Apical segmental bronchus of left lung

The apical segmental bronchus of the left lung (B1) is the bronchial branch that supplies the apical segment (S1) of the left upper lobe. 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 apical segmental bronchus.

The left upper lobe bronchus arises from the left main bronchus and divides into a superior division and a lingular division. The superior division gives rise to the apicoposterior segmental bronchus (B1+2) and the anterior segmental bronchus (B3).

The most common branching pattern of the left superior division is a common stem of the apical and posterior segmental bronchi (B1+2), occurring in approximately 6476% of individuals. Other patterns include trifurcation of B1, B2, and B3 (~1723%) and a common stem of B1+3 with a separate B2 (~610%).

B1+2 further subdivides into subsegmental branches: B1+2a (apical subsegment), B1+2b (posterior subsegment), and B1+2c (lateral subsegment), which can be identified on thin-section CT.