Figure 1b. Internal area of hyperlucency in stool of 58-year-old man. (a) Three-dimensional volume-rendered endoluminal CT image shows a lobulated mass (arrow) suspected of being a polyp in the transverse colon. (b) Transverse CT colonographic image shows a tiny gas bubble in the center of the mass (arrow); this finding confirmed the presence of residual fecal material. No polyp was seen at colonoscopy.