Oesophagus, Thoracic Duct and Thoracic Nerves

Extent:

• Muscular tube extending from the pharyngo-oesophageal junction (approximately C6 vertebral level, continuous with the trachea's origin) to the gastro-oesophageal junction (approximately T11 level, just below the diaphragm).
• Divided into cervical, thoracic, and (short) abdominal parts by the regions it traverses.

Course:

• Descends through the neck posterior to the trachea, enters the superior mediastinum, continues through the posterior mediastinum, passes through the oesophageal hiatus of the diaphragm at T10, and terminates a short distance below at the gastro-oesophageal junction.
• Not perfectly straight: deviates slightly to the left in the neck and lower thorax, with a rightward deviation in the mid-thorax (relative to the midline), reflecting its relations to the aortic arch and left atrium.

Relations:

• Anterior: Trachea (upper two-thirds), left main bronchus (crosses anteriorly at the level of the tracheal bifurcation), pericardium/left atrium (lower third), this posterior relationship of the left atrium to the oesophagus is the basis for transoesophageal echocardiography (TOE), which provides excellent imaging of the left atrium and mitral valve given their close proximity.
• Posterior: Vertebral column, thoracic duct (crosses from right to left behind the oesophagus around T5), azygos vein (lower portion, before it arches to join the SVC), descending thoracic aorta (comes to lie posterior/left as both structures descend).
• Right side: Azygos vein (arches over the right main bronchus to reach the oesophagus's posterior/right relation), mediastinal pleura.
• Left side: Aortic arch (crosses the oesophagus's left side at the level of T4), left subclavian artery, descending thoracic aorta (comes to lie to the left as it descends), mediastinal pleura.

Constrictions (clinically important: sites where swallowed material or endoscopes may lodge, and classic sites of stricture/carcinoma):

1. Upper (cricopharyngeal) constriction: at the pharyngo-oesophageal junction, C6 level; narrowest point of the entire oesophagus, caused by cricopharyngeus muscle.
2. Aortic/bronchial constriction (thoracic inlet is sometimes also cited, but the classic teaching centres on this level): where the aortic arch crosses (T4) and where the left main bronchus crosses anteriorly (just below, around T4-5), often described as one broad "middle" constriction, or as two closely related sites.
3. Diaphragmatic constriction: at the oesophageal hiatus, T10 level.

Blood supply:

• Upper third: Inferior thyroid artery (a branch of the thyrocervical trunk, from the subclavian artery).
• Middle third: Oesophageal branches directly from the descending thoracic aorta (typically 4–6 small branches).
• Lower third: Left gastric artery (a branch of the coeliac trunk) and left inferior phrenic artery, ascending from the abdomen.
• This tripartite, overlapping supply from three different major arterial systems (subclavian, aortic, coeliac) has surgical significance in oesophageal resection and reconstruction, since disruption of the collateral network can compromise the remaining segment's viability.

Venous drainage:

• Mirrors the arterial supply: upper third drains via the inferior thyroid vein, middle third via oesophageal veins into the azygos system, lower third via the left gastric vein into the portal venous system.
• The anastomosis between the azygos system (systemic) and the left gastric vein (portal) at the lower oesophagus is a clinically critical portosystemic anastomosis, forming oesophageal varices in the setting of portal hypertension (e.g., liver cirrhosis).

Lymphatics:

• Upper third: deep cervical nodes; middle third, superior and posterior mediastinal (tracheobronchial, paratracheal) nodes; lower third, left gastric and coeliac nodes.
• Rich submucosal lymphatic plexus allows for extensive longitudinal spread of oesophageal carcinoma, often beyond the visible/palpable extent of the primary tumour, a key factor in oesophageal cancer's typically advanced stage at diagnosis and its surgical management approach (wide longitudinal resection margins).

Innervation:

• Parasympathetic: Vagus nerve, upper striated muscle portion under somatic/branchial motor control (via the pharyngeal plexus and recurrent laryngeal nerves), lower smooth muscle portion under autonomic control from the oesophageal plexus (anterior and posterior vagal trunks, formed as the vagus nerves reorganise around the lower oesophagus).
• Sympathetic: Thoracic sympathetic trunk, via periarterial plexuses; mediates pain sensation (visceral referred pain, often perceived retrosternally, overlapping with cardiac pain patterns, a diagnostic challenge in differentiating oesophageal spasm from angina).

Important anatomical relations (summary):

• Trachea: Directly anterior in the upper two-thirds, relevant to tracheo-oesophageal fistula (congenital or acquired, e.g., from malignant erosion) and to the shared muscular wall allowing bulging during swallowing.
• Left atrium: Directly anterior in the lower third, basis for TOE imaging, and for oesophageal compression/dysphagia in severe left atrial enlargement (e.g., from mitral stenosis).
• Aorta: Crosses anteriorly at T4 (arch), then comes to lie posterior/left as the descending aorta, relevant to aortic aneurysm compression of the oesophagus, and to the risk of aorto-oesophageal fistula in severe untreated aneurysmal disease.
• Diaphragm: Passes through the oesophageal hiatus at T10, surrounded by right crus fibres, relevant to hiatus hernia.

