Anatomy of the Oesophagus Duct, the Azygos Vein and Its Tributaries And, Near the Diaphragm, the Lower Part of the Descending Aorta, Which Edges Behind It

Home , Gastric folds, Hemiazygos vein, Inferior phrenic vein

BASIC SCIENCE

Posteriorly lie the thoracic vertebrae down to T10, the thoracic Anatomy of the oesophagus duct, the azygos vein and its tributaries and, near the diaphragm, the lower part of the descending aorta, which edges behind it. Harold Ellis On the left side the oesophagus is hidden behind the left subclavian artery, the aortic arch, the left recurrent laryngeal nerve and the thoracic duct and is then overlapped by the Abstract postero-laterally placed descending aorta. The oesophagus measures approximately 25 cm in length and is divided into On the right side the oesophagus relates to the mediastinal cervical, thoracic and intra-abdominal parts. It extends from the pharynx, at pleura and is crossed by the termination of the azygos vein. Thus the level of vertebra C6, to the cardia of the stomach after traversing the dia- the right side, in contrast to the left, allows excellent surgical phragm at T10 level. The usual surgical approach to the length of the oesoph- access in oesophageal mobilization; the terminal part of the agus is through the right chest, where it is only crossed by the termination of azygos vein, if necessary, can be tied and divided. the azygos vein. The oesophagus is lined throughout by a stratiﬁed squa- Distal to the hila of the lungs the vagus nerve on each side joins mous mucosa. It has a rich blood supply from the inferior thyroid artery, to form a plexus on the wall of the oesophagus, from which emerge multiple branches directly from the aorta and from the oesophageal branch the anterior and posterior vagal trunks, lying directly on the walls of the left gastric artery. At the lower end there is an important porto- of the oesophagus and emerging with it at the oesophageal hiatus systemic anastomosis between the oesophageal branch of the left gastric of the diaphragm. vein and the tributaries of the azygos vein, which accounts for the develop- The abdominal part of the oesophagus (Figure 2), about 2.5 ment of oesophageal varices in portal hypertension. Although there is no cm in length, passes through the opening formed by the two anatomical sphincter to be demonstrated at the lower end of the oesophagus crura of the diaphragm and comes to lie in the oesophageal in man, a multifactorial ‘physiological’sphincter mechanism is present, which groove on the posterior surface of the left lobe of the liver. It is relaxes in belching and vomiting. tethered to the diaphragm by the phreno-oesophageal ligament.

Keywords Cervical; oesophagus; porto-caval venous anastomosis, Structure complex sphincter mechanism; stratified squamous mucosa; thoracic and The mucosal lining of the oesophagus comprises a stratified abdominal parts squamous epithelium. This passes abruptly into the columnar epithelium of the cardia at the oesophago-gastric junction. The underlying submucosa is made up of connective tissue contain- The oesophagus extends from the distal termination of the ing mucous glands. Deep to this, the muscle layer comprises pharynx at the level of the sixth cervical vertebra to the cardiac inner circular and outer longitudinal fibres, striated in the upper orifice of the stomach. Its upper extremity can easily be defined third, mixed striated and unstriated in the mind-oesophagus, as the level of the lower border of the cricoid cartilage of the then entirely unstriated in the lower third. There is an outer larynx. It is 25 cm in length and can be divided, for descriptive connective tissue sheath. Note that there is no anatomical purposes, into cervical, thoracic and abdominal part (Figure 1a sphincter at the lower end of the oesophagus in man, (although and b). this can be demonstrated in a number of animal species). In the neck, the oesophagus lies immediately behind the However, a sphincter mechanism exists, as we do not normally trachea, separated only by loose connective tissue. Posteriorly, reflux gastric contents on lying down or bending over. This the dense prevertebral fascia separates it from the sixth and ‘sphincter’ relaxes to allow belching and vomiting. The mecha- seventh cervical vertebrae, while on either side lie the common nism is a complex affair comprising: carotid arteries and the recurrent laryngeal nerves, the latter positive intra-abdominal pressure acting on the short lying in the trachea-oesophageal groove. On the left side it relates abdominal part of the oesophagus to the termination of the thoracic duct. The thyroid gland lateral a physiological high-pressure zone at the lower end of the lobe projects over the side of the cervical oesophagus on each oesophagus, which can be demonstrated by oesophageal side. manometry The bulk of the oesophagus lies in the thorax, where it valve-like effect of the obliquity of the oesophago-gastric traverses the superior and then the posterior mediastinum, here angle it passes forward and to the left to reach the oesophageal hiatus pinch-cock effect of the crural sling of the diaphragm of the diaphragm at the level of T10 (Figure 1a and b). plug-like action of the mucosal folds at the cardiac orifice. Anteriorly the thoracic oesophagus lies successively behind the trachea, the left main bronchus, the pericardium, which Blood supply (Figure 3a and b) separates it from the left atrium of the heart and, finally, the The oesophagus has a rich arterial supply; above, from the diaphragm. inferior thyroid artery, then, segmentally, from a series of branches passing directly from the adjacent thoracic aorta and then from the oesophageal branch of the left gastric artery which Harold Ellis CBE MCh FRCS was Professor of Surgery at Westminster ascends through the oesophageal hiatus of the diaphragm. Medical School until 1989. Since then he has taught anatomy, first in The veins from the cervical oesophagus drain into the interior Cambridge and now at Guy’s Hospital, London, UK. Conflicts of interest: thyroid veins. The thoracic oesophagus drains into the azygos none declared. system, while the lower part of the organ empties into the

