Surgical anatomy of the external branch of the superior laryngeal nerve and its clinical significance in head and neck surgery

Key points for protecting the external branch of the superior laryngeal nerve in open thyroidectomy: A possible exploration technique

OBJECTIVE

Injury of the external branch of the superior laryngeal nerve (EBSLN) is easily overlooked in thyroidectomy, and voice changes caused by the injury have a negative effect on an increasing number of patients. This study aimed to reduce the injury rate of EBSLN by expanding the sternothyroid-laryngeal triangle and standardizing the exploration procedure.

METHODS

A total of 520 patients who had undergone thyroidectomy at the First Affiliated Hospital of Nanchang University between September 2021 and April 2022 were analyzed. During the operation, the exposure rate of the EBSLN before and after sternothyroid-laryngeal triangle expansion was compared, and all EBSLNs were anatomically classified.

RESULTS

The exposure rate of EBSLN after sternothyroid-laryngeal triangle expansion reached 82.7%, which is much higher than that before sternothyroid-laryngeal triangle expansion (33.7%), and voice change caused by injury of the EBSLN was reported in one case (the injury rate was 0.2%). The classification and proportion of the EBSLN were as follows: Type 1 (55.3%), the nerve ran within 1 cm above the STP, but no coincidence or crossover with blood vessels was observed in this region; Type 2 (14.7%), the nerve travelled within 1 cm above the STP and overlapped or intersected with blood vessels in this region; Type 3 (12.7%), the EBSLN ran below the level of the STP; and Type 4 (17.3%), no EBSLN was observed within 1 cm above the STP.

CONCLUSION

In thyroidectomy, injury to the EBSLN can be effectively reduced by expanding the sternothyroid-laryngeal triangle and exploring the upper pole area of the thyroid as far as possible, which has great clinical significance in reducing postoperative voice box injury.

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

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.

Assessment of different classification systems for predicting the risk of superior laryngeal nerve injury during thyroid surgery: a prospective cohort study

Background

A multitude of anatomical variations have been noted in the external branch of the superior laryngeal nerve (EBSLN). In this study, intraoperative neuromonitoring (IONM) was used to assess the potential value of the different classical EBSLN classifications for predicting the risk of EBSLN injury.

Methods

In total, 136 patients with thyroid nodules were included in this prospective cohort study, covering 242 nerves at risk (NAR). The EBSLN was identified by observing the cricothyroid muscle twitch and/or typical electromyography (EMG) biphasic waveform. The EBSLNs were classified by Cernea classification, Kierner classification, and Friedman classification, respectively. The EMG parameters and outcomes of vocal acoustic assessment were recorded.

Results

The distribution of Cernea, Kiernea, and Friedman subtypes were, respectively, Cernea 1 (40.9%), Cernea 2A (45.5%), Cernea 2B (10.7%), Kierner 1 (40.9%), Kierner 2 (45.5%), Kierner 3 (10.7%), Kierner 4 (2.9%) and Friedman 1 (15.7%), Friedman 2 (33.9%), Friedman 3 (50.4%). The amplitudes of EBSLN decreased significantly after superior thyroid pole operation, respectively, in Cernea 2A (193.7 vs. 226.6μV, P=0.019), Cernea 2B (185.8 vs. 221.3μV, P=0.039), Kierner 2 (193.7vs. 226.6μV, P=0.019), Kierner 3 (185.8 vs. 221.3μV, P=0.039), Kierner 4 (126.8vs. 226.0μV, P=0.015) and Friedman type 2 (184.8 vs. 221.6μV, P=0.030). There were significant differences in Fmax and Frange for Cernea 2A (P=0.001, P=0.001), 2B (P=0.001, P=0.038), Kierner 2 (P=0.001), Kierner 3 (P=0.001, P=0.038), and Friedman 2 (P=0.004, P=0.014). In the predictive efficacy of EBSLN injury, the Friedman classification showed higher accuracy (69.8% vs. 44.3% vs. 45.0%), sensitivity (19.5% vs. 11.0% vs. 14.0%), and specificity (95.6% vs. 89.9% vs. 89.9%) than the Cernea and Kierner classifications. However, the false negative rate of Friedman classification was significantly higher than other subtypes (19.5% vs. 11.0% vs. 14.0%).

Conclusion

Cernea 2A and 2B; Kierner 2, 3, and 4; and Friedman 2 were defined as the high-risk subtypes of EBSLN. The risk prediction ability of the Friedman classification was found to be superior compared to other classifications.

Improving classification of the external branch of the superior laryngeal nerve with neural monitoring: a research appraisal and narrative review

Objective

To review the published literature on external branch of superior laryngeal nerve (EBSLN) neural monitoring and propose a new EBSLN classification system using intraoperative neural monitoring (IONM).

Background

The injury rate of the external branch of the superior laryngeal nerve (EBSLN) in thyroid surgery is 0-58%. Symptoms of EBSLN injury are not consistent, and patients often complain of modification of the voice timbre with the preservation of vocal cord function. Standards for the diagnosis of EBSLN injury are lacking.

Methods

The PubMed database was searched using the terms 'External branch of the superior laryngeal nerve' and 'Intraoperative neuromonitoring' from 2010 through March 2020.

Conclusions

This paper reviewed the anatomy of the EBSLN, the diagnosis and treatment of injury, and the application of IONM in the EBSLN. The traditional EBSLN classification method was analyzed and compared with our new classification method. The diagnosis of EBSLN injury is a problem that still needs to be resolved. For anatomic classifications of the EBSLN, we found that the conventional classification systems may not accurately reflect the real status of the EBSLN and the surgical risks that may occur intraoperatively. Using IONM, we developed an EBSLN classification method that was consistent with conventional diagnosis and treatments and can be widely and easily utilized during surgery.

