ANATOMY OF LARYNX, TRACHEA, BRONCHI AND ESOPHAGUS, ENDOSCOPICALLY CONSIDERED

ANATOMY OF LARYNX, TRACHEA, BRONCHI AND ESOPHAGUS, ENDOSCOPICALLY CONSIDERED

The larynx is a cartilaginous box, triangular in cross-section, with the apex of the triangle directed anteriorly. It is readily felt in the neck and is a landmark for the operation of tracheotomy. We are concerned endoscopically with four of its cartilaginous structures: the epiglottis, the two arytenoid cartilages, and the cricoid cartilage. The epiglottis, the first landmark in direct laryngoscopy, is a leaf-like projection springing from the anterointernal surface of the larynx and having for its function the directing of the bolus of food into the pyriform sinuses. It does not close the larynx in the trap-door manner formerly taught; a fact easily demonstrated by the simple insertion of the direct laryngoscope and further demonstrated by the absence of dysphagia when the epiglottis is surgically removed, or is destroyed by ulceration. Closure of the larynx is accomplished by the approximation of the ventricular bands, arytenoids and aryepiglottic folds, the latter having a sphincter-like action, and by the raising and tilting of the larynx. The arytenoids form the upper posterior boundary of the larynx and our particular interest in them is directed toward their motility, for the rotation of the arytenoids at the cricoarytenoid articulations determines the movements of the cords and the production of voice. Approximation of the arytenoids is a part of the mechanism of closure of the larynx.

The cricoid cartilage was regarded by esophagoscopists as the chief obstruction encountered on the introduction of the esophagoscope. As shown by the author, it is the cricopharyngeal fold, and the inconceivably powerful pull of the cricopharyngeal muscle on the cricoid cartilage, that causes the difficulty. The cricoid is pulled so powerfully back against the cervical spine, that it is hard to believe that this muscles is inserted into the median raphe and not into the spine itself (Fig. 68).

The ventricular bands or false vocal cords vicariously phonate in the absence of the true cords, and assist in the protective function of the larynx. They form the floor of the ventricles of the larynx, which are recesses on either side, between the false and true cords, and contain numerous mucous glands the secretion from which lubricates the cords. The ventricles are not visible by mirror laryngoscopy, but are readily exposed in their depths by lifting the respective ventricular bands with the tip of the laryngoscope. The vocal cords, which appear white, flat, and ribbon-like in the mirror, when viewed directly assume a reddish color, and reveal their true shelf-like formation. In the subglottic area the tissues are vascular, and, in children especially, they are prone to swell when traumatized, a fact which should be always in mind to emphasize the importance of gentleness in bronchoscopy, and furthermore, the necessity of avoiding this region in tracheotomy because of the danger of producing chronic laryngeal stenosis by the reaction of these tissues to the presence of the tracheotomic cannula.

The trachea just below its entrance into the thorax deviates slightly to the right, to allow room for the aorta. At the level of the second costal cartilage, the third in children, it bifurcates into the right and left main bronchi. Posteriorly the bifurcation corresponds to about the fourth or fifth thoracic vertebra, the trachea being elastic, and displaced by various movements. The endoscopic appearance of the trachea is that of a tube flattened on its posterior wall. In two locations it normally often assumes a more or less oval outline; in the cervical region, due to pressure of the thyroid gland; and in the intrathoracic portion just above the bifurcation where it is crossed by the aorta. This latter flattening is rhythmically increased with each pulsation. Under pathological conditions, the tracheal outline may be variously altered, even to obliteration of the lumen. The mucosa of the trachea and bronchi is moist and glistening, whitish in circular ridges corresponding to the cartilaginous rings, and reddish in the intervening grooves.

