Congenital saccular aneurysm of the superior vena cava.

It is important to recognize the true nature of the rare superior vena caval aneurysm with nonoperative techniques, in order to avoid needless diagnostic thoracotomy. Two distinct types exist--the fusiform and the saccular. The presence of such an aneurysm should be suspected if there is size variation during respiration on roentgenographic evaluation, and can be confirmed venographically. That these aneurysms do not enlarge, rupture, or thrombose argues for conservative management.