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.

Two trajectories of functional recovery in thyroid surgery related unilateral vocal cord paralysis

BACKGROUND

Iatrogenic unilateral vocal fold paralysis caused by thyroid surgery induces profound physical and psychosocial distress in patients. The natural course of functional recovery over time differs substantially across subjects, but the mechanisms underlying this difference remain unclear. In this study, we examined whether the anatomic site of the lesion affected the trajectory of recovery.

METHODS

In this prospective case series study in a single medical center, patients with thyroid surgery-related unilateral vocal fold paralysis were evaluated using quantitative laryngeal electromyography, videolaryngostroboscopy, voice acoustic analysis, the Voice Outcome Survey, and the Short Form-36 quality-of-life questionnaire. Patients with and without superior laryngeal nerve injuries were compared.

RESULTS

Forty-two patients were recruited, among whom 15 and 27 were assigned to the with and without superior laryngeal nerve injury groups, respectively. Compared with the group without superior laryngeal nerve injury, the group with superior laryngeal nerve injury group demonstrated less improvement in the recruitment of vocal fold adductors, and the group also had more severe impairment of vocal fold vibration, maximum phonation time, jitter, shimmer, and harmony-to-noise ratio at the first evaluation. This difference was also found in the glottal gap and maximum phonation time 12 months after the injury.

CONCLUSION

Among patients with thyroid surgery-related unilateral vocal fold paralysis, superior laryngeal nerve injury induces a distinctively different recovery trajectory compared with those without superior laryngeal nerve injury characterized by less reinnervation of vocal fold adductors and worse presentation in terms of the glottal gap and maximum phonation time. This study emphasizes the importance of superior laryngeal nerve function and its preservation in thyroid surgery.

Functional vagotopy in the cervical vagus nerve of the domestic pig: implications for the study of vagus nerve stimulation

OBJECTIVE

Given current clinical interest in vagus nerve stimulation (VNS), there are surprisingly few studies characterizing the anatomy of the vagus nerve in large animal models as it pertains to on-and off-target engagement of local fibers. We sought to address this gap by evaluating vagal anatomy in the pig, whose vagus nerve organization and size approximates the human vagus nerve.

APPROACH

Here we combined microdissection, histology, and immunohistochemistry to provide data on key features across the cervical vagus nerve in a swine model, and compare our results to other animal models (mouse, rat, dog, non-human primate) and humans.

MAIN RESULTS

In a swine model we quantified the nerve diameter, number and diameter of fascicles, and distance of fascicles from the epineural surface where stimulating electrodes are placed. We also characterized the relative locations of the superior and recurrent laryngeal branches of the vagus nerve that have been implicated in therapy limiting side effects with common electrode placement. We identified key variants across the cohort that may be important for VNS with respect to changing sympathetic/parasympathetic tone, such as cross-connections to the sympathetic trunk. We discovered that cell bodies of pseudo-unipolar cells aggregate together to form a very distinct grouping within the nodose ganglion. This distinct grouping gives rise to a larger number of smaller fascicles as one moves caudally down the vagus nerve. This often leads to a distinct bimodal organization, or 'vagotopy'. This vagotopy was supported by immunohistochemistry where approximately half of the fascicles were immunoreactive for choline acetyltransferase, and reactive fascicles were generally grouped in one half of the nerve.

SIGNIFICANCE

The vagotopy observed via histology may be advantageous to exploit in design of electrodes/stimulation paradigms. We also placed our data in context of historic and recent histology spanning multiple models, thus providing a comprehensive resource to understand similarities and differences across species.

[Update of the S2k guidelines : Surgical treatment of benign thyroid diseases]

Thyroid resections represent one of the most common operations with 76,140 interventions in the year 2016 in Germany (source Destatis). These are predominantly benign thyroid gland diseases. Recommendations for the operative treatment of benign thyroid diseases were last published by the CAEK in 2010 as S2k guidelines (Arbeitsgemeinschaft der Wissenschaftlichen Medizinischen Fachgesellschaften e.V. [AWMF] 003/002) against the background of increasingly more radical resection procedures. Hemithyroidectomy and thyroidectomy are routinely performed for benign thyroid disease in practice. The operation-specific risks show a clear increase with the extent of the resection. Therefore, weighing-up of the risk-indications ratio between unilateral lobectomy or thyroidectomy necessitates an independent evaluation of the indications for both sides. This principle in particular has been used to update the guidelines. In addition, the previously published recommendations of the CAEK for correct execution and consequences of intraoperative neuromonitoring were included into the guidelines, which in particular serve the aim to avoid bilateral recurrent laryngeal nerve paralysis. Moreover, the recommendations for the treatment of postoperative complications, such as hypoparathyroidism and postoperative infections were revised. The updated guidelines therefore represent the current state of the science as well as the resulting surgical practice.

Importance of incorporating intraoperative neuromonitoring of the external branch of the superior laryngeal nerve in thyroidectomy: A review and meta-analysis study

BACKGROUND

Voice changes are frequently reported after thyroidectomy due to injury to the external branch of the superior laryngeal nerve (EBSLN) and paralysis of the cricothyroid muscle, The objective is to evaluate the advantage of intraoperative neuromonitoring (IONM) in identifying EBSLN during thyroid surgery.

