Stool Tagging

Fig. 4.7a,b. Examples of stool tagging (arrow and arrowheads). Confusion with a true lesion is excluded. No comparison between supine and prone images is necessary to exclude a lesion... 

Pickhardt PJ, Choi JH (2003) Electronic cleansing and stool tagging in CT colonography advantages and pitfalls with primary three-dimensional evaluation. Am J Roentgenol 181 799-805... 

Thomeer M, Carbone 1, Bosmans H et al. (2003) Stool tagging applied in thin-slice multidetector computed tomography colonography. JCAT 27 132-139... 

Betapol , a human milkfat substitute produced by Loders Croklaan (Wormerveer, the Netherlands), is produced by interesterification of vegetable oils in which the component TAGs have been modified to more closely resemble those found in breast milk. This product closely mimics the specific structure and fatty acid composition of human milkfat and resembles breast milk in terms of its nutritional value and high content of palmitic acid at the sn-2 position than other milkfat substitutes. In addition, the use of Betapol in infant formula can lead to improved mineral and fat absorption and less calcium soap formation within the intestinal lumen resulting in softer stools. 

However bowel preparation should be tailored to the indication, with full or reduced cathartic preparation associated to tagging of fluids or stool. Adequate colonic distension (pneumocolon) is cru-dal for identification of colorectal polyps and differentiation between obstructive cancers and a collapsed segment. Distension is achieved by rectal air or carbon-dioxide insufflation, and standard scout view in lateral and anterior-posterior projections are acquired to verify the distension of the entire colon. The intravenous administration of a muscle rdaxant, to reduce large bowel movement and... 

Fig. 4.1. The residual stool in the ascending and descending colon is tagged and appears white on the two-dimensional images, facilitating diagnosis...

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. 4.8. Patient with right sided sigmoid. There is tagged stool (arrowhead). There is also non-tagged material (orrow). This should be considered a lesion unless the contrary is proved. A correct diagnosis of an 8-mm sessile polyp was made...

As with optical colonoscopy, tagged stool frequently abuts a lesion. This makes polyps more conspicuous for detection (Figs. 4.8, 4.9, and 4.10). In these cases polyp conspicuity is improved using soft tissue settings. 

In a minority of cases a small amount of stool remains non-tagged. 

In our experience non-tagged stool >6 mm is present in 3-5% of segments. Mostly it presents as one or two non-tagged stool balls completely surrounded by some barium or floating in barium pools (Fig. 4.12). This stool may also present with the typical imaging... 

Fig. 4.12.Non-tagged stool >1 cm in the sigmoid (arrow). This non-tagged material shows the characteristics of non-tagged stool completely surrounded by barium, hooked appearance, some minute air inclusions...

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