Location and Origin
The right main bronchus begins at the site of tracheal division — the bifurcation (bifurcatio tracheae, carina tracheae).
- Projection of origin: Anteriorly, the bifurcation projects at the sternal angle (level of the second intercostal space); posteriorly, it projects at the T4–T5 intervertebral disc (or T5–T6 vertebrae).
- Depth: In the region of the bifurcation, the depth from the skin surface is 6–12 cm.
- Angles of divergence: The total angle of tracheal bifurcation is 55–60°. The right bronchus deviates much less from the midline than the left, forming an obtuse angle of approximately 155° with the trachea. Because of this, it appears as a natural continuation of the trachea.
From its origin, the bronchus courses obliquely downward and laterally, as the pulmonary hila lie inferior to the level of the bifurcation.
Wall Structure
The right main bronchus is shorter and wider than the left (average diameter of 2 cm).
- Cartilaginous framework: The framework consists of 6–8 hyaline cartilage rings (cartilagines tracheales).
- Membranous wall: The posterior wall of the bronchus lacks cartilage. This is the membranous wall (paries membranaceus), which contains smooth muscle fibers (m. trachealis).
- Mucosa: The inner surface is lined with mucous membrane (tunica mucosa). It is covered by pseudostratified ciliated columnar epithelium and contains mucous glands (glandulae bronchiales).
Topography and Neighboring Structures
The right main bronchus is closely related to major blood vessels and nerves:
- Superiorly and posteriorly: At the level of the 4th thoracic vertebra, the azygos vein (v. azygos) arches over the right main bronchus before draining into the superior vena cava.
- Anteriorly: Near the bifurcation, the right bronchus is partially crossed by the right pulmonary artery (a. pulmonalis dextra).
- Medially and rightward: The right vagus nerve (n. vagus dexter) runs within the paratracheal loose connective tissue along the right side of the trachea and above the bifurcation, where the superior vena cava is also adjacent.
- Fascial apparatus: The trachea, bronchi, and esophagus are enclosed within a common esophagotracheal fascial sheath. This sheath is densest near the bifurcation, forms anchoring ligaments with the pulmonary vessels, and delimits the interbronchial space.
- Regional lymph nodes: Regional nodes for the bronchus include paratracheal, tracheobronchial, and bifurcation (subcarinal) lymph nodes.
Clinical and Surgical Significance
The anatomical features of the right main bronchus dictate specific pathologies and surgical approaches in this region:
- Foreign body aspiration: Because the right bronchus is wider and diverges at a more obtuse angle, acting as a nearly direct continuation of the trachea, foreign bodies enter it in 70% of cases.
- Right pneumonectomy: During removal of the right lung, the main bronchus is dissected up to the trachea, secured with a stapler, clamped, and divided near its origin.
- Tracheal tumors: When a malignancy extends into the right main bronchus and the stump cannot be mobilized for a safe anastomosis, a circular resection of the tracheal bifurcation combined with a right-sided pneumonectomy is indicated. Access is typically achieved via a lateral thoracotomy through the 4th or 5th intercostal space.