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Lateral basal segmental bronchus of left lung (B9)

The lateral basal segmental bronchus (B9) is one of the basal segmental branches of the left lower lobar bronchus, alongside the anterior basal (B8), posterior basal (B10), and superior basal (B6) branches. B9 arises from the lower lobe bronchus and courses laterally toward the lateral basal segment of the left lower lobe, ventilating lung parenchyma along the lateral costophrenic recess. Its anatomic location makes it important in segmentectomy, lobectomy planning, and radiological interpretation, particularly in lower lobe pathology.

Synonyms

  • B9 bronchus

  • Left lateral basal bronchus

  • Lateral basal segmental bronchus of left lower lobe

Function

  • Conducts air to the lateral basal segment of the left lower lobe

  • Ensures ventilation and gas exchange in the lateral costophrenic recess

  • Facilitates mucus clearance in gravity-dependent lung regions

  • Serves as a radiological and surgical landmark for thoracic imaging and resection

CT Appearance

Lung Window:

  • B9 appears as an air-filled, hypodense (black) tubular structure branching laterally from the left lower lobar bronchus

  • Normally, the bronchial wall is thin and barely perceptible

  • Pathological changes: wall thickening (bronchitis), mucus plugging (airway obstruction), endobronchial mass, or tree-in-bud opacities (infection)

Mediastinal Window:

  • Shows the bronchial wall as a thin soft tissue rim surrounded by lung parenchyma

  • Better for assessing wall thickening, endobronchial nodules, or extrinsic compression from lymphadenopathy or masses

Contrast-enhanced CT (CECT):

  • Enhances the bronchial wall and adjacent pulmonary vessels

  • Useful for evaluating endobronchial tumors, peribronchial spread, or vascular compression

  • HRCT provides precise detail of bronchial caliber, branching, and parenchymal changes

MRI Appearance

T1-weighted images:

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

  • Bronchial wall appears as a thin hypointense rim relative to mediastinal fat

T2-weighted images:

  • Air-filled lumen remains a signal void

  • If fluid, mucus, or secretions are present, lumen becomes bright hyperintense

  • Bronchial wall thickening (infection, tumor, edema) appears intermediate to hyperintense

T1 Post-Contrast (Gadolinium-enhanced):

  • Normal bronchial wall shows mild, thin enhancement

  • Pathological findings (tumor, granuloma, inflammatory thickening) appear as irregular, nodular, or thickened enhancement

CT image

Lateral basal segmental bronchus of left lung (B9) anatomy CT coronal image -img-00000-00000