Upper margin of aortic arch

In the IASLC lymph node map, the upper margin (top) of the aortic arch serves as a key anatomical landmark that defines the boundary between several mediastinal lymph node stations. Its role can be summarized as follows:

The upper margin of the aortic arch corresponds to the most cranial aspect of the aortic arch as visualized on axial CT imaging. In the IASLC lymph node map proposed by Rusch et al. (2009), this landmark functions as a critical boundary for the left-sided paratracheal and aortopulmonary lymph node stations:

• Station 2L (left upper paratracheal): The lower boundary of station 2L is defined by the upper margin of the aortic arch. Station 2L extends from this level superiorly up to the upper border of the manubrium (in the midline).

• Station 4L (left lower paratracheal): The upper boundary of station 4L is defined by the upper margin of the aortic arch. Station 4L extends inferiorly from this level to the upper border of the left main pulmonary artery, medial to the ligamentum arteriosum.

• Station 5 (subaortic / aortopulmonary window): Station 5 nodes lie lateral to the ligamentum arteriosum, in the aortopulmonary window. The upper boundary of station 5 is also defined by the lower border of the aortic arch (or equivalently, the inferior margin of the aortic arch), while the upper margin of the aortic arch delineates the transition from the aortopulmonary zone to the upper paratracheal zone.

• Station 6 (para-aortic / ascending aorta or phrenic): Station 6 nodes lie anterior and lateral to the ascending aorta and aortic arch. The upper margin of the aortic arch helps define the cranial extent of this station.