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.

Utility of video-assisted method for identifying and preserving the external branch of the superior laryngeal nerve during thyroidectomy.

Background: The EBSLN is vulnerable to damage during thyroidectomy, results in voice related complications, negatively affect patient quality of life, routine identification of the EBSLN prior to surgical manipulation is necessary for a complication-free thyroidectomy. We aimed to validate a video-assisted procedure for identifying and preserving the external branch of the superior laryngeal nerve (EBSLN) during thyroidectomy and analyze the EBSLN Cernea classification and the localization of the nerve entry point (NEP) from the insertion of the sternothyroid muscle. Methods: A prospective descriptive study was performed; 134 patients, who scheduled for lobectomy with an intraglandular tumor max diameter ≤ 4 cm and without extrathyroidal extension, were randomly divided into the video-assisted surgery (VAS) and conventional open surgery (COS) groups. We used the video-assisted surgical procedure for visually identifying the EBSLN directly, and compared the differences in the visual identification rate and total identification rate of the two groups. We also measured the localization of the NEP using the insertion of the sternothyroid muscle as a reference. Results: There was no statistically significant difference in clinical characteristics between the two groups. The visual identification rate and total identification rate were significantly higher in the VAS group than the COS group (91.04% vs. 77.61%, 100% vs. 89.6%). The EBSLN injury rate was 0 in both groups. The mean vertical distance (VD) of the NEP from the sternal thyroid insertion was 1.18 mm (SD 1.12 mm, range, 0-5 mm), with approximately 88.97% of the results occurring within the 0-2 mm range. The mean horizontal distance (HD) was 9.33 mm (SD 5.03 mm, range, 0-30 mm), with over 92.13% of the results occurring within the 5-15 mm range. Conclusion: Both the visual and total identification rates of the EBSLN were significantly higher in the VAS group. This method provided a good visual exposure rate of the EBSLN, aiding in identifying and protecting the EBSLN during thyroidectomy.

Role of Stroboscope in Injury of External Branch of Superior Laryngeal Nerve During Thyroid Surgery.

Role of stroboscope in injury of External branch of superior laryngeal nerve during thyroid surgery. Study conducted in a tertiary care hospital. 40 patients were selected and divided into two groups as Group A and B. Benign thyroid swellings were included, excluding preoperative vocal cord pathology by performing videolaryngoscope and videostroboscope. After thyroidectomy procedure stroboscopic fundamental frequency, symmetry, periodicity, glottic closure and mucosal wave pattern were assessed in both the groups and compared. The mean difference in fundamental frequency between pre operative and postoperative in Group A was 37.85 (SD = 33.69) and in Group B was 58.40 (SD = 77.55) with p-value of 0.287. Symmetry of cords in Group A was 90% and asymmetry was 10%, while in Group B symmetry of cords was 75% and asymmetry of 25% with p-value of 0.407. Other parameters like regular periodicity, complete glottic closure, normal mucosal pattern was 95% in Group A and 75% in Group B. Irregular periodicity, incomplete glottis closure, decreased mucosal wave pattern was 5% in Group A and 25% in Group B. Stroboscope is an essential and useful tool in diagnosing EBSLN injury. It is useful in assessing pre operative voice assessment before and after thyroid surgery than a video laryngoscope.

Can we routinely identify the external branch of the superior laryngeal nerves with neural monitoring?: a prospective report on 176 consecutive nerves at risk.

