azygos fissure

az·y·gos fis·sure

the four-layered pleural fold that separates an azygos lobe from the rest of the right upper lobe of the lung, seen as an oblique line curving down from the right apex toward the mediastinal shadow on a chest radiograph. The azygos vein is projected as a teardrop shadow at the inferior end of the azygos fissure.