b a Pharyngeal muscles Common Trachea Thyroid gland, left lobe carotid artery Thyroid gland, right lobe Common carotid artery Common Subclavian Common carotid artery carotid artery artery Internal jugular vein Subclavian Internal jugular vein Oesophagus, artery cervical part Subclavian artery and vein Subclavian artery Brachiocephalic trunk and vein Right main bronchus Aortic arch Left brachiocephalic vein

Right brachiocephalic Ligamentum vein arteriosum Tracheal cartilages Brachiocephalic trunk Carina Aortic arch Superior vena cava Right superior Ligamentum arteriosum lobar bronchus Left main Azygos vein bronchus Bronchial branches Tracheal Thoracic aorta bifurcation Left pulmonary Right main artery bronchus

Oesophagus, Left main Right pulmonary thoracic part bronchus artery Left pulmonary Diaphragm, central Oesophageal veins tendon hiatus Right pulmonary Left ventricle veins Oesophagus, Posterior intercostal arteries Caval opening abdominal part Oesophagus, thoracic part Right crus of diaphragm, Stomach, Diaphragm lumbar part cardiac part Inferior vena cava Inferior phrenic arteries Central tendon Aortic hiatus Left crus of Coeliac trunk diaphragm, Thoracic lumbar part aorta

Abdominal aorta Oesophageal hiatus

Figure 1 The oesophagus: anterior view (a), posterior view (b). (From Gray’s Anatomy 40th edition).

Longitudinal oesophageal muscle Circular oesophageal muscle

Gradual slight muscular thickening Oesophageal mucosa Phreno-oesophageal ligament (ascending or upper limb) Submucosa Supradiaphragmatic fascia

Diaphragm Diaphragm Infradiaphragmatic (transversalis) fascia Phreno-oesophageal ligament (descending limb)

Phreno-oesophageal ligament (descending limb)

Subhiatal fat ring

Zigzag (Z) line: juncture of oesophageal and Peritoneum gastric mucosa Cardiac notch

Cardiac part (cardia) of stomach Gastric folds (rugae)

Figure 2 The lower end of the oesophagus and oesophago-gastric junction. (From Gray’s Anatomy 40th edition).

a b Inferior thyroid artery Inferior thyroid artery, Inferior thyroid vein Oesophagus, cervical part oesophageal branches Vertebral vein Right common Internal jugular vein Left brachiocephalic vein Vertebral artery carotid artery Subclavian artery Right subclavian vein

Left common carotid artery Accessory hemiazygos vein Trachea Superior vena cava Thoracic aorta, bronchial branches Posterior intercostal veins Oesophageal veins Oesophagus Thoracic aorta, oesophageal branches Oesophagus, thoracic part

Left gastric artery, oesophageal branches Hemiazygos vein Azygos vein Diaphragm Diaphragm, caval opening Diaphragm, Coeliac trunk central tendon Lower Left gastric artery oesophageal veins Oesophagus, abdominal part

Inferior phrenic vein Left gastro-epiploic vein Inferior vena cava Stomach Left gastric vein

Figure 3 Oesophagus: arterial supply (a), venous drainage (b). (From Gray’s Anatomy 40th edition).

SURGERY 29:11 539 Ó 2011 Elsevier Ltd. All rights reserved. BASIC SCIENCE oesophageal tributaries of the left gastric vein, which itself drains Lymphatic drainage directly into the portal vein. This obeys the universal rule, that ‘lymphatics of an organ Note that the anastomosis between the azygos (systemic) and follow its blood supply’. A peri-oesophageal lymphatic plexus left gastric (portal) venous tributaries in the submucosa of the drains into posterior mediastinal nodes which drain both lower end of the oesophagus is of great clinical importance. In upwards into the supraclavicular nodes and downwards, portal hypertension these veins distend into large collateral along nodes around the left gastric vessels. Involved hard channels, (oesophageal varices), which may rupture, resulting in supraclavicular nodes may be palpated quite frequently in massive haematemesis. patients with advanced oesophageal carcinoma. A