AbstractBackgroundThis study aimed to determine the sensitivity of computed tomographic colonography (CTC) in diagnosing colorectal cancer and to explore the reasons why these cancers are missed on CTC.MethodsPatients who underwent CTC in the 56-month period from 1 January 2004 to 1 September 2008, and all cases of colorectal cancer recorded in the National Cancer Registry database from 1 January 2004 to 1 December 2008, were identified. Cases from the two data sets were then matched to identify all patients in whom CTC had been performed more than 6 weeks before a histological report was available. CTC reports and patients' records were reviewed to determine the cancer site, and images were reviewed.ResultsA total of 3888 patients underwent CTC over a 56-month interval. After matching with the National Cancer Registry database, colorectal cancer was identified in 131 patients, whereas it had been suspected on CTC in 123 patients. One of the patients with missed cancer was excluded, leaving seven (5·3 per cent) missed cancers, four of which were located in the caecum. Five cancers were missed because of technical limitations of CTC and two were due to perceptive errors. Systems errors and severe patient co-morbidity contributed to three of the cases. The sensitivity of CTC for colorectal cancer was 95 (95 per cent confidence interval 89 to 98) per cent.ConclusionThe sensitivity of 95 per cent for CTC in the diagnosis of colorectal cancer compares favourably with that of double-contrast barium enema (92 per cent) and colonoscopy (94 per cent).