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(true vocal cords)

_ Subglottic larynx figure 1-3 External laryngeal relationships. Anterior (A) and lateral (B) views. Note the position of the true vocal cords (vocal folds) in the midlarynx. The cricoid cartilage shows the configuration of a reversed signet ring. The inferior cornu of the thyroid cartilage is close to the entry point of the inferior laryngeal nerve. C, Lateral view of the interior of the larynx. Anterior surface to the left. Note the relationships of the ventricular fold (false vocal cord), ventricle and vocal fold (true vocal cord), and their locations. The subglottic larynx lies between the glottis and inferior cricoid border. D, Diagram of interior configuration of larynx (anterior view). Note the dome-shaped airway beneath the glottis. This is the conus elasticus, shaped by intrinsic muscles. See Chapter 35, "Laryngologic Problems Related to Tracheal Surgery," for description of intrinsic laryngeal musculature.

(Figure 1-4). In many old people, the trachea becomes increasingly horizontal in its course from the larynx to the carina and may approach a nearly transverse position. This worsens with severe kyphosis. The sternum also tends to flare out with aging. The larynx lies closer to the sternal notch with increasing age and the trachea loses mobility upon attempted cervical extension. This explains how subglottic damage may be occasioned by upward and backward erosion of a tracheostomy tube, even though the stoma was placed at a correct level in the trachea. In youth, a large proportion of the trachea presents in the neck above the level of the sternal notch even when the neck is in neutral position. With extension, more than half of the trachea rises into the neck, and sometimes, by as much as two-thirds (see Figure 1-4A). In contrast, attempted cervical extension in old age may bring very little, if any, trachea into the neck (see Figure 1-4B). The surgical implications are clear. The amount of trachea that can be brought into the neck on hyperextension of the cervical spine determines the percentage of trachea that may be resected and approximation obtained by cervical flexion alone.8

The esophagus lies in close relation to the trachea throughout its course (Figure 1-5). The esophagus commences at the level of the posterior cricoid, attached to it by the sling of cricopharyngeus muscle. Since the esophagus is a little to the left, the right posterior margin of the trachea is immediately in front of the vertebral bodies. In inflammatory disease, this portion of the posterior tracheal wall can adhere to the vertebral bodies. A layer of areolar tissue lies between the membranous wall of the trachea and the esophagus. This close juxtaposition of the walls of these two organs has been termed the "party wall." Normally, the plane is easily separable. A common blood supply, as noted below, is shared by these two tubular organs.

Anteriorly, the thyroid isthmus usually crosses and is closely applied to the trachea at the level of the second and third rings (see Figure 1-5A). The isthmus is sometimes very broad, but in a very few patients is absent. The pyramidal lobe commonly arises from the isthmus, often slightly to the left. The lateral lobes of the thyroid gland are also closely applied to the anterolateral and lateral walls of the trachea. Multiple small blood vessels, lymphatic channels, and fibrous attachments bind the isthmus and adjacent portions of the thyroid lobes to the tracheal wall.9 The inferior thyroid artery supplies the lower portion of the thyroid gland and contributes importantly to the blood supply of the upper trachea. Details are provided below.

The superior laryngeal nerves concern the tracheal surgeon in connection with laryngeal release procedures and thyroidectomy. An external branch lies deep and parallel to the superior laryngeal artery and innervates the cricothyroid muscle. It gives a branch to the inferior pharyngeal constrictor. The internal branch passes into the thyrohyoid membrane with the superior laryngeal artery. It provides sensation to laryngeal mucosa and hence reflex protection to the larynx.10

The recurrent laryngeal nerves follow different courses right and left (see Figure 1-5). The left nerve originates from the vagus beneath the arch of the aorta and lies close to the tracheoesophageal groove along its entire course. The right nerve loops around the subclavian artery and therefore approaches the tracheo-esophageal groove from a more lateral position. The right recurrent laryngeal nerve often passes between branches of the right inferior thyroid artery whereas the left often is posterior to the left inferior thyroid artery.10 They enter the larynx between the cricoid and thyroid cartilages deep to the inferior cornua of the thyroid cartilage, behind the articulation of the thyroid and cricoid cartilages, to innervate the intrinsic laryngeal muscles.10-12 Small branches travel to the trachea, trachealis muscle, esophagus, and inferior constrictors, including the cricopharyngeus muscle. Proximal branches near the recurrent nerve loops lying beneath the right subclavian artery and aorta on the left contribute to the cardiac plexus intrathoracically.10

Rarely, the right inferior laryngeal nerve is not recurrent but crosses the neck transversely from the vagus in one or more branches to enter the larynx. This occurs in conjunction with an anomalous right subclavian artery arising from a left aortic arch and passing posterior to the esophagus. The nonrecurrent nerve passes from the vagus beneath the carotid artery, may have two terminal branches, and may also give off branches to the trachea, esophagus, and thyroid. Even more rarely, the left inferior laryngeal nerve may be nonrecurrent in conjunction with the right aortic arch and left retroesophageal aberrant subclavian artery. Estimated incidence is 0.63% on the right and 0.04% on the left.13

The left brachiocephalic vein is well anterior to the pretracheal plane. The brachiocephalic artery, however, crosses over the midtrachea obliquely from its point of origin from the aortic arch to reach the right side of the neck (see Figures 1-5 through 1-7). In children, the artery rises higher and is encountered in the lower part of the extended neck. In young adults also, this artery crosses the trachea at the base of the neck with even moderate cervical extension. Thus in the young, a large proportion of the trachea and the bra-chiocephalic artery regularly rise into the neck on extension (see Figure 1-4). If a tracheostomy is placed in a child or young adult with reference to the sternal notch rather than the cricoid cartilage, it is easy to see how tracheal arterial fistula can occur (see Chapter 13, "Tracheal Fistula to Brachiocephalic Artery"). The brachiocephalic artery branches into the right common carotid and subclavian arteries a short distance to the right of the trachea and behind the origin of the internal jugular vein. The left common carotid nor mally arises a short distance from the origin of the brachiocephalic artery from the aorta forming a "V" slightly to the left of the tracheal midline. The brachiocephalic artery and the left common carotid artery may arise from a common arterial trunk, which overlies the trachea (see Figure 1-7).14 Anatomic variation can be important if the trachea is adherent to the back of a common trunk (see Figure 1-7) as a result of inflammation or prior tracheal surgery. Occasionally (less than 10%), a small thyroidea ima artery arises from the back of the brachiocephalic artery and travels superiorly to the thyroid gland.

At the carinal level, the left main bronchus passes beneath the aortic arch and the right main bronchus beneath the azygos vein. The superior vena cava lies just anterior and to the right of the trachea. The pulmonary artery lies inferiorly in front of the carina (see Figures 1-5, 1-6). Thus, in anterior approach to the carina, a deep quadrilateral space is developed transpericardially in front of the carina, bordered by the

Right vagus nerve

Right subclavian artery

Right recurrent laryngeal nerve

Right and left brachiocephalic veins

Brachiocephalic artery

Superior vena cava

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