Vascular rings causing pulmonary collapse.

Mediastinal vascular anomalies (rings) have not previously been reported to cause pulmonary collapse. We record two cases where anomalous subclavian arteries were involved in the ring. This association can be predicted by considering the embryology of the subclavian arteries which arise from the lowest intersegmental arteries and migrate in a cephalad direction. An anomalous subclavian artery which did not complete this migration could cross the mediastinum at the carina. Investigation of a suspected vascular ring is firstly by a barium swallow which will show extrinsic compression of the oesophagus by the anomalous vessel. Arteriography demonstrates the exact anatomy of the vascular ring, but is a pre-surgical investigation undertaken in cases where the collapsed lung may re-expand following division of the vascular ring.