Lower border of bronchus intermedius

The lower border of the bronchus intermedius serves as a key anatomic landmark in the IASLC lymph node map. The lower border of the bronchus intermedius is defined as the level where the bronchus intermedius terminates that is, the point at which it bifurcates into the [1] right middle lobe bronchus and the right lower lobe bronchus. This landmark is significant for the following stations:

Station 7 (Subcarinal nodes)

The subcarinal station extends from the carina superiorly down to the upper border of the lower lobe bronchus on the left and the lower border of the bronchus intermedius on the right (i.e., the origin of the right middle lobe bronchus). This was an important clarification introduced by the IASLC map, providing a more precise inferior boundary for the subcarinal space.

Station 11 (Interlobar nodes)

Station 11 nodes are located between the origins of the lobar bronchi. On the right side, Station 11s (right interlobar) nodes lie adjacent to the bronchus intermedius, from the origin of the right upper lobe bronchus down to the lower border of the bronchus intermedius. The lower border of the bronchus intermedius thus marks the transition from the interlobar region to the lobar bronchial stations (Station 12).

Station 10 (Hilar nodes)

Station 10R nodes are located adjacent to the right mainstem bronchus and bronchus intermedius, extending from the lower rim of the azygos vein to the region of the interlobar area. The lower border of the bronchus intermedius helps delineate the inferior extent of the hilar zone on the right side.