Page 303 - Clinical Anatomy

ECA5 7/18/06 6:50 PM Page 288

288 The head and neck

them; a laryngeal carcinoma may thus seed throughout the lymphatic
drainage area of the larynx.

Nerve supply
The nerve supply of the larynx is of great practical importance and com-
prises the superior and recurrent laryngeal branches of the vagus nerve (X).
The superior laryngeal nerve passes deep to the internal and external
carotid arteries where it divides; its internal branch pierces the thyrohyoid
membrane together with the superior laryngeal vessels to supply the
mucosa of the larynx down to the vocal cords. The external branch passes
deep to the superior thyroid artery to supply the cricothyroid muscle.
The recurrent laryngeal nerve has a different course on each side. The
right arises from the vagus as this crosses the front of the subclavian artery,
passes deep to and behind this vessel, then ascends behind the common
carotid to lie in the tracheo-oesophageal groove accompanied by the
inferior laryngeal vessels (Fig. 188). The nerve then passes deep to the infe-
rior constrictor muscle of the pharynx to enter the larynx behind the
cricothyroid articulation.
The left nerve arises on the arch of the aorta, winds below it, deep to the
ligamentum arteriosum, and ascends to the trachea. It then lies in the
tracheo-oesophageal groove and is distributed as on the right side.
The recurrent nerves supply all the intrinsic laryngeal muscles, apart
from the cricothyroid, (supplied by the superior laryngeal nerve), and the
mucosa below the vocal cords.

Clinical features

1◊◊The laryngeal nerves bear relationships to the thyroid arteries which are
of considerable practical importance in thyroidectomy. The external branch
of the superior laryngeal nerve lies immediately deep to the superior
thyroid artery and may be injured in ligating this vessel.
The recurrent laryngeal nerve, lying in the tracheo-oesophageal groove,
is usually behind the terminal branches of the inferior thyroid artery. Occa-
sionally, however, the nerve lies in front of these vessels or passes between
them (Fig. 191). Moreover, when a large thyroid is pulled forward during
thyroidectomy, the nerve becomes dragged forward with it and is therefore
placed in further jeopardy. To avoid nerve damage during ligation of the
inferior thyroid artery, this procedure should be carried out well laterally,
just as the artery emerges from behind the carotid sheath and before it takes
up its intimate and inconstant relationship to the nerve.
2◊◊Damage to the superior nerve causes some weakness of phonation due
to the loss of the tightening effect of the cricothyroid muscle on the cord.
3◊◊Complete division of a recurrent laryngeal nerve causes the cord on the
affected side to take up the neutral (or paramedian) position between
abduction and adduction. Usually the other cord is able to compensate in a
remarkable way and speech is not greatly affected; if both nerves are