Relation of Superior Laryngeal Nerve and Superior Thyroid Artery with Superior Pole of Thyroid During Thyroid Surgery

Abstract

The purpose of this study was to evaluate relation between superior thyroid vessels, external branch of superior laryngeal nerve and superior pole of thyroid based on Cernea classification in Jammu population. The present study was conducted on 50 patients in Department of ENT & Head and Neck Surgery, SMGS Hospital, Government Medical College Jammu during a time period of January 2018 to March 2020. Patients undergoing selective thyroid surgeries for various pathologies were included in the study. Patients with preoperative vocal cord palsy and patients with malignant thyroid neoplasms were excluded from the study. All patients were operated under general anaesthesia, with supine neck extended position. The bifurcation and the branches of STA were meticulously dissected preserving all the branches and any anastomoses if present. Once visualization of the nerve was attained, various measurements were taken to assess Cernea classification type. Depending on extent of lesion appropriate surgical procedure was done so as remove all the diseased tissue. Out of total 62 lobes, Cernea’s Type 1 pattern was seen in 33 (53.2%) of patients, Cernea’s Type 2a was seen in 11 patients (17.7%) and Cernea’s Type 2b was seen in 14 patients (22.5%). No specific pattern was seen in 4 (6.4%) of patients. Cernea classification system is a simple and reliable guide to identify and preserve the nerve.

Introduction

The superior laryngeal nerve (SLN) arises from the vagus nerve close to the caudal end of nodose ganglion and descends in neck behind the external carotid artery to the carotid bifurcation. At the level of hyoid bone, it divides into an internal (sensory) branch and an external (motor) branch. The internal branch perforates the thyrohyoid membrane, providing sensory innervation of the pharyngeal and laryngeal mucosa from the base of the tongue to glottis and subglottic region. The course of EBSLN (external branch of superior laryngeal nerve) is more caudal and near the superior thyroid vessels and thus it is at risk of lesion during thyroidectomy. After SLN, the EBSLN runs in close proximity to the medial aspect of superior thyroid artery and curves medially to provide motor innervation of the cricothyroid muscle [1].

The relationship between the nerve and the standard an atomical landmarks—the superior thyroid artery (STA) and the superior pole of the thyroid—is highly variable. In addition, there is considerable an atomical variability of both artery and superior pole themselves [2].Although different classifications describe the nerve’s path in relation to the superior thyroid artery (STA) Cernea [3] and Kierner [4] and relationship between the entryof the nerve into the CTM, the STA and the cricoid cartilage, Friedman [5], Selvan [6], the Cernea scheme is commonly used in clinical research and practice. In Cernea’s [3] classification, in most of patients, nerve crosses medially into the cricothyroid muscle more than 1 cm cranially to upper pole (Cernea’s type I). In remaining patients, the EBSLN runs within a distance of < 1 cm from the upper pole of thyroid gland. Half of these patients, the nerve remains cranial to upper pole of thyroid gland (Cernea’s type II), while in remaining cases, the ESBLN has a more caudal course and lies below the superior thyroid pole (Cernea’s type III).

Because of the close anatomical relationship between the EBSLN and the thyroid gland, the nerve is especially in danger of inadvertent trauma during thyroid surgery, inflammation and fibrosis such as in thyroiditis, malignancy, radiation damage or previous surgery, increases that risk [2]. Injury to EBSLN results in paralysis of cricothyroid muscle results in voice changes characterized by loss of high tone and pitch volume and fatigue after extensive use. Such changes are usually well tolerated by most patients, but may be career threatening in voice professionals, such as singers, public speakers, teachers and lawyers. The reported incidence of injury to EBSLN ranges from 0 to 20 per cent in literature with most studies quoting a rate of < 5% [2].

Meticulous dissection is therefore imperative to avoid injury to the ELN, thus it is of utmost importance to have adequate knowledge of the anatomic variations of the course of the nerve, its relation to the superior thyroid artery (STA) and to relate the position of the ELN to the superior pole of the thyroid gland. Hence, we undertook this study to determine these relations according Cernea’s classification system.

Materials and Methods

This is a prospective study of 50 patients who underwent surgery for thyroid neoplasms at our department between January 2018 and March 2020. Patients undergoing selective thyroid surgeries for various pathologies were included in the study.

All patients included in study underwent preoperative laryngoscopic evaluation. Patients with preoperative vocal cord palsy and patients with malignant thyroid neoplasms were excluded from the study. Risks and consequences of the suggested surgery were explained to the patient and written informed consent was taken each time.

