The empty azygos fissure.

The azygos fissure is typically visible on chest radiography as a right paramediastinal supernumerary line in projection of the right lung apex. The azygos vein, located at the bottom of the fissure, is visible as a teardrop-shaped opacity. The empty azygos fissure is a rare finding. It is the consequence of the displacement of the azygos vein out of the fissure with a close paramediastinal position. This phenomenon, related to lung collapse, has been described in the literature as the migration of the azygos vein due to various etiologies such as increased intrathoracic pressure, spontaneous or iatrogenic pneumothorax, or even during sudden development of kyphosis. In our clinical case, the empty azygos fissure was developed after drainage of a large right pleural effusion. An empty azygos fissure must therefore suggest a history of pulmonary atelectasis related to pneumothorax or large drained effusion.