Topographic Relationships Contours and Normal Constrictions of Esophagus
The esophagus begins in the neck as a continuation of the pharynx (cervical esophagus). This point of origin corresponds to the inferior border of the cricoid cartilage and the lower margin of the inferior pharyngeal constrictor muscle, also called the cricopharyngeus muscle, at about the level of the sixth cervical vertebra. The esophagus extends inferiorly through the neck and through the superior and posterior mediastina of the thorax. It then passes through the esophageal hiatus of the diaphragm to join the cardiac region of the stomach at about the level of the 10th thoracic vertebra.
The esophagus generally follows the anteroposterior curvature of the vertebral column, except in the inferior portion, which is tethered by its relationship with the diaphragm. It also forms two lateral curvatures, so that in a coronal view, it assumes the form of a gentle reversed “S.” The upper of the two lateral curvatures is convex toward the left, and the lower curvature, in the lower thorax and abdomen, is convex toward the right. From its commencement at the lower margin of the cricoid cartilage, the esophagus inclines slightly to the left until its left border projects approximately onefourth inch to the left of the tracheal margin. It then swings somewhat to the right, reaching the midline at about the level of the fourth thoracic vertebra behind the aortic arch. It continues its inclination to the right until about the level of the seventh thoracic vertebra, where it again turns left somewhat more sharply than in its previous curves, and in this direction it passes through the esophageal hiatus.
The esophagus has cervical, thoracic, and abdominal portions. Anterior to the cervical portion lies the membranous posterior wall of the trachea, to which it is rather loosely connected by loose connective tissue and some smooth muscular strands, so that the anterior esophageal and the posterior tracheal walls are occasionally referred to as the “common party wall.” In the grooves on each side between the trachea and the esophagus are the recurrent laryngeal nerves, which ascend from the vagus nerves in the upper thorax to reach the larynx. Posteriorly, the esophagus lies upon the prevertebral fascia, covering the anterior surface of the longus colli muscles and cervical vertebral bodies. On the left and right, the carotid sheath and the structures it contains (vagus nerve, carotid arteries, and internal jugular vein) accompany the cervical esophagus. Owing to the curvature of the esophagus in this region, it lies closest to the left carotid sheath. The lobes of the thyroid gland partially overlap the esophagus on each side. The thoracic duct ascends in the root of the neck on the left side of the esophagus and then arches laterally posterior to the carotid sheath and anterior to the vertebral artery and vein to enter the left brachiocephalic or left subclavian vein at the medial margin of the anterior scalene muscle.
The thoracic esophagus also lies posterior to the trachea as far as the level of the fifth thoracic vertebral body, at which point the trachea bifurcates. The trachea deviates slightly to the right at its lower end, so that the left main bronchus crosses anterior to the esophagus. Below this point the esophagus is separated anteriorly from the left atrium of the heart by the pericardium. In the very lowest portion of its thoracic course, the esophagus passes posterior to the central tendon of the diaphragm to reach the esophageal hiatus. On the left side in the superior thoracic region, the esophageal wall contacts the ascending portion of the left subclavian artery and the parietal pleura; at about the level of the fourth thoracic vertebra, the arch of the aorta passes posteriorly alongside the esophagus. Below this point the descending aorta lies to the left, but when it passes posterior to the esophagus, the left mediastinal pleura again comes to abut on the esophageal wall. On the right side the right parietal pleura is intimately applied to the esophagus, except when, at about the level of the fourth thoracic vertebra, the azygos vein intervenes as it turns anteriorly. The short abdominal portion of the esophagus lies upon the diaphragm and ma es an impression on the liver with its anterior aspect.
The left and right vagus nerves associate with the esophagus, and below the tracheal bifurcation, they interweave to form the esophageal plexus of nerves. This plexus then coalesces with the anterior and posterior vagal trunks that pierce the diaphragm along the esophagus.
The course of the esophagus is marked by several indentations and constrictions:
1. The first narrowing of the esophagus is found at its commencement, caused by the cricopharyngeus muscle at the inferior border of the inferior pharyngeal constrictor and the cricoid cartilage.
2. The esophagus is indented on its left side by the arch of the aorta (aortic constriction), and at this level the aortic pulsations may often be observed through the esophagoscope.
3. Just inferior to this point the left main bronchus causes an impression on the left anterior aspect of the esophagus.
4. At its lower end the esophagus is narrowed by the diaphragmatic constriction (inferior esophageal sphincter) as it passes through the right diaphragmatic crus.
The overall length of the esophagus varies in accordance with the length of the trunk of the individual. The average distance of the cardia from the upper incisor teeth is approximately 40 cm, but in some “long” individuals this distance may be as much as 42 or 43 cm. This average distance of 40 cm may be sub divided as follows: The distance from the incisor teeth to the cricopharyngeus muscle, which corresponds to the commencement of the esophagus, averages 16 cm. It is thus apparent that the average length of the esophagus itself is 40 minus 16 cm equals 24 cm, or approximately 10 inches. At about 23 cm from the incisor teeth, the arch of the aorta crosses the esophagus on its left side. This crossing is therefore about 7 cm below the cricopharyngeus. A few centimeters below this point the left main bronchus passes anterior to the esophagus. The diaphragmatic constriction, or commencement of the abdominal part of the esophagus, is located at about 37 to 38 cm from the incisor teeth. It is of considerable significance to note that the esophageal hiatus of the diaphragm is slightly inferior (≈ 1 cm) to this point, and the cardiac region of the stomach is at a still slightly lower level. The figures given above are for adults; in children the dimensions are proportionately smaller. At birth the distance from the incisor teeth to the cardiac region is usually only 18 cm, at 3 years approximately 22 cm, and at 10 years approximately 27 cm.
Although the esophagus is usually described as tubelike, it is generally flattened so that the transverse axis is somewhat larger than the anteroposterior axis. In the resting state the esophageal walls are in approximation. The width or diameter of the esophagus varies considerably with its state of tonus but the average resting width is approximately 2 cm.