Luminal contrast and distension CT enterography
Neutral or low-density oral contrast media are a prerequisite for good-quality CT enterography [3-5] because they maximise contrast between the lumen and enhancing small bowel wall, facilitating assessment of mucosal thickening and wall stratification/enhancement patterns [1-8]. Water–methylcellulose solution, polyethylene glycol, commercially available low-density barium, 0.1% Volumen (Bracco, Milan, Italy) and milk are examples of neutral oral contrast agents with CT attenuation properties similar to that of water. Water alone usually results in inadequate distension due to rapid reabsorption, although some authors advocate its use [9].
Use of Volumen has been shown to improve the quality of bowel distension compared with water alone [4,10-12], but it remains unlicensed for use in the UK and therefore is not available. Milk was shown to give similar results as Volumen [13], but although less expensive and freely available in Europe, it may be deemed unpalatable by many patients when drunk in large volumes. Kuehle et al [14] reported that good small bowel distension could be achieved when using a 1-l solution of 2.5% mannitol/0.2% locust bean gum prior to MR enterography, with relatively minimal side effects. However, they found increased side effects such as diarrhoea, vomiting and spasms with increasing volumes (1200 and 1500 ml), without any significant improvement in small bowel distension.
Various studies have investigated the optimal volume of oral contrast that should be ingested, balancing the need for good distension with patient compliance and side effect profile. Maglinte [9] stated that a volume of <1.5 l is unlikely to be sufficient to adequately distend the small bowel without active inflammation, and a subcentimetre mass could be missed; although, in the authors' experience, good-quality examinations can be achieved with smaller volumes. Other authors have used contrast volumes of 1000–2500 ml, with variable results. Boudiaf et al [6] used <2 l of water in all the 107 patients who underwent CT enteroclysis. Boudiaf et al classified small bowel distension using a grading system based on diameters of jejunum and ileum graded 0–3 (where 0 was for no distension and 3 was optimal distension). They observed poor distension in only 2 of the 107 patients [6].
Positive oral contrast agents (containing iodine or barium) are not routinely used for CT enterography because they obscure mucosal enhancement, intraluminal haemorrhage and assessment of subtle mural disease [15,16]. Use of positive oral contrast should particularly be avoided in obscure gastrointestinal bleeding because the contrast can obscure the bleeding site. However, positive contrast can occasionally help establish fistula patency or the exact site of mechanical obstruction, because it will track the flow of luminal contents [16]. With this in mind, choice of standard abdomino-pelvic CT or CT enterography will be determined by the target of investigation, individualised according to clinical scenario. As discussed below, use of CT should be restricted in younger patients, particularly when not presenting acutely.
Use of Volumen has been shown to improve the quality of bowel distension compared with water alone [4,10-12], but it remains unlicensed for use in the UK and therefore is not available. Milk was shown to give similar results as Volumen [13], but although less expensive and freely available in Europe, it may be deemed unpalatable by many patients when drunk in large volumes. Kuehle et al [14] reported that good small bowel distension could be achieved when using a 1-l solution of 2.5% mannitol/0.2% locust bean gum prior to MR enterography, with relatively minimal side effects. However, they found increased side effects such as diarrhoea, vomiting and spasms with increasing volumes (1200 and 1500 ml), without any significant improvement in small bowel distension.
Various studies have investigated the optimal volume of oral contrast that should be ingested, balancing the need for good distension with patient compliance and side effect profile. Maglinte [9] stated that a volume of <1.5 l is unlikely to be sufficient to adequately distend the small bowel without active inflammation, and a subcentimetre mass could be missed; although, in the authors' experience, good-quality examinations can be achieved with smaller volumes. Other authors have used contrast volumes of 1000–2500 ml, with variable results. Boudiaf et al [6] used <2 l of water in all the 107 patients who underwent CT enteroclysis. Boudiaf et al classified small bowel distension using a grading system based on diameters of jejunum and ileum graded 0–3 (where 0 was for no distension and 3 was optimal distension). They observed poor distension in only 2 of the 107 patients [6].
Positive oral contrast agents (containing iodine or barium) are not routinely used for CT enterography because they obscure mucosal enhancement, intraluminal haemorrhage and assessment of subtle mural disease [15,16]. Use of positive oral contrast should particularly be avoided in obscure gastrointestinal bleeding because the contrast can obscure the bleeding site. However, positive contrast can occasionally help establish fistula patency or the exact site of mechanical obstruction, because it will track the flow of luminal contents [16]. With this in mind, choice of standard abdomino-pelvic CT or CT enterography will be determined by the target of investigation, individualised according to clinical scenario. As discussed below, use of CT should be restricted in younger patients, particularly when not presenting acutely.
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