Computed tomography colonography: underutilised in Australia

To the Editor:

We read with interest Mendelson and colleagues’ article regarding the underutilisation of computed tomography colonography (CTC) for colorectal cancer detection in Australia.1 The authors state that “CTC is less accurate in the diagnosis of small or diminutive polyps … However, in the context of symptomatic patients, this is not relevant”.1 This overlooks the importance of detecting small adenomas as well as flat, right-sided colonic lesions such as sessile serrated polyps. It is well established that the early detection and treatment of these lesions reduces interval colorectal cancer.2 To state that these are “not relevant” in symptomatic patients is inaccurate. High definition white light with the aid of chromoendoscopy tools such as narrow band imaging in optical colonoscopy (OC) has significantly improved the ability of endoscopists to detect diminutive and subtle lesions. CTC has a markedly limited ability to detect small and flat lesions when compared with OC.3

The authors reference phase 2 data from the National Bowel Cancer Screening Program, stating that “the great majority of OCs (about nine in ten) were normal”. However, polyps were detected in 34.9% of participants.4 The authors appear to define normality as the absence of a cancer or advanced adenoma (one in ten colonoscopies). We argue that the detection of any adenoma is important and is not “normal”, as it highlights a cohort of patients at risk of colorectal cancer and requiring ongoing polyp surveillance.

We also question the authors’ suggestion that a negative CTC obviates the need for OC in lower risk patients with positive faecal immunochemical test results. OC provides the opportunity to detect and treat a range of polypoid and non-polypoid colonic pathology and although a negative CTC may help exclude a cancer, it does not address the range of other potentially morbid or precancerous causes of occult faecal blood. Given these limitations, a cautious approach should be adopted if CTC is to be used as an alternative to OC in all lower risk patients.