Neurovascular supply and lymphatic drainage of the esophagus
The oesophagus is a muscular tube, typically 25 cm long, which connects the pharynx to the stomach. Except for the vermiform appendix, the oesophagus is the narrowest part of the alimentary tract. It begins in the neck, level with the lower border of the cricoid cartilage and the 6th cervical vertebra (at which point it forms the upper oesophageal sphincter).
It descends largely anterior to the vertebral column through the superior and posterior mediastinal. It then passes through the diaphragm (the oesophageal opening of the diaphragm or the oesophageal aperture), which is level with the 10th thoracic vertebra and ends at the gastro-oesophageal junction or gastric cardiac orifice of the stomach (lower oesophageal sphincter), at the level of the 11th thoracic vertebra.
- Blood supply
- Venous drainage
- Lymphatic drainage
- Esophageal varices
The oesophagus is divisible into three parts:
- a cervical part between the level of 6th cervical vertebra and upper border of 1st thoracic vertebra
- a thoracic part between the level of 1st thoracic vertebra to the diaphragm
- an abdominal part, which commences as it crosses the diaphragm and runs a short course of about 1 - 2.5 cm before reaching the stomach
Although the oesophagus is generally vertical in its course, it has two shallow curves, and also bends in an anteroposterior plane to follow the cervicothoracic curvatures of the vertebral column. It can also bend slightly to the right as it is pushed by the aorta before bending to the left to reach the oesophageal hiatus.
The cervical oesophagus is supplied by the inferior thyroid artery.
The thoracic oesophagus is supplied by the brachial and oesophageal branches of the thoracic aorta. Four or five oesophageal branches arise from the anterior surface of the aorta and descend obliquely to the oesophagus. Here, they form a vascular chain that anastomoses above with the oesophageal branches of the inferior thyroid arteries, and below with the ascending branches from the left phrenic and left gastric arteries.
The oesophagus is drained by oesophageal veins which arise from the peri-oesophageal venous plexus. Blood from the oesophagus drains into a submucous plexus and then into a peri-oesophageal venous plexus which gives rise to the oesophageal veins. Veins of the abdominal oesophagus return blood through plexuses to the left gastric and upper short gastric veins. The left gastric vein meets the lower oesophageal veins at the oesophageal opening in the lesser curvature and then drains into the portal vein .
Those from the thoracic oesophagus drain predominantly into the azygos veins and, to a lesser extent, the hemiazygous, intercostal and bronchial veins. Those from the cervical oesophagus drain into the inferior thyroid vein.
- Cervical part receives parasympathetic supply from the recurrent laryngeal nerve, while the sympathetic supply comes from the cervical sympathetic trunk.
- Thoracic part is innervated by the autonomic esophageal plexus. The sympathetic source for this plexus is the sympathetic trunk, while the parasympathetic input comes from the vagus nerve (CN X).
- Sympathetic supply of the abdominal part comes from the fifth to twelfth thoracic spinal nerves (T5-T12), while the parasympathetic source is the esophageal plexus.
The lymphatic drainage of the abdominal oesophagus occurs to the left gastric and left and right paracardial nodes. Lymph from the posterior surface is drained directly to the uppermost para-aortic nodes.
The cervical and thoracic oesophagus have an extensive, longitudinally continuous submucosal lymphatic system, which presumably explains remote para-oesophageal lymphadenopathy in oesophageal carcinoma. Efferent vessels from the cervical oesophagus drain to the deep cervical nodes either directly or through the para-tracheal nodes. Vessels from the thoracic oesophagus drain to the posterior mediastinal nodes and those from the abdominal oesophagus drain to the left gastric lymph nodes. Some may pass directly to the thoracic duct.
Causes and characteristics
Cirrhosis or fibrosis of the liver affects the vascular tree within the liver and results in a decrease in hepatic vascular compliance. There is also an increased vascular tone, possibly reflecting a reduction in endothelial vasodilators such as nitric oxide. The portal resistance increases, leading to the formation of a collateral circulation, and there is a concomitant increase in the systemic and splanchnic blood flow. Portosystemic shunting of blood occurs between the short gastric coronary veins and the oesophageal veins, largely as the result of the dilation of pre-existing embryonic channels.
Varices in the distal oesophagus are easily visible at endoscopy, because they are situated superficially in the lamina propria. The blood from the superficial veins drains into a superficial venous plexus, then into a deeper intrinsic venous plexus and finally into the peri-oesophageal veins via perforating veins. Bi-directional flow is normally possible in this region, a phenomenon that permits pressure changes during breathing and Valsalva manoeuvres. However, in portal hypertension, the valves within the perforating vessels become incompetent and blood flow is retrograde, causing dilation of the deep intrinsic veins. The greater pressure within this region predisposes the varices to brisk and life threatening bleeding.
Treatment is directed towards controlling the formation of a collateral circulation and the obliteration of varices that are susceptible to bleeding. This is achieved by para-variceal endoscopic injection of a sclerosant, which causes obliteration of the varices as a result of thrombus formation. Fibrosis is also induced within the mucosa, which reduces the formation of new collateral vessels. Alternatively, rubber bands may be applied in an attempt to ligate the varices. Bleeding from the varices is associated with a mortality rate of 25%, reflecting the problems of rebleeding and underlying comorbidity.
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