The external branch of the superior laryngeal nerve (EBSLN) provides motor function to the cricothyroid muscle (CTM). EBSLN damage produces changes in voice quality and projection. Intraoperative neuromonitoring (IONM) in thyroid surgery aims to optimize EBSLN control during dissection. We prospectively collected the data of 88 consecutive patients who underwent total thyroidectomy with IONM from July 2019 to December 2019. IONM was offered in the intermittent mode of application. We routinely searched for the EBSLN electromyographic (EMG) signal before (S1) and after (S2) dissection of the superior vascular peduncle. In the absence of the EMG signal, we observed the CTM twitch. We identified 141 (80%) S1 EMG signals, while we recorded the CTM twitch in 15 cases (8.5%). In 20 (11.3%) cases, we were unable to identify the EMG signal. Analysing the S2 results, we found loss of EBSLN signal in 11/141 cases (7.8%) identified with IONM in pre-dissection stimulation. Among the 20 cases without pre-dissection identification (we had not identified the external branch of the superior laryngeal nerve or the muscle twitch), in the post-dissection evaluation, we confirmed the loss of signal in 17 of 20 cases, equal to 85% (p < 0.001). Our data clearly show that intraoperative stimulation and recognition of EBSLN, performed before any dissection manoeuvre to the superior vascular thyroid pole, leads to a much higher rate of nerve conservation.

Factors Influencing the Relationship of the External Branch of the Superior Laryngeal Nerve with the Superior Pole Vessels of the Thyroid Gland.

OBJECTIVES: In a thyroidectomy, the external branch of the superior laryngeal nerve (EBSLN) is a potential risk during the superior pole dissection due to its close anatomical relationship with the superior thyroid artery and its highly variable anatomy. In this study, we aimed to evaluate the relationship of EBSLN with the superior pole considering Cernea classification and the factors affecting this relationship. METHODS: The data of thyroidectomized 126 patients (95 female, 31 male) with 200 neck sides (mean age of 45.6±12.1 years) using intraoperative neuromonitoring (IONM) for the EBSLN exploration were evaluated retrospectively. During the superior pole dissection, the EBSLN course was classified according to Cernea classification after being confirmed with IONM. It was defined as a large goiter in the case of the thyroid lobe volume being >50 cc. The factors influencing the presence of type 2b, which has the highest risk of injury, were evaluated using logistic regression analysis. RESULTS: Of the 200 EBSLNs evaluated, 52 (26%) were type 1, 134 (68%) were type 2a, and 14 (7%) were type 2b. The mean volumes of the resected thyroid lobes were 22±25 cc (min-max: 2-136), 23±20 cc (3-163), and 39±24 cc (3-65) in type 1, 2a and 2b, respectively, which was significantly higher in type 2b (p=0.035). Presence of large goiter rates were 5.8% (n=3), 8.2% (n=11), 64.3% (n=9) in type 1, 2a, and 2b, respectively, and was significantly higher in type 2b (p=0.0001). There was no significant difference between EBSLN Cernea types concerning age, sex, nerve side, presence of cancer and hyperthyroidism. In logistic regression analysis, large goiter was the only independent factor associated with Cernea type 2b. In case of a lobe volume greater than 50 cc, the probability of type 2b presence was approximately 25 times higher (p<0.001, odds ratio: 25.262). CONCLUSION: Type 2b course of EBSLN is more common in large goiters, and it is 25 times more likely to be seen in the presence of a lobe volume over 50 cc. Thus, it should be considered that the probability of this high-risk course is significantly higher in large goiters.

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.

Correlation between the Cernea Classification of External Branch of Superior Laryngeal Nerve in Relation to the Ultrasound-based Volume of Thyroid Gland.

INTRODUCTÍON: Goiter is a very common problem dealt with by surgeons. Surgical treatment of thyroid requires removal of a part (hemi) or whole of the gland (total thyroidectomy). The external branch of the superior laryngeal nerve (EBSLN) is an important but less researched structure to be preserved during surgery. Various studies have described the incidence of different types of EBSLN, but have not described regarding the relationship between the change in volume of the gland to the nerve. MATERIALS AND METHODS: A prospective analysis of 100 patients who underwent total thyroidectomy in our department was done. All patients underwent preoperative ultrasonography and the volume of the gland was calculated. Intraoperatively, the EBSLN was identified and preserved prior to ligating the superior thyroid vessels. The nerve was classified as per the Cernea classification. The gland was divided into high and low volume, taking 20 ml as the cutoff. The incidence of Type 2 nerve in a low-volume gland was compared with that of a high-volume gland. RESULTS: In 100 patients (200 nerves), 191 nerves were identified. The nerve was type 1 in 56/200 (28%), Type 2a in 116/200 (58%), and Type 2b in 19/200 (9%) patients. In large-volume glands, Type 2 nerve was more common (87%). CONCLUSION: Dissection of thyroid gland requires expertise to preserve the EBSLN. Large volume glands pose a more difficult challenge, as the gland is more closer to the nerve.