• The largest lymphatic vessel in the body, draining the majority of the body's lymph (everything except the right side of the head/neck/thorax/right upper limb, which drains via the smaller right lymphatic duct).
• Origin: Continuation of the cisterna chyli, a lymphatic sac typically located at the L1-L2 vertebral level in the abdomen, receiving lymph from the lower limbs, pelvis, and abdominal viscera.
• Course: Enters the thorax through the aortic hiatus (T12) alongside the aorta, ascends through the posterior mediastinum initially on the right side of the midline (between the azygos vein on the right and the descending aorta on the left, posterior to the oesophagus), then crosses to the left side at approximately the T5 vertebral level, continuing its ascent through the superior mediastinum on the left side of the oesophagus.
• Relations: Posterior to the oesophagus for much of its course (a key relation, given the risk of thoracic duct injury during oesophageal surgery); passes behind the aortic arch and the left subclavian artery in the superior mediastinum/root of the neck.
• Termination: Arches laterally in the root of the neck, draining into the venous system at (or near) the junction of the left internal jugular vein and left subclavian vein (the left venous angle).
• Drainage territory: The entire body except the right side of the head, neck, and thorax, and the right upper limb (which drain via the much smaller right lymphatic duct into the right venous angle).

Right vagus:

• Descends through the neck, enters the thorax anterior to the right subclavian artery (giving off the right recurrent laryngeal nerve here, which loops under the right subclavian artery, a notably shorter, more direct course than its left counterpart), continues posterior to the right lung root, contributing to the posterior oesophageal plexus/posterior vagal trunk.

Left vagus:

• Descends through the neck and superior mediastinum, crosses the aortic arch anteriorly (giving off the left recurrent laryngeal nerve, which loops under the aortic arch, posterior to the ligamentum arteriosum, a much longer course than the right recurrent laryngeal nerve, extending well down into the thorax before ascending again), continues anterior to the left lung root, contributing to the anterior oesophageal plexus/anterior vagal trunk.

Recurrent laryngeal nerves:

• Both ascend within the tracheo-oesophageal groove back to the larynx, supplying all intrinsic laryngeal muscles except cricothyroid (which is supplied by the external laryngeal nerve), plus sensation below the vocal folds.
• The differing course length and hooking points (right: subclavian artery, in the root of the neck; left, aortic arch, well down in the thorax) explain why the left recurrent laryngeal nerve is more frequently injured by thoracic pathology (aortic aneurysm, mediastinal masses, cardiac surgery) given its longer intrathoracic course, while both nerves are similarly vulnerable during neck surgery (e.g., thyroidectomy).

Pulmonary plexus:

• Formed at each lung root by vagal (parasympathetic) and sympathetic contributions; distributes along the bronchial tree (see Sections 5 and 6).

Oesophageal plexus:

• Formed around the lower oesophagus by both vagus nerves, which lose their discrete left/right identity here and reorganise into anterior and posterior vagal trunks (predominantly derived from the left and right vagus respectively, though with significant intermingling of fibres) before passing through the diaphragm alongside the oesophagus into the abdomen.

• Roots: C3, C4, C5 (principally C4), arising from the cervical plexus, not the thoracic nerves, despite their long course through the thorax.
• Course: Descend through the neck (anterior to anterior scalene), enter the thorax, run anterior to the lung root on each side (a key distinguishing relation from the vagus nerve, which runs posterior to the lung root), between the mediastinal pleura and the fibrous pericardium, accompanied by the pericardiacophrenic vessels, to reach and supply the diaphragm.
• Relations: Right phrenic nerve runs alongside the SVC and right atrium; left phrenic nerve runs across the pericardium overlying the left ventricle, more exposed given the greater left-sided cardiac bulge, both are vulnerable during cardiac and thoracic surgery.
• Motor supply: Sole motor supply to the diaphragm.
• Sensory supply: Central diaphragm, mediastinal pleura, and fibrous/parietal pericardium, explaining referred shoulder-tip pain from irritation of any of these structures.

Thoracic sympathetic chain:

• Paired paravertebral chains of ganglia, running along the heads of the ribs (posterior thoracic wall), from the neck (continuous with the cervical sympathetic chain) to the diaphragm (continuous with the lumbar sympathetic chain, passing posterior to the medial arcuate ligament).
• Each thoracic ganglion (typically 11-12 per side, though the first often fuses with the inferior cervical ganglion to form the stellate ganglion) gives grey and white rami communicantes to the corresponding intercostal nerve, providing sympathetic innervation to the thoracic wall, and contributes cardiopulmonary branches to the cardiac and pulmonary plexuses (upper thoracic ganglia) and the splanchnic nerves (lower thoracic ganglia).

Greater splanchnic nerve:

• Formed from fibres of the T5–T9 (approximately) sympathetic ganglia.
• Pierces the diaphragmatic crus to reach the abdomen, synapsing predominantly in the coeliac ganglion, providing sympathetic innervation to foregut structures (stomach, liver, spleen, proximal duodenum, pancreas).

Lesser splanchnic nerve:

• Formed from fibres of the T10–T11 (approximately) sympathetic ganglia.
• Pierces the diaphragmatic crus, synapsing predominantly in the aorticorenal ganglion, providing sympathetic innervation partly overlapping midgut territory and contributing to renal/adrenal innervation.

Least (lowest) splanchnic nerve:

• Formed from fibres of the T12 sympathetic ganglion (variable/inconsistent, not always present as a discrete named nerve).
• Pierces the diaphragm, contributing to the renal plexus.

• All three splanchnic nerves carry preganglionic sympathetic fibres (synapsing in abdominal prevertebral ganglia, rather than in the paravertebral chain itself, unlike most other sympathetic outflow) and visceral afferent (pain) fibres from the abdominal organs they supply, a key point for understanding referred abdominal pain patterns, since these visceral afferents travel back to the same spinal cord segments (T5-T12) that gave rise to the corresponding splanchnic nerve, producing the classic poorly localised, midline-referred pattern of visceral (as opposed to somatic) abdominal pain.