There are four structures that are to be saved in Thyroidectomy, two nerves and two glands on each side.
The two nerves are Superior laryngeal nerve and recurrent laryngeal nerve.
and the glands are superior and inferior para-thyroid glands.
External branch of Superior Laryngeal Nerve
External branch of superior laryngeal nerve is called the nerve of "Amelita Galli Curci" after a legendary opera singer. Her singing career ended due to damage to this nerve while undergoing surgery for goiter under local anaesthesia.
Identifying the External branch of superior laryngeal nerve
The nerve is usually found in "space of Reeves" that opens up once the medial dissection is performed at the superior pole.
The thyroid lobe is given traction in downward and outward direction to open up the sternothyroid laryngeal triangle or "Joll's Triangle". The sternothyrolaryngeal triangle of Joll is formed laterally by the upper pole of the thyroid gland and the superior thyroid vessels, superiorly by the attachment of the strap muscles to the thyroid cartilage and medially by the midline. On its floor lies the cricothyroid muscle supplied by the External Branch of Superior Lyngeal Nerve.
The superior thyroid artery and vein that divide into anterior and posterior branches. These branches are ligated individually and as close to thyroid as possible. mass ligature of the the artery and vein together can cause inadvertent damage to the nerve and also a risk of developing of aterio-venous fistula.
Classification of External branch of superior laryngeal nerve (Cernea classification)2
Type I - most common presentation - nerve crossing the superior thyroid vessels approximately 1 cm or more above a horizontal plane passing thryough the upper border of superior thyroid pole.
Type IIa - Nerve crossing the vessel less than 1 cm above the horizontal plane of the superior thyroid pole
Type IIb - Nerve below the plane of the superior thyroid pole (highest risk of damage)
Type 1 - Crosses Superior thyroid artery more than 1 cm above upper pole of thyroid
Type 2 - Crosses Superior thyroid artery less than 1 cm above upper pole of thyroid
Type 3 - Crosses Superior thyroid artery under cover of upper pole of thyroid
Type 4 - Descends dorsal to artery and crosses Superior thyroid artery branches immediately above upper pole of thyroid
Friedman has described three variants of the EBSLN
Type 1: The nerve runs superficial to the inferior constrictor muscle.
Type 2: The nerve penetrates the lower part of the inferior constrictor muscle.
Type 3: The nerve runs deep to the inferior constrictor muscle.
The Type 3 variant may account for the fact that many authors state that the nerve could not be identified in the region of the upper pole of the thyroid gland during thyroid surgery.
The morbidity of damage to the external branch of superior laryngeal nerve is loss of the pitch, timber and quality of voice that may jeopardize the professional life of singers, preachers and of all those that use higher pitch notes of speech.
There are distinct features of the damage to the nerve revealed on indirect laryngoscopy - the vocal cord is shorter, hyperemic and may be at a lower level, glottic chink may be oblique due to rotation of posterior commissure to paralyzed side.
The Recurrent Laryngeal Nerve
This nerve was first described by Galen in the second century. unlike in the past when it was believed that "seen is damaged", the paradigm shifted to "not seen is damaged".
The recurrent laryngeal nerve must be seen and preserved in all cases. The incidence of injury to recurrent laryngeal nerve is between 0 to 13%.
Approaches to identification of the nerve.
There are many approaches to identify the nerve but the most commonly followed are inferior, lateral and superior approach. Inferior approach is useful when dealing with large goiter or recurrence.
The nerve is identified as a white shiny structure with almost always a vein (vasa nervosa) running on its surface. The nerve should not be skeleteonized as it may produce ischemic damage.
Lateral approach: after ligation of the superior and inferior poles, the gland is retracted medially. The inferior prarathyroid is dissected away rom the inferior pole and the nerve is sheen as white shiny structure that feels like a string of a guitar.
Inferior approach: This approach involves identification of the the nerve at thoracic inlet where it is often sighted in the recurrent laryngeal triangle. (the recurrent laryngeal triangle - apex of the triangle inferiorly formed by thoracic inlet, trachea medially and laterally the medial edge of retracted strap muscles while superiorly by the lower edge of the inferior pole.) The nerve exits as a single trunk here and this approach is suitable for large cervical thyroid goiters and recurrent disease.
Superior approach: this approach involves identification of ligament of Berry - laryngeal point of entry and inferior cornu of the thyroid cartilage is a a useful landmark.
Tubercle of Zuckerkandl - the nerve lies deep and medial to the tubercle of Zuckerkandl
Recurrent laryngeal nerve and inferior thyroid artery - Nerve lies deep to the artery
Galen's Loop - rarely the sensory branch of the recurrent laryngeal nerve may join the internal branch of superior laryngeal nerve to form Galen's loop.
- Uma Patnaik, Ajith Nilakantan. Identification of External Branch of the Superior Laryngeal Nerve in Thyroid Surgery: Is it Always Possible?. Thyroid Disorders Ther 2013, 2.2
Cernea CR, Nishio S, Hojaij FC. Identification of the external branch of the superior laryngeal nerve (EBSLN) in large goiters. Am J Otolaryngol. 1995 Sep-Oct;16(5):307-11. PubMed PMID: 7503373. (Abstract)
Kierner AC, Aigner M, Burian M. The external branch of the superior laryngeal nerve: its topographical anatomy as related to surgery of the neck. Arch Otolaryngol Head Neck Surg. 1998 Mar;124(3):301-3. PubMed PMID: 9525515. (Abstract).
Friedman M, Lo Savio P, Ibrahim H (2002) Superior laryngeal nerve identification and preservation in thyroidectomy. Arch Otolaryngol Head Neck Surg 128: 296-303.