METHODS

Data sources were MEDLINE, PubMed, Web of Science, and Cochrane Library from January 1, 1995, through July 1, 2018. Published studies of adult patients who had thyroid surgery and an attempt to identify EBSLN done by conventional methods and/or IONM were selected.

RESULTS

Seven studies met all inclusion criteria. Patients who had IONM during thyroid surgery had a significantly increased number of identified EBSLN at risk, compared to the control group.

CONCLUSION

The use of IONM during open thyroid surgery increases EBSLN identification/visualization, and hence it may decrease the incidence of post-thyroidectomy voice disorders.

Efficiency of intraoperative neuromonitoring on voice outcomes after thyroid surgery

OBJECTIVE

Voice disturbance is an important problem after thyroidectomy. The aim of this study was to evaluate the efficiency of intraoperative neuromonitoring (IONM) in reducing early phonation change by comparing postoperative voice outcomes.

METHODS

The study retrospectively enrolled 68 consecutive female patients who had undergone IONM thyroidectomy for papillary thyroid carcinoma occurring between January 2014 and November 2014. A historical group of 117 similar female patients not receiving IONM thyroidectomy was used as an external control. Voice analyses were performed preoperatively and at 1 week, 1 month, and 3 months postoperatively. Voice outcomes between the IONM group and no IONM group were compared in patients who underwent hemithyroidectomy and total thyroidectomy.

RESULTS

In patients who underwent IONM, there were significantly smaller changes in the fundamental frequency at postoperative 1 month and in the maximum voice pitch of the voice range profile at postoperative 1 week irrespective of the extent of thyroid surgery.

CONCLUSION

IONM during thyroid surgery resulted in better outcomes regarding fundamental frequency and high-pitch voice in the early postoperative period. IONM appears to be an effective method to reduce temporary phonation alteration after thyroid surgery.

Effect of energy-based devices on voice quality after total thyroidectomy

Voice alteration is an important complication of thyroid surgery and is closely related to patients' quality of life. There are no studies analyzing effect of energy-based devices (EBD) on voice quality (VQ). Aim of this prospective study is to evaluate impact of sutureless total thyroidectomy performed with EBDs on objective voice parameters of patients without recurrent laryngeal nerve (RLN) and/or external branch of superior laryngeal nerve (EBSLN) injury. Sixty patients underwent total thyroidectomy with meticulous dissection of EBSLN. Patients were assigned to Group L (Ligasure™), Group H (Harmonic), or Group C (Conventional) through random ballot. For analysis of alteration in VQ, digital videolaryngostroboscopy (VLS), voice handicap index (VHI), multidimensional voice program (MDVP), and electroglottography (EGG) were used. VLS was performed by 70°-angled indirect laryngoscopy and evaluation was standardized by VLS scale and laryngeal function scoring. This study is registered on clinicaltrials.gov with number NCT01865006. Forty eight patients were female. There was no difference on demographic data. On post-operative laryngoscopic examination, none of the patients had vocal fold palsy. When mean VHI scores at post-operative 1st week and 2nd month were compared to pre-operative values for each groups, groups L and H demonstrated a significant increase in VHI in the early post-operative evaluation, while there was no significant increase for group C. No significant increase was seen in late post-operative period compared to pre-operative period for any groups. In the early post-operative period, VQ is better with the conventional technique than EBDs; however, in late post-operative period, VQ is detected better in EBDs (especially in Group L) than the conventional technique, but no statistical difference was observed.

EBSLN and Factors Influencing its Identification and its Safety in Patients Undergoing Total Thyroidectomy: A Study of 456 Cases

BACKGROUND

The external branch of the superior laryngeal nerve (EBSLN) is at surgical risk during superior thyroid pole ligation during thyroidectomy. Majority of studies have addressed the identification of these nerves and its reported incidence. Very few studies have addressed the relationship of these nerves with the volume of the thyroid gland and presence of toxicity.

MATERIALS AND METHODS

A retrospective evaluation of 456 patients who underwent total thyroidectomy were analysed from the prospectively maintained database. The EBSLN was diligently identified and preserved before individual ligation of the superior thyroid pedicle. The nerve was graded as per the Cernea classification (type I, IIa and IIb). Goitres are classified into toxic & non-toxic based on hyperthyroidism, further sub classified as large (>50 cc) and small (≤50 cc) based on volume of each lobe. The grading of EBSLN was correlated with hyperthyroidism and volume of each lobe.

RESULTS

In 456 patients (912 nerves), EBSLN was identified in 849/912(93.09%), type I in 156/912(17.1%), type IIa in 522/912(57.23%) and type IIb in 171/912(18.75%). The prevalence of large goitres was 180/912(19.73%).Type IIb nerve was predominantly seen in 161/180(89.4%) of large goitres. Type IIb nerves was more common in toxic 141/372(37.9%) than non-toxic lobes 25/540(5.46%).

CONCLUSION

Large goitres are not uncommon in toxic cases. The EBSLN is at highest risk of injury in this subgroup of patients and surgical expertise is essential to identify this entity of EBSLN to perform a safe thyroidectomy.

