Azygos Fissure

Azygos Fissure

• Normal variant, found in 1% of anatomic specimen and about 0.4% of chest radiographs
• Right posterior cardinal vein (precursor of azygos vein) fails to migrate over lung apex, instead penetrating the lung and carrying pleural layers with it.
• Two folds of parietal and visceral pleural layers create a "fissure"
• Enclosed lung is a part of apical or posterior segment of the right upper lobe

Findings

• Fine, convex line crosses the apex of the right lung.
• Azygos vein visible in the lowermost portion of the fissure "teardrop" shape.
• Absence of azygos vein at the right tracheobronchial angle.

Mimics of Azygos Fissure

• Scars
• Walls of bullae
• Displaced fissures
• Supernumerary fissures

Reference:

Mata J, Caceres J, Alegret X, Coscojuela P, De Marcos JA. Imaging of the azygos lobe: normal anatomy and variations. AJR 1991;156:931-937.