Medial basal segmental bronchus of left lung

The medial basal segmental bronchus of the left lung (B7) is the bronchus that supplies the medial basal segment (S7) of the left lower lobe. It is the airway branch that ventilates the portion of the left lower lobe directed medially toward the mediastinum, resting on the diaphragm.

Anatomical characteristics:

• In the standard Boyden classification of bronchopulmonary segments, the left lower lobe basal segments include the anteromedial basal (B8), lateral basal (B9), and posterior basal (B10) segments. The medial basal segment (S7/B7) on the left has historically been considered frequently absent or fused with the anterior basal segment (forming a combined "anteromedial basal segment B7+8").

• However, a recent large study using 3DCT bronchography found that left B7 is present as a distinct structure in approximately 75.6% of patients, challenging the traditional teaching that it is typically absent. Six distinct branching patterns were identified: [1]

  • Type 1 (most common, 61.4%): B7 arises from B8

  • Type 2 (6.3%): B7 arises higher than B8-B10

  • Type 3 (5.5%): B7 arises from B9

  • Type 4 (1.6%): B7 arises from both B8 and B9

  • Type 5 (0.8%): B7 arises from both B8 and B10

  • Type 6 (24.4%): B7 is absent