Clinical case: Button battery ingestion

Objectives

• The surgical anatomy of a tracheostomy and the conditions under which this procedure is done rather than a cricothyrotomy.
• The structure of the larynx including its cartilages , ligaments and compartments.
• The muscles of the larynx, including their attachments, innervation and actions. Also, the clinical aspects of damage to the nerves that innervate the muscles of the larynx.

Tracheostomy and cricothyrotomy

A cricothyrotomy (also called crike, thyrocricotomy, cricothyroidotomy, inferior laryngotomy, intercricothyrotomy, coniotomy or emergency airway puncture) is an incision made through the skin and cricothyroid membrane to establish an alternative air passage when the normal airway is compromised such as airway obstruction by a foreign body, angioedema, or massive facial trauma. Cricothyrotomy is almost always performed only when orotracheal and nasotracheal intubation are impossible or contraindicated.

Cricothyrotomy is easier and quicker to perform than tracheotomy. However, whereas cricothyrotomy may be life-saving in extreme circumstances, this technique is only used until a permanent airway can be established. The cricothyroid membrane is bounded by the cricoid cartilage inferiorly and the thyroid cartilage superiorly (Figures 7&12).

In older children and adults, the laryngeal prominence at the upper border of the thyroid cartilage is easily felt. The thyroid cartilage can then be followed inferiorly to locate the cricothyroid membrane. In infants and younger children, the laryngeal prominence is not developed, making it difficult to identify the thyroid cartilage. Thus, in such cases the tracheal rings can be followed superiorly to locate the prominence of the cricoid cartilage. The cricothyroid membrane is located just superior to the cricoid cartilage. However, the larynx is located relatively higher in a child than in an adult (Figure 8; compare the vertebral levels in A and B) so the physician needs not to be confused by the relatively high level of this membrane in young children.

Performing a tracheostomy (artificial air passage in trachea) is more difficult in pediatric patients than in adults because the trachea is very soft and pliable, the neck is short and the dome of the pleura extends into the neck and is thus vulnerable to injury. A tracheostomy is done between the cricoid cartilage and first tracheal ring (Figure 7).

Structure of the larynx

The larynx functions as an organ of phonation and is also an air passageway and sphincteric mechanism (Figure 9).

It extends from the root of the tongue to the trachea. In sagittal section, its upper end (the tip of the epiglottis) lies at C3 and its lower ends (lower border of cricoid) at C6 - but it is slightly higher in women than in men and, as indicated above, it is also higher in children (Figure 8). When the neck is extended, the larynx rises relative to the vertebrae and when the neck is flexed, the larynx is lowered. During swallowing the larynx undergoes a major excursion in which the upward movement of the thyroid cartilage can be seen and felt. 

Relations of the Larynx

The relations of the larynx are the following:

• Posteriorly: pharynx (it forms anterior wall of pharynx) and retropharyngeal space
• Laterally: thyroid gland; 
• Anterolaterally: infrahyoid (strap) muscles 
• Posterolaterally: carotid sheath and contents 
• Superiorly: opens into laryngeal part of pharynx
• Inferiorly: continues as the trachea.

Until puberty, the male and female larynx differs little in size, but at puberty the male laryngeal cartilages undergo a significant increase in size whereas the female larynx only undergoes a small increase in size. In the male the increased size of the thyroid cartilage results in a marked projection into the anterior median line of the neck (laryngeal prominence) that is not evident in females.

Cartilages of the larynx

The cartilages of the larynx include the following:

