azygous lobe

azygous lobe, a congenital malformation of the lung caused by a fold of pleural tissue carried by the azygous vein during descent into the thorax during embryonic development. It produces an extra lobe in the right upper lung and may appear on x-ray film as a fissure in the shape of an upside-down comma.

Azygous lobe (González et al, 2009)