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Superior segmental bronchus of right lung (B6)

The superior segmental bronchus of the right lung (B6) is the first and most prominent segmental branch of the right lower lobar bronchus. It arises posteriorly from the bronchus intermedius just beyond the origin of the right middle lobe bronchus. B6 courses dorsally and slightly laterally to ventilate the superior segment of the right lower lobe, an area located in the posterior aspect of the lung, adjacent to the vertebral column and diaphragm. It is clinically significant as the most common site of aspiration pneumonia, due to gravitational deposition of secretions when patients lie supine.

Synonyms

  • B6 bronchus

  • Superior segmental bronchus of right lower lobe

  • Apical basal bronchus of right lower lobe (older term, rarely used)

Function

  • Conducts air to the superior segment of the right lower lobe

  • Plays a role in ventilation and gas exchange in the posterior basal region of the lower lobe

  • Important in mucus clearance in the dependent portion of the lung

  • Serves as a key surgical and radiological landmark in lobectomy, segmentectomy, and infection assessment

CT Appearance

Lung Window:

  • B6 appears as a tubular, air-filled hypodense (black) structure arising from the right lower lobar bronchus and projecting dorsally

  • Normally has thin, smooth walls barely visible in healthy lungs

  • Pathology: wall thickening (bronchitis), endobronchial obstruction (tumor, mucus plug), bronchiectasis (dilated irregular B6), or consolidations (aspiration pneumonia) in its segment

Mediastinal Window:

  • Bronchial wall is seen as a thin soft tissue rim

  • Better delineates adjacent vessels, nodes, and mediastinal fat

  • Useful for detecting extrinsic compression by lymphadenopathy or masses

Contrast-enhanced CT (CECT):

  • Bronchial wall and surrounding vessels enhance with contrast

  • Excellent for identifying endobronchial lesions, peribronchial tumor spread, or vascular compression

  • HRCT allows precise visualization of bronchial caliber, patency, and branching pattern

MRI Appearance

T1-weighted images:

  • Air-filled lumen appears as a signal void (black)

  • Bronchial wall shows low signal intensity compared to surrounding fat and mediastinum

T2-weighted images:

  • Lumen remains a signal void if air-filled

  • Retained mucus or fluid makes lumen appear bright hyperintense

  • Wall thickening or inflammation appears as intermediate to high signal

T1 Post-Contrast (Gadolinium-enhanced):

  • Normal bronchial wall enhances mildly and uniformly

  • Pathological walls (tumor, infection, inflammation) show thicker, irregular, heterogeneous enhancement

CT image

Superior segmental bronchus of right lung (B6) anatomy CT coronal image -img-00000-00000

CT image

Superior segmental bronchus of right lung (B6) anatomy CT coronal image -img-00000-00000_00001