Figure 1a. Residual stool in a 47-year-old man with a high familial predisposition for colorectal cancer. (a) Three-dimensional endoluminal CT image shows a broad-based, polypoid filling defect (arrow). (b) On a supine contrast material–enhanced CT scan, the pseudolesion (arrow) is unenhanced, has inhomogeneous attenuation, and contains trapped gas.