Azygos lobe
In human anatomy, an azygos lobe is a congenital variation of the upper lobe of the right lung. Embryologically, it arises from an anomalous lateral course of the azygos vein in a pleural septum within the upper lobe. As it has no bronchi, veins and arteries of its own, it is not a true, or even accessory, pulmonary lobe, but rather an anatomically separated part of the upper lobe. It is usually an incidental finding on chest x-ray or computed tomography and is as such not associated with any morbidity but can cause technical problems in thoracoscopic procedures .
Further reading
Mata J, Cáceres J, Alegret X, Coscojuela P, De Marcos JA (May 1991). "Imaging of the azygos lobe: normal anatomy and variations" (PDF). AJR Am J Roentgenol 156 (5): 931–7. doi:10.2214/ajr.156.5.2017954. PMID 2017954.