Incidental presence of non recurrent laryngeal nerve in our series of thyroidectomy

INTRODUCTION

Goiters are managed universally using medications to make it euthyroid and then surgically removed. Among the complications of thyroidectomies, the most dreaded and commonly encountered ones are vocal cord paralysis and post-operative hypocalcaemia. The thyroid surgeon should be familiar with the anatomy of the RLN, including all its anatomical variations.

Recurrent laryngeal nerve (RLN) injury is one of the most important and preventable complications of thyroidectomy which is the cause of post-operative (iatrogenic) vocal cord paralysis.¹ It is also one of the common reasons for litigation after thyroid surgery in the West.²

The RLN arises from the vagus nerve that supplies all the intrinsic laryngeal muscles, except for the crico-thyroid muscles. In thyroid surgery, RLN identification and preservation are fundamental steps. Non-recurrent laryngeal nerve (NRLN) is known as a rare anatomical variant of RLN with the proportion of 0.3%- 0.8% on the right side, and 0.004% (exceptionally rare) on the left side.³

The preservation of proper nerve activity has paramount importance for safer thyroid surgery. Its intra-operative identification and preservation can be a challenge even for the most experienced endocrine surgeons. Thus, early identification of the non-RLN at the beginning of thyroid surgery may minimize the risk of its injury during surgery.

Objectives

To highlight the incidence of NRLN in our series of thyroidectomy cases.

METHODS

In the department of Otorhinolaryngology, Pondicherry a retrospective analysis of all the thyroid surgeries that were operated between August 2006-November 2018 for various indications on a total of 1006 patients was done with specific interest in the lookout for anatomical variant of recurrent laryngeal nerve and findings were recorded.

Inclusion criteria

Inclusion criteria were all the patients with thyroid swelling/goiter irrespective of benign or malignant status as per FNAC; all the patients were in Euthyroid state after confirming with Thyroid profile before surgery.

Exclusion criteria

Exclusion criteria were patients who were not in Euthyroid state; patients who were not fit to undergo the procedure because of severe systemic comorbidities.

All the patients were completely informed regarding the possible outcome and complications and accordingly consent was obtained. Routine blood tests, along with thyroid function tests, thyroid ultrasonography, serum calcium and fine needle aspiration cytology were performed. 96 patients were found to be in hyperthyroid state with toxic features for which anti-thyroid medications were used before surgery to attain the euthyroid state.

Indirect laryngoscopies as well as video-laryngoscopic examinations were performed to evaluate the vocal cord functions 24 hours prior to surgery, immediate post-operative and 48 hours later, in all the patients.

Thyroidectomies were performed by a standard technique of extra capsular dissection. The total thyroidectomy technique involved the removal of the entire gland while in hemi-thyroidectomy, the affected lobe of gland was removed along with the isthumus. Dissection was done avoiding the sharp instruments while tracing the nerve using the brush technique. After identification of the recurrent laryngeal nerve (RLN), it was routinely traced until its entry into cricothyroid membrane. Superior and inferior thyroid vessels were ligated close to the gland and every attempt was made to identify and preserve the parathyroid glands and their blood supply. Wound was closed in layers and finger glove was used as a drain. In the absence of any collection, the drain was removed on an average 2^nd postoperative day and the patient was discharged on the 3^rd day and was asked to report after 7 days for removal of the sutures.

All surgical specimens were routinely subjected to histopathology. Post-operative serum calcium levels were estimated routinely after 48 hours of surgery and then subsequently as required. Transient hypocalcaemia when encountered was treated accordingly. An assessment of symptom relief, RLN injury, transient hypocalcaemia and permanent hypoparathyroidism was noted. Post-operative hypocalcaemia was defined as serum calcium level less than 8.2 mg/dl (normal range 8.2–10.1 mg/dl) in our laboratory. Thyroid hormonal replacement therapy was started postoperatively. A standard dose of 100 µg was administered to both the groups and thyroid function tests were monitored in an interval of every month. Based on their reports, titration of the dosage of L-thyroxine was done on monthly review.

