Image A is a CT from a normal patient in the axial plane, displayed with lung windows. When there are enlarged nodes, they can be accessed using a mediastinoscope, which is a rigid metal tube through which visualization instruments and biopsy devices can be deployed.

Through this instrument, surgeons can do biopsies of any enlarged nodes they can see. Several possible sites for access are shown on the labeled image sequence B in green. The course of an important nerve is shown in blue. What nerve is this and how could damage cause the CXR findings?