Expansion
A normal variant formed when the azygos vein cuts through the apex of the right upper lobe
Expansion
During development the azygos vein normally migrates over the apex of the right lung. If it instead migrates through it, the vein drags a mesentery of pleura with it, isolating a portion of the right upper lobe.
- Present in about 0.5 per cent of people
- Creates the azygos fissure, seen on a chest radiograph as a fine curved line running down to a teardrop-shaped shadow, the vein itself
- Contains four pleural layers, since both parietal and visceral layers are invaginated
It is not a true accessory lobe, because it does not have its own bronchus; it is simply a partitioned part of the apical segment.
It is clinically silent, but worth recognising so it is not mistaken for a bulla, a pneumothorax line or scarring, and because it can complicate thoracoscopic surgery in that region.