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Superior lingular bronchus of left lung (B4)

The superior lingular bronchus (B4) is a segmental bronchus of the left upper lobe, arising from the lingular bronchus, which is a division of the left superior lobar bronchus. It courses anteroinferiorly to ventilate the superior lingular segment of the left lung, an area anatomically analogous to the middle lobe segments of the right lung. The B4 bronchus is a critical anatomical landmark in thoracic imaging, bronchoscopy, and pulmonary surgery, especially in segmentectomy for lingular lesions.

Synonyms

  • B4 bronchus

  • Superior lingular segmental bronchus

  • Segmental bronchus to superior lingular segment

Function

  • Supplies air to the superior lingular segment of the left lung

  • Ensures ventilation and gas exchange in the lingula

  • Contributes to mucus clearance from the lingular segment

  • Serves as a surgical and radiological landmark in left upper lobe resections

CT Appearance

Lung Window:

  • B4 appears as an air-filled hypodense (black) tubular structure branching from the lingular bronchus and coursing anteriorly and inferiorly

  • Normally thin-walled, barely perceptible against adjacent lung parenchyma

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

Mediastinal Window:

  • Bronchial wall appears as a thin soft tissue rim

  • Demonstrates relation to lingular pulmonary artery and vein

  • Helps differentiate endobronchial lesions from peribronchial lymphadenopathy or extrinsic compression

Contrast-enhanced CT (CECT):

  • Enhances bronchial walls and surrounding vasculature

  • Detects endobronchial tumors, infiltrative disease, or compression by hilar masses

  • High-resolution CT (HRCT) provides detailed assessment of lumen caliber and branching morphology

MRI Appearance

T1-weighted images:

  • Lumen with air appears as a signal void (black)

  • Bronchial wall is low signal intensity, surrounded by hyperintense peribronchial fat

T2-weighted images:

  • Air-filled lumen remains a signal void

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

  • Inflammatory or thickened walls demonstrate intermediate to high signal

T1 Post-Contrast (Gadolinium-enhanced):

  • Normal bronchial wall enhances as a thin rim

  • Pathological changes (tumor, granuloma, inflammation) appear as irregular, thickened, or nodular enhancing walls

CT image

Superior lingular bronchus of left lung (B4) anatomy CT coronal image -img-00000-00000