Medicolegal implications of surgical errors and complications in neck surgery: A review based on the Italian current legislation

Aim of the present paper is the review of the principal complications associated to endocrine neck surgery considering how expertise, full adoption of guidelines, appropriate technology and proper informed consent may limit the medicolegal claims at the light of the incoming new regulation of the medical professional legal responsibility. A literature search, using the Medline/PubMed database for full-length papers, was used. Postoperative recurrent laryngeal nerve (RLN) palsy and hypoparathy-roidism remain the principal causes of surgical malpractice claims . In the procedure of neck lymphadenctomy intra-operative haemorrhage, thoracic duct injury, injuries to loco-regional nerves can be observed and can be source of claims. After many years of increased medicolegal litigations, the Italian government is proposing a drastic change in the regulations of supposed medical malpractice in order to guarantee the patient's right to a safe treatment and in the meantime to defend clinicians from often unmotivated and prejudicial legal cases. Surgical errors and complications in neck surgery are a relevant clinical issue. Only the combination of surgical and clinical expertise, application of guidelines, appropriate technology and a routinely use of specific informed consent can contain potential medicolegal implications.

Distinct Disease and Functional Characteristics of Thyroid Surgery-Related Vocal Fold Palsy

BACKGROUND

Iatrogenic trauma induced by thyroid surgery is the most common etiology of unilateral vocal fold paralysis (UVFP). UVFP after thyroid surgery may lead to profound physical and psychosocial distress. This study comprehensively evaluated UVFP caused by thyroid surgery, and compared the results with those caused by other surgical trauma.

METHODS

Patients with surgery-related UVFP were evaluated using quantitative laryngeal electromyography, videolaryngostroboscopy, voice acoustic analysis, the Voice Outcome Survey, and the Short Form-36 Health Survey quality-of-life questionnaire. Patients with thyroid surgery and other surgeries were compared.

RESULTS

A total of 105 patients were recruited, of whom 52 and 53 were assigned to the thyroid surgery and the other surgery group, respectively. Patients in the thyroid surgery group had a higher proportion of external branch of superior laryngeal nerve (eSLN) involvement, longer duration from disease onset to the first laryngeal electromyography examination, lower jitter, higher harmonic-to-noise ratio, and better quality of life compared with the other surgery group. Specifically for patients in the thyroid surgery group, those with eSLN involvement tended to have more pronounced impairment in jitter and shimmer compared with patients without eSLN involvement.

CONCLUSION

UVFP caused by thyroid surgery has a distinct clinical presentation with relatively high involvement in the eSLN, better voice acoustics, longer waiting time before asking for evaluation, and less impact on quality of life. The involvement of eSLN in these patients further impaired their voice. Early referral is suggested for these patients, especially with suspected eSLN injury.

Efficacy of Intraoperative Neuro-Monitoring to Localize the External Branch of the Superior Laryngeal Nerve

BACKGROUND

This study investigated whether visual localization of the external branch of the superior laryngeal nerve (EBSLN) coincides with its localization via intraoperative neuro-monitoring (IONM) during thyroidectomy and whether its use influences the frequency of injuries.

METHODS

A prospective, comparative, cross-sectional, observational study was performed in 240 superior thyroid poles. The metrics were visual identification of the EBSLN and its corroboration with IONM. The frequency of EBSLN injuries was also determined. Statistical analysis was achieved via kappa and chi-square tests, as well as odds ratios (OR).

RESULTS

Of the 240 superior thyroid poles, IONM identified 234 (97.5%) EBSLN, whereas 190 (79.1%) were identified visually: OR = 10.35 [CI 4.37-24.65] p < 0.0001. Of the 190 EBSLN identified visually, 150 were confirmed through IONM. Indeed, their structure corresponded to an EBSLN to yield a kappa with a linear weighting value of 0.362. The standard error was 0.0467 [CI 0.2686-0.4554], indicating a fair agreement between the visual and IONM classification.

CONCLUSION

IONM identified 97.5% of EBSLN cases. It was higher than the visual identification. There were no injuries to EBSLN identified through IONM.

Proposal for anatomical classification of the superior pole in thyroid surgery

OBJECTIVE

To propose a distinct anatomical classification for the superior thyroid pole that may serve as a surgical landmark and could help reduce complications in thyroid surgery.

MATERIALS AND METHODS

A comprehensive anatomical study based on existing literature and surgical observations.

RESULTS

The proposed superior pole classification is based on two parameters that closely interact: one is the shape of the superior pole and the other is the structure of the vascular pedicle of the superior pole. We have come up with three distinct types of superior thyroid pole anatomical structure that may be predictive of the risk for both hemorrhage and nerve injury.

CONCLUSIONS

Superior pole classification may serve as a guiding tool during thyroid surgery in order to reduce complications such as bleeding and injury to the external branch of the superior laryngeal nerve.

Intraoperative neuromonitoring of the external branch of the superior laryngeal nerve during thyroidectomy: the need for evidence-based data and perioperative technical/technological standardization

The external branch of the superior laryngeal nerve (EBSLN) is surgically relevant since its close anatomical proximity to the superior thyroid vessels. There is heterogeneity in the EBSLN anatomy and EBSLN damage produces changes in voice that are very heterogenous and difficult to diagnose. The reported prevalence of EBSLN injury widely ranges. EBSLN iatrogenic injury is considered the most commonly underestimated complication in endocrine surgery because vocal assessment underestimates such event and laryngoscopic postsurgical evaluation does not show standardized findings. In order to decrease the risk for EBSLN injury, multiple surgical approaches have been described so far. IONM provides multiple advantages in the EBSLN surgical approach. In this review, we discuss the current state of the art of the monitored approach to the EBSLN. In particular, we summarize, providing our additional remarks, the most relevant aspects of the standardized technique brilliantly described by the INMSG (International Neuromonitoring Study Group). In conclusion, in our opinion, there is currently the need for more prospective randomized trials investigating the electrophysiological and pathological aspects of the EBSLN for a better understanding of the role of IONM in the EBSLN surgery.

