Relations of the Thoracic Oesophagus

Relations of the thoracic oesophagus change at different vertebral levels as the oesophagus descends through the superior and posterior mediastinum.

Anterior Relations

Level	Anterior Structure
T1–T4 (superior mediastinum)	Trachea
T4–T5	Left principal bronchus and right pulmonary artery (oesophagus passes behind both)
T5–T7	Left atrium (separated by the oblique sinus of the pericardium and pericardium)
T7–T10	Diaphragm (below)

Clinical importance: Enlargement of the left atrium produces a smooth, curved posterior indentation on the oesophagus — visible on barium swallow examination. This is the most common cause of an oesophageal indentation below that produced by the left principal bronchus.

Posterior Relations

The oesophagus is separated from the vertebral column by a series of structures which vary by level:

From above downward, the following structures intervene between the oesophagus and the vertebral bodies:

1. Longus colli muscles (upper thoracic)
2. Thoracic duct (in the upper posterior mediastinum, lying between azygos vein and oesophagus)
3. Azygos vein (right side of vertebral column)
4. Upper six or seven right posterior intercostal arteries (cross behind oesophagus to enter their spaces)
5. Descending thoracic aorta (lower posterior mediastinum — lies posterior to and then to the left of the oesophagus below T7)

Right-Sided Relations

Structure	Notes
Right pleura and right lung	Adjacent throughout (mediastinal pleura)
Arch of azygos vein	Arches over the right lung root — lies to the right of the oesophagus in the upper thorax
Right vagus nerve	Descends on the right side of the trachea, then passes posterior to the right bronchus, then to the right and anterior surface of the oesophagus

Clinical importance: The right pleura lies adjacent to the right side of the oesophagus — oesophageal rupture or perforation typically produces right-sided pleural effusion.

Left-Sided Relations

Structure	Notes
Left pleura and left lung	Adjacent in the upper thorax (above aortic arch)
Left subclavian artery	In the superior mediastinum
Thoracic duct	Lies to the left of the oesophagus in the upper posterior mediastinum (before crossing to the right at T5)
Arch of the aorta	Crosses the left side of the oesophagus at T4 level (from T4 to T7, the descending aorta lies to the left of the oesophagus)
Descending thoracic aorta	Left side T4–T7; then the oesophagus moves left and aorta moves right — they exchange positions around T7
Left recurrent laryngeal nerve	Ascends in the groove between the left side of the trachea and oesophagus (in the superior mediastinum)

Summary Diagram (Cross-Sectional)

At mid-thoracic level (approximately T6):

         Anterior
    Left atrium / pericardium
           |
Left      Oesophagus     Right
vagus  ←    |     →    vagus
           |
     Descending aorta
    (left and posterior)
         Posterior
         Vertebrae

Thoracic Duct Relationship

The thoracic duct runs between the oesophagus and the vertebral column in the upper mediastinum. At approximately T5 vertebral level (near the arch of the aorta), it passes obliquely from right to left behind the oesophagus to reach the left side of the mediastinum, where it ascends to the root of the neck.