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

Abstract

Injury of the external branch of the superior laryngeal nerve (EBSLN) increases the morbidity following a variety of neck procedures and can have catastrophic consequences in people who use their voice professionally. Identification and preservation of the EBSLN are thus important in thyroidectomy, parathyroidectomy, carotid endarterectomy, and anterior cervical spine procedures, where the nerve is at risk. There are large variations in the anatomical course of the EBSLN, which makes the intraoperative identification of the nerve challenging. The topographic relationship of the EBSLN to the superior thyroid artery and the upper pole of the thyroid gland are considered by many authors to be the key point for identifying the nerve during surgery of the neck. The classifications by Cernea et al. ([1992a] Head Neck 14:380-383; [1992b] Am. J. Surg. 164:634-639) and by Kierner et al. ([1998] Arch. Otolaryngol. Head Neck Surg. 124:301-303), as well as clinically important connections are discussed in detail. Along with sound anatomical knowledge, neuromonitoring is helpful in identifying the EBSLN during neck procedures. The clinical signs of EBSLN injury include hoarseness, decreased voice projection, decreased pitch range, and fatigue after extensive voice use. Videostroboscopy, electromyography, voice analysis, and electroglottography can provide crucial information on the function of the EBSLN following neck surgery.

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

“…In humans the ELN runs either superficially or deeply to the inferior pharyngeal constrictor muscle, after which the terminal branches of the ELN penetrate the horizontal and the oblique bellies of the cricothyriod muscle and the inferior pharyngeal constrictor muscle. 10 In our study, all the ELNs except one innervated the cricothyriod muscle and the caudal pharyngeal constrictor muscle. Most of the ELNs (73.3%) only had one branch arriving in the cricothyriod muscle.…”

Total thyroidectomy by loupe magnification: a comparative study

“…The average identification rate of 85.1% over the past 20 years was reported while the recent years demonstrated a higher than 90% success rate of identification [11,27]. The topographic relationship of the external branch of superior laryngeal nerve to the superior thyroid artery and the upper pole of the thyroid gland are considered by many authors to be the key point for identifying the nerve during surgery of the neck [28] while nerve monitoring aided by placement of a special endotracheal tube equipped with electrodes or a disposable nerve stimulator is used to identify the terminal branches of the EBSLN as they enter the cricothyroid bellies allowing their preservation [11,29,30]. The anatomical course of the external branch of the superior laryngeal nerve (EBSLN) is variable, and a consistent approach to its preservation during thyroid surgery is needed to reduce risk of postoperative voice impairment.…”

German Association of Endocrine Surgeons practice guidelines for the surgical treatment of benign thyroid disease

“…The external branch of the superior laryngeal nerve overcrosses, crisscrosses, or undercrosses the superior pole vessels in close proximity to the superior thyroid pole [25,33,52]. Damage to the nerve branch can result in dysphonia with impaired vocal performance in the forms of a reduced frequency range and rapid fatigue.…”

“…Iodine-induced thyrotoxicosis or other forms of thyrotoxic crisis may demand surgery, even if the patient is hyperthyroid, when these conditions are uncontrolled and emergent or refractory to conservative treatment or when such treatment causes severe side effects [25].…”