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.
Thus, 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 abdominal oesophagus is supplied by the oesophageal branches of the left gastric artery. These branches ascend as an anterior and posterior branch beneath the visceral peritoneum to supply perforating branches to the intramural and submucosal plexuses. The posterior surface of the abdominal oesophagus usually receives an additional supply through:
- branches of the upper short gastric arteries
- the terminal branches of the oesophageal branches of the thoracic aorta
- occasionally an ascending branch of the posterior gastric artery.
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.
The upper oesophagus is innervated by branches of the recurrent laryngeal nerve and by postganglionic sympathetic fibres that reach it by travelling along the inferior thyroid arteries. The lower oesophagus is supplied by the oesophageal plexus, a wide-meshed autonomic network that surrounds the oesophagus below the level of the roots of the lung.
Motor fibres to the striated and smooth muscle of the oesophageal wall travel in the vagus nerve (CN X). Axons derived from neuronal cell bodies in the nucleus ambiguous travel via the recurrent laryngeal nerve and supply cricopharyngeus and the striated muscle of the upper one-third of the oesophagus. Axons with cell bodies in the dorsal nucleus of the vagus pass through the oesophageal plexus and supply the smooth muscle that makes up the lower two-thirds of the oesophagus, after local relay in the oesophageal wall. Other branches are given-off by the vagus as it travels through the mediastinum , and pass directly to the oesophagus. The vagus nerve also carries secretomotor fibres to mucous glands in the oesophageal mucosa, and visceral afferent (sensory) fibres to cell bodies in its inferior ganglion.
Vasomotor sympathetic fibres destined for the oesophagus arise from the upper 4 – 6 thoracic spinal cord segments. Those from the upper ganglia pass to the middle and inferior cervical ganglia, where they synapse on postganglionic neurons that give rise to axons which innervate the vessels of the cervical and upper thoracic oesophagus. Those from the lower ganglia pass either directly to the oesophageal plexus or to the coeliac ganglion (via the greater splanchnic nerve), where they synapse. The postganglionic axons innervate the distal thoracic oesophagus.
Afferent visceral pain fibres travel through the sympathetic fibres to the first four segments of the thoracic spinal cord. As these segments also receive afferents from the heart, it is sometimes difficult to distinguish between oesophageal and cardiac pain.
The abdominal oesophagus is innervated by sympathetic and parasympathetic fibres. The parasympathetic fibres are derived directly from the peri-oesophageal thoracic plexus and to a lesser extent from the anterior and posterior vagi. They are motor to the distal oesophagus and both stimulatory and inhibitory to the functional lower oesophageal sphincter (LOS). They maintain both background tone and co-ordinate distal oesophageal peristalsis, with relaxation of the LOS during swallowing. The sympathetic supply originates from the 5th – 12th thoracic spinal segments and is mainly distributed through the greater and lesser splanchnic nerves and the coeliac 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.