Prospective randomized study on injury of the external branch of the superior laryngeal nerve during thyroidectomy comparing intraoperative nerve monitoring and a conventional technique

BACKGROUND

The external branch of the superior laryngeal nerve (SLN) is susceptible to injuries during thyroidectomy, causing voice impairment. Intraoperative nerve monitoring may facilitate identification of the nerve, reducing voice impairment.

METHODS

A total of 252 patients undergoing thyroidectomy were randomly assigned to group N (the NIM-Response 3.0 system was used) or group C (the conventional technique using the Vari-Stim 3 was used) to identify the external branch of the SLNs. The primary endpoint was the identification rate of the external branch of the SLN. The secondary endpoint was the incidence of postoperative voice impairment.

RESULTS

The visual and the electrostimulatory identification rates of the external branch of the SLN in group N and group C were 48.8% versus 17.8% (p < .001) and 89.2% versus 17.8% (p < .001), respectively. The proportion of female patients who had subjective voice impairment was significantly smaller in group N than in group C.

CONCLUSION

The use of the NIM-Response 3.0 significantly improved the identification rate of the external branch of the SLN during thyroidectomy, reducing voice impairment.

An applied anatomical study on the external laryngeal nerve loop and the superior thyroid artery in the neck surgical region

This study was conducted to investigate the topographic relationship between the external laryngeal nerve (ELN) loop and the superior thyroid artery (STA), in order to provide the anatomical foundations for protecting the ELN during surgery. In the present study, 48 adult human cadavers were dissected and analyzed. For the 21 (21.9%) low-position ELN loops observed, the neurovascular relationship between the STA and the nerve was classified into four types: (1) the artery overlapped the nerve; (2) the artery passed through the ELN loop; (3) the muscular branch of the ELN loop and the laryngeal branch of the STA coursed together; and (4) the branches of the STA and the ELN loop were interlaced. Our study suggested that the patterns of ELN loops are so complicated that they have not been statistically defined in any previous study, which should be kept in mind when attempting to protect the nerve from injury. Also, because of the variable morphology of the ELN loop and its complicated topographic relationship to the STA, the vessels should be individually isolated and then ligated during thyroidectomy. When ligating the laryngeal branch of the STA during larynx surgery, special attention should be paid to avoiding damage to the muscular branch of the ELN/ELN loop.

Retrograde thyroidectomy: a technique for visualization and preservation of the external branch of superior laryngeal nerve

INTRODUCTION

The external branch of the superior laryngeal nerve (EBSLN) should be identified during thyroidectomy to prevent injury and post-operative voice change. Identification is rendered difficult during a standard thyroidectomy where there is a large gland with upper pole enlargement. We describe the retrograde thyroidectomy technique to facilitate nerve preservation.

PRESENTATION OF CASE

A retrograde thyroidectomy was performed in a 53-year old woman with a difficult goiter. Operative steps are described.

DISCUSSION

This technique allows the upper pole to be completely mobilized caudally providing unparalleled visualization of the upper pole vascular pedicle, thereby preserving the EBSLN.

CONCLUSION

There is better visualization of the superior thyroid pedicle and the EBSLN with retrograde thyroidectomy, potentially reducing the incidence of EBSLN injury during a difficult thyroidectomy.

Neurological complications in thyroid surgery: a surgical point of view on laryngeal nerves

THE CERVICAL BRANCHES OF THE VAGUS NERVE THAT ARE PERTINENT TO ENDOCRINE SURGERY ARE THE SUPERIOR AND THE INFERIOR LARYNGEAL NERVES: their anatomical course in the neck places them at risk during thyroid surgery. The external branch of the superior laryngeal nerve (EB) is at risk during thyroid surgery because of its close anatomical relationship with the superior thyroid vessels and the superior thyroid pole region. The rate of EB injury (which leads to the paralysis of the cricothyroid muscle) varies from 0 to 58%. The identification of the EB during surgery helps avoiding both an accidental transection and an excessive stretching. When the nerve is not identified, the ligation of superior thyroid artery branches close to the thyroid gland is suggested, as well as the abstention from an indiscriminate use of energy-based devices that might damage it. The inferior laryngeal nerve (RLN) runs in the tracheoesophageal groove toward the larynx, close to the posterior aspect of the thyroid. It is the main motor nerve of the intrinsic laryngeal muscles, and also provides sensory innervation to the larynx. Its injury finally causes the paralysis of the omolateral vocal cord and various sensory alterations: the symptoms range from mild to severe hoarseness, to acute airway obstruction, and swallowing impairment. Permanent lesions of the RNL occur from 0.3 to 7% of cases, according to different factors. The surgeon must be aware of the possible anatomical variations of the nerve, which should be actively searched for and identified. Visual control and gentle dissection of RLN are imperative. The use of intraoperative nerve monitoring has been safely applied but, at the moment, its impact in the incidence of RLN injuries has not been clarified. In conclusion, despite a thorough surgical technique and the use of intraoperative neuromonitoring, the incidence of neurological complications after thyroid surgery cannot be suppressed, but should be maintained in a low range.