Contribution of intraoperative neural monitoring to preservation of the external branch of the superior laryngeal nerve: a randomized prospective clinical trial.

PURPOSE: The purpose of this study was to evaluate the effect of intraoperative neuromonitoring (IONM) on the injury rate of the external branch of the superior laryngeal nerve (EBSLN) during thyroidectomy. METHODS: A total of 133 consenting patients (98 female, 35 male; mean age, 45.6 ± 11.7 years) undergoing thyroidectomy were randomly assigned to 2 groups. In group 1 (n = 65 patients, 105 nerves), superior thyroid pole dissection was performed with no attempt to identify the EBSLN; in group 2 (n = 68 patients, 106 nerves), IONM was used to identify the EBSLN during surgery. EBSLN function was evaluated by intraoperative electromyography of the cricothyroid muscle. The EBSLN Voice Impairment Index-5 (VII-5) was conducted preoperatively and at 1, 3, and 6 months postoperatively. The primary outcome was the prevalence of EBSLN injury. The secondary outcomes were the identification rate of the EBSLN using IONM and changes in postoperative voice performance. RESULTS: EBSLN injury was detected in eight (12.3%) patients and nine (8.6%) nerves in group 1 and in one (1.5%) patient and one (0.9%) nerve in group 2 (patients, p = 0.015; nerves, p = 0.010). IONM contributed significantly to visual (p < 0.001) and functional (p < 0.001) nerve identification in group 2. The VII-5 indicated more voice changes in group 1 than 2 at 1, 3, and 6 months postoperatively (p = 0.012, p = 0.015, and p = 0.02, respectively). CONCLUSION: IONM contributes to visual and functional identification of the EBSLN and decreases the rate of EBSLN injury during superior pole dissection. Routine use of IONM to identify the EBSLN will minimize the risk of injury during thyroidectomy.

Prospective validation study of Cernea classification for predicting EMG alterations of the external branch of the superior laryngeal nerve.

PURPOSES: Cernea classification is applied to describe the external branch of the superior laryngeal nerve (EBSLN). Using intraoperative neural monitoring we evaluated whether or not this classification is useful for predicting which EBSLN subtype has an increased risk of injury. METHODS: An analysis of 400 EBSLN. The identification of EBSLN was achieved with both cricothyroid muscle twitch and the glottis evoked electromyography response. We defined S1 initial EBSLN stimulation at identification and S2 final nerve stimulation achieved in the most cranial aspect of the nerve exposed above the area of surgical dissection after superior artery ligation. RESULTS: The mean S1 amplitude acquired was 259+/67 (180-421), 321 +/79 (192-391), 371 +/38 (200-551) µV, respectively, for type 1, 2A, 2B (p = 0.08). The S1 and S2 amplitudes were similar in type 1 (p = 0.3). The S1 and S2 determinations changed significantly in type 2A and 2B (p = 0.04 and 0.03). EBSLN which demonstrated a >25 % decreased amplitude in S2 increased significantly from Type 1 (4.9 %) to Type 2A (11.2 %) and 2B (18 %) (p = 0.01). None of type 1, 2.8 % type 2A and 3 % type 2B showed a loss of EBSLN conductivity. The latency determinations did not vary significantly for any parameter compared. CONCLUSIONS: The Cernea classification was, therefore, found to predict the risk of EBSLN stress. We identified amplitude differences between S1 and S2 determinations in type 2A and 2B, thus confirming that surgical dissection in these subtypes is, therefore, extremely difficult to perform.