Cardiac CT acquisition and image analysis:
All cCT scans were performed on a 256 slice scanner (Seimens Somatom) with a retrospective electrocardiogram (ECG) gating technique. Helical scanning was performed after bolus administration of 100 cc Isovue 370 (Bracco) with a region of interest (ROI) on the ascending aorta at the level of the carina. The scanning parameters included a 128 x 0.6 mm collimation, a rotation time of 0.28 sec, and a pitch of 0.23. Scans were performed with a heart rate of 75 beats per minute or lower.
Images with a reconstruction interval of 0.6 mm were transferred to a workstation with 3D software capabilities (Vitrea, Vital), and 3D volume rendered images of the left atrium and pulmonary veins were acquired. 3D volume rendered images were primarily used for global assessment of atriopulmonary anatomy, evaluation of PV anatomic variants, and branching patterns and not used for quantitative analysis. Thin slice 0.6 mm acquisitions were used at the picture archive and communication system (PACS) workstation (McKesson) to manually obtain Multiplanar Reconstructed images (MPR) of each PV in cross-section at its ostium. The maximum and minimum diameter measurements of each PV ostium were then obtained manually using a caliper tool (Figure 1) . An LCPV ostium was defined when the superior and inferior left PV carina joined at a distance greater than 5 mm prior to entering the LA. The length of this common trunk was then measured. Anatomic variants recorded were accessory PVs such as the right middle pulmonary vein (RMPV) draining the middle lobe to an isolated ostium on the left atrium (LA). All cases were retrospectively analyzed by an American Board of Radiology certified attending Cardiac Radiologist with four years of experience blinded to the outcomes of the CBA procedure.