Anatomical anomalies of the laryngeal branches of the vagus nerve in pigs (Sus scrofa)

To delineate the anomaly and frequency of their occurrence in a pig model, we reported the topography of the vagus laryngeal branches and compared the differences with humans. Thirty sides of cervical vagus nerve in 15 fresh cadavers (Sus scrofa) were microdissected. We measured the branch diameters and lengths of the laryngeal branches using a Vernier caliper with a resolution of 0.01 mm. Two patterns of the vagus laryngeal branches were shown: 56.7% with the cranial laryngeal nerve (CLN) and 43.3% without the CLN. The diameters and the length of the CLN were not affected by the side of the neck (P > 0.05), but the diameters of the recurrent laryngeal nerve (RLN) and the nodose ganglion were significantly different between left and right sides (P < 0.05). The left RLN was thinner than the right side in diameter (P < 0.05). Four of the 30 sides had anastomoses between the vagus and the cervical sympathetic chain. There were some differences between the pig anatomy and human anatomy, but the patterns were largely similar. The similarities support the utility of this model, which is closer in size to humans than the standard rodent models.

Interrelationships between the innervations from the laryngeal nerves and the pharyngeal plexus to the inferior pharyngeal constrictor

PURPOSE

The inferior constrictor is innervated by the pharyngeal plexus and the external and recurrent laryngeal nerves. The communication between these nerves may influence the innervations. However, the relations of their anastomoses with the innervations have been unclear. This gross anatomical study re-examined the configuration of the inferior constrictor and investigated the variations of the anastomoses and the innervations of the constrictor to clarify their interrelationships.

METHODS

The inferior constrictor and the branches of the superior and recurrent laryngeal nerves and the pharyngeal plexus were examined under a binocular microscope in 30 Japanese cadavers.

RESULTS

The inferior constrictor consisted of the oblique fibers from the thyroid and cricoid cartilages and the horizontal ones from the cricoid. The oblique fibers were innervated by the pharyngeal plexus from the dorsal and ventral surfaces. The external laryngeal nerve gave twigs to the oblique fibers and the cricothyroid from the lateral surface. The recurrent laryngeal nerve supplied the horizontal fibers from the ventral surface. The internal laryngeal nerve sometimes and the main trunk of the superior laryngeal nerve rarely supplied the upper oblique fibers. The communicating branches between the laryngeal nerves and the pharyngeal plexus sometimes gave twigs to the constrictor from the dorsal surface.

CONCLUSIONS

The innervations to the inferior constrictor from the laryngeal nerves and the pharyngeal plexus are classified into some types based on their branching patterns and anastomoses, suggesting that the dysfunctions of the laryngopharyngeal region vary according to the positional relationships between the affected part and the innervations types.

Unilateral superior laryngeal nerve lesion in an animal model of dysphagia and its effect on sucking and swallowing

We tested two hypotheses relating to the sensory deficit that follows a unilateral superior laryngeal nerve (SLN) lesion in an infant animal model. We hypothesized that it would result in (1) a higher incidence of aspiration and (2) temporal changes in sucking and swallowing. We ligated the right-side SLN in six 2-3-week-old female pigs. Using videofluoroscopy, we recorded swallows in the same pre- and post-lesion infant pigs. We analyzed the incidence of aspiration and the duration and latency of suck and swallow cycles. After unilateral SLN lesioning, the incidence of silent aspiration during swallowing increased from 0.7 to 41.5%. The durations of the suck containing the swallow, the suck immediately following the swallow, and the swallow itself were significantly longer in the post-lesion swallows, although the suck prior to the swallow was not different. The interval between the start of the suck containing a swallow and the subsequent epiglottal movement was longer in the post-lesion swallows. The number of sucks between swallows was significantly greater in post-lesion swallows compared to pre-lesion swallows. Unilateral SLN lesion increased the incidence of aspiration and changed the temporal relationships between sucking and swallowing. The longer transit time and the temporal coordinative dysfunction between suck and swallow cycles may contribute to aspiration. These results suggest that swallow dysfunction and silent aspiration are common and potentially overlooked sequelae of unilateral SLN injury. This validated animal model of aspiration has the potential for further dysphagia studies.

A detailed study of the relationship between the external laryngeal nerve and superior thyroid artery, including its glandular branches

The external layrngeal nerve (ELN) may be at risk during thyroidectomy. Because the relationship between the ELN and superior thyroid artery (STA) can be variable, we aimed to investigate their relationship in detail. In human cadavers, 81 ELN and STA and their branches were carefully dissected. The position of the nerve was classified as medial (Group I, on 76.5% sides), lateral (Group II, on 20.9% sides), or posterior (Group III, on 2.4% sides) to the origin of the STA. In Group Ia, the nerve did not cross the artery while it did cross the artery in Group Ib. In Group II, the nerve was located lateral to the origin of the artery and crossed it. In Group III, the nerve coursed downward posterior to the artery. In conclusion, the topography of the ELN showed much more variability in its relationship to the STA than is described in the literature. Such variations should be kept in mind during surgery of the anterior neck. It is our hope that such data will decrease surgical morbidity following surgery of the anterior neck.

The anatomy of the external branch of the superior laryngeal nerve in Koreans

BACKGROUND

Preservation of the external branch of the superior laryngeal nerve (EBSLN) during thyroidectomy is important because its injury may lead to frequent occurrence of vocal fatigue and the inability to perform superenergetic phonation. Most studies on the anatomy of EBSLN have been performed in Western countries and, thus, have some limitations in their application to Koreans. We explored the anatomy of EBSLNs using intraoperative neuromonitoring (IONM) in Korean adults.

METHODS

Between August 2011 and December 2011, 50 patients underwent thyroidectomy at Korea University, Anam Hospital in Seoul, Korea. IONM was performed with the NIM response 3.0 system.

