Figure 20a.  Aneurysm of the true lumen in a patient with polycystic kidney disease. (a) Enhanced CT scan shows an abdominal aortic dissection (arrow). (b) Enhanced CT scan obtained 11 years later shows an aneurysm of the true lumen (arrows). (c) Oblique sagittal MPR image shows the anterior abdominal aneurysm of the true lumen (large arrow) and slow flow in the false lumen (F) (small arrows).