Azygos continuation syndrome with aneurysm of the azygos vein: CT and MR appearances.

We present a case of azygos vein continuation with aneurysm of the azygos vein simulating a tumor in the right upper mediastinum. The dynamic CT examination initially showed a structure of malignant appearance during the early arterial phase. Further dynamic CT revealed marked enhancement of the mass during the late venous phase, suggesting a vascular structure. Confirmation of diagnosis was made by MRI using a fast gradient echo imaging technique in cine mode, showing turbulent flow in the azygos aneurysm, and contrast-enhanced MR angiography, demonstrating a dilated azygos vein. Dynamic CT has a potential pitfall in the diagnosis of vascular structures.