RESULTS

Forty-two total thyroidectomies and eight lobectomies were performed with IONM and 92 EBSLNs were evaluated. Type I EBSLN was observed in 15 of the 92 nerves (16.3%), type IIa EBSLN was noted in 52 (56.5%) and type IIb EBSLN was noted in 25 (27.2%). Patients with types IIa and IIb were at higher risk of injuries and these types were more frequently observed (83.7%) compared with previous Western studies. We found that 35.9% of distal insertion sites of EBSLNs were located within 1cm of the center of the cricoid cartilage.

CONCLUSION

Surgeons should pay close attention to preserving the EBSLN during thyroidectomy in Korean patients because their EBSLNs are more frequently located beneath the superior thyroid vessels.

Randomized controlled trial of visualization versus neuromonitoring of the external branch of the superior laryngeal nerve during thyroidectomy

BACKGROUND

Injury to the external branch of the superior laryngeal nerve (EBSLN) during thyroidectomy results in a lowered fundamental frequency of the voice and deteriorated voice performance in producing high-frequency sounds. It remains unclear if the use of intraoperative nerve monitoring (IONM) can improve the clinical outcome of thyroidectomy in terms of preserved individual voice performance. This study was designed to test that hypothesis.

METHODS

A total of 210 consenting female patients planned for total thyroidectomy were randomly assigned to two groups equal in size (n = 105): visual inspection of the EBSLN and RLN vs. this plus additional EBSLN and RLN monitoring. The primary outcome was the identification rate of the EBSLN. The secondary outcomes included: anatomical variability of the EBSLN according to the Cernea classification and changes in postoperative voice performance. Voice assessment included pre- and postoperative videostrobolaryngoscopy and an analysis of maximum phonation time (MPT), voice level (VL), fundamental frequency (Fo), and voice quality rating on the GRBAS scale.

RESULTS

The following differences were found for operations without vs. with IONM: identification rate of the EBSLN was 34.3 % vs. 83.8 % (p < 0.001), whereas a 10 % or higher decrease in phonation parameters was found in 10 % vs. 2 % patients for MPT (p = 0.018), 13 % vs. 2 % for VL (p = 0.003), and 9 % vs. 1 % for Fo (p = 0.03), a change in the GRBAS scale > 4 points in 7 % vs. 1 % (p = 0.03), and temporary RLN injury was found in 2 % vs. 1 % (p = 0.56), respectively.

CONCLUSIONS

The use of IONM significantly improved the identification rate of the EBSLN during thyroidectomy, as well as reduced the risk of early phonation changes after thyroidectomy.

Superior laryngeal nerve loop: patterns and surgical implications

This study clarifies the patterns of the superior laryngeal nerve loop (SLN loop), connecting the cervical sympathetic chain (CSC) and the SLN and its branches, so as to provide an anatomic basis for decreasing the risk of injury to the external laryngeal nerve (ELN) during neck surgery. Fifty Chinese adult human cadavers fixed with 4 % formalin were dissected, and their SLN loop patterns were analyzed and summarized. In 98 of 100 sides the CSC anastomosed with the SLN and its branches, forming a looped nerve structure which we called the SLN loop. The SLN loops could be divided into five types: e ( n ), t ( n ), i ( n ), t ( n ) e ( n ), and i ( n ) e ( n ) based on morphological variations. The results demonstrated that e ( n ) was most frequently found in the samples (82/100) followed by t ( n ) (9/100), i ( n ) (3/100), t ( n ) e ( n ) (2/100), and i ( n ) e ( n ) (2/100). Comparing with the previous work, we identified additional 18 subtypes of the SLN loop. The relations of the SLN loop to the surrounding structures were complicated, which brought more challenges to thyroidectomy. Thus, we do not advocate routine identification of ELN/ELN loop during the process of thyroidectomy, especially systematic identification of ELN during operation. However, this study introduces the possibility that nerve injury can be avoided by exposure of the nerve via careful dissection in the region of the superior pole of the thyroid gland to the extent that we can initiate individual ligation of the superior polar vessels, along with the help of neuromonitors, video monitors, and magnifying loupes.

Thyroid surgery

Diseases of the thyroid are common and surgical treatment is often the preferred option. Thyroid surgery is becoming subspecialised and falls within the repertoire of maxillofacial, and head and neck surgeons. Multidisciplinary management of most patients with diseases of the thyroid is key to providing the best care particularly for those with malignancies and retrosternal extension. To reduce postoperative complications a meticulous search for, and protection of the recurrent laryngeal nerve and parathyroid glands, with an incision along the skin crease in the lower neck, which can be extended for neck dissection, are paramount. Recent advances in thyroid surgery include ultrasound-guided cervical plexus block, use of the Harmonic Scalpel(®) (Ethicon Endo-Surgery, Inc., USA), intraoperative nerve stimulation to monitor the recurrent laryngeal nerve, use of TissuePatch™ 3 (Tissuemed Ltd., Leeds, UK) adhesive sealant, and minimal access surgery.

Confocal imaging reveals three-dimensional fine structure difference between ventral and dorsal nerve roots

Peripheral nerve injury repair is one of the most challenging problems in neurosurgery, partially due to lack of knowledge of three-dimensional (3-D) fine structure and organization of peripheral nerves. In this paper, we explored the structures of nerve fibers in ventral and dorsal nerves with a laser scanning confocal microscopy. Thick tissue staining results suggested that nerve fibers have a different 3-D structure in ventral and dorsal nerves, and reconstruction from serial sectioning images showed that in ventral nerves the nerve fibers travel in a winding form, while in dorsal nerves, the nerve fibers form in a parallel cable pattern. These structural differences could help surgeons to differentiate ventral and dorsal nerves in peripheral nerve injury repair, and also facilitate scientists to get a deeper understanding about nerve fiber organization.

