CT colonography can pinpoint cancerous colorectal segments more accurately than colonoscopy, according to Italian investigators. They say virtual, not optical, colonoscopy should be the gold standard for the preoperative staging of colorectal cancer.

The prognosis for patients diagnosed with colorectal cancer depends largely on the correct localization of diseased segments prior to tumor resection. Colonoscopy, the standard of care for this indication, could be plagued by multiple anatomical or physiological hurdles that hinder precise segment tracking in about three of every 10 patients. But CTC can overcome most of these limitations, said principal investigator Dr. Emanuele Neri, an assistant professor of diagnostic and interventional radiology at the University of Pisa.

"Gastroenterologists and surgeons should be aware of this and before surgery should always ask for a staging CT colonography," Neri told Diagnostic Imaging.

Neri and colleagues enrolled 65 patients diagnosed with colorectal cancer who underwent segmental localization of their tumors with colonoscopy and CTC before surgery. Of this group, 45 patients (69%) had to be referred to CTC after incomplete colonoscopy results due to discomfort or because of bowel narrowing from cancer.

CTC allowed a complete evaluation in all but two cases, where an obstructing lesion of the sigmoid prevented proper cleansing and insufflation. CTC accurately identified all diseased segments while colonoscopy missed 16 of them (24%). CTC's sensitivity, specificity, and positive and negative predictive values for precise location of colonic masses were, respectively, 100%, 96%, 85%, and 100%. Results appeared online in the Sept. 18 issue of Abdominal Imaging.

The accumulation of data keeps fueling the discussion regarding the value of CTC vis-à-vis colonoscopy. What is beyond any doubt is that CTC should at least replace double contrast barium enema, which has become an obsolete diagnostic tool, Neri said. Patients nowadays prefer CTC over barium enemas and the reasons go beyond comfort. For one, studies have shown a consistent reduction in radiation dose, averaging 2 to 3 mSv. Cost-effectiveness comes to the fore as well. In addition to a contrast-enhanced CTC, many surgeons still ask for a DCBE for preoperative staging and to get information on the precise location of cancer. This is absolute overkill, Neri said.

"CT colonography alone could get them better preoperative and staging information than two exams," he said.