The oesophagus is a hollow viscous that connects the pharynx to the stomach.
Structure
The oesophagus is a muscular tube, about 25 cm in length, which is continuous with the laryngopharynx superiorly and the stomach inferiorly. It begins at the inferior border of the cricoid cartilage and C6; the gastro-oesophageal junction usually lies at T11. It is typically considered in three parts, based on the body cavities it runs through:
- The cervical oesophagus, most superior of the three, begins at the junction with the laryngopharynx and passes inferiorly to enter the thorax through the thoracic inlet
- The thoracic oesophagus, the longest part, descends from the thoracic inlet to the diaphragm, which it pierces (through the oesophageal hiatus) to enter the abdominal cavity.
- The abdominal oespohagus is a short segment (1.5 - 2 cm) that unites with the stomach at the gastro-oesophageal junction
There are several narrowings of the oesophagus which are related to sphincters or neighbouring structures
- The junction of the oesophagus and laryngopharynx (15 cm from incisor teeth)
- As the aortic arch passes anteriorly (22.5 cm from incisor teeth)
- As the left main bronchus passes anteriorly (27.5 cm from incisor teeth)
- At the gastro-oesophageal junction (40 cm from incisor teeth)
These provide important landmarks on gastroscopy.
Relations
The cervical oesophagus is related:
- Anteriorly with the trachea
- Anterolaterally with the thyroid gland and recurrent laryngeal nerves
- Laterally with the common carotid artery, with the internal jugular vein beyond this
- Posteriorly with the pre-vertebral muscles (longus colli) and the vertebral bodies of C6 and C7
The thoracic oesophagus has numerous relations:
- Above the roots of the lungs:
- Anteriorly with the trachea; the oesophagus is crossed by the left main bronchus, brachiocephalic artery and left brachiocephalic vein
- Anterior and right with the brachiocephalic artery and right common carotid.
- Anterior and left with the aortic arch and left common carotid
- Laterally with the pleura and lungs; the azygos vein passes across its right lateral surface to reach the superior vena cava
- Posteriorly with the thoracic vertebral bodies T1-T4
- Below the roots of the lungs:
- The heart lies anteriorly, separated by the pericardium
- The azygos vein lies posteriorly, often separated by a segment of pleura and lung. The vertebral bodies of T5-T10 are also posterior.
- The descending thoracic aorta is left lateral
- The vagus nerves descend laterally before becoming the oesophageal plexus; they accompany the oesophagus through the oesophageal hiatus to reach the abdomen
The abdominal oesophagus has few relations:
- The left lobe of the liver lies anteriorly and right lateral
- The left diaphragmatic crus and left inferior phrenic artery lie posteriorly; separating the oesophagus from the vertebral body of T11
- The stomach is left lateral
Microscopic Structure
The oesophagus has four histologically distinct layers:
- The mucosa lines the lumen of the oesophagus.
- The epithelium is normally stratified squmaous of non-keratinising type. Metaplastic change to simple columnar epithelium can be seen in the distal oesophagus
- The lamina propria contains numerous vessels and nerves in connective tissue
- The boundary between epithelium and lamina propria is uneven, with papillae of connective tissue serving as anchors for the overlying mucosa.
- The muscularis mucosae is a narrow band of smooth muscle that forms the outer component of the mucosa. The fibres are usually arranged longitudinally, except at the gastro-oesophageal junction.
- The submucosa lies between the mucosa and muscularis externa; it is an elastic tissue and contains oesophageal glands. These glands are tubuloacinar and are found in greatest density adjacent to the gastro-oesophageal junction
- The muscularis externa consists of two thick layers (total width ≈ 300 μm); the inner layer is circular and the outer layer longitudinal
- The muscle coat is interesting as it is comprised of striated muscle for the upper third; mixed striated and smooth for the middle third, and smooth muscle only for the lower third of the oesophagus
- The adventitia is thin and formed by loose connective tissue. In the abdominal oesophagus there is an additional serosal layer of peritoneum in the adventitia.
Function
The oesophagus is controlled by the enteric nervous system. When food is passed into the superior oesophagus during swallowing, the oesophagus begins peristaltic movements that propels the bolus to the lower oesophageal sphincter - this normally takes 8 - 20 seconds.
