Laxative-free CT colonography may be as effective as standard colonoscopy in detecting high-risk polyps

Issue: July 25, 2012

Laxative-free CT colonography correctly identified 91% of adenomas that measured 10 mm or larger, suggesting the screening technique could be as effective as standard colonoscopy in detecting polyps most likely to become cancerous, according to study results.

The new technique uses computer-aided systems to virtually cleanse and analyze the acquired images, so it does not require pre-examination laxative bowel cleansing. If it is proven to be a viable alternative to colonoscopy, a larger percentage of individuals may decide to undergo colon cancer screening, the researchers wrote.

“While we know that colon screening can save lives, not enough people participate, in part because of the discomfort of the required laxative preparation,” Michael E. Zalis, MD, director of CT colonography at Massachusetts General Hospital’s department of imaging, said in a press release. “In our study, the laxative-free form of CT colonography performed well enough that it might someday become an option for screening, which we hope would increase patient participation.”

Traditional CT colonography does not require sedation and has been demonstrated to be as effective as colonoscopy in detecting polyps, but it still requires laxative preparation.

The laxative-free CT colonography technique evaluated in this study requires participants to follow a two-day low-fiber diet and orally ingest small doses of a contrast agent that helps identify fecal material in the colon. Software programs developed by the researchers perform “electronic cleansing,” removing fecal matter from the CT scan and analyzing the remaining images for polyps, Zalis and colleagues wrote.

Zalis and colleagues enrolled 605 asymptomatic adults in a prospective study designed to compare how well optical colonography — one of the most accepted and effective colorectal cancer screening methods — and laxative-free, computer-aided CT colonography detected adenomas 6 mm or larger.

The participants, aged 50 to 85 years, were at average to moderate risk for colon cancer.

All participants underwent laxative-free CT colonography, then underwent optical colonoscopies within the next 5 weeks.

The study results suggest laxative-free CT colonography is comparable to optical colonoscopy for detecting adenomas 10 mm or larger.

In those cases, the per-patient sensitivity of laxative-free CT colonography was 0.91 (95% CI, 0.71-0.99) vs. 0.95 (95% CI, 0.77-1.00) for optical colonography. The per-patient specificity of laxative-free CT colonography was 0.85 (95% CI, 0.82-0.88) vs. 0.89 (95% CI, 0.86-0.91) for optical colonography.

The laxative-free CT technique did not perform as well as optical colonography in identifying smaller polyps, but researchers emphasized 85% of colonoscopy-confirmed lesions that showed cellular changes associated with higher risk for cancer development were 10 mm or larger.

Zalis and colleagues also asked patients to complete written surveys about their experiences and note which technique they preferred. Sixty-two percent of participants who completed the questionnaire said they preferred laxative-free CT colonography to optical colonoscopy.

“If [the study results] hold up in larger trials, we would expect this procedure would first be offered to moderate-risk patients who are otherwise unable or unwilling to be screened,” Zalis said in a press release. “If we can validate that this form of CT colonography performs reasonably well for screening and is easier for patients, it could have a significant impact on reducing the incidence of colon cancer and related cancer deaths.”

Disclosure: Dr. Zalis and other researchers involved in the study are co-inventors of electronic cleansing and computer-aided detection software patents assigned to their home institution but do not receive associated royalties.

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Source:

Zalis ME. Ann Intern Med. 2012;156:692-702.