Azygous lobe: a normal variant of pulmonary anatomy

T he azygous lobe is a normal anatomical variant with reported incidence of 0.2 1.2% (1). We report a case of a 51-year-old man with past medical history significant for drug and alcohol abuse, who presented to the emergency department with altered mental status and hypoxic respiratory failure. Given his altered mental status, history was unable to be obtained. Laboratory workup was positive for opiates and benzodiazepines. Imaging was unremarkable, with the exception of a chest computed tomography (CT) showing an incidental finding of an accessory azygous lobe (Fig. 1). During embryogenesis, the right posterior cardinal vein (a precursor of the azygous vein) penetrates the right upper lobe of the lung instead of traveling over the apex. This later invaginates and creates what is known as the azygous fissure. This fissure contains the azygous vein which can easily be visible on plain chest films (2). This anatomical variant (azygous lobe) can also be visible on CT imaging, as a thickened fissure from the posterior vertebral body extending to the superior vena cava. This can be seen in our case. The azygous lobe formation is a benign process and is often found incidentally. However, it is important for radiologists and surgeons to recognize this, as this can alter the approach for lobectomies or segmental resections (3).