Left inferior lobar bronchus

The left inferior lobar bronchus (Left lower lobe bronchus) is the airway that supplies the left lower lobe of the lung. It arises from the left main bronchus after the takeoff of the left upper lobe bronchus, descending posteroinferiorly into the left lower lobeand giving these branches:

• Superior segmental bronchus [B VI]

• Medial basal segmental bronchus [B VII]

• Anterior basal segmental bronchus [B VIII]

• Lateral basal segmental bronchus [B IX]

• Posterior basal segmental bronchus [B X]

• Variations are possible like an anteromedial basal segmental bronchus of left lung (B7+8) or a subsuperior segmental bronchus of left lung (B*)

Anatomical definition and key features:

• The left main bronchus divides into two lobar bronchi: the left upper lobe bronchus and the left lower lobe (inferior lobar) bronchus. The left lower lobe bronchus is the continuation of the left main bronchus after the left upper lobe bronchus branches off.

• The first branch of the left inferior lobar bronchus is the superior segmental bronchus (B6), which supplies the apical (superior) segment of the lower lobe. The bronchus then continues as the basal trunk, which further divides into the basal segmental bronchi (B7 through B10), supplying the medial basal, anterior basal, lateral basal, and posterior basal segments:

• On the left side, the medial basal segment (B7) is often smaller or shares a common origin with B8 (anterior basal), which is the most common pattern (~55% of cases). The basal bronchi most commonly divide in a bifurcation pattern (~75-80%) or trifurcation pattern (~19%).

• The left inferior lobar bronchus is closely related to the left lower lobe pulmonary artery posteriorly and the left inferior pulmonary vein anteriorly and medially.

• On the lateral chest radiograph, the anterior wall of the left lower lobe bronchus can be visualized as a stripe, with its appearance influenced by adjacent vascular structures.