Figure 3c. Preoperative single-section CT scans (5-mm collimation, 1-mm reconstruction interval, pitch of 2) obtained in a 53-year-old man with a type A dissecting thoracic aneurysm. Two-dimensional axial CT sections obtained from inferior (a) to superior (c) show a common retroatrial chamber formed by the confluence of the two inferior PVs. Note the clear delineation from the main left atrium. Compare this structure with the uniformly smooth posterior left atrial wall shown in Figure 1b. LI = left inferior, LS = left superior, RI = right inferior, RS = right superior.