• Thyroid: largest, forms most of the anterior and lateral walls; two lamina join at about an angle of 90° in men and 120° in women; from the posterior border of each lamina a superior horn projects upward and an inferior horn projects downward to articulate with the cricoid cartilage (Figures 7 & 12). 
• Cricoid: smaller and thicker than thyroid cartilage, lies mainly below it, clasped by its two inferior horns; has a narrow arch in front and a broader quadrate lamina behind. 
• Arytenoid: small pyramidal shaped cartilages placed on the superior border of the lamina of the cricoid; a synovial articular surface of cricoid forms a base upon which the arytenoid cartilage can slide laterally and medially, forward and backward or rotate; projecting laterally from the base of arytenoid is a short blunt muscular process (for attachment of the posterior and lateral cricoarytenoid muscles). Projecting anteriorly is a thinner process, the vocal process, to which the vocal cords are attached. 
• Corniculate: Two small nodules of cartilage located in the aryepiglottic folds of mucous membranes that articulate with the summits of the arytenoid cartilages and serve to prolong them backward and medially, but do not move independently of arytenoid cartilages and sometimes are fused with them. 
• Cuneiform: two small pieces of cartilage in each aryepiglottic fold that give rise to elevations of the mucous membrane antero-superior to each corniculate cartilage. 
• Epiglottic: thin, leaf-like piece of elastic fibrocartilage that projects obliquely upward behind tongue and body of hyoid and anterior to the entrance to the larynx; connected by an elastic ligament, the thyroepiglottic ligament to the angle formed by the two lamina of the thyroid cartilage; left and right sides of the epiglottis are attached to the arytenoid cartilages by the quadrangular membrane; upper part of the anterior surface of the epiglottis is covered with mucous membrane that is reflected onto the pharyngeal part of the tongue and onto the lateral wall of the pharynx forming a median glossoepiglottic fold and two lateral glossoepiglottic folds; depression on each side of the median fold is named the valleculae (Figure 8); lower part of the anterior surface lies posterior to the hyoid bone and is connected to it by the hyoepiglottic ligament; posterior surface is smooth and covered with mucous membrane. 

Extrinsic membranes of the larynx

The extrinsic membranes of the larynx include the following:

• Thyrohyoid (Figures 7 & 12); attaches to the hyoid bone and thyroid cartilages, median and thicker part is termed the median thyrohyoid ligament, lateral thyrohyoid ligaments are round elastic cords that form the posterior border of the membrane; 
• Hyoepiglottic – (see above)
• Cricotracheal (Figure 7): unites inferior border of cricoid with first tracheal ring.

Between the mucous membrane of the larynx (internally) and the intrinsic musculature (externally) is a broad sheet of fibrous tissue that has a number of named parts; upper portion, the quadrangular membrane and it extends between the arytenoid cartilage and the cartilage of the epiglottis; this membrane is thickened superior to form the vestibular ligaments, which are the supporting structures for the vestibular folds (Figure 8).

The inferior portion of this fibrous tissue of the larynx is called the cricothyroid ligament and it is further divided into median (anterior) and lateral divisions; the median cricothyroid ligament connects adjacent margins of the anterior aspects of the two cartilages; the lateral ligament (also called the cricovocal membrane) extends from the internal aspect of the cricoid cartilage superiorly where its free thickened edge attaches to the dorsal surface of the thyroid cartilage and vocal process of the arytenoid. This thickening forms the basis of the vocal folds and is called the vocal ligament (Figure 8); the term conus elasticus is usually considered equivalent to the entire cricothyroid ligament. 

The larynx is divided into three parts by upper and lower pairs of folds (mucous membrane) that project into the cavity. The folds include the following:

• Upper pair: vestibular folds and fissure between them is called rima vestibuli. 
• Lower folds: vocal folds and fissure between them is called the rima glottidis. The fissure is commonly referred to as the glottis but technically glottis refers to the vocal folds and the space between them (Figure 10). 

Cavities of the larynx

There are three cavities in the larynx:

• Vestibule: the superior cavity of the larynx. It runs between laryngeal inlet and vestibular folds; 
• The middle compartment: it is known as the middle section and contains the left and right ventricles (lateral indentations between vestibular and vocal folds); from the anterior end of the ventricle extends a narrow diverticulum called the laryngeal saccule; formation of a laryngocele involves abnormal dilation of the saccule and ventricle of the larynx. 
• Infraglottic space: this is the lower section of the larynx; it extends from the vocal folds to the inferior border of the cricoid cartilage and is continuous with the cavity of the trachea. 

