CXR Case 135

There is an azygos lobe visible in the right upper zone.
Normal parenchyma and pleura

An azygos lobe is a rare variant of normal anatomy, seen in approximately 1-2% of the population.

The clinical importance of an azygos lobe is that it can become consolidated with infection and mimic a lung mass.

The azygos lobe is not a true accessory lobe as it does have its own bronchus or bronchopulmonary segment.

It is formed by the right posterior cardinal vein (embryological precursor to the azygos vein) passing through the right upper lobe, rather than over the surface of the lobe.