'You didn't see them, but now you do!': use of balloon occlusion angiography in the identification of systemic venous anomalies before and after cavopulmonary procedures.

We describe the importance of angiographic identification of collateral venous channels by balloon occlusion venography after bidirectional cavopulmonary connections. Use of the balloon occlusion technique is essential for identification of these vessels, as they can easily be missed by standard venous angiography, with possible clinical consequences for postoperative management.