Location and Course
The thoracic aorta lies in the posterior mediastinum, resting directly against the vertebral column.
It extends from the IV to the XII thoracic vertebrae, running along their bodies just to the left of the midline. In its upper portion, it lies to the left of the spine; more inferiorly, it shifts slightly to the right. At the level of the IV–VI thoracic vertebrae, it shifts posteriorly and to the left of the esophagus. At the level of Th12, the aorta passes through the aortic hiatus of the diaphragm and transitions into the abdominal aorta (pars abdominalis aortae).
The vessel is enclosed in a fascial sheath that connects with the adventitia of the aorta itself, as well as with surrounding structures: the mediastinal pleura, prevertebral fascia (fascia prevertebralis), and fibrous pericardium.
Topography and Adjacent Structures
The thoracic aorta has the following syntopy:
- Anteriorly: root of the left lung, left vagus nerve, left main bronchus. Inferior to the lung root, the esophagus crosses the aorta anteriorly from right to left.
- Posteriorly: hemiazygos vein and left posterior intercostal veins. The thoracic duct lies adjacent to its posterior surface on the right.
- Right side: azygos vein (v. azygos).
- Left side: hemiazygos veins (vv. hemiazygos). The left outer semi-circumference of the aorta is covered by the mediastinal pleura.
- Externally: branches of the sympathetic trunk (truncus sympathicus) and their associated plexuses lie adjacent to the fascial sheath of the aorta. Lymph nodes are located in the periaortic adipose tissue.
Relationship to the Esophagus
The position of the esophagus relative to the aorta changes at different levels:
- Upper third: the esophagus lies to the right of the aorta.
- Middle third: the esophagus lies anterior to the aorta.
- Lower third: the esophagus lies to the left of the aorta.
Inferior to the root of the lung, the esophagus crosses the aorta anteriorly from right to left. At the level of the VII–X thoracic vertebrae, the esophagus and vagus nerves lie against the anteroposterior-right surface of the aorta, while the mediastinal pleura approaches from the right. Arteries branching from the thoracic aorta run along and supply the walls of the esophagus.
Branches of the Thoracic Aorta
The branches of the thoracic aorta are divided into two groups:
- Parietal branches (parietales).
- Visceral branches (viscerales).
Clinical Significance
Endovascular Surgery (Mapping)
To plan endovascular treatment, the aorta and iliac arteries are divided into zones. The descending thoracic aorta corresponds to zones 4 and 5. The boundary between them is approximately at the level of the mid-descending thoracic aorta, near the T6 vertebra.
Thoracic Aortic Aneurysms
- Traumatic: occur due to mechanical injury to the vessel wall. Most commonly located in the thoracic aorta during chest compression, such as in motor vehicle accidents.
- Syphilitic: a complication of tertiary syphilis — syphilitic mesaortitis. Specific inflammatory infiltrates destroy the elastic fibers of the tunica media of the aorta, replacing them with fibrous tissue. Localization includes the thoracic aorta, ascending aorta, or aortic arch. The shape can vary, most commonly saccular, with a size of 15–20 cm. Potential complications include erosion of the ribs and vertebral bodies, cardiac dysfunction, esophageal compression with dysphagia, recurrent laryngeal nerve compression with persistent cough, airway compression with respiratory distress, pain syndrome, and aneurysm rupture.
Diagnostics and Decision-Making Factors
CT angiography of the aorta, MR angiography, and PET-CT are used to identify inflammatory foci and assess large vessel involvement. Treatment with glucocorticosteroids (GCS) can suppress the vascular wall inflammatory signal; 3–5 days after starting GCS therapy, imaging results may become false-negative. Determining surgical indications takes into account patient body size, aortic wall condition, and the diameter ratio between the ascending and descending aorta.