Laxative-Free CTC Examined as Potential Alternative to Standard Colonoscopy

Michael E. Zalis, MD

Computer-aided computed tomographic colonography (CTC) that does not require a laxative preparation nearly rivals conventional optical colonoscopy (OC) for identifying asymptomatic adults with adenomas ≥10 mm, new data suggest. However, laxative-free CTC performed less well for smaller lesions.

“Our results suggest a role for CTC as an alternate screening method to OC with which participants would experience improved preparation and examination comfort—factors that could contribute positively to overall screening participation,” Michael E. Zalis, MD, associate professor of Radiology at Massachusetts General Hospital in Boston, Massachusetts, and associates wrote.

The researchers evaluated the diagnostic performance of laxative-free CTC for the detection of colonic adenomas ≥6 mm in 605 asymptomatic men and women aged 50 to 85 years with an average-tomoderate risk for colon cancer. It is widely agreed that adenomas ≥6 mm should be removed. Individuals with polyps (except for polyposis syndrome or cancer) were eligible for the study provided that they had not undergone colon screening during the past 5 years.

Study participants had laxative-free CTC after ingestion of oral contrast material for 2 days before their examination in order to thoroughly tag feces. After images were obtained, computer software digitally subtracted tagged feces from the colon images, without altering the size and appearance of mucosal folds and polyps. Each patient later underwent standard OC.

The study found that per-patient sensitivity of CTC was 0.91 (95% CI, 0.71-0.99) for adenomas ≥10 mm versus 0.95 (CI, 0.77-1.00) for OC. However, overall performance of laxative-free CTC for adenoma detection was inferior to that of first-pass OC.

Patients reported a better experience with CTC examination versus standard cathartic preparation. Most said they would prefer CTC over OC for future examinations.

There were no major adverse events with either technique.

The authors cautioned that the study was performed at highly specialized centers and used only three expert radiologist readers, all of whom were abdominal radiologists. Also, only a small percentage of eligible persons agreed to participate in the study.

Colon cancer is the second most common cause of death from cancer in developed countries, the authors noted. Although CTC has been shown to be an acceptable colorectal cancer screening method in patients who decline OC, both methods require pre-examination laxative bowel cleansing, which is a strong disincentive to screening.

Zalis ME, Blake MA, Cai W, et al. Diagnostic accuracy of laxative-free computed tomographic colonography for detection of adenomatous polyps in asymptomatic adults: a prospective evaluation. Ann Intern Med. 2012;156(10):692-702.