Computed tomographic colonography using a fecal-tagging bowel preparation performed well, showing high sensitivity, specificity, and negative predictive value for polyps measuring 8 mm or more, as reported at an international symposium on virtual colonoscopy sponsored by Boston University.
Although patients prefer the non-invasive nature of computed tomographic colonography (CTC) as compared to optical colonoscopy, both procedures require purgative bowel preparation. But a non-laxative preparation may be an adequate alternative that proves to yield good results.
In a study of 75 patients undergoing CTC because of family or personal history of colorectal carcinoma or suspicion of colonic pathology, a nonlaxative fecal-tagging bowel preparation allowed sufficient visualization of polyps measuring 8 mm or larger as said by a doctor of University Hospital Gasthuisberg and Katholieke Universiteit Leuven, both in Leuven, Belgium. The patients (mean age 61) consumed a low-fiber diet for two days before the exam. Fecal tagging was achieved with 100 mL water-soluble, iodinated contrast medium given the day prior to the exam. After the CTC was completed, additional bowel preparation was performed with 4-5 L of an electrolyte solution to allow for a same-day comparison to optical colonoscopy. CTC detected 14 to 20 polyps measuring 6 mm or more in 12 patients and one tumor in another patient. Specifically, CTC detected three of eight polyps measuring 6-7 mm, four of five polyps that were 8-9 mm, all seven polyps measuring 10 mm or more, and the single tumor.
The sensitivity and specificity of CTC per patient for polyps measuring 6-9 mm were 50% and 98.6%, respectively. The negative predictive value for the same polyp size was 95.8%. For polyps of 10 mm or more, the sensitivity, specificity, and negative predictive value were 100%. With the fecal-tagging preparation, residual fluid was present, but it covered less than 20% of the colonic surface and tagging was homogeneous in most patients. Residual stool was present in some patients, and although its tagging was insufficient in most cases, the stool could be easily recognized because it was floating in tagged fluid.
Preliminary results from a screening population study also looked promising. Subjects consume a low-fiber diet for 2 days, and stool tagging is achieved with 800 cc of 40% barium solution in six divided doses over the 2 days. Gastrografin (60 cc) is also given the night before the CTC. In the 50 subjects enrolled to data, 30 polyps measuring 6 mm or more have been identified.