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Anteromedial basal bronchus of left lung (B7+8)

The anteromedial basal bronchus (B7+8) is a combined segmental bronchus of the left lower lobe, formed by the fusion of the anterior basal (B8) and medial basal (B7) bronchi. This fusion occurs because the left lung has only four basal bronchi (B7+8, B9, B10, plus superior segment B6), unlike the right lung which has five. The B7+8 bronchus arises from the left lower lobe basal trunk, then courses anteriorly and medially to ventilate the anteromedial basal segment of the left lower lobe, adjacent to the diaphragm and mediastinum. It is an important bronchial segment for ventilation, surgical planning, and imaging evaluation of basal lung disease.

Synonyms

  • B7+8 bronchus

  • Left anteromedial basal bronchus

  • Anterior + medial basal bronchus (fused)

  • Anteromedial segmental bronchus of left lower lobe

Function

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

  • Provides ventilation and gas exchange in basal lung regions adjacent to the heart and diaphragm

  • Plays a role in mucus clearance from dependent lung segments

  • Serves as a surgical and radiological landmark in left lower lobectomy or segmentectomy

CT Appearance

Lung Window:

  • B7+8 appears as an air-filled hypodense (black) tubular structure branching from the left lower lobe basal trunk

  • Courses anteromedially toward the diaphragm and mediastinum

  • Normally has thin, barely visible walls

  • Pathology: wall thickening (bronchitis), luminal obstruction (tumor, mucus plug), bronchiectasis, or tree-in-bud nodularity (infection)

Mediastinal Window:

  • Wall appears as a thin soft tissue rim

  • Provides clear visualization of adjacent pulmonary vessels, heart border, and mediastinal structures

  • Useful in distinguishing endobronchial mass vs. extrinsic compression by lymphadenopathy or cardiac enlargement

Contrast-enhanced CT (CECT):

  • Enhances the bronchial wall and peribronchial vasculature

  • Demonstrates endobronchial lesions, stenosis, peribronchial tumor spread, or extrinsic compression

  • HRCT reconstructions allow precise assessment of segmental bronchial branching and lumen patency

MRI Appearance

T1-weighted images:

  • Air-filled lumen = signal void (black)

  • Bronchial wall appears as a thin hypointense rim

  • Surrounded by hyperintense mediastinal and peribronchial fat, which provides contrast

T2-weighted images:

  • Air-filled lumen remains signal void

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

  • Wall thickening (inflammation, tumor) = intermediate to hyperintense signal

T1 Post-Contrast (Gadolinium-enhanced):

  • Normal bronchial wall enhances as a thin, smooth rim

  • Pathological processes (bronchogenic carcinoma, granuloma, infection) show irregular, thickened, or nodular enhancement

  • Useful for differentiating endobronchial tumor vs. peribronchial infiltration

CT image

Anteromedial basal bronchus of left lung (B7+8) anatomy CT coronal image -img-00000-00000