New study on laxative-free colon polyp detection

Robin Wulffson MD's picture
colon cancer, adenomas, cancer detection, colonoscopy, laxatives, radiation

Colonoscopy has been proven to be a valuable diagnostic tool for the detection of colon polyps before they turn into a deadly colon cancer. Two major deterrents to the procedure exist: (1) Pretreatment colon cleansing with laxatives; and (2) Insertion of an optical device into the colon. Many individuals forego a colonoscopy because of those two factors. An alternate procedure is a laxative-free computed tomography, which avoids those discomforts.

To establish the diagnostic accuracy of the X-ray procedure, researchers affiliated with the University of California in San Francisco, California and Massachusetts General Hospital, Brigham and Women's Hospitalin Boston, Massachusetts conducted a study comparing optical colonoscopy (OC) or computed tomographic colonography (CTC), which requires a laxative bowel preparation. They published their findings in the May 14 issue of the Annals of Internal Medicine.

The goal of the study was to detect adenomas 6 mm or larger and evaluate patient experiences of laxative-free, computer-aided CTC. Adenomas are growths in the colon, which can become malignant over time. The researchers compared the two procedures by subjecting the subjects to both procedures. Examiners performing the OC were blinded (unaware) of the results of the CTC. After completing the colonoscopy, the examiners were provided with the CT results; thus. They were able to conduct a repeat examination to resolve any discrepancies.

The study group was comprised of 605 adults aged 50 to 85 years who had an average to moderate risk for colon cancer. Before undergoing CTC, the subjects followed a low-fiber diet; just prior to the procedure, they ingested a small dose of contrast material, which labeled fecal material. A computer program electronically "cleansed" the colon by subtracting the labeled fecal material from the colon images without affecting the size or appearance of colon wall or polyps.


For adenomas 10 millimeters (0.4 inch) or larger, the per-patient sensitivity of CTC was 0.91 and the specificity was 0.85. (Sensitivity refers to detecting a lesion and specificity refers to correctly identifying a lesion. The sensitivity of OC was 0.95 and the specificity was 0.89. For adenomas 8 millimeters (0.3 inch) or larger, the sensitivity of CTC was 0.70; it was 0.59 for those 6 millimeters (0.2 inch) or larger. The sensitivity of OC for adenomas 8 millimeters or larger was 0.88 and 0.76 for those 6 millimeters or larger. The specificity of OC at the threshold of 8 millimeters or larger was 0.91; at 6 millimeters or larger, the specificity was 0.94. The researchers found that the specificity for OC was greater than that for CTC, which was 0.86 at the threshold of 8 millimeters or larger and 0.88 at 6 millimeters or larger (P = 0.02). Not surprisingly, the patient experience regarding comfort and difficulty of examination preparation was better with CTC than OC.

The authors noted that a limitation of the study was that three different CTC examiners viewed the X-rays. Furthermore, the scanners were not independently validated.

The authors concluded that computed tomographic colonography was accurate in detecting adenomas 10 millimeters or larger; however, it was less accurate in detecting smaller growths. Patient experience was better with laxative-free CTC. They noted that their results suggest a possible role for laxative-free CTC as an alternate screening method.

Take home message:
This study reports the superiority of optical colonoscopy to laxative-free CT colonography as well as improved patient acceptance of the CT procedure. One disadvantage of a CT scan is the exposure to ionizing radiation. From a strictly diagnostic and patient safety standpoint, optical colonoscopy is a better procedure. However, for those patients who would not undergo screening because of an aversion to the colon preparation and instrumentation, the CT procedure is worth consideration. Another factor to consider is one’s personal risk of colon cancer. Those with close relatives are at higher risk. Before undergoing either procedure, individual situations should be thoroughly discussed with a healthcare professional familiar with colon cancer screening.

Reference: Annals of Internal Medicine