The right bronchus is shorter, wider, and more nearly vertical than its fellow of the opposite side, and is practically the continuation of the trachea, while the left bronchus might be considered as a branch. The deviation of the right main bronchus is about 25 degrees, and its length unbranched in the adult is about 2.5 cm. The deviation of the left main bronchus is about 75 degrees and its adult length is about 5 cm. The right bronchus considered as a stem, may be said to give off three branches, the epiarterial, upper- or superior-lobe bronchus; the middle-lobe bronchus; and the continuation downward, called the lower- or inferior-lobe bronchus, which gives off dorsal, ventral and lateral branches. The left main bronchus gives off first the upper-or superior-lobe bronchus, the continuation being the lower-or inferior-lobe bronchus, consisting of a stem with dorsal, ventral and lateral branches.

[FIG. 44.—Tracheo-bronchial tree. LM, Left main bronchus; SL, superior lobe bronchus; ML, middle lobe bronchus; IL, inferior lobe bronchus.]

The septum between the right and left main bronchi, termed the carina, is situated to the left of the midtracheal line. It is recognized endoscopically as a short, shining ridge running sagitally, or, as the patient lies in the recumbent position, we speak of it as being vertical. On either side are seen the openings of the right and left main bronchi. In Fig. 44, it will be seen that the lower border of the carina is on a level with the upper portion of the orifice of the right superior-lobe bronchus; with the carina as a landmark and by displacing with the bronchoscope the lateral wall of the right main bronchus, a second, smaller, vertical spur appears, and a view of the orifice of the right upper-lobe bronchus is obtained, though a lumen image cannot be presented. On passing down the right stem bronchus (patient recumbent) a horizontal partition or spur is found with the lumen of the middle-lobe bronchus extending toward the ventral surface of the body. All below this opening of the right middle-lobe bronchus constitutes the lower-lobe bronchus and its branches.

[FIG. 45.—Bronchoscopic views. S; Superior lobe bronchus; SL, superior lobe bronchus; I, inferior lobe bronchus; M, middle lobe bronchus.]

[56] Coming back to the carina and passing down the left bronchus, the relatively great distance from the carina to the upper-lobe bronchus is noted. The spur dividing the orifices of the left upper- and lower-lobe bronchi is oblique in direction, and it is possible to see more of the lumen of the left upper-lobe bronchus than of its homologue on the right. Below this are seen the lower-lobe bronchus and its divisions (Fig. 45).

Dimensions of the Trachea and Bronchi.—It will be noted that the bronchi divide monopodially, not dichotomously. While the lumina of the individual bronchi diminish as the bronchi divide, the sum of the areas shows a progressive increase in total tubular area of cross-section. Thus, the sum of the areas of cross-section of the two main bronchi, right and left, is greater than the area of cross section of the trachea. This follows the well known dynamic law. The relative increase in surface as the tubes branch and diminish in size increases the friction of the passing air, so that an actual increase in area of cross section is necessary, to avoid increasing resistance to the passage of air.

The cadaveric dimensions of the tracheobronchial tree may be
epitomized approximately as follows:
Adult
Male Female Child Infant
Diameter trachea, 14 X 20 12 X 16 8 X 10 6 X 7
Length trachea, cm. 12.0 10.0 6.0 4.0
Length right bronchus 2.5 2.5 2.0 1.5
Length left bronchus 5.0 5.0 3.0 2.5
Length upper teeth to trachea 15.0 23.0 10.0 9.0
Length total to secondary bronchus 32.0 28.0 19.0 15.0

In considering the foregoing table it is to be remembered that in life muscle tonus varies the lumen and on the whole renders it smaller. In the selection of tubes it must be remembered that the full diameter of the trachea is not available on account of the glottic aperture which in the adult is a triangle measuring approximately 12 X 22 X 22 mm. and permitting the passage of a tube not over 10 mm. in diameter without risk of injury. Furthermore a tube which filled the trachea would be too large to enter either main bronchus.

The normal movements of the trachea and bronchi are respiratory, pulsatory, bechic, and deglutitory. The two former are rhythmic while the two latter are intermittently noted during bronchoscopy. It is readily observed that the bronchi elongate and expand during inspiration while during expiration they shorten and contract. The bronchoscopist must learn to work in spite of the fact that the bronchi dilate, contract, elongate, shorten, kink, and are dinged and pushed this way and that. It is this resiliency and movability that make bronchoscopy possible. The inspiratory enlargement of lumen opens up the forceps spaces, and the facile bronchoscopist avails himself of the opportunity to seize the foreign body.

