Introduction Colorectal cancer is the second cause of cancer-related death in the United States and Europe
(1).Computerised tomography Colonography (CTC) is used to examine the colon and rectum to detect for abnormalities such as cancers and polyps often in those where direct visualisation is difficult or contraidindicated. There are diagnostic pitfalls that are unique to evaluation of the rectum(2). The presence of a rectal balloon and enema tube can compress masses rendering them more difficult to detect at cross-sectional imaging. Fortunately, most large masses that are low enough in the rectum can be detected by digital rectal examination. The anorectal pitfalls that seem to cause the most trouble at CTC interpretation are hypertrophied anal papillae, internal haemorrhoids and low rectal tumours(3).
Method To determine if a digital rectal examination (DRE) or rigid sigmoidoscopy was performed prior to a patient referral for a CTC. Retrospectively all CTCs performed between January 2013 and December
2013 in two separate NHS Trust hospitals were analysed. Retrospective data was collected at the point of referral to see if a DRE or rigid sigmoidoscopy was performed. We followed up patients who underwent lower endoscopic evaluation following their index CTC to see if we missed any potentially avoidable pathology in the rectum and anus.
Results 172 CTCs were analysed, 31 patients had a follow-up lower endoscopy following their index CTC. Twenty-five patients were referred for CTC due to a change in bowel habits, three were referred for anaemia and three were referred for abdominal pain. 20/31 (65%) patients had a physical examination of their rectum prior to CTC.
17/21( 85%) referrals for ctc from surgical clinics performed a physical examination compared with 3/10 (30%) referrals from gastroenterology clinics (p<0.002). In the 11 patients who did not have a physical examination of the rectum prior to CTC, follow-up endoscopy found two rectal cancers. Both lesions were not detected on index CTC.
Conclusion CTC has the potential to miss serious rectal pathology. A physical examination of the anus and rectum should routinely be performed in any patient being considered for a CTC to avoid missing potentially serious pathology. It is important that we also inform patients on the limitations of investigations which may include the chance of missed pathology.
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. Alvin C, Silva MD. Evaluation of benign and malignant rectal lesions with CT colonography and endoscopic correlation. Radiographics. 2006;4
. Pickhardt PJ. Differential diagnosis of polypoid lesions seen at CT colonography(virtual colonoscopy) Radiographics. 2004;24:1535–56.
Disclosure of Interest None Declared
- anal lesions
- CT colonography