Location and skeletotopy
The thoracic part of the trachea is localized in the superior mediastinum. On the anterior chest wall, the organ is projected onto the sternum, with a slight displacement to the right of the midline. The depth of the trachea varies: while it lies superficially at the jugular notch (at a depth of 3–4 cm), this figure reaches 6–12 cm as it descends into the thoracic cavity.
Anatomical boundaries:
- Superior boundary: anteriorly corresponds to the jugular notch of the sternum, and posteriorly to the level of the second thoracic vertebra.
- Inferior boundary (bifurcation zone): anteriorly projected onto the sternal angle or the level of the second intercostal space. Posteriorly, this point corresponds to the intervertebral disc between the IV and V thoracic vertebrae.
Clinical note: When determining the projection of the bifurcation onto the vertebral column, the level of the V–VI thoracic vertebrae is usually used as a landmark; however, in patients with a narrow and long chest, this boundary may be shifted somewhat higher.
Anatomy of the bifurcation and main bronchi
The division of the respiratory tube into two main bronchi is called the tracheal bifurcation (bifurcatio tracheae). The total divergence angle of the bronchi is 55–60°, but their anatomy is asymmetrical, which has direct applied significance in surgery and pulmonology.
- Right main bronchus (bronchus principalis dexter): departs from the trachea at an obtuse angle of about 155°. Topographically, it deviates from the midline to a lesser degree, serving as a nearly direct continuation of the trachea. Because of this feature, 70% of cases of aspirated foreign bodies enter the right bronchial tree.
- Left main bronchus (bronchus principalis sinister): departs at a sharper angle, which is approximately 120°.
Syntopy: relationship with adjacent organs
The organs and large vessels of the mediastinum lie closely adjacent to the trachea and bronchi, forming a complex topographic complex.
- Anterior surface: At the level of the upper boundary, the left common carotid artery (a. carotis communis sinistra) and the brachiocephalic trunk (truncus brachiocephalicus) lie adjacent to the trachea. Below, in the bifurcation area, the right pulmonary artery passes anteriorly (partially covering the right bronchus).
- Inferior surface: Immediately below the bifurcation zone lie the pericardium and the right atrium.
- Right lateral surface: Along the trachea here lies the paratracheal adipose tissue, through which the right vagus nerve (n. vagus dexter) passes. The superior vena cava lies adjacent superiorly to the bifurcation itself. Posteriorly and superiorly, the right bronchus is arched by the azygos vein (v. azygos) before it drains into the superior vena cava system.
- Left lateral surface: In the lower section, the aortic arch (arcus aortae) arches over the left main bronchus.
- Posterior surface: The esophagus (esophagus) lies behind and is slightly shifted to the left. At the junction of the two organs, the tracheoesophageal groove is formed, which serves as a bed for the passage of the left recurrent laryngeal nerve (n. laryngeus recurrens sinister).
Fascial apparatus and lymphatic system
Lymph drainage from this segment is directed into the system of regional lymph nodes: paratracheal, tracheobronchial, and bifurcation nodes. It is important to note that these same nodes collect lymph from the esophagus and the fascial spaces of the mediastinum.
The trachea, bronchi, and esophagus are enclosed in a common tracheoesophageal fascial sheath.
Features of the fascial apparatus:
- The sheath has maximum density in the bifurcation area, as well as on the anterior and lateral walls of the trachea.
- Strong stabilizing ligaments depart from the fascia to the thymus bed, the endothoracic fascia, the pulmonary vessels, and the aortic arch.
- The sheath plays the role of a barrier, isolating and limiting three important fascial spaces: interbronchial, pretracheal, and periesophageal.
Vessels and nerves of the topographic region
When studying cross-sections of this region (according to classical anatomical diagrams), the following are also identified in the immediate vicinity of the tracheobronchial tree:
- Branches of the aortic arch, including the left and right subclavian arteries (a. subclavia sinistra et dextra) and the right common carotid artery (a. carotis communis dextra).
- Bronchial arteries (a. bronchialis), providing blood supply to the bronchi themselves, and esophageal branches of the aorta (rr. esophagei aortae).
- Elements of the autonomic nervous system: the sympathetic trunk (truncus sympathicus) and the esophageal plexus of the vagus nerves (plexus esophagus nn. vagorum).
- Intercostal neurovascular bundles (a., v. et n. intercostales).
Briefly: answers to topical questions
Which nerves are involved in the innervation of the trachea and main bronchi?
- Recurrent laryngeal nerves (nn. laryngei recurrentes).
- Branches of the pulmonary plexus.
Right bronchus — Straight and Wide (155° angle). It serves as an almost direct continuation of the trachea, which is why Objects End Up There (70% of foreign bodies).
Class and exam questions
Where does the left recurrent laryngeal nerve run?
It runs in the tracheoesophageal groove, which is formed between the posterior wall of the trachea and the esophagus (the latter being shifted somewhat to the left).
Why do foreign bodies enter the right bronchus in 70% of cases?
Because the right main bronchus deviates from the midline by a smaller angle (about 155°) and is practically a direct geometric continuation of the trachea.
What fascial spaces does the tracheoesophageal fascia limit?
This fascial sheath limits the periesophageal, pretracheal, and interbronchial fascial spaces.
What else to study on this topic
- Topography of paratracheal and bifurcation lymph nodes
- Anatomy of the tracheoesophageal groove
- Syntopy of the right and left vagus nerves in the mediastinum
- Formation of the ligamentous apparatus of the tracheoesophageal fascia
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