The MRI reports also gave additional information not available from BaFT. Bowel wall enhancement postgadolinium was reported, which helped distinguish inflammatory from fibrotic strictures in 5 patients (although the radiologists stated that they cannot reliably do this on enhancement pattern alone). MRI detected incidental extraintestinal pathology in 3 patients.
MRI is a tool that is being increasingly used in the diagnosis and reassessment of both paediatric and adult CD. This practice is being driven by increasing concern about radiation exposure, particularly in children; however, practice varies widely and there is little evidence on its methodology and use. The present study demonstrates the feasibility of our institution's protocol for use in young people without the need for nasojejunal intubation. It provides diagnostic images that certainly compare favourably, particularly in the terminal ileum, to what has previously been considered the criterion standard radiological investigation in paediatric IBD, BaFT.
The Porto criteria were developed through the European Society of Paediatric Gastroenterology, Hepatology, and Nutrition to aid in diagnosing IBD in children (1). These guidelines suggest contrast studies as the modality of choice for small bowel imaging. The newer guidelines of the European Crohn's and Colitis Organisation suggest that MRI may be used in centres with expertise (8), but this is based on few comparative data. There have been several publications using MRI in children with IBD, but most of these do not provide direct comparison with the previous criterion standard, BaFT (5,6,9).
Perhaps the most attractive reason for the increasing use of MRI in paediatrics is the lack of radiation exposure. This is particularly true in a chronic relapsing disease such as CD, in which repeated imaging is often required during a lifetime of illness. The mean dose for a BaFT in the paediatric population in the United Kingdom has been measured and varies according to age, but for ages 10 and 15 years, it is 4.5 and 7.2 mSv (10), respectively, giving a lifetime adjusted risk of up to 0.3% for developing a malignancy. More significantly, Desmond et al (4) showed that in CD, a cumulative dose of radiation of >75 mSv increased cancer mortality by 7.3% and one of the significant risk factors for this occurring was diagnosis before age 17 years.
Apart from the lack of radiation, in the present study, MRI has been shown to be superior to BaFT for detecting small intestinal pathology. Using our protocol, the sensitivity and specificity of the MRI in detecting terminal ileal disease are similar to other studies (5,9,11,12). These studies have used different protocols, in particular different oral contrast solutions. Probably the most commonly used agent is polyethylene glycol (9,11), but this along with others requires a large volume to be consumed. Our protocol was adopted because of the small volume of liquid required, palatability, and ability to give the contrast agent orally. The lactulose acts as an osmotic agent, allowing improved visualisation of the small bowel loops. The lactulose is nonabsorbable and (in the absence of small bowel overgrowth) remains largely unmodified in the small bowel, links with water molecules, fills the lumen, and thus distends the loops (13). The tolerability is particularly important in a largely adolescent patient group, who may require repeat examinations. It may be that this small volume compromises proximal jejunal distension, but this does not appear to significantly affect the diagnostic quality of the investigation. Another important advantage of MRI is the ability of gadolinium contrast enhancement to help differentiate between inflammatory and fibrotic narrowing (14). Finally, our study also demonstrated incidental lesions, although the clinical relevance of these types of findings is unclear. An adult study suggests that there is no clinical benefit from the detection of such extraintestinal lesions (15).
Apart from MRI, other alternative modalities have been considered in IBD. Computerised tomography (CT) has also been used to image the small bowel and has been shown to be effective in paediatric IBD (16); however, it has a much higher radiation exposure than BaFT (17), and a recent study has shown an equivalent accuracy of magnetic resonance enterography compared with CT in a paediatric cohort (18). CT also accounted for the majority of the radiation in the patients in the study of Desmond et al (4).
Wireless capsule endoscopy may be considered in symptomatic children with suspected small bowel involvement, after exclusion of strictures or stenoses. Capsule endoscopy may be superior in sensitivity to the conventional techniques in detecting mucosal lesions in the small bowel (19–21), although a recent publication showed that MRI was superior (22); however, studies comparing the different techniques excluded patients with strictures, which limits their conclusions. In addition, bowel wall thickness, stenoses with prestenotic dilation, as well as extraluminal complications cannot be identified with capsule endoscopy. Wireless capsule endoscopy is considered safe, with a low risk of capsule impaction beyond infancy (23). This may suggest a role for this investigation in children who are unable to tolerate other imaging modalities; however, the low risk of impaction remains, which a small bowel follow-through or a pretest with ingestion of a dissolvable patency capsule are not sensitive enough to exclude (21). In patients with IBD, the risk for capsule impaction is higher than that for other indications (eg, bleeding, protein-losing enteropathy), because of the incidence of stricturing disease. Finally, young children may not swallow the capsule and therefore may require endoscopic replacement of the capsule in the duodenum (21) under general anaesthetic. Given these practical difficulties alone, it is likely that wireless capsule endoscopy will remain a reserve investigation tool and nonroutine for imaging in paediatric IBD.
Ultrasound is also being used increasingly to image the bowel in IBD and other conditions and has the shared advantage with MRI of no radiation exposure. It has been shown to be sensitive and specific in detecting small bowel disease (24,25), but there has been paediatric evidence that it is inferior at detecting disease that is not in the terminal ileum (26). The conflicting nature of the evidence in this field implies that the results are still extremely operator dependent and that perhaps with time this may become an increasingly used tool; however, given that its place in adult practice is not yet established, it is unlikely to be considered a criterion standard investigation in children in the short term.
This is the largest series of children with IBD undergoing abdominal MRI for detecting small bowel pathology to our knowledge, and one of the few studies that compares directly to BaFT. The data confirm the feasibility of MRI as a routine investigation in children with IBD. Only 1 patient in 88 failed to tolerate the procedure. The technical difficulties have had minimal adverse effect on image quality and may continue to reduce with time and experience of the protocol. The numbers of MRI sequences performed for paediatric small bowel MRI have already been reduced to make the examination more child friendly. We use a small volume of palatable contrast without the need for a nasogastric tube. The sensitivity and especially specificity of MRI for detecting small bowel pathology were superior to BaFT, with no radiation burden. Although there may be issues around availability, expertise, and cost, MRI should replace BaFT as the criterion standard in investigating paediatric IBD.
The authors acknowledge the help of the diagnostic imaging department of the Royal London Children's Hospital, particularly the MRI staff, for helping with the new protocol.
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Keywords:Copyright 2012 by ESPGHAN and NASPGHAN
barium follow-through; Crohn disease; inflammatory bowel diseases; magnetic resonance imaging