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Left inferior lobar bronchus

The left inferior lobar bronchus (also called the left lower lobar bronchus) is a direct continuation of the left main bronchus, distal to the origin of the superior lobar bronchus. It descends posteroinferiorly toward the hilum of the left lower lobe and divides into five segmental bronchi: the superior (B6), and the basal bronchi — anteromedial basal (B7+8), lateral basal (B9), and posterior basal (B10). This bronchus supplies the entire left lower lobe, which is responsible for a significant portion of gas exchange and is a common site for aspiration-related pathology due to its more vertical and posterior orientation.

Synonyms

  • Left lower lobar bronchus

  • Inferior lobar bronchus of left lung

  • Bronchus lobaris inferior sinister

Function

  • Conducts air to the left lower lobe of the lung

  • Facilitates ventilation and gas exchange in both the superior and basal segments

  • Plays a role in mucus clearance and maintaining lung aeration

  • Serves as a key bronchoscopic and radiological landmark in thoracic imaging and surgery

CT Appearance

Lung Window:

  • Appears as a hypodense (black), air-filled tubular structure arising from the left main bronchus below the superior lobar bronchus

  • Courses posteroinferiorly into the hilum of the lower lobe

  • Normally has thin, barely perceptible bronchial walls

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

Mediastinal Window:

  • Shows the bronchial wall as a thin soft tissue rim

  • Provides better visualization of adjacent pulmonary arteries and veins

  • Useful for evaluating endobronchial masses, extrinsic compression from lymphadenopathy, or vascular invasion

Contrast-enhanced CT (CECT):

  • Bronchial wall enhances, improving delineation

  • Helps in detecting bronchial stenosis, intraluminal tumors, peribronchial spread of carcinoma, or post-obstructive pneumonia

  • HRCT provides detailed visualization of bronchial lumen, branching, and segmental anatomy

MRI Appearance

T1-weighted images:

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

  • Bronchial wall shows low signal intensity

  • Surrounded by hyperintense mediastinal and peribronchial fat, aiding visibility

T2-weighted images:

  • Air in lumen remains a signal void

  • Fluid or mucus within the lumen appears bright hyperintense

  • Thickened or inflamed walls appear intermediate-to-hyperintense compared to normal bronchial wall

T1 Post-Contrast (Gadolinium-enhanced):

  • Normal wall shows thin, mild homogeneous rim enhancement

  • Pathology (tumor, infection, granulomatous disease) causes irregular, thickened, or nodular enhancing walls

  • Useful for differentiating intraluminal tumor vs. peribronchial disease

CT images

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

CT images

Left inferior lobar bronchus anatomy CT coronal image -img-00000-00000_00002

MRI IMAGE

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