Pickhardt PJ et al. (2004) The effect of diagnostic confidence on the probability of optical colonoscopic confirmation of potential polyps detected on CT colonography: prospective assessment in 1,339 asymptomatic adults. AJR 183: 1661–1665

A new study by Pickhardt and colleagues has explored the relationship between CT colonography (CTC) and optical colonoscopy findings. The results show that the diagnostic 'confidence score' for a polyp detected on CTC correlates with the likelihood of finding a matching lesion using optical colonography.

CTC, or virtual colonography, helps to avoid unnecessary optical colonoscopy in patients with small (≤5 mm) polyps. Patients with large (≥10 mm) polyps on CTC tend to require optical colonoscopy for polypectomy, but the significance of 6–9 mm lesions detected on CTC is unclear, and so further criteria for CTC screening algorithms are needed.

The new study included 1,339 asymptomatic adults who had been referred for colorectal cancer screening. All patients underwent same-day CTC and optical colonoscopy. For the 305 potential polyps detected on CTC, the diagnostic confidence level of the interpreting radiologist was recorded on a scale from 1 (least certain) to 3 (most certain). The higher the diagnostic confidence score for CTC, the higher the chance of detecting a matched polyp on optical colonoscopy: for lesions ≥6 mm, matching lesions were found in 33.3%, 50.0% and 66.8% of polyps that had been diagnosed by CTC with confidence scores of 1, 2, or 3, respectively (P <0.01).

While the size of a potential polyp remains the major factor in deciding whether a patient should undergo optical colonoscopy, this study shows that the CTC diagnostic confidence score is a useful additional criterion.