The arch of the azygous vein can be found directly above the right upper lobe bronchus. In an upright patient, its transverse diameter is usually not greater than 7 mm. Enlargement of the azygous vein (see figure below) can be seen with increased right atrial pressure or vena cava obstruction.

Enlargement of the azygous vein (arrow) in a patient with right ventricular failure secondary to left ventricular failure.