The morbidity and mortality of colonoscopy are well recognised and described (Vallera and Bailie 1996; Bowles et al. 2004; Waye et al. 1992; Muhldorfer et al. 1992), and larger series report perforation rates in the region of approximately 0.2% (i.e. 1/500). Since its introduction, proponents of CT colonography have proclaimed an excellent safety profile in comparison to endoscopy, assumptions based on its relatively non-invasive nature and the ability to perform the investigation without a need for intravenous sedation. However two recent case reports of colonic perforation during CT colonography have questioned its safety. The first case of perforation followed CT colonography in a patient two weeks after a deep rectal biopsy in the presence of a near obstructing rectosigmoid tumour (Kamar et al. 2004). A rectal balloon catheter and manual insufflation of room air were also utilised. It is generally accepted that clinically non-obstructing tumours can prevent the retrograde passage of both liquid and gas due to a change in morphology when under distal pressure. Given this, an inflated rectal balloon could generate critically high intra-luminal pressure during inflation. The second case was performed in a patient with fulminant ulcera-tive colitis, generally considered a contraindication to CT colonography (Coady-Fariborzian et al. 2004). Indeed, the referring gastroenterologist had requested CT colonography because of concerns that colonoscopy would involve a higher risk of perforation. Again, an inflated rectal balloon catheter was used with manual insufflation of room air. These case reports further underline the principle that rectal balloon catheters should be used judiciously and with great care. They are contraindicated in patients with inflammatory bowel disease and in patients with potentially obstructing tumours. It is possible that the use of automated insufflator devices may have prevented perforation in these two cases by automatically terminating insufflation at a safe intracolonic pressure.
CTC is a relatively new technique and no large scale studies of complication rates have appeared in the peer-reviewed literature. Because of this, it is difficult to determine accurately the overall perforation rate in clinical practice. Given the well-defined, albeit small, risk during barium enema, it seems inevitable that CT related perforations will occur. Recently, abstracted data has been presented that investigated the perforation rate in 3 USA centres, finding 3 perforations out of 7180 patients studied (0.04%), and again the use of rectal balloon catheters were implicated in these (Sosna et al. 2004). There are now international efforts to establish the true perforation rate for CT colonography but preliminary data suggests the rate will lie between barium enema (0.01%; Gharemani 2000) and colonoscopy (0.2%; Vallera and Bailie 1996; Bowles et al. 2004; Waye et al. 1992; Muhldorfer et al. 1992).
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