RESULTS

Among the 1006 patients operated, 946 (≈94%) were females and 60 (6%) were males. Age ranged from 21 to 60 years with a mean age of 39 years (Tables 1, 2). A total of 200 patients had difficulty in breathing and 340 had difficulty in swallowing (Table 3). These 540 (53.67%) patients with pressure symptoms were considered for total thyroidectomy and the rest 466 (46.33%) patients which involved only one lobe of the thyroid were considered for hemi-thyroidectomy.

The decision to either do a total thyroidectomy or hemi-thyroidectomy was based on the symptomatology. In compressive symptoms with massive multi nodular goitre involving both the lobes, total thyroidectomy was preferred and hemi-thyroidectomy in others. Also the patients who were diagnosed with Hashimoto’s thyroiditis depending on the FNAC and anti-thyroid antibodies also underwent total thyroidectomy. Bleeding during surgery was variable in both the groups since some of the glands were very vascular. Meticulous dissection was used to minimize the blood loss. We did not use blood or blood products in any of the cases. We dint encounter any case of post- operative temporary or permanent RLN Palsy. No permanent hypoparathyroidism was recorded.

Among all the cases, two patients with MNG who had underwent total thyroidectomy were found to have anatomical variants of recurrent laryngeal nerve (non-recurrent laryngeal nerve) intra operatively (Table 6). In both the patients intraoperatively, on the right side, after careful dissection, the surgeons found that the right recurrent laryngeal nerve was not recurrent and it originated directly from the vagus nerve turning medially into the crico-thyroid membrane (Figure 2) it was isolated and both the thyroid lobes and the isthmus were removed preserving the para-thyroids. Post operatively the patients did not have any complications and the voice was normal.

DISCUSSION

Non-recurrent laryngeal nerve was first reported by Stedman in 1823.⁵ The incidence of the right NRLN is 0.3–1.6% and that of the left NRLN is about 0.04%.⁶ In terms of embryology, the presence of NRLN is closely related to sub-clavian artery anomaly. Normally, the right sub-clavian artery originates from the 4^th arch structure and the RLN originates from the 6^th arch structure. When the heart descends during embryo-genesis, it drags the 6^th arch structure along. Therefore, when it comes to the anomaly of the right sub-clavian artery, the failure in the descending of RLN would occur.^7,8 In 80% of the cases, the right sub-clavian artery travels behind the oesophagus, 15% between the oesophagus and trachea, and in 5% of the cases it courses in front of the trachea. This is called arteria lusoria (Figure 1B).⁹ Its prevalence is estimated around 0.5–2% of the population.^10,11

According to Toniato’s assessment from 31 cases of NRLN (2004), there are 2 types of NRLN, with respect to their origin.¹⁰ Type 1indicates that the NRLN is closely related to the superior thyroid vessels. Type 2 is further divided into sub-types A and B. Type 2a shows that NRLN is parallel and over the trunk of the inferior thyroid artery, meanwhile in type 2b, the NRLN runs parallel to but under or between the branches of the inferior thyroid artery, as shown in Figure 4. In our study, both the cases can be categorized into type1 NRLN and the percentage also amounted to 0.2% and is concurrent with the literature. According to a study done by Hisham, Sarojah, Alvin et al in Malaysia, the overall incidence of non-recurrent laryngeal nerve in their study was 0.2% out of 585 patients in a period of 3 years which was similar to the findings in our study.¹¹ However, in all variations of the NRLN and RLN, the nerve travels to the larynx at the level of cricothyroid joint, close to berry ligament. Therefore, identification of NRLN at this site could minimize the risk of NRLN injury during thyroidectomy.

CONCLUSION

The NRLN is a rare, but clinically relevant structure and is associated with an increased risk in iatrogenic injury especially during thyroid surgeries. Thorough anatomical knowledge and cautious dissection are essential to identify anatomical variants of RLN especially during the beginning of the surgery in order to minimize the risk of post-operative vocal cord paralysis to the patient. Additionally, in embryological terms, the presence of NRLN is mostly associated with right sub-clavian artery anomalies.

Funding: No funding sources

Conflict of interest: None declared

Ethical approval: The study was approved by the Institutional Ethics Committee

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