treated for SLNN. Nineteen patients were treated with oral nonsteroidal anti-inflammatory drugs (NSAIDs) and/or a therapeutic neck injection with 2% lidocaine and 40% triamcinolone acetonide. All patients completed a visual analog scale (VAS) to rate the level of pain before and after treatment. Four patients rated their pain as mild, 14 as moderate, and 1 as severe according to the VAS. Of the 19 patients, 8 chose to proceed with a 2-week course of NSAIDs and only 1 of them had complete resolution of their symptoms. A total of 18 patients underwent therapeutic neck injections, with a complete response to injection therapy in 10 patients. Five patients described a minimal residual foreign body sensation and 3 patients complained of mild residual pain. In this study, we found that therapeutic neck injections are effective not only in confirming the diagnosis but also in treating pain.

Anatomy of the external branch of the superior laryngeal nerve in Asian population

Injury to the external branch of the superior laryngeal nerve (eSLN) can cause a hoarse or weak voice with dysergia of the cricothyroid. The present study provided the topographic information of the eSLN in the Asian and verified anatomical validity of the landmarks previously recruited to localize the eSLN. Thirty specimens were dissected from 16 human embalmed cadavers (12 men and four women; mean age: 80.5 years). The vertical distance between the eSLN and the apical pole of the thyroid gland (AP) was 8.2 ± 4.2 mm. It descended over the AP with <1 cm distance in 51.7%, >1 cm distance in 27.6% and under the AP in 20.7%. The piercing point (PP) of the eSLN to the muscles located 26.0 ± 5.5 mm posterior and 14.7 ± 5.0 mm inferior to the laryngeal prominence. Generally, the PP located superoposterior to the midpoint of the joint between the joint of inferior constrictor and cricothyroid (ICJ). The distance between the PP and the midpoint was 8.7 ± 5.1 mm. We found that 1) the Asian had the eSLN located over the AP with <1 cm distance about half cases, 2) the PP can be a consistent reference for the eSLN identification, 3) the ICJ can be a useful landmark to preserve the eSLN at the PP.

Surgical treatment of bronchial asthma by resection of the laryngeal nerve

BACKGROUND

Management of asthma in chronically affected patients is a serious health problem. Our aim was to show that surgical treatment of chronic bronchial asthma by unilateral resection of the internal branch of the superior laryngeal nerve (ib-SLN) is an adequateand lasting remedial response.

PATIENTS AND METHODS

In a retrospective study, 41 (26 male and 15 female) patients with bronchial chronic asthma were treated surgically during the period between 2005 and 2013. It consisted of a unilateral resection of the ib-SLN under optical zoom, on patients placed in supinator position. 35 patients (24 male and 11 female) who were un-operated were included as a control.

RESULTS

In all patients, medication was reduced progressively. When the results were compared with the control group, it was seen that in 26% of the patients, both forced expiratory volume (FEV) and peak expiratory flow (PEF) increased significantly (p <05) and only modestly in 53.6% of patients (FEV, p <05 and PEF, p <05). In the remaining 20% of patients, these parameters remained however unchanged. Overall, in 80% of patients unilateral resection of the ib-SLN gave satisfactory results because it shortened the intervals and duration of asthmatic attacks, rendering thereby a reduction in medication.

CONCLUSION

This minimal-invasive method helped prevent/cure asphyxias in chronic bronchial asthma without affecting cough reflex,respiratory control and phonation and it helped patients avoid severe crisis. This approach is of interest for patients with severe and/or uncontrolled bronchial asthma in settings with limited access to drug treatment.