An enlarged azygos vein traversing an azygos lobe reveals a connection between the inferior vena cava and azygos vein.

We report a rare case where the inferior vena cava connected to the azygos vein, a diagnosis triggered by observation of an enlarged azygos vein traversing an azygos fissure. A 16-year-old male patient presented with an abnormal shadow on chest X-ray. Chest computed tomography showed an enlarged azygos vein connecting to the inferior vena cava, with no other connection to the atrium. There were no associated malformations. The patient remains alive and has been asymptomatic for the past two years. If the flow through the connection was to be interrupted during the course of thoracic or abdominal surgery, this would invariably prove to be fatal. In addition, this abnormality prevents direct access to the atrium on attempting interventional radiology via the inferior vena cava, for example, during ablation. When an azygos lobe is identified on a chest X-ray, a prominent solid structure traversing it may represent an engorged azygos vein with an anomalous course.