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Right apical segmental bronchus (B1)

The right apical segmental bronchus (B1) is one of the three segmental branches of the right superior lobar bronchus, along with the posterior (B2) and anterior (B3) branches. It arises early from the superior lobar bronchus and ascends upward and laterally to ventilate the apical segment of the right upper lobe. This bronchus supplies the superior-most lung parenchyma, corresponding to the apex of the right lung. It is a critical landmark in bronchoscopy, thoracic imaging, and pulmonary surgery, especially in segmentectomy and lobectomy planning.

Synonyms

  • B1 bronchus

  • Right apical bronchus

  • Apical segmental bronchus of right upper lobe

Function

  • Conducts air to the apical segment of the right upper lobe

  • Maintains ventilation and gas exchange at the apex of the right lung

  • Plays a role in mucus clearance from the apical segment

  • Serves as a radiological and surgical landmark in thoracic procedures

CT Appearance

Lung Window:

  • B1 appears as an air-filled, hypodense (black) tubular structure arising from the right superior lobar bronchus and coursing superiorly toward the lung apex

  • Normally has thin, barely perceptible bronchial walls

  • Pathology: wall thickening (bronchitis), luminal obstruction (mucus plug, tumor), or tree-in-bud opacities (infection)

Mediastinal Window:

  • Bronchial wall appears as a thin soft tissue rim

  • Provides better visualization of adjacent vessels and mediastinal structures

  • Helps differentiate between endobronchial mass, peribronchial lymphadenopathy, or extrinsic compression

Contrast-enhanced CT (CECT):

  • Enhances the bronchial wall and surrounding mediastinal vessels

  • Useful for detecting endobronchial tumors, peribronchial spread of carcinoma, and vascular compression

  • HRCT gives excellent detail of bronchial caliber, lumen, and branching pattern

MRI Appearance

T1-weighted images:

  • Air within B1 lumen appears as a signal void (black)

  • Bronchial wall shows low signal intensity, surrounded by hyperintense fat in the hilum

T2-weighted images:

  • Lumen remains a signal void when air-filled

  • If fluid or mucus is present, lumen appears bright hyperintense

  • Thickened or inflamed bronchial walls show intermediate to high signal intensity

T1 Post-Contrast (Gadolinium-enhanced):

  • Normal bronchial wall shows thin, mild rim enhancement

  • Pathology (tumor, granuloma, infection) appears as irregular, thickened enhancing walls or nodular endobronchial masses

CT image

Right apical segmental bronchus (B1) anatomy CT coronal image -img-00000-00000