A mediastinal tumor simulated by a sacculated aneurysm of the azygos vein.

A rare case of a true idiopathic aneurysm of the azygos vein is reported. A 54 year old female with signs of obstruction of the superior caval vein was submitted to a chest X-ray-examination. It showed a giant mass in the right chest with a diameter of 12 cm. Mediastinal phlebography, CT and NMR-scans of the thorax yielded an aneurysmatic tumor, which seemed to originate from the superior caval vein near to the right atrium. With the clinical diagnosis of an aneurysm of the superior caval vein a right thoracotomy was carried out. Intraoperatively we found a sacculated aneurysm of the azygos vein near to the superior caval vein. Despite of extensive, clinical and radiographic investigations no cause for the aneurysm could be detected. This is one of the very rare cases of congenital aneurysm of the azygos vein.