Miss rate of colorectal cancer at CT colonography in average-risk symptomatic patients

Objectives: Computed tomographic colonography (CTC) is a less burdensome alternative to colonoscopy in excluding colorectal cancer (CRC) in symptomatic patients. We evaluated the proportion of patients who underwent CTC in whom CRC was missed. Methods: Patients who had undergone CTC in the period 1 January 2007 to 1 January 2011 were merged with all cases of CRC recorded in the Cancer Registry between 1 January 2007 and 1 July 2011 to identify all patients who had undergone CTC less than 2 years before CRC had been diagnosed. Results: In 53 out of 1,855 patients who had undergone CTC, CRC was diagnosed. Of these, 40 patients had suspected CRC and 5 had large polyps at CTC. In five patients with an indeterminate mass, further investigation confirmed malignancy. One cancer in the caecum was missed because of poor distension. Two cancers were missed: one in the distal rectum and one in the ascending colon. Sensitivity of CTC for CRC was 94.3 % (95 % CI 88-100 %). The true miss rate, excluding the inadequate distended study, was 2 out of 53 (3.8 %). Conclusion: This study shows that the miss rate for CTC is low, which means that CTC is accurate in excluding CRC in symptomatic patients at a relatively low risk of CRC. Key Points: • The miss rate for colorectal cancer (CRC) on CT colonography (CTC) is low. • CTC is accurate at excluding CRC in symptomatic patients. • CTC is the method of choice in symptomatic patients to exclude CRC.

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