BOSTON — 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, Dr. Didier Bielen reported at an international symposium on virtual colonoscopy sponsored by Boston University.
Although patients prefer the noninvasive nature of computed tomographic colonography (CTC) as compared to optical colonoscopy, both procedures require purgative bowel preparation. But a nonlaxative 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, said Dr. Bielen of University Hospital Gasthuisberg and Katholieke Universiteit Leuven, both in Leuven, Belgium.
The patients (mean age 61) consumed a low-fiber diet for 2 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 of 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, Dr. Bielen reported.
Preliminary results from a screening population study also looked promising, reported Maj. Richard P. Moser III, MC, USA, of Walter Reed Army Medical Center in Washington. 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 date, 30 polyps measuring 6 mm or more have been identified, he said.
Deflation Maneuver Reduces Pain in Virtual Colonoscopy
Dr. Abraham H. Dachman described another innovation in virtual colonoscopy in a separate presentation at the meeting.
A deflation maneuver that lasts only 4 seconds can alleviate roughly 6 minutes of pain during virtual colonoscopy, he reported.
“This maneuver works for every patient and should now become routine,” said Dr. Dachman of the University of Chicago. “It makes virtual colonoscopy more tolerable and theoretically should reduce the risk of colonic perforation.”
Insufflation of the colon with carbon dioxide is necessary during virtual colonoscopy (VC) to allow adequate visualization, he said. But the resulting abdominal distension, required for the full duration of the 7- to 15-minute exam, causes pain, which is sometimes severe.
In his study of 38 patients, partial deflation between the supine and prone portions of the exam reduced perceived pain in all patients without compromising quality or significantly prolonging the duration of the procedure.
“We turn off the CO2 flow and disconnect the rectal tubing for about 4 seconds after completion of the supine scan. This deflates the rectum but not the colon,” he explained.
After the deflation maneuver, the patients' average visual analog pain scores dropped from 3.4 to 1.6 and the average colonic pressure dropped by 14 mm Hg. Patients then turned over, and the scanner was prepared and initialized for the prone scan. Reinflation to adequate colonic distension in the prone position took between 5 and 20 seconds.
Although the entire deflation maneuver prolonged the virtual colonoscopy procedure by only 15–30 seconds, it reduced pain for 6 minutes, said Dr. Dachman, adding that the improvement was so significant in all patients that he did not feel it was ethical to include a control group.
“Theoretically, this reduction in colonic pressure should also reduce the risk of colonic perforation, although we have not studied that,” he noted.