Muscles of the larynx

There are numerous muscles in the larynx as follows:

• Cricothyroid (Figure 7): originates from the anteriolateral part of cricoid cartilage, runs superiorly and posteriorly to inserts into the inferior border of the thyroid cartilage and its inferior horn; when the two muscles act together they pivot the thyroid and cricoid cartilages on each other moving the thyroid forward relative to the cricoid; as a consequence they lengthen the distance between the posterior surface of the thyroid cartilage and the vocal processes of the arytenoid cartilages and thus tend to lengthen and straighten (tense) the vocal cords, which results in the cords being brought closer to the midline. 
• Posterior cricoarytenoid (Figure 11): originates from the posterior aspect of the cricoid lamina and run superiorly and laterally to insert on the muscular process of the arytenoid cartilage; by their contraction, these muscles pull the muscular processes of the arytenoid cartilages medially and backward, thus producing a rotation of the arytenoid cartilages at the cricoarytenoid joints and swinging the vocal processes laterally; the result is abduction of the vocal cords; this is particularly important in the preservation of the airway at the rima glottidis.

• Lateral cricoarytenoid (Figure 12): arises from upper border of posterior part of arch of cricoid and run superiorly and posteriorly to insert on muscular process of arytenoid cartilage; they pull the muscular process of the arytenoid cartilage forward and lateral, thus adducting the vocal folds. 
• Transverse arytenoid (arytenoid muscle; Figure 11): unpaired muscle that stretch between the posterior surfaces of the two arytenoid cartilages; draw the two arytenoid cartilages together, thus tending to close the rima glottidis. 
• Oblique arytenoid: posterior to transverse arytenoid muscle; arises from muscular processes of the two arytenoid cartilages, and the fibers swing superiorly across the midline, crossing those of the other side to reach the apex of the opposite arytenoid cartilage where many of them insert; the remainder runs into the aryepiglottic fold, forming the aryepiglottic muscle (Figure 11). This muscle and the oblique arytenoids constitute a sphincter of the laryngeal opening. 
• Thyroarytenoid (Figure 12): originates from angle of thyroid cartilage and adjacent cricothyroid ligament, fibers radiate posteriorly, both superiorly and horizontally, the horizontal fibers are attached to anterolateral surface of arytenoid cartilage and the deepest fibers of this group are called the vocalis muscle; the thyroarytenoids pull the arytenoid cartilages forward toward the thyroid cartilage, thus relaxing the vocal ligament; they also rotate the arytenoid cartilages medially, approximating the vocal folds.

• Vocal muscle (musculus vocalis): lies parallel and lateral to the vocal ligament to which many of its fibers attach; the vocalis provides a fine adjustment on the tension of the vocal folds and is intimately concerned in vocalization.

All of the intrinsic muscles of the larynx except the cricothyroid are innervated by the recurrent laryngeal nerve. The cricothyroid is innervated by the external laryngeal nerve. Sensory supply of the larynx - superior to vocal folds is by the internal laryngeal nerve. Inferior to vocal folds sensory innervation is by the recurrent laryngeal nerve. In quiet inspiration, the vocal cords are slightly abducted and somewhat curved, and the arytenoid cartilages are also apart so that there is a fair-sized slit at the rima glottidis. During forced inspiration the rima glottidis is widened as much as possible through the actions of the posterior cricoarytenoids. During phonation, except for the lowest tones, the vocal cords become straight and move together to meet at the midline.

If the recurrent laryngeal nerve is sectioned, the vocal cord of that side is at first bowed outward and can neither be abducted or adducted. The other vocal cord cannot meet it and the voice is poor. Often, however, the paralyzed cord gradually becomes less bowed due to the action of the un-paralyzed cricothyroid. This action, with compensation by the opposite cord, results in remarkable good speech.

If both recurrent nerves are sectioned, speech is lost and as the vocal cords adduct the airway is simultaneously narrowed. The narrowing may be so severe that operative intervention, usually involving removal of the arytenoid cartilages, is necessary. If the superior laryngeal nerve or its external branch is sectioned (as it may be in ligating the superior thyroid artery in a thyroidectomy) the cricothyroid cannot lengthen the vocal cord, and thus the cord is not straight and tense. The result is a tendency to hoarseness and easy tiring of the voice.