Polyp False negative

This preparation is routinely used at our institution in all patients referred for screening for colorectal cancer, change in bowel habit, iron deficiency anaemia, constipation, heme positive stool, etc. (see Chap. 2). Intravenous contrast is never used as the polyps may enhance and simulate tagged stool causing a false negative finding. 

Fig. 8.5a,b. False negative diagnosis polyps simulating fecal residue in mobile segments. Differential diagnosis of mobile stool or small sessile lesions in a mobile transverse colon a supine scan shows two lesions in the transverse colon, (arrows) b prone scan shows the lesions in the transverse colon in an apparent different position (arrows). Conventional colonoscopy revealed the presence of two small sessile polyps. Lesson Polyps, located in mobile colonic segments such as the transverse colon can cause erroneous diagnosis of mobile residual stool... 

Fig. 8.6a,b. False negative diagnosis rectal balloon catheter hiding rectal polyp a prone scan after removing the rectal balloon clearly shows a large stalked polyp (arrow) b the polyp is hidden by the rectal balloon on supine image.(orrow). Lesson Thidc rectal balloon catheters can hide rectal lesions. Therefore, remove rectal balloon catheter on prone scan... 

Fig.8.7a-c. False negative diagnosis differentiate small sessile polyps located on the ileocecal valve from normal variations of the ileocecal valve. Although the ileocecal valve is an important mimicker of pathology, one has to keep in mind that polyps can arise on the ileocecal valve (arrows). Evaluation in a intermediate window setting as well as b abdominal window setting , combined with c 3D endolu-minal view are helpful to differentiate polyps from tumoral (see Fig. 8.9) or lipomatous transformation of the ileocecal valve (see Fig. 8.26). Lesson For the evaluation of pathology of the ileocecal valve, always use different window settings, in combination with endoluminal 3D evaluation...

Representative examples of CAD false negatives are shown in Figure 11.6. Figure 11.6a shows a magnified view of a 6-mm polyp at the proximal transverse colon (white arrow), and Fig. 11.6b shows its 3D endoscopic view (white arrow). This polyp was located in a narrow valley where two folds merge, and thus the shape of the polyp was distorted. Moreover, a motion artifact made the polyp appear blurred, and thus it was a false-negative polyp. The neighboring polyp (black arrow), located below the... 

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