Accessory Azygous Fissure

History: 50 year old male with cough.

Frontal chest radiograph reveals a curvilinear opacity convex toward the chest wall extending from the right tracheobronchial angle to the apex of the right lung.

This is the typical appearance of the accessory azygous fissure, which demarcates a portion of the right upper lobe of the right lung supplied by branches of the apical segment bronchus. It is a normal variant which is seen in about 0.4% of the population.