THE ESOPHAGUS

A few of the anatomical details must be kept especially in mind when it is desired to introduce straight and rigid instruments down the lumen of the gullet. First and most important is the fact that the esophageal walls are exceedingly thin and delicate and require the most careful manipulation. Because of this delicacy of the walls and because the esophagus, being a constant passageway for bacteria from the mouth to the stomach, is never sterile, surgical procedures are associated with infective risks. For some other and not fully understood reason, the esophagus is, surgically speaking, one of the most intolerant of all human viscera. The anterior wall of the esophagus is in a part of its course, in close relation to the posterior wall of the trachea, and this portion is called the party wall. It is this party wall that contains the lymph drainage system of the posterior portion of the larynx, and it is largely by this route that posteriorly located malignant laryngeal neoplasms early metastasize to the mediastinum.

[58] [FIG 46.—Esophagoscopic and Gastroscopic Chart

BIRTH 1 yr. 3 yrs. 6 yrs. 10 yrs. 14 yrs.ADULTS 23 27 30 33 36 43 53 Cm. GREATER CURVATURE 18 20 22 25 27 34 40 Cm. CARDIA 19 21 23 24 25 31 36 Cm. HIATUS 13 15 16 18 20 24 27 Cm. LEFT BRONCHUS 12 14 15 16 17 21 23 Cm. AORTA 7 9 10 11 12 14 16 Cm. CRICOPHARYINGEUS 0 0 0 0 0 0 0 Cm. INCISORS FIG. 46.—The author’s esophagoscopic chart of approximate distances of the esophageal narrowings from the upper incisor teeth, arranged for convenient reference during esophagoscopy in the dorsally recumbent patient.]

The lengths of the esophagus at different ages are shown diagrammatically in Fig. 46. The diameter of the esophageal lumen varies greatly with the elasticity of the esophageal walls; its diameter at the four points of anatomical constriction is shown in the following table:

Constriction Diameter Vertebra

Cricopharyngeal Transverse 23 mm. (1 in.) Sixth cervical
Antero-posterior 17 mm. (3/4 in.)
Aortic Transverse 24 mm. (1 in.) Fourth thoracic
Antero-posterior 19 mm. (3/4 in.)
Left-bronchial Transverse 23 mm. (1 in.) Fifth thoracic
Antero-posterior 17 mm. (3/4 in.)
Diaphragmatic Transverse 23 mm. (1 in+) Tenth thoracic
Antero-posterior 23 mm. (in.—)

For practical endoscopic purposes it is only necessary to remember that in a normal esophagus, straight and rigid tubes of 7 mm. diameter should pass freely in infants, and in adults, tubes of 10 mm.

The 4 demonstrable constrictions from above downward are at 1. The crico-pharyngeal fold. 2. The crossing of the aorta. 3. The crossing of the left bronchus. 4. The hiatus esophageus. There is a definite fifth narrowing of the esophageal lumen not easily demonstrated esophagoscopically and not seen during dissection, but readily shown functionally by the fact that almost all foreign bodies lodge at this point. This narrowing occurs at the superior aperture of the thorax and is probably produced by the crowding of the numerous organs which enter or leave the thorax through this orifice.

The crico-pharyngeal constriction, as already mentioned, is produced by the tonic contraction of a specialized band of the orbicular fibers of the lowermost portion of the inferior pharyngeal constrictor muscle, called the cricopharyngeal muscle. As shown by the author it is this muscle and not the cricoid cartilage alone that causes the difficulty in the insertion of an esophagoscope.