The lower oesophageal sphincter is controversial. There seems to be two components; a functional sphincter of circular smooth muscle at the gastro-oesophageal junction and an anatomical sphincter formed by the oesophageal hiatus of the diaphragm.
Neurovascular Supply
The supply of the oesophagus is complex as it passes through three different body cavities and is not supplied from a single source.
Arterial supply
The oesophagus is supplied by branches of numerous arteries:
- The cervical oesophagus is predominately supplied by branches from the inferior thyroid artery, a branch of the thyrocervical trunk (itself arising from the subclavian arteries)
- The thoracic oesophagus is supplied by branches from the bronchial arteries as well as from oesophageal arteries that arise directly from the aorta.
- The abdominal oesophagus is supplied by branches of the left gastric artery and left inferior phrenic artery
The vessels of the thoracic oesophagus have extensive anastamoses with each other as well as with the vessels supplying the cervical and abdominal portions.
Venous drainage
Capillaries collect into a submucosal plexus of veins, from which efferent vessels pass through the muscularis externa into a peri-oesophageal venous plexus. In the neck, blood is returned via the inferior thyroid veins to the brachiocephalic veins. In the thorax, most blood returns through the azygos vein although the bronchial veins, hemiazygos vein and even intercostal veins may receive venous blood from the oesophagus. In the abdomen, the oesophageal plexus forms the left gastric vein which drains to the portal vein and the liver.
Obstruction of venous return through the liver leads to development of oesophageal varices, which are enlarged vessels within the lamina propria of the oesophagus. These are prone to rupture with minimal trauma, leading to rapid loss of blood and death.
Lymphatic drainage
The lymphatics of the oesophagus are especially important in oncology. The long length of the oesophagus, as well its varying sources of vascular supply and drainage, lead to many potential routes of lymphatic spread. This is not helped by the rich lymphatic network that lies within the oesophagus, allowing communication of lymph fluid for almost the entire oesophagus.
- Lymph collects into an anastamosing network that is predominately situated in the submucosa and continuous for the entire length of the oesophagus
- Lymph from the cervical oesophagus usually drains to inferior deep cervical nodes (level IV) but may also pass to paratracheal nodes initially
- Lymph from the thoracic oesophagus usually drains to posterior mediastinal nodes (station 8)
- Lymph from the abdominal oesophagus usually drains to left gastric nodes
Innervation
The superior oesophagus is predominately supplied by the recurrent laryngeal nerve, which carries both motor and sensory input.
The inferior oesophagus is supplied by the oesophageal plexus, which is formed by the vagus nerves below the roots of the lungs. Parasympathetic is
Sympathetic supply to the oesophagus arises from T4-T6 (similar to the sympathetic supply of the heart); these are deployed to the heart via the cervical ganglia or the greater splanchnic nerve. Symphathetic supply is mostly vasomotor.
Routes of Malignant Spread
Local Invasion
Local invasion of oesophageal malignancies can impact on many organs, depending on the level of the tumour.
- Cervical malignancy can invade into the trachea, larynx or pharynx, causing severe obstruction of the airway or gastrointestinal tract. Lateral invasion can cause obstruction of the great vessels of the neck
- Thoracic malignancy can pass anteriorly into the great vessels, heart and trachea, laterally into the lungs and pleura (resulting in effusions) or posteriorly into the spinal column causing radicular pain.
- Abdominal malignancy can spread into the stomach or coeliac nerves.
Lymphatic Spread
The rich lymphatic plexus of the oesophagus facilitates widespread dissemination of malignancy. Involved lymph nodes extend from the neck, to the mediastinum and into the upper abdomen.
Haematogenous Spread
Oesophageal malignancy typically spreads to the lungs and liver.
Coding
The oesophagus is coded as C15. It can be divided into cervical, thoracic and abdominal parts (C15.0, C15.1 and C15.2) or upper, middle and lower thirds (C15.3, C15.4, C15.5). Tumours of the gastro-oesophageal junction are classified as C16.0 (cardia of stomach). See coding.
