Detection of flat lesions in the colon with CT colonography

AbstractBackground:We investigated whether flat lesions of the colon could be detected on computed tomographic colonography (CTC). Methods: CTC and conventional colonoscopy were performed on 547 consecutive patients. A subset of 22 polyps was described as flat on colonoscopy (n= 16) or CTC (n= 6) and are the basis of this report. CTC was performed with a standard technique (5-mm collimation, 3-mm reconstruction intervals). Patients were scanned in supine and prone positions. Examinations were randomly assigned and reviewed in a blinded fashion by two of three radiologists. Prospective interpretations were recorded. All patients had conventional colonoscopy, which served as the gold standard. Results: Twenty-two flat lesions ranging from 0.4 to 3.5 cm were histologically classified as adenomatous (n= 8) or hyperplastic (n= 14). The sensitivities for detecting all flat lesions and flat adenomas by each reviewer were 43% and 100%, 65% and 100%, and 15% and 13%, respectively. “Double reading” resulted in detection of 68% of all lesions and 100% of adenomas. Of the seven hyperplastic polyps missed by both reviewers, four were identified retrospectively. Conclusion: Flat lesions of the colon represent an important source of false negative CTC examinations. Awareness of their morphology can assist radiologists in finding most of these challenging lesions.

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