Posterior segmental bronchus of left lung

The posterior segmental bronchus of the left lung is the airway that ventilates the posterior segment (S2) of the left upper lobe. In Boyden's nomenclature, it is designated B2 on the left side. However, a key distinguishing feature of left lung anatomy is that the apical and posterior segments are typically fused, making the leftsided equivalent most commonly the apicoposterior segmental bronchus (B1+2) rather than an independent posterior segmental bronchus.

The left upper lobe bronchus (also called the upper division bronchus) gives rise to the segmental bronchi supplying the upper division. Unlike the right lung where the apical (B1), posterior (B2), and anterior (B3) segmental bronchi arise as three separate branches the left lung most commonly has a combined apicoposterior bronchus (B1+2) that shares a common stem before dividing into apical and posterior subsegmental branches. [1-2]

Branching Pattern Variations

Multidetector CT studies of large populations have identified the following major branching patterns of the left upper lobe segmental bronchi:

• Common stem of apical and posterior segmental bronchi (B1+2, B3) the most prevalent pattern, seen in approximately 6476% of individuals. Here, B1+2 arises as a single trunk that subsequently divides into apical (B1+2a, B1+2b) and posterior (B1+2c) subsegmental branches, while the anterior segmental bronchus (B3) arises separately.

• Trifurcation (B1+2+3) all three segments arise from a single point, seen in approximately 1723% of cases.

• Common stem of apical and anterior segmental bronchi (B1+3, B2) in this less common variant (~510%), the posterior segmental bronchus (B2) arises as an independent branch, while B1 and B3 share a common stem.

• Rare variants (B1a+B3, B1b+B2) seen in <1% of cases. [2]