Upper border of lower left lobe bronchus

In the IASLC lymph node map, the upper border of the left lower lobe bronchus serves as a key anatomical landmark that defines the lower boundary of Station 7 (subcarinal lymph nodes) on the left side. Specifically, the subcarinal zone extends inferiorly from the carina down to the level of the origin (upper border) of the left lower lobe bronchus (and the right middle lobe bronchus on the right side).