ORLANDO — CT colonography continues to show promise as an adjunct to colonoscopy for colorectal cancer screening, according to study findings.
Dr. Ruben D. Acosta and his associates assessed 170 average-risk patients at the National Naval Medical Center in Bethesda, Md. All patients had computed tomographic colonography (CTC) followed by a colonoscopy. Polyp histology was used to compare results from 92 participants with a positive CTC and another 60 randomly selected patients with a negative CTC. Mean age was 56 years, 32% were women, and 82% were white.
In previous studies, the researchers had demonstrated that CTC could detect polyps 6 mm or larger as accurately as colonoscopy on a per-patient basis (Gastroenterology 2006;130:A46).
In the current study, the histology showed that 6 of the 60 patients with a negative CTC had adenoma and 2 had advanced adenoma. In addition, 58% of patients with a normal CTC had at least one polyp detected on colonoscopy, Dr. Acosta said at the annual meeting of the American College of Gastroenterology.
“This underscores the complementary relationship between CTC and colonoscopy programs,” said Dr. Acosta, a gastroenterologist at the center.
Of the 348 polyps detected by colonoscopy, 59% were smaller than 6 mm, 26% were 7–9 mm, and 15% were 10 mm or larger. Histology suggested that 167 of these polyps were adenomas (48%). A total of 76, or 46%, of these polyps were noted on the initial CTC report.
However, CTC missed 222 polyps detected by colonoscopy, including 87 hyperplastic polyps and 84 adenomas. In addition, CTC missed seven advanced adenomas (an overall 3% miss rate).
Two of the seven advanced adenomas missed by CTC were smaller than 10 mm (a 0.9% miss rate).
The miss rate for CTC was inversely associated with polyp size, Dr. Acosta said. As expected, 79% of the 222 polyps missed by CTC, but detected by follow-up colonoscopy, were smaller than 6 mm.
Among the 16% of missed polyps in the 7-mm to 9-mm range, 15 polyps were hyperplastic and 17 were adenomas. The remaining polyps that were missed by CTC were 10 mm or larger and included five hyperplastic polyps and five adenomas.
The CTC miss rate for polyps greater than 10 mm was 4.5%. Dr. Acosta said this miss rate is comparable to the rate of large polyps missed with tandem colonoscopy (Am. J. Gastroenterol. 2006;101:343–50). In this systematic review of six studies with 465 patients, researchers found a 2.1% miss rate for polyps 10 mm or larger.
Dr. Acosta reported having no disclosures related to his presentation.