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Tracheal bifurcation

The tracheal bifurcation, also known as the carina, is the anatomical point where the trachea divides into the right and left main bronchi. It is located at the level of the sternal angle (T4–T5 vertebral level) in adults. The carina forms an internal ridge of cartilage and mucosa that projects between the two bronchi.

The right main bronchus is shorter, wider, and more vertical, making it a common site for aspirated foreign bodies. The left main bronchus is longer, narrower, and more horizontal. The bifurcation is closely related to the aortic arch, pulmonary arteries, and lymph nodes, which are clinically relevant in mediastinal disease and lung cancer staging.

The tracheal bifurcation is an important landmark in bronchoscopy, thoracic surgery, and cross-sectional imaging. Widening or distortion of the carina may indicate subcarinal lymphadenopathy, tumors, or mediastinal pathology.

Synonyms

  • Carina of trachea

  • Bifurcatio tracheae

  • Tracheal carina

Function

  • Directs inspired air into the right and left main bronchi

  • Acts as a protective cough reflex zone when stimulated

  • Serves as a bronchoscopic and imaging landmark for diagnosis and staging of thoracic disease

Branches

  • Right main bronchus → supplies right lung

  • Left main bronchus → supplies left lung

MRI Appearance

T1-weighted images:

  • Tracheal lumen appears hypointense (black) due to air; walls appear intermediate signal

  • The bifurcation is seen as a Y-shaped structure at the thoracic inlet

T2-weighted images:

  • Air remains signal void; surrounding mediastinal fat and vessels show high signal contrast

  • Pathological changes (e.g., peribronchial edema, tumor) appear hyperintense relative to cartilage

STIR:

  • Fat suppression improves delineation of the bifurcation against mediastinal fat

  • Highlights peribronchial inflammation, edema, or lymphadenopathy

T1 Post-Gadolinium (Gd-enhanced MRI):

  • Tracheal lumen remains non-enhancing (air-filled)

  • Enhancing surrounding soft tissue masses or nodes help in staging and diagnosis

MRI Non-Contrast Cardiac-Gated 3D Imaging:

  • Provides a 3D airway map showing the trachea bifurcating into right and left bronchi

  • Used for airway reconstruction, preoperative planning, and congenital anomaly assessment

CT Appearance

CT Post-Contrast (Chest CT / CT Angiography):

  • Tracheal bifurcation clearly visualized as a Y-shaped air-filled structure

  • Contrast delineates adjacent vascular structures (aorta, pulmonary arteries, SVC)

  • Detects carinal widening, subcarinal lymphadenopathy, tumors, extrinsic compression, or airway stenosis

  • Multiplanar and 3D reconstructions provide excellent anatomical detail for thoracic surgery and oncology

CT images

Tracheal bifurcation CT axial image -img-00000-00000

CT images

Tracheal bifurcation CT axial image -img-00000-00000_00001

CT images

Tracheal bifurcation CT CORONAL image -img-00000-00000