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Lateral basal segmental bronchus of right lung (B9)

The lateral basal segmental bronchus (B9) is one of the five segmental bronchi of the right lower lobe, along with the superior (B6), medial basal (B7), anterior basal (B8), and posterior basal (B10) bronchi. It arises from the right lower lobe basal trunk and courses laterally to supply the lateral basal segment of the right lower lobe. This bronchus ventilates the lateral portion of the basal lung, playing a critical role in gas exchange and mucus clearance. It is a key anatomical structure in bronchoscopy, thoracic imaging, and segmental lung resection surgery.

Synonyms

  • B9 bronchus

  • Right lateral basal bronchus

  • Lateral basal segmental bronchus of right lower lobe

Function

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

  • Supports ventilation and gas exchange in the lateral basal lung tissue

  • Contributes to mucus drainage from the basal regions of the lung

  • Serves as an important surgical and radiological landmark in thoracic procedures, particularly lower lobectomy and segmentectomy

CT Appearance

Lung Window:

  • Appears as an air-filled, hypodense (black) tubular structure branching laterally from the right lower lobe basal bronchial trunk

  • Normally has thin, barely perceptible walls

  • Pathological findings: wall thickening (bronchitis), mucus plugging, or narrowing due to tumor or fibrosis

  • Tree-in-bud opacities or air trapping may indicate infection or small airway disease

Mediastinal Window:

  • Wall appears as a thin soft tissue rim against surrounding parenchyma

  • Provides better delineation of adjacent vessels and lymph nodes

  • Helps in assessing peribronchial masses, extrinsic compression, or lymphadenopathy

Contrast-enhanced CT (CECT):

  • Bronchial wall and adjacent vessels enhance with contrast

  • Useful for detecting endobronchial lesions, peribronchial spread of carcinoma, or compression by hilar/mediastinal lymphadenopathy

  • High-resolution CT (HRCT) provides detailed assessment of lumen, branching pattern, and segmental involvement in interstitial lung disease

MRI Appearance

T1-weighted images:

  • Lumen appears as a signal void (black) when air-filled

  • Bronchial wall is low signal intensity, with surrounding fat hyperintense, enhancing visibility

T2-weighted images:

  • Air-filled lumen remains a signal void

  • If filled with fluid or mucus, lumen becomes bright hyperintense

  • Inflamed or thickened bronchial walls appear intermediate to high signal intensity

T1 Post-Contrast (Gadolinium-enhanced):

  • Normal bronchial wall may show thin rim enhancement

  • Pathological conditions (tumor, granuloma, infection) appear as irregular enhancing nodules or thickened walls

CT image

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