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Apicoposterior segmental bronchus of left lung

The apicoposterior segmental bronchus (B¹+²) is a segmental bronchus of the left upper lobe. It results from the fusion of the apical bronchus (B¹) and posterior bronchus (B²), which remain separate on the right but merge on the left to form a single bronchus.

It arises from the left upper lobe bronchus, coursing dorsally and superiorly into the apicoposterior bronchopulmonary segment (S¹+²). This segment occupies the apical and posterior aspects of the left upper lobe, adjacent to the vertebral column and superior mediastinum. B¹+² travels with its segmental pulmonary artery branch (A¹+²) and drains into segmental veins (V¹+²).

This bronchus is of high clinical importance in segmentectomy, bronchoscopy, and CT-guided procedures, and serves as a key landmark for defining bronchopulmonary segments.

Synonyms

  • Apicoposterior bronchus (B¹+²)

  • Apical-posterior bronchus of left upper lobe

  • Segmental bronchus to S¹+²

Function

  • Provides airflow to the apicoposterior segment (S¹+²) of the left upper lobe

  • Ensures effective ventilation and gas exchange in the apical and posterior lung fields

  • Serves as a bronchoscopic landmark in diagnostics and interventions

  • Important for planning segmental resections in lung surgery

MRI Appearance

T1-weighted images:

  • Appears as a hypointense branching airway lumen filled with air (signal void), outlined by hyperintense peribronchial fat and vessels

T2-weighted images:

  • Air-filled lumen remains a signal void, while surrounding lung parenchyma and vessels provide contrast

  • Mucus plugging or fluid appears hyperintense within the lumen

T2 TRUFISP (cardiac/respiratory-gated):

  • Shows sharp lumen outline with high contrast against parenchyma

  • Dynamic cine evaluation allows assessment of airway motion and compression

STIR:

  • Highlights peribronchial edema, lymphadenopathy, or inflammation as hyperintense zones

  • Air-filled bronchus remains dark

T1 Post-Contrast (Gadolinium-enhanced MRI):

  • Bronchial wall may enhance if inflamed or thickened

  • Useful for detecting peribronchial tumor infiltration or vascular involvement

MRI Non-Contrast 3D Cardiac/Respiratory-Gated Imaging:

  • Provides 3D reconstructions of the bronchial tree

  • Clearly depicts the B¹+² bronchus arising from the left upper lobe bronchus and its course to S¹+²

  • Valuable for pre-surgical planning and bronchoscopic correlation without contrast

CT Appearance

CT Coronary Angiography / CT Bronchography:

  • High-resolution CT (HRCT) shows B¹+² as a segmental airway branch arising from the left upper lobe bronchus

  • Course traced dorsally into apicoposterior segment of the upper lobe

  • Multiplanar reconstructions (axial, coronal, sagittal) allow detailed mapping of segmental anatomy

  • CT detects airway narrowing, obstruction, stenosis, or mass invasion

  • 3D CT bronchography provides excellent visualization for segmentectomy planning or bronchoscopic navigation

CT image

Apicoposterior segmental bronchus of left lung anatomy CT coronal image -img-00000-00000