Location of Adenomas Missed by Optical Colonoscopy

View larger version (23K): [in a new window]   Figure 1. Polyp flowchart. Flowchart shows the total number of polyps detected; the number of polyps eligible for unblinding (size 5 mm); and the number of unblinded adenomas that measured 6 mm or larger, which represent the primary study group. The 10 unblinded adenomas that measured 5 mm were excluded because of their diminutive size. VC = virtual colonoscopy.

View larger version (71K): [in a new window]   Figure 2. Unblinded 6-mm tubular adenoma located on the proximal aspect of a fold at the hepatic flexure.Left. Three-dimensional endoluminal view from virtual colonoscopy shows a sessile polyp situated on the backside of a colonic fold. Right. Digital photograph from optical colonoscopy shows the same polyp, which was found after segmental unblinding of the virtual colonoscopy results. Note the adjacent calibrated guidewire used for polyp measurement in the study.

View larger version (70K): [in a new window]   Figure 3. Unblinded 6-mm tubular adenoma located at the inner aspect of a sigmoid flexure.Left. Three-dimensional endoluminal view from virtual colonoscopy shows a sessile polyp situated between folds. The centerline path for automated navigation is shown (line). Right. Colon map generated from the supine computed tomography data set that shows the vantage point (arrow) for the image on the right. The polyp location (circle) is situated at the inner turn of the flexure.

View larger version (74K): [in a new window]   Figure 4. Unblinded 7-mm tubular adenoma located in the distal rectum.Left. Three-dimensional endoluminal view from virtual colonoscopy that simulates retroflexed view of rectal ampulla shows a subtle flat lesion (arrow) that measured 7 cm from the anal verge. Note the tip of small rectal catheter (arrowhead) that was used for air insufflation. Right. Two-dimensional axial computed tomography image with soft tissue windowing confirms the presence of a flat rectal lesion (arrow).

View larger version (68K): [in a new window]   Figure 5. Unblinded 11-mm malignant polyp located near the hepatic flexure.Left. Three-dimensional endoluminal view from virtual colonoscopy shows a large polypoid lesion on the edge of a fold. Right. Digital photograph from optical colonoscopy shows the same polyp, which was found only after several attempts to reposition the instrument because of repeated slippage in this region. Invasive adenocarcinoma was confirmed at surgery.

View larger version (115K): [in a new window]   Figure 6. Potential colonoscopic "blind spots." Antegrade endoluminal view (that is, looking distally toward rectum) from virtual colonoscopy indicates the portions of colonic mucosa that were visualized during retrograde flight toward the cecum by "painting" the surface green. The unpainted regions involving the proximal aspects of colonic folds are readily evaluated during antegrade flight on virtual colonoscopy. These regions, however, are the most common sites for missed adenomas at optical colonoscopy because of its unidirectional nature.