All patients were operated under general anaesthesia, with supine neck extended position. Collar incision (two finger breadth above suprasternal notch) was used and superior and inferior sub-platysmal flaps raised. If necessary straps were divided to aid direct visualisation of the EBSLN. The bifurcation and the branches of STA were meticulously dissected preserving all the branches and any anastomoses if present. The area of the inferior constrictor, cricothyroid muscles and around the superior pole of the thyroid was carefully observed in order to visualize the EBSLN. Once visualization of the nerve was attained, various measurements were taken to assess Cernea classification type. Where required, operating microscope was also used. Depending on extent of lesion appropriate surgical procedure was done so as to remove all the diseased tissue. The wound was closed and suction drain kept.

Results

Out of total 50 patients, 43 were females and 7 were males. The mean age of presentation was 39.7 ± 6.92.

Out of 50 patients undergoing thyroidectomies, 28 underwent hemi-thyroidectomy; right 15 and left 13. 10 patients underwent subtotal thyroidectomy and 12 patients underwent total thyroidectomy.

In our study, out of total 62 lobes, Cernea’s Type 1 pattern was seen in 33 (53.2%) of patients, Cernea’s Type 2a was seen in 11 patients (17.7%) and Cernea’s Type 2b was seen in 14 patients (22.5%). No specific pattern was seen in 4 (6.4%) of patients.

Discussion

Thyroid surgery was associated with high mortality rates during early nineteenth century. The high mortality was attributed to lack of meticulous dissection techniques and asepsis [7]. With advanced surgical techniques, mortality has almost disappeared, but morbidity remains a concern for most of the surgeons. Mostly the morbidity following thyroid surgery is due to technical failure to identify the vital structures and variation in surgical anatomy of thyroid gland. The Cernea classification is beneficial and educational for predicting the intraoperative risk associated with EBSLN during surgery.

Most of patients in our study belonged to the age group of 41–50 years with mean age of presentation at 39.7 years. Majority of the patients were females, which is in accordance to increased incidence of benign thyroid disease in middle aged females.

Majority of patients in our study (28) underwent hemi-thyroidectomy, among which right hemi-thyroidectomy was done in 15 patients and left hemi-thyroidectomy was done in 13 patients. This is explained by relatively small size of thyroid swelling at the time of presentation. Females of middle age group may seek immediate medical attention for cosmetic disfigurement caused by thyroid swelling. However, 10 patients underwent subtotal thyroidectomy and 12 patients underwent total thyroidectomy. These patients had relatively large goitres and/or involvement of both lobes of thyroid gland.

For determination of anatomical relation between upper pole of thyroid, STA and EBSLN, thyroid lobes were studied individually. Hence 12 patients who underwent total thyroidectomy were considered as 24 lobes, thus total lobes in our study were 62. The percentage of each pattern varies among patients with small or large goitres owing to anatomical alterations that take place as the gland enlarges. Maximum number of lobes in our study belonged to Cernea’s Type 1 group (53.2%), which fortunately has lowest risk of nerve injury during thyroidectomy. Here the EBSLN crosses STA at more than 1 cm away from the superior pole of thyroid gland. According to Cernea et al. Type 2a and 2b nerves are considered to be the nerves at an increased risk of iatrogenic lesion during a thyroidectomy, owing to their low-lying course. Cernea’s Type 2a was seen in 11 lobes (17.7%) and Cernea’s Type 2b was seen in 14 lobes (22.5%). Here the EBSLN crosses STA less than 1 cm away from superior lobe of thyroid gland. However, no specific pattern was seen in 4 (6.4%) of patients in our study. In one patient undergoing total thyroidectomy, multiple tiny, twig-like nerve branches were observed in place of EBSLN on both sides, making categorisation into one of the Cernea’s groups difficult. Another patients undergoing total thyroidectomy had a large thyroid tumor with grossly altered anatomy making the description of vascular and neural structures difficult in both the lobes. Seven et al. [8] found the ELN was consistent with type 1 in 51.8% lobes and type 2 in 48.2% lobes; type 2a in 37.1% and type 2b in 11.1%. Cernea CR et al. found Type 1 pattern in 60%, Type 2a in 17%, Type 2b in 20% and 3% patients, nerve was not identified.

Conclusion

External branch of superior laryngeal nerve preservation during thyroidectomy poses a challenging task for the surgeon because of unpredictable variation in the course of nerve. In depth knowledge of common variations in EBSLN anatomy is an absolute necessity for the operating surgeon in the careful dissection and preservation of the facial nerve thyroidectomy. Cernea classification system is a simple and reliable guide to identify and preserve the nerve.

Funding

None.

Compliance with Ethical Standards

Conflict of interest

None.

Ethics Approval

The study was approved by Institutional Ethics Committee.