Topography and syntopy of the thoracic aorta
The thoracic aorta is located in the posterior mediastinum and lies directly against the vertebral bodies. At its very beginning, in the upper parts of the thoracic cavity, the vessel is situated slightly to the left of the midline of the vertebral column. As it descends, the aorta gradually shifts to the right, coming to lie strictly in the center, and at the level of the twelfth thoracic vertebra (Th12) leaves the thoracic cavity through the aortic hiatus of the diaphragm, continuing as the abdominal aorta.
The surroundings of the thoracic aorta (syntopy) are of great clinical significance. Anteriorly and to the right of the vessel run the azygos vein (v. azygos), while to the left are situated the hemiazygos veins (vv. hemiazygos). The thoracic duct is also in close contact. Anteriorly, the vessel is crossed by the left main bronchus.
Special attention should be paid to the relationship between the aorta and the esophagus, which changes as they descend:
- In the upper third of the thoracic region, the esophagus is located to the right of the aortic trunk.
- In the middle third, the esophagus passes anterior to the aorta.
- In the lower third, just before crossing the diaphragm, the esophagus shifts to the left.
Parietal branches
These branches supply blood to the walls of the thoracic cavity, including the muscles, skin, and diaphragm. They include the superior phrenic and posterior intercostal arteries.
1. Superior phrenic arteries (aa. phrenicae superiores) are 1–2 thin arterial trunks that arise from the lowest part of the thoracic aorta. They head toward the upper surface of the diaphragm, where they form anastomoses with the inferior phrenic arteries.
2. Posterior intercostal and subcostal arteries The posterior intercostal arteries (aa. intercostales posteriores, from III to XI) and one subcostal artery (a. subcostalis, XII) arise from the posterolateral surface of the aorta. In total, 10 intercostal and 1 subcostal artery arise from the aorta on each side. It is important to remember that the first and second posterior intercostal arteries usually arise from the a. intercostalis suprema (a branch of the costocervical trunk).
The posterior intercostal arteries run laterally and enter the corresponding intercostal spaces, passing along the groove of the lower border of the rib. At the level of the angle of the rib, each artery divides into a number of branches:
- Collateral branch (r. collateralis) — runs along the upper border of the underlying rib and anastomoses with the anterior intercostal arteries (from the internal thoracic artery).
- Posterior cutaneous branch (r. cutaneus lateralis) — pierces the intercostal musculature, supplying blood to the skin of the lateral chest and abdominal wall. In women, it also gives off branches to the mammary gland.
- Dorsal branch (r. dorsalis) — heads toward the deep muscles of the back and the overlying skin. It gives off the crucial spinal branch that enters the vertebral canal.
The terminal parts of the left intercostal arteries cross the costal margin, emerge between the broad muscles of the abdomen, and reach the rectus abdominis muscle, where they form anastomoses with the superior and inferior epigastric arteries.
Visceral branches
This group of vessels supplies blood to the internal organs located in the thoracic cavity. All of them arise from the anterior wall of the aorta.
- Bronchial branches (rr. bronchiales): usually 2–4 in number, they originate from the anterior wall of the initial part of the thoracic aorta. They head toward the bronchi, lymph nodes of the lung root, pleura, and partially to the esophagus.
- Esophageal branches (rr. esophagei): 3 to 6 vessels supplying the esophageal wall. They form important anastomoses with the esophageal branches of the left gastric artery (from the celiac trunk system) and the inferior phrenic arteries.
- Mediastinal branches (rr. mediastinales): numerous small branches supplying the tissue of the posterior mediastinum and the lymph nodes located there.
- Pericardial branches (rr. pericardiaci): head toward the posterior surface of the heart sac (pericardium).
Briefly: answers to topical questions
Which nerves and nerve plexuses are adjacent to the thoracic aorta in the posterior mediastinum?
The vagus nerves, as well as branches of the sympathetic trunk and the plexuses formed by them, are adjacent to the thoracic aorta in the posterior mediastinum. The topography of the neural structures depends on the level:
- Left vagus nerve — located anterior to the aorta.
- Vagus nerves — adjacent to the anteroposterior surface of the aorta at the level of the VII–X thoracic vertebrae.
- Branches of the sympathetic trunk — located externally to the fascial sheath of the aorta along with the plexuses they form.
Which specific branches arise from the dorsal branch of the posterior intercostal artery?
The spinal branch to the vertebral canal arises from the dorsal branch (r. dorsalis) of the posterior intercostal artery. The dorsal branch itself runs toward the deep back muscles and skin.
To remember how the esophagus wraps around the aorta from top to bottom, use the rule: First Right, then Anterior, finally Left.
Class and exam questions
At what level does the thoracic aorta transition into the abdominal aorta?
The transition occurs at the level of the twelfth thoracic vertebra (Th12) through the aortic hiatus of the diaphragm.
Where do the first and second posterior intercostal arteries arise from?
The first and usually the second posterior intercostal arteries arise not from the thoracic aorta, but from the supreme intercostal artery (a. intercostalis suprema), which is a branch of the costocervical trunk.
Which arteries do the esophageal branches of the thoracic aorta anastomose with?
They anastomose with the esophageal branches of the left gastric artery (from the abdominal aorta basin) and the inferior phrenic arteries.
What else to study on this topic
- Anastomoses of the anterior and posterior intercostal arteries
- Blood supply to the spinal cord: spinal branches of the dorsal arteries
- Topography of the posterior mediastinum and thoracic duct
- Blood supply to the diaphragm: superior and inferior arteries
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