Congenital left superior vena cava with absent right superior vena cava: a cause of progressive mediastinal widening.

We wish to report a patient with the rare anomaly of congenital left superior vena cava and absent right superior vena cava. This became apparent on chest radiographs by the development of a left mediastinal "mass" over a one-year period. The role of contrast-enhanced computed tomographic scanning in the detection of venous anomalies is stressed.