Benign anatomical variant that affects 3 to 5 % of the population. A partial pulmonary split, consisting of the passage of the azygos vein at the level of the upper lobe of the right lung, separates an accessory lobe called 'azygos' from the rest of the upper lobe.

During the fetal evolution, when the azygos vein is located above the right upper lobe, it can attract downwards the parietal pleura thus creating a meso at the same time as it digs a gutter into the lobe. This pseudoscissure formed by four pleural leaflets thus isolates a more or less large portion of pulmonary parenchyma of the upper lobe between the mediastinum and this meso: this portion is called the 'azygos lobe'.

When it exists, this split named azygos is often seen on the frontal X-Rays as a thin opaque vertical band starting from the top of the right lung, parallel and outside the right edge of the mediastinum, in the right upper lobe.

Anesthetic implications:

none, except in case of surgical repair of a spontaneous pneumothorax: hemorrhagic risk if the presence of the azygos vein within the lung tissue is unknown.

References :

-        Sadikot RT, Cowen ME, Arnold AG.
Spontaneous pneumothorax in a patient with an azygos lobe.
Thorax 1997; 52: 579-80.

-        Karre PR, Cooper GB.
The azygos lobe vein: interesting and typical image.
BMJ Case Reports 2011; doi: 10.1136/bcr.05.2011.4266

Updated: March 2021