A clear map of the lower cranial nerves at the superior carotid triangle

BACKGROUND

The lower cranial nerves must be identified to avoid iatrogenic injury during skull base and high cervical approaches. Prompt recognition of these structures using basic landmarks could reduce surgical time and morbidity.

METHODS

The anterior triangle of the neck was dissected in 30 cadaveric head sides. The most superficial segments of the glossopharyngeal, vagus and its superior laryngeal nerves, accessory, and hypoglossal nerves were exposed and designated into smaller anatomic triangles. The midpoint of each nerve segment inside the triangles was correlated to the angle of the mandible (AM), mastoid tip (MT), and bifurcation of the common carotid artery.

RESULTS

A triangle bounded by the styloglossus muscle, external carotid artery, and facial artery housed the glossopharyngeal nerve. This nerve segment was 0.06 ± 0.71 cm posterior to the AM and 2.50 ± 0.59 cm inferior to the MT. The vagus nerve ran inside the carotid sheath posterior to internal carotid artery and common carotid artery bifurcation in 48.3% of specimens. A triangle formed by the posterior belly of digastric muscle, sternocleidomastoid muscle, and internal jugular vein housed the accessory nerve, 1.90 ± 0.60 cm posterior to the AM and 2.30 ± 0.57 cm inferior to the MT. A triangle outlined by the posterior belly of digastric muscle, internal jugular vein, and common facial vein housed the hypoglossal nerve, which was 0.82 ± 0.84 cm posterior to the AM and 3.64 ± 0.70 cm inferior to the MT.

CONCLUSIONS

Comprehensible landmarks can be defined to help expose the lower cranial nerves to avoid injury to this complex region.

Combined Injury of the Accessory Nerve and Brachial Plexus

BACKGROUND:

Stretch-induced spinal accessory nerve palsy has been considered extremely rare, with only a few cases reported.

OBJECTIVE:

In 357 patients with stretch lesions of the brachial plexus, we investigated the prevalence, course, and surgical treatment of accessory nerve palsy.

METHODS:

Accessory nerve palsy was ascertained when the patient was unable to shrug the ipsilateral shoulder. Patients underwent brachial plexus reconstruction between 6 and 8 months after trauma. To confirm paralysis, during surgery, the accessory nerve was stimulated electrically.

RESULTS:

Accessory nerve palsy occurred in 19 of the 327 patients (6%) with upper type or complete palsy of the brachial plexus. Proximal injuries of the accessory nerve accompanied by voice alteration and complete palsy of the sternocleidomastoid and trapezius muscle occurred in 2 patients. Proximal palsy without vocal alterations was observed in 6 patients. Palsy of the trapezius muscle with preservation of the sternocleidomastoid muscle occurred in 11 patients. All 7 patients who demonstrated muscle contractions upon electrical stimulation of the accessory nerve during surgery recovered completely. Patients with surgical reconstruction of the accessory nerve through grafting (n = 2) or repair by platysma motor nerve transfer (n = 2) recovered active shoulder shrugging within 36 months of surgery. Seven of the 8 patients without accessory nerve reconstruction recovered from their drop shoulder and head tilt, but remained unable to shrug.

CONCLUSION:

If intraoperative electrical stimulation produces contraction of the upper trapezius muscle, no repair is needed. In proximal injuries, the platysma motor branch should be transferred to the accessory nerve; whereas in paralysis distal to the sternocleidomastoid muscle, the accessory nerve should be explored and grafted.

[Anatomical variations of external laryngeal nerve and thyroid chirurgical: about 32 dissections]

AIMS AND SCOPE

The aim of this study is to improve our knowledge about external laryngeal nerve anatomical and its variations at the superior extremity of thyroid and to estimate the risk of its injury during surgical thyroid procedures.

MATERIALS AND METHODS

Anatomical, descriptive study performed in the service of pathology and forensic medicine of the university hospital of Treichville. Sixteen fresh adults cadavers have been dissected (32 dissections of the superior thyroid pedicle).

RESULTS

We found the external nerve laryngeal and the higher thyroid artery in 100% of cases. The 32 dissected nerves were born on the level of the greater horn of the hyoid bone. The situation of the external laryngeal nerve in relation to the branches of the superior thyroid artery were: (1) in 75% of cases non-intermingled; (2) in 25% of cases intermingled. The risks of lesions of the external laryngeal nerve are: (1) 25% overall; (2) 12,5% on the right; (3) 37,5% on the left.

CONCLUSION

The risk of injury of the external laryngeal nerve during thyroid surgery procedure is never zero. It is more important on the left side.

Unusual external branch of the superior laryngeal nerve: a case report

Introduction

The knowledge of the branching pattern of external branch of the superior laryngeal nerve and its relationship with the superior thyroid artery is the key point for identifying the external branch of the superior laryngeal nerve during surgeries of the neck.

Case presentation

During routine dissection of the left head and neck region of a 50 years old female cadaver, we observed a variation of the external branch of the superior laryngeal nerve around the superior thyroid artery. The external branch of the superior laryngeal nerve has presented one medial and three lateral branches. The medial branch was running on the surface of the inferior constrictor and pierced it; where as the lateral three branches are located laterally to the superior thyroid artery. The medial two lateral branches were piercing the substance of the thyroid gland, where as the lateral most branch was communicating with the left sympathetic chain.

Conclusion

It is very important that surgeons carefully dissect the region of the superior pole of the thyroid gland to expose the abnormal branching pattern of external branch of the superior laryngeal nerve prior to ligation of individual thyroid vessels.