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Left superior lobar bronchus

The left superior lobar bronchus (also called the left upper lobe bronchus) is a major branch of the left main bronchus that supplies the upper lobe of the left lung. It arises after the left main bronchus passes beneath the aortic arch and courses laterally and superiorly toward the hilum of the left lung. The left superior lobar bronchus divides into two divisions:

  • Upper (apicoposterior division): forms the apical (B1+2) and posterior (B2) bronchi (commonly fused as apicoposterior B1+2)

  • Lower (lingular division): forms the superior lingular (B4) and inferior lingular (B5) bronchi

This bronchus is essential for ventilation of the apical, posterior, anterior, and lingular segments of the left upper lobe. It is clinically significant in bronchoscopy, thoracic surgery (segmentectomy and lobectomy), and lung cancer staging.

Synonyms

  • Left upper lobe bronchus

  • Superior lobar bronchus of left lung

  • Bronchus lobaris superior sinister

Function

  • Conducts air into the segments of the left upper lobe (apicoposterior, anterior, superior lingular, inferior lingular)

  • Ensures ventilation and gas exchange of the upper lobe of the left lung

  • Plays a role in mucus transport and clearance

  • Serves as an important anatomical and surgical landmark in thoracic procedures

CT Appearance

Lung Window:

  • Appears as an air-filled hypodense (black) tubular structure branching from the left main bronchus

  • Courses superiorly and laterally toward the left upper lobe

  • Normally has thin, barely perceptible walls

  • Pathology: wall thickening (bronchitis), intraluminal obstruction (mucus, tumor), or tree-in-bud nodules (infection/bronchiolitis)

Mediastinal Window:

  • Wall appears as a thin soft tissue rim against surrounding mediastinal fat and vessels

  • Useful for detecting endobronchial masses, peribronchial lymphadenopathy, or vascular compression

  • Aids in differentiating between intrinsic vs. extrinsic bronchial narrowing

Contrast-enhanced CT (CECT):

  • Enhances the bronchial wall and adjacent pulmonary vessels

  • Essential for detecting endobronchial tumors, peribronchial infiltration, or compression by hilar lymph nodes

  • HRCT provides excellent detail of lumen caliber, wall thickness, and segmental branching

MRI Appearance

T1-weighted images:

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

  • Bronchial wall is seen as a low-signal rim, with surrounding fat hyperintense

  • Useful for anatomical localization but limited in bronchial lumen evaluation

T2-weighted images:

  • Lumen remains signal void unless filled with fluid/mucus, which appears bright hyperintense

  • Thickened or diseased bronchial walls appear intermediate to high signal intensity

T1 Post-Contrast (Gadolinium-enhanced):

  • Normal bronchial wall shows thin, mild rim enhancement

  • Pathological conditions (tumor, granuloma, inflammatory thickening) show irregular or nodular enhancement

CT images

Left superior lobar bronchus anatomy CT coronal image -img-00000-00000

MRI image

Left superior lobar bronchus anatomy MRI coronal image -img-00000-00000