Thoracic Aorta

The thoracic aorta is the portion of the descending aorta located within the thoracic cavity. It begins at the level of the T4 vertebra, where it continues from the aortic arch, and descends through the posterior mediastinum on the left side of the vertebral column. It terminates at the aortic hiatus of the diaphragm at the level of T12, where it continues as the abdominal aorta. The thoracic aorta serves as a major arterial trunk delivering oxygenated blood to the thoracic wall, lungs, esophagus, and upper abdominal structures.

Location and Course

The thoracic aorta lies within the posterior mediastinum and follows a descending path:

• Begins: At the lower border of T4 vertebra (continuation of the aortic arch)
• Ends: At the lower border of T12 vertebra (where it passes through the aortic hiatus of the diaphragm)

Initially, it lies on the left side of the vertebral column but gradually shifts medially to lie directly anterior to the vertebrae by the time it reaches the diaphragm.

Anterior Relations

• Left lung root (superiorly)
• Esophagus (initially to the right of the aorta, then anterior)
• Pericardium and left atrium (via esophagus)

Posterior Relations

• Vertebral bodies of T5 to T12

Right Side Relations

• Azygos vein
• Thoracic duct (initially)
• Esophagus (lower half)

Left Side Relations

• Left lung and pleura
• Left sympathetic trunk

Branches of the Thoracic Aorta

The thoracic aorta gives rise to both paired and unpaired branches that supply thoracic organs, the body wall, and diaphragm. The major branches are:

Posterior Intercostal Arteries

There are typically nine pairs (from T3 to T11). Each artery runs laterally into an intercostal space, located between the innermost and internal intercostal muscles. They supply the thoracic wall and associated musculature. The first two intercostal spaces are supplied by branches of the costocervical trunk, not the aorta.

Subcostal Arteries

These are the terminal branches of the thoracic aorta located below the 12th rib, supplying the abdominal wall in the subcostal region.

Bronchial Arteries

Typically, there are one right and two left bronchial arteries. These vessels supply the bronchial tree and connective tissue of the lungs, independent of the pulmonary arteries.

Esophageal Arteries

Several small branches (usually 4–5) arise from the thoracic aorta to supply the middle third of the esophagus. These arteries anastomose superiorly with esophageal branches of the inferior thyroid artery and inferiorly with branches from the left gastric artery.

Pericardial Branches

Small vessels that supply the posterior aspect of the pericardium.

Superior Phrenic Arteries

These arise from the lower portion of the thoracic aorta and supply the superior surface of the diaphragm. They may anastomose with branches from the musculophrenic and pericardiacophrenic arteries.

Relations with Surrounding Structures

Anterior

• Root of the left lung
• Esophagus (lower down)
• Pericardium via the esophagus

Posterior

• Thoracic vertebral bodies (T5 to T12)

Right

• Azygos vein
• Thoracic duct
• Esophagus (midway)

Left

• Mediastinal pleura and lung
• Descending thoracic sympathetic trunk

Anatomical Transition

At the level of T12, the thoracic aorta passes through the aortic hiatus in the diaphragm and becomes the abdominal aorta. The aortic hiatus also transmits the thoracic duct and the azygos vein (sometimes).

Topographic Summary

• Level of Origin: T4 vertebra (as continuation of the aortic arch)
• Level of Termination: T12 vertebra (becomes abdominal aorta)
• Compartment: Posterior mediastinum
• Main Branches: Posterior intercostal, subcostal, bronchial, esophageal, pericardial, and superior phrenic arteries