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The Recurrent Laryngeal Nerve and Thyroid Surgery; Who to Scope, When to Visualize, Who to Stimulate

Aruyaru Stanley Mwenda

Aga Khan University, Nairobi

Correspondence to: Dr. Aruyaru Stanley Mwenda, P.O Box 30270-00100 Nairobi, Kenya.

Email:arumwesta@gmail.com

 

Summary

Thyroid surgery is a common general and specialist surgical procedure. Recurrent laryngeal nerve injury during thyroid surgery, though rare, is the most feared surgical complication. Various steps and perioperative assessments can minimize recurrent laryngeal nerve injury. In this opinion article, two clinical vignettes are used at the introduction to discuss this topic. Literature is reviewed and conclusions made in the aspects of intra-operative recurrent laryngeal nerve exposure, the utility of intra-operative nerve monitoring and the use of peri-operative laryngoscopy where indicated. In conclusion, the literature shows that nerve exposure during thyroidectomy is a must. Nerve monitoring does not reduce the incidence of recurrent laryngeal nerve injury. All patients with pre-operative voice changes, cancer, prior head and neck surgery and those due for re-do thyroidectomy require pre-operative laryngocsopy.

 

Keywords: Recurrent Laryngeal Injury, Thyroidecto-my, Nerve Exploration, Laryngoscopy

Ann Afr Surg. 2016;13(2): 72-6.

DOI: http://dx.doi.org/10.4314/aas.v13i2.9

Introduction

Thyroid surgery is a common general and specialist procedure (1). Larynx and trachea form the surgical bed irrespective of extent (1). Recurrent laryngeal nerve palsy is the feared complication post thyroid surgery (2). The recurrent laryngeal nerve is a branch of the vagus nerve carrying motor and sensory supply to the larynx. It has the sole motor supply to the sole abductor of the cord (posterior cricoarytenoid) (2). The following two clinical vignettes and the accompanying questions will assist us in the discussion of the topic of the recurrent laryngeal nerve during thyroid surgery. The aim of this article is to revisit the topics of nerve exploration during thyroid surgery, the need and indications for peri-operative laryngoscopy and role of intra-operative nerve stimulation.

 

Case 1

A 49 year old female with no co-morbidities presented to our clinic after an incidental finding of anterior neck swelling during ENT review for short lived sore throat. She denied any symptoms of hyper- or hypothyroidism. She did not have pressure or infiltrative symptoms and her medical history was unremarkable. Examination was remarkable for a right nodular goitre. She was clinically and biochemically euthyroid. Ultrasound revealed multiple mixed nodules and image guided cytology showed suspicious follicular cells. She was scheduled for surgical lobectomy to get a histological diagnosis. Intra-operatively capsular dissection was carried out. The recurrent laryngeal nerve was visualized in the tracheoseophangeal groove and protected. Histology was benign. She complained of a sore throat the following day but was reassured and discharged. Six weeks later she presented again with persistent hoarseness and episodes of breathlessness. Indirect laryngoscopy showed immobile paramedian right vocal cord.

​What’s the problem? Is her recurrent laryngeal nerve injured? Is this permanent or transient palsy? How should we proceed next?

 

Case 2

A 42 year old female with controlled asthma presented to our clinic with a long standing progressive anterior neck swelling. This was painless but was associated with recent onset of dysphagia and hoarseness. She denied any symptoms of hyper- or hypothyroidism. Examination revealed a right lobe nodular goitre with retrosternal extension. She was clinically and biochemically euthyroid. Neck ultrasound revealed an enlarged right thyroid lobe with mixed nodules and retrosternal extension. The fine needle aspiration cytology was benign. She was schedule for surgery based on her pressure symptoms. Pre-operative indirect laryngoscopy was normal. Intra-operatively a subcapsular right lobectomy was performed. The recurrent laryngeal nerve was not explored. She made uneventful post operative recovery. She is due for follow-up in the clinic.

What if she comes with hoarseness during the follow up visit? Should we do laryngoscopy during her next visit?

 

Discussion

Anatomic Variation

Anatomic variation is the main reason for most nerve injuries (1). These variations can occur in the pattern of division, relations of the nerve to the inferior thyroid artery and its branches and the existence of the nerve in a non-recurrent fashion (1-3). It is worth noting that up to 28 variations have been described in anatomy studies (2). Similarly, variations have been assessed relative to the ligament of berry and the tubercle of Zuckerkandl (3). But for the surgeon, it is easier to look at these variations relative to the inferior thyroid artery and its branches as the surgeon has to always address this artery as a step in thyroid surgery. One way is to classify the recurrent laryngeal nerve into type A (anterior to the artery), type B (between branches of the artery) or type C (posterior to the artery) (1, 2).

​In a systematic review and meta analysis of 32 papers with 8655 recurrent laryngeal nerve sides assessing for the anatomic variation of the nerve relative to the inferior thyroid artery, Ling et al found the nerve to anterior (type A) in 20%, in between the branches (type ) in 28% and posterior(type C) in 52% of the cases (1). These findings are reflected in a local dissection study by Kaisha et al which was included in the Meta analysis by Ling et al (3). In the same systematic review, the authors reviewed 21 articles with 38,568 recurrent laryngeal nerve sides searching for a non-recurrent laryngeal nerve as a variation. They found the prevalence of a non-recurrent laryngeal nerve to be 0.57% (1). Although the sides were not indicated, it is common anatomic knowledge that a non-recurrent nerve is usually on the right owing to alterations in vascular embryology of the head and neck.

​Risk Factors for Recurrent Laryngeal Nerve Injury Recurrent laryngeal nerve injury is classified as transient or permanent. Permanent injury is diagnosed after 12 months of persistent palsy (4). Permanent injury will occur in 0-6% of surgeries while transient injury/palsy occurs in 3-12% (1, 4, 5). The mechanisms of injury vary including ligation, traction, clamping, diathermy and ischemia (4). Transection occurs in only 0.3% of the injured nerves with majority of the injuries occurring on intact nerves (4). There’s a slight preponderance to the right but this is not strongly supported as most of the documented injuries lack indication of the affected side (4). Various risk factors have been postulated to contribute to nerve injury (4). Firstly, re-operation increases risk of permanent injury by 2-30%. This is due to altered tissue planes and difficult nerve visualization. In re-operation for cancer surgery, the rates of nerve injury are up to 6%. Secondly, cancer surgery is associated with 20-50% incre