Azygos lobe

In human anatomy, an azygos lobe is a normal anatomical variation of the upper lobe of the right lung.[1] It is seen in 1% of the population. Embryologically, it arises from an anomalous lateral course of the azygos vein,[2] in a pleural septum within the apical segment of the right upper lobe or in other words an azygos lobe is formed when the right posterior cardinal vein, one of the precursors of the azygos vein, fails to migrate over the apex of the lung and penetrates it instead, carrying along two pleural layers that invaginates into the upper portion of the right upper lobe. As it has no bronchi, veins and arteries of its own or corresponding alteration in the segmental architecture of the lung, so it is not a true (misnomer), or even accessory, pulmonary lobe, but rather an anatomically separated part of the upper lobe.

Azygos lobe on chest x-ray. Arrowheads show the delineation of the lobe. Arrow points to the azygos vein.

Clinical significance

An azygos lobe is usually an incidental finding on chest x-ray or CT scan, and is not associated with any morbidity.[3][4] However, it can cause technical problems in thoracoscopic procedures.[5]

Additional images
Azygos lobe in axial computertomography. Arrow on azygos vein.
HRCT thorax, axial section delineates a well-defined, convex-shaped fold (Blue arrow), the azygos fissure. A tear-drop shaped density noted at the bottom of the fold (Green arrow) is the azygos vein.

References
  1. Amini B. "Azygos lobe | Radiology Reference Article | Radiopaedia.org". Radiopaedia.
  2. Demos TC, Posniak HV, Pierce KL, Olson MC, Muscato M (May 2004). "Venous anomalies of the thorax". AJR. American Journal of Roentgenology. 182 (5): 1139–50. doi:10.2214/ajr.182.5.1821139. PMID 15100109.
  3. Akhtar J, Lal A, Martin KB, Popkin J (2018-01-01). "Azygos lobe: A rare cause of right paratracheal opacity". Respiratory Medicine Case Reports. 23: 136–137. doi:10.1016/j.rmcr.2018.02.001. PMC 5925948. PMID 29719800.
  4. Caceres J, Mata JM, Andreu J (March 1998). "The azygos lobe: normal variants that may simulate disease". European Journal of Radiology. 27 (1): 15–20. doi:10.1016/s0720-048x(97)00146-0. PMID 9587765.
  5. Sieunarine K, May J, White GH, Harris JP (August 1997). "Anomalous azygos vein: A potential danger during endoscopic thoracic sympathectomy". Australian and New Zealand Journal of Surgery. 67 (8): 578–9. doi:10.1111/j.1445-2197.1997.tb02046.x.

Further reading
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