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Aneurysm of the superior vena cava.

Abstract A case is reported of a superior vena caval aneurysm presenting as a right superior mediastinal mass. Prior to a definitive venographic study, in-spiratory-expiratory films and supine and upright films of the chest may show significant change in size and shape of the lesion, suggesting its venous nature. Dilatation of the azygos vein must be differentiated.