CXR quiz 1


This Xray is taken from an 18 year old with influenza pneumonitis, but it also shows an anatomical variant.  

What is it?

swine flu plus azygous lobe.jpg


Azygous lobe

An Azygous Lobe is a harmless anatomical variant that is found in up to 1% of normal patients [1].  

In the upper mediastinum, the Azygous vein usually passes medial to the right lung from posterior to anterior, arching over the right main bronchus into the Superior Vena Cava.  

In 1% of patients, the vein is abnormally positioned more laterally.  It arches over the apex of the right lung, invaginating it, thereby creating a deep fissure in the parietal AND viseral pleura, known as the Azygous Fissure.  The fissure is classically concave medially, with the vein sitting at its base.

This gives the appearance of a separate lobe at the apex of the right lung.  However, since it does not possess its own bronchi, veins and arterial supply, it is not a true accessory lobe in anatomical terms.

The depth of the invagination is somewhat variable.

Seen end on in a PA or AP chest Xray, the vein often appears as a tear-drop opaque structure in the right upper zone.  


  1. Mata J, Cáceres J, Alegret X et-al. Imaging of the azygos lobe: normal anatomy and variations. AJR Am J Roentgenol. 1991;156 (5): 931-7.



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Past QUizzes

Chest Xrays

Quiz 1 - Chest trauma

Quiz 2 - Fall from a bike

Quiz 3 - Hypoxia after intubation

Abdominal Xrays

Quiz 1 - Fever and distension

CT Brain

Quiz 1 - Altered conscious state


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