There is wider scope for using more flexible and thinner catheters during CT colonography compared to barium enema because of the requirement to transmit only gas and because the consequences of anal incontinence are less dramatic. The choice of rectal catheter will mainly depend on local availability, method of insufflation, and individual patient but there is some evidence suggesting that thin tubes are adequate for most circumstances.
Perhaps the simplest catheter is a thin plastic or rubber tube, for example a standard 14F rectal tube (Jacques Nelaton rectal catheter; Rusch, Bucks, UK) or a Foley catheter. The former was shown to be as effective as a standard inflatable rectal balloon catheter (Trimline DC; E-Z-EM, Westbury, NY) for achieving adequate distension (Taylor et al. 2003). Alternatively, the Foley catheter is almost ubiquitous and can be used effectively when attached to a bulb insufflator. The soft tip allows safe insertion and it has a relatively small inflatable balloon, which can be used to assist continence if necessary.
Routine use of an inflated rectal balloon catheter is discouraged for barium enema following evidence that the risk of rectal perforation is increased (BlakeborougH et al. 1997), usually due to tearing the rectal wall either during insertion of the stiff catheter or due to the radial force applied by inflating the balloon. This also likely holds true for CT colonography, not least because insufflation of the balloon cannot be performed under fluoroscopic control. Most experts recommend choosing the most appropriate catheter according to an individual's requirements; for example, most patients can be optimally scanned using a thin, flexible rectal tube whereas those with anal incontinence may require judicious use of an inflated rectal balloon catheter. In the latter situation, most complications can be avoided by performing a rectal examination (see section above), careful catheter insertion and gentle balloon inflation.
Automated insufflation systems demand specific tubes which are designed to simply plug into the front of the device. Even here there is a choice of both standard larger bore balloon catheter and the slimmer so-called paediatric tip. In our experience, insertion of the larger catheters is, for many patients, the most uncomfortable part of the study. In response to this, the manufacturers have recently developed thin balloon catheters.
Some groups advocate removing the tube for the second acquisition to enhance patient comfort and to facilitate subsequent rectal assessment. However, this issue is much less relevant with thin catheters. Even if using larger catheters, the advantage of being able to insufflate additional gas likely outweighs any potential benefit of early removal.
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