Volume 208 - Issue 5
Computed tomography colonography: underutilised in Australia
Authors: Richard M Mendelson, Tom R Sutherland and Andrew F Little
Med J Aust 2018; 208 (5): 234. || doi: 10.5694/mja17.00975
Published online: 19 March 2018
Published online: 19 March 2018
In reply
In reply:
We thank Hew and Ardalan for their interest in our article.1 Not all polyps are the same and should not be treated as such. A study comparing computed tomography colonography (CTC) and endoscopy2 showed similar detection rates for cancer and advanced adenoma despite five times more polyps being removed in the endoscopy arm. Studies have shown that over 80% of detected polyps are 5 mm or under;3 polyps under 6 mm can be safely ignored and the interval cancer rates following negative CTC and negative colonoscopy are comparable.4 Less than 25% of 6–9 mm polyps will progress, and when these small polyps are detected and left in situ, the 5-year death rate from colorectal cancer is 0.08%, which reduces to 0.03% if the patient undergoes follow-up CTC at 3 years.5 While the death rate is reduced to 0.02% if an immediate polypectomy is performed, to save one life from CRC, about 10 000 colonoscopies would be required, resulting in ten additional perforations.5
We are pleased that endoscopists in expert centres are using technological advances to improve colonoscopy accuracy. Australian data estimate a 20% prevalence of sessile serrated polyps; disappointingly, however, the detection rate of these by most colonoscopists undergoing voluntary recertification is under 10%.6 Their detection is challenging both for CTC and colonoscopy, but interval cancer rates following negative CTC are extremely low, suggesting that their malignant potential may be overstated.
Hew and Ardalan cite Corley and colleagues7 as establishing that early detection and treatment of small lesions reduces interval cancer. Our interpretation of this article differs. No data on small or flat lesions are presented and we believe it merely demonstrates the varied performance of colonoscopists — those who miss lesions have higher interval cancer rates.
The statement that CTC “does not address the range of other morbid or pre-cancerous causes of occult faecal blood” in asymptomatic individuals is difficult to understand. If the correspondents are referring to inflammatory bowel disease, how is this relevant if subjects are asymptomatic? CTC is as capable as OC at diagnosing diverticular disease and is irrelevant in asymptomatic individuals.
We reiterate our concern that failure to fund CTC — a highly accurate, available and well tolerated test — is leading to delayed diagnosis and increased morbidity and mortality for Australians.
Competing interests
No relevant disclosures.
References
- Mendelsen R, Sutherland T, Little A, et al. Computed tomography colonography: underutilised in Australia. Med J Aust 2017; 207: 139-140.
- Kim D, Pickhardt P, Taylor A, et al. CT colonography vs optical colonoscopy for detection of advanced neoplasia. N Engl J Med 2007; 357: 1403-1412.
- Graser A, Stieber P, Nagel D, et al. Comparison of CT colonography, optical colonoscopy, sigmoidoscopy and fecal occult blood tests for the detection of advanced adenoma in an average risk population. Gut 2009; 58: 241-248.
- Pickhardt P, Pooler B, Mbah I, et al. Colorectal findings at repeat CT colonography screening after initial CT colonography screening negative for polyps larger than 5 mm. Radiology 2017; 282(1): 139-148.
- Pickhardt P, Hassan C, Laghi A, et al. Clinical management of small (6- to 9-mm) polyps detected at screening CT colonography: a cost-effectiveness analysis. Am J Roentgenol 2008; 191: 1509-1516.
- Katelaris P. Conjoint recertification: why should I do it? Proceedings of Gastroenterological Society of Australia, Australian Gastroenterology Week; 2017 Aug 20-22; Gold Coast, Australia.
- Corley DA, Jensen CD, Marks AR, et al. Adenoma detection rate and risk of colorectal cancer and death. N Engl J Med 2014; 370: 1298-1306.