Giant Azygos Vein Aneurysm Mimicking a Mediastinal Mass With Segmental Partial Anomalous Pulmonary Venous Return

We present the case of an 87-year-old man in whom a giant azygos vein aneurysm was incidentally detected on chest radiography (CXR) performed following an acute stroke. The radiograph demonstrated a right paratracheal mediastinal opacity with attenuation similar to the adjacent aortic arch, raising suspicion of a vascular abnormality. Contrast-enhanced CT confirmed a large azygos vein aneurysm draining into the superior vena cava. Retrospective review demonstrated subtle right paratracheal prominence dating back to 2007, with gradual interval enlargement over more than a decade. No acquired cause was identified, and the patient remained asymptomatic throughout follow-up, supporting conservative management in selected patients. The patient also demonstrated concurrent isolated segmental partial anomalous pulmonary venous return (PAPVR) draining into the superior vena cava. This case highlights the importance of recognising azygos vein aneurysms as a differential for mediastinal masses on CXR and considering associated congenital vascular anomalies.