Middle lobar bronchus

The middle lobar bronchus (Right middle lobe bronchus; RMLB) is the airway that arises from the bronchus intermedius on the right side and supplies the right middle lobe of the lung. It originates after the right upper lobe bronchus has branched off from the right main bronchus, with the remaining airway (the bronchus intermedius) continuing inferiorly before dividing into the middle lobar bronchus anteriorly and the right lower lobe bronchus posteroinferiorly.

The middle lobar bronchus typically divides into two segmental bronchi:

• B4 - the lateral segmental bronchus

• B5 - the medial segmental bronchus

This bifurcation pattern (B4, B5) is the predominant anatomy, observed in approximately 91% of individuals. A less common variant is a trifurcation pattern (B4, B5, B*), seen in roughly 89% of cases.