Coloured computed tomography (CT) scan of a chest from above showing an azygos lobe in the left lung (segmented area centre-left). An azygos lobe is an anatomical variant in the upper lobe of the lung in which a segment of the lung is separated by a deep groove called an azygos fissure, which consists of the azygos vein and pleura (thin tissue). It is a rare variation, occurring in around 0.3% of people during embryonic development. It causes no symptoms, but may make certain surgical procedures more difficult.