The<unk>  is a normal variant that is found in 1% of anatomic specimens and on about 0.4% of chest radiographs. It occurs when the right posterior cardinal vein, one of the precursors of the<unk>  vein, fails to migrate over the apex of the lung and penetrates it instead, carrying along pleural layers that entrap a portion of the right upper<unk> .
The<unk>  is usually well seen on the chest radiograph, where it is limited by a fine, convex (relative to the mediastinum) line that crosses the apex of the right lung.
CT shows the deep penetration of the lung behind the SVC and the trachea.
The<unk>  fissure ends anteriorly at the right brachiocephalic vein and SVC, and posteriorly at the lateral aspect of the vertebral body near the location of the right superior intercostal vein.
The<unk>  vein is seen as a thicker structure following the same path as the fissure. The position of the arch is higher than when it follows an intramediastinal course
The<unk>  vein ends in the SVC and occasionally in the right brachiocephalic vein
Azygous lobe
Costodiaphragmatic recess
Hilum of lung
Renal lobe
Costomediastinal recess
Azygos vein
Mediastinal pleura
Hilum