The Pharynx May Be Opened Just Below The Hyoid Bone

subhyoidean pharyn-gotomy. The larynx may be opened in the median line, - thyrotomy. The cricothyroid membrane may be opened, - laryngotomy. The trachea may be opened, - tracheotomy.

Subhyoidean pharyngotomy is the entering of the pharynx by means of an incision below the hyoid bone. This is an extremely rare operation. It may be performed for the removal of foreign bodies or tumors. The incision may be made just below the hyoid bone and parallel to its border. This will divide the commencement of the anterior jugular vein, perhaps near the median line, perhaps toward the side. A transverse vein usually runs from one anterior jugular vein to the other across the median line at this point. Attached to the hyoid bone nearest to the median line is the sternohyoid muscle, then farther out the omohyoid, and still farther out the thyrohyoid. A small artery, the thyrohyoid, a branch of the superior thyroid, or sometimes of the lingual, will be divided.

The thyrohyoid membrane being incised, access is obtained to the fatty tissue at the base of the epiglottis. If the incision is carried directly backward the epiglottis will be cut through at its base. If, however, it is kept close to the hyoid bone and made upward, the pharynx will be entered in front of the epiglottis and at the root of the tongue. If the incision is carried too far toward the sides the superior thyroid artery and even the external carotid itself will be cut; if carried too low down on the thyrohyoid membrane, then the superior laryngeal artery and nerve may both be wounded. Attention has already been called to the thyrohyoid branch.

Thyrotomy is the division of the thyroid cartilage in the median line. The sternohyoid muscles almost touch in the median line. The division should be exactly in the median line. This will avoid wounding the anterior jugular veins. It not in the median line the incision will wound one of the vocal cords. Impairment of the voice certainly follows this operation; it is only performed for the removal of foreign bodies or growths. 11

Laryngotomy is the opening of the cricothyroid membrane. It is rarely-done, but it is of service in cases of choking from obstruction of the larynx, foreign bodies, etc.

There is not sufficient room between the cricoid and thyroid cartilages to do this operation properly until puberty has been reached and the larynx has enlarged. The cricoid cartilage is narrow in front but wide behind. Its upper edge rises rapidly as it passes backward, forming an upper crescentic border, the concavity being upward. The lower edge of the thyroid is concave downward. Thus the two edges make an oval opening in front which in children is too small to hold the tracheotomy tube. The nearness to the vocal cords is also a serious objection. Performing a laryngotomy is the easiest and quickest way to enter the air-passages. Both the thyroid and cricoid cartilages in the median line are practically subcutaneous. A longitudinal incision of the skin is usually advised, after which a transverse incision is employed for opening the cricothyroid membrane. The tube is to be shorter than the one ordinarily used for tracheotomy. The cricothyroid artery, running across the membrane, is usually too insignificant to cause any trouble; it is nearer the thyroid cartilage, therefore the cut through the membrane should be close to the cricoid cartilage.

Tracheotomy is the opening of the trachea. There are two varieties, the high and the low, according as the tube is inserted above or below the isthmus of the thyroid gland. When in the adult male the neck is in line with the axis of the body the lower border of the cricoid cartilage is about 4 cm. (1 1/2 in.) above the sternum. When the head is tilted far back the larynx is drawn upward and the lower border of the cricoid is 6 cm. (about 2 1/2 in.) above the sternum. Hence in doing a tracheotomy the head is to be tilted far back. The total length of the trachea is 10 to 12 cm. (Morris, Hensman), beginning opposite the sixth cervical vertebra, - upper border in the child and lower in adults, - and ending opposite the fifth dorsal. About half of it is above and half below the top of the sternum. It is composed of 14 to 20 rings. In the adult the isthmus of the thyroid gland covers the second, third, and fourth rings. There are about eight rings above the sternum.

According to Symington and Guersant (Treves) the diameter of the trachea is about as follows:

1 1/2

to

2 years.................

5 mm.

2

to

4 years.................

6 min

4

to

8 years..................

8 min

8

to

12 years..............

10 min

12

to

15 years..........

12 min

Adults

......................

12-15 mm.

A knowledge of the size of the trachea is necessary in order to select a tracheotomy tube of a size suitable to the particular case. The liability is to select too large a tube for young children, particularly infants. If this is done it may be very difficult to introduce the tube, or the trachea may even be torn in the attempt. In operating, an incision 2.5 to 3 cm. long is to be made in the median line. This may cut the anterior jugular vein. If carried near to the sternum it will certainly divide the communicating branch between the anterior jugulars at that point. The top of the incision in a child will be over the cricoid cartilage, and as soon as the skin has been divided the finger is to be inserted and the cricoid cartilage felt and recognized. This will show how deep the trachea lies. In very young children the isthmus of the thyroid gland is liable to come up to the cricoid cartilage and the difficulty of displacing it far enough down to allow the tube to be inserted is such that it may be best to divide it. Therefore after the skin and deep fascia have been divided and the cricoid recognized by the finger the soft tissues covering the trachea immediately below the cricoid are grasped on each side with a haemostatic forceps and divided between them. These tissues may embrace the isthmus of the thyroid gland, the edges of the sternohyoid muscles, some veins, branches from the superior and inferior thyroids, and the fascia covering the gland and overlying the trachea.

The trachea should be cleared before opening it. A sharp hook is inserted into the cricoid cartilage to steady it and an incision is made into the trachea from below upward. In making this incision the utmost care must be taken not to cut through the trachea and wound the oesophagus behind. The trachea of a child is not the hard resisting structure of the adult. It is a soft tender tube easily compressed and readily torn by roughness, or punctured with a knife. Forceps do not readily hold in it and stitches through it are liable to tear out. Only the very tip of the point of the knife should be allowed to enter the tube. The utmost care must be taken to keep in the median line. This is to be accomplished by using the cricoid cartilage as a guide and by seeing that the position of the head is straight. Cutting to either side of the trachea will cause wounding of the common carotid arteries. Below the isthmus of the thyroid gland and running down on the trachea are the inferior thyroid veins. The superior and middle thyroid veins empty into the internal jugular vein, but the inferior thyroids go downward to empty into the innominate. These veins will be cut if a low tracheotomy is done. In the infant the innominate artery and sometimes, though rarely, the left carotid encroach on the suprasternal notch and may be wounded if the incision is carried too low. The left innominate vein as it crosses to the right side is liable, especially in very young children, to show quite plainly above the sternum and would certainly be cut if the deep incision was carried as far down as the top of the sternum. An anomalous artery, the thyroidea ima, a branch of the innominate, sometimes passes upward on the trachea. On account of the presence of all these vessels it is not allowable to do any cutting of the deep parts just above the sternum; they are simply to be depressed by blunt dissection and kept out of the way with retractors while the trachea is being incised. The cricoid cartilage is never to be incised. It is far more firm and resistant than the trachea and it serves to keep the trachea from collapsing. The proximity of the tracheotomy tube to the vocal cords would result in interference with their function.

Fig. 183.   Dissection showing the parts involved in operations on the thyroid gland and air passages.

Fig. 183. - Dissection showing the parts involved in operations on the thyroid gland and air-passages.

The method of Bose consists in dividing the fascia overlying the trachea near the cricoid cartilage and pushing it down, carrying the isthmus and veins with it, and introducing the tube into the space so cleared. This is so difficult that it is better to divide the isthmus, as already described.