This muscle is attached laterally to the edges of the signet of the cricoid which it pulls with an incomprehensible power against the posterior wall of the hypopharynx, thus closing the mouth of the esophagus. Its other attachment is in the median posterior raphe. Between these circular fibers (the cricopharyngeal muscle) and the oblique fibers of the inferior constrictor muscle there is a weakly supported point through which the esophageal wall may herniate to form the so-called pulsion diverticulum. It is at this weak point that fatal esophagoscopic perforation by inexperienced operators is most likely to occur.

The aortic narrowing of the esophagus may not be noticed at all if the patient is placed in the proper sequential “high-low” position. It is only when the tube-mouth is directed against the left anterior wall that the actively pulsating aorta is felt.

The bronchial narrowing of the esophagus is due to backward displacement caused by the passage of the left bronchus over the anterior wall of the esophagus at about 27 cm. from the upper teeth in the adult. The ridge is quite prominent in some patients, especially those with dilatation from stenoses lower down.

The hiatal narrowing is both anatomic and spasmodic. The peculiar arrangement of the tendinous and muscular structure of the diaphragm acts on this hiatal opening in a sphincter-like fashion. There are also special bundles of muscle fibers extending from the crura of the diaphragm and surrounding the esophagus, which contribute to tonic closure in the same way that a pinch-cock closes a rubber tube. The author has called the hiatal closure the “diaphragmatic pinchcock.”

Direction of the Esophagus.—The esophagus enters the chest in a decidedly backward as well as downward direction, parallel to that of the trachea, following the curves of the cervical and upper dorsal spine. Below the left bronchus the esophagus turns forward, passing through the hiatus in the diaphragm anterior to and to the left of the aorta. The lower third of the esophagus in addition to its anterior curvature turns strongly to the left, so that an esophagoscope inserted from the right angle of the mouth, when introduced into the stomach, points in the direction of the anterior superior spine of the left ileum.

It is necessary to keep this general course constantly in mind in all cases of esophagoscopy, but particularly in those cases in which there is marked dilatation of the esophagus following spasm at the diaphragm level. In such cases the aid of this knowledge of direction will greatly simplify the finding of the hiatus esophageus in the floor of the dilatation.

The extrinsic or transmitted movements of the esophagus are respiratory and pulsatory, and to a slight extent, bechic. The respiratory movements consist in a dilatation or opening up of the thoracic esophageal lumen during inspiration, due to the negative intrathoracic pressure. The normal pulsatory movements are due to the pulsatile pressure of the aorta, found at the 4th thoracic vertebra (24 cm. from the upper teeth in the adult), and of the heart itself, most markedly felt at the level of the 7th and 8th thoracic vertebrae (about 30 cm. from the upper teeth in adults). As the distances of all the narrowings vary with age, it is useful to frame and hang up for reference a copy of the chart (Fig. 46).

The intrinsic movements of the esophagus are involuntary muscular contractions, as in deglutition and regurgitation; spasmodic, the latter usually having some pathologic cause; and tonic, as the normal hiatal closure, in the author’s opinion may be considered. Swallowing may be involuntary or voluntary. The constrictors are anatomically not considered part of esophagus proper. When the constrictors voluntarily deliver the bolus past the cricopharyngeal fold, the involuntary or peristaltic contractions of the esophageal mural musculature carry the bolus on downward. There is no sphincter at the cardiac end of the esophagus. The site of spasmodic stenosis in the lower third, the so-called cardiospasm, was first demonstrated by the author to be located at the hiatus esophageus and the spasmodic contractions are of the specialized muscle fibers there encircling the esophagus, and might be termed “phrenospasm,” or “hiatal esophagismus.” Regurgitation of food from the stomach is normally prevented by the hiatal muscular diaphragmatic closure (called by the author the “diaphragmatic pinchcock”) plus the kinking of the abdominal esophagus.

In the author’s opinion there is no spasm in the disease called “cardiospasm.” It is simply the failure of the diaphragmatic pinchcock to open normally in the deglutitory cycle. A better name is functional hiatal stenosis.

At retrograde esophagoscopy the cardia and abdominal esophagus do not seem to exist. The top of the stomach seems to be closed by the diaphragmatic pinchcock in the same way that the top of a bag is closed by a puckering string.

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