Question:

Which statements are true regarding the azygos fissure:
1. It is composed by a total of 2 layers of visceral pleura, called mesoazygos.
2. It develops after the failure of migration of the posterior cardinal vein during fetal development.
3. It defines an accessory lobe called Adam`s lobe, functionally independent from the other lobes.
4. It is visualized on chest radiography as a supernumerary line in projection of the right lung apex, in a paramediastinal position.
5. An azygos fissure may develop following an atelectasis of the right lung.





Answer:

The correct answers for the question "Which statements are true regarding the azygos fissure:" are:

2. It develops after the failure of migration of the posterior cardinal vein during fetal development.

4. It is visualized on chest radiography as a supernumerary line in projection of the right lung apex, in a paramediastinal position.



Explanation
1. The mesoazygos is composed by two layers of visceral pleura and two layers of parietal pleura. [The vein carries the parietal and visceral layers of pleura to form an accessory fissure comprising a total of four pleural layers, called mesoazygos]

2. [During fetal development, the right posterior cardinal vein, precursor of the thoracic segment of the azygos vein, normally migrates over the apex of the right upper lung to occupy a medial mediastinal position. In some cases, a migration anomaly occurs and the vein penetrates into the right upper lobe.]

3. Adam`s lobe is not a real functional independent lobe to the other lung lobes. [The lung parenchyma positioned medially to the accessory fissure is called azygos lobe or Adam`s lobe. It should be noted that the azygos lobe is not an independent segment composed of a bronchovascular tree unlike the other lung lobes. Indeed the azygos lobe is not strictly a lung lobe.]

4. [The azygos fissure is typically visible on chest radiography as a right para-mediastinal supernumerary line in projection of the right lung apex.]

5. An azygos fissure appears during fetal development. An empty azygos fissure may develop following a right lung collapse. [During fetal development, the right posterior cardinal vein, precursor of the thoracic segment of the azygos vein, normally migrates over the apex of the right upper lung to occupy a medial mediastinal position. This particular anatomical condition associated with collapse of the right upper lung lobe, may allow the displacement of the azygos vein outside the azygos fissure.]



From the manuscript:
The Empty Azygos Fissure
Radiology Case. 2013 Apr; 7(4):10-15


This article belongs to the Chest section.




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From the manuscript

The Empty Azygos Fissure

Free full text article: The Empty Azygos Fissure

Abstract
The azygos fissure is typically visible on chest radiography as a right para-mediastinal 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.






References



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