Abstract
The cervical branches of the vagus nerve that are pertinent to endocrine surgery are the superior and the inferior laryngeal nerves: their anatomical course in the neck places them at risk during thyroid surgery. The external branch of the superior laryngeal nerve (EB) is at risk during thyroid surgery because of its close anatomical relationship with the superior thyroid vessels and the superior thyroid pole region. The rate of EB injury (which leads to the paralysis of the cricothyroid muscle) varies from 0 to 58%. The identification of the EB during surgery helps avoiding both an accidental transection and an excessive stretching. When the nerve is not identified, the ligation of superior thyroid artery branches close to the thyroid gland is suggested, as well as the abstention from an indiscriminate use of energy-based devices that might damage it. The inferior laryngeal nerve (RLN) runs in the tracheoesophageal groove toward the larynx, close to the posterior aspect of the thyroid. It is the main motor nerve of the intrinsic laryngeal muscles, and also provides sensory innervation to the larynx. Its injury finally causes the paralysis of the omolateral vocal cord and various sensory alterations: the symptoms range from mild to severe hoarseness, to acute airway obstruction, and swallowing impairment. Permanent lesions of the RNL occur from 0.3 to 7% of cases, according to different factors. The surgeon must be aware of the possible anatomical variations of the nerve, which should be actively searched for and identified. Visual control and gentle dissection of RLN are imperative. The use of intraoperative nerve monitoring has been safely applied but, at the moment, its impact in the incidence of RLN injuries has not been clarified. In conclusion, despite a thorough surgical technique and the use of intraoperative neuromonitoring, the incidence of neurological complications after thyroid surgery cannot be suppressed, but should be maintained in a low range.
Highlights
The neurological issues that might appear after thyroid surgery are those related to lesions of motor or sensory nerves whose anatomical course is in the neck
The main structures that are jeopardized during thyroid surgery are those arising from the vagus nerve at various heights: the external branch of the superior laryngeal nerve (EB-SLN) and the inferior laryngeal nerve
In a tertiary care referral center, this morbidity should be maintained in a due range, according to different factors that can generally be preoperatively identified: the incidence of a permanent lesion of the inferior laryngeal nerve in a surgery performed for a benign disease should be maintained below 1%
Summary
The neurological issues that might appear after thyroid surgery are those related to lesions of motor or sensory nerves whose anatomical course is in the neck. The main structures that are jeopardized during thyroid surgery are those arising from the vagus nerve at various heights: the external branch of the superior laryngeal nerve (EB-SLN) and the inferior laryngeal nerve These nerves and their branches have mainly motor activity on the laryngeal muscles, being responsible for both the motility of the vocal cords and of all the distinctive features of one’s voice. THE SUPERIOR LARYNGEAL NERVE The EB-SLN, previously called the “Galli-Curci Nerve,” has been named after the famous Italian opera singer who saw her career declining after a total thyroidectomy performed for a huge goiter in the presence of a remarkably normal motility of the vocal cords This event has been considered related to the lesion of this tiny motor branch (that for this reason was named after the singer) until recently, when it was clarified that Galli-Curci suffered from a physiological decline of her performances due to the normal aging process.
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