- Cross-sectional imaging with computed tomography (CT) or magnetic resonance imaging (MRI) is an important tool in diagnosing inflammatory bowel disease and assessing the severity and extent of disease activity
- There is growing interest in using CT and MRI to follow patients over time for purposes of prognostication, assessing response to treatment and detecting disease-related complications
- CT enterography, MR enterography and contrast ultrasonography are newer, specialized modalities that can aid in the management of inflammatory bowel disease
Ileocolonoscopy is the gold standard for evaluating the extent and severity of inflammatory bowel disease (IBD). However, it has substantial limitations, including poor patient acceptability, the need for sedation and inability to visualize mucosa proximal to strictures.
In Crohn's disease (CD), it's now recognized that inflammation can be transmural and may skip the terminal ileum. Thus, the entire thickness and length of the small bowel needs to be examined.
Over the past decade, computed tomography (CT) and magnetic resonance imaging (MRI) have been used more often to assess the severity and extent of CD and ulcerative colitis (UC), as well as disease-related complications. Newer techniques also have applications for prognostication, determining response to therapy and identifying cumulative irreversible damage.
Ashwin N. Ananthakrishnan, MD, MPH, director of the Crohn's and Colitis Center at Massachusetts General Hospital, and colleagues recently reviewed the important role of CT, MRI and ultrasonography in the management of IBD. A central feature of their paper in Gastrointestinal Endoscopy Clinics of North America is a table that compares the indications, advantages and disadvantages of each modality.
Of particular interest, the reviewers discuss how three of the newest modalities—CT enterography (CTE), MR enterography (MRE) and contrast ultrasonography—are being applied to the evaluation of patients with IBD.
Computed Tomography Enterography
CTE is a specialized protocol for CT of the abdomen and pelvis, designed to image the lumen and wall of the small bowel using a multidetector CT scanner.
In all UC patients, CTE can be used to detect toxic megacolon and bowel perforation. CTE is also useful for detecting small bowel inflammation in patients who have atypical symptoms or endoscopic features that raise suspicion for CD.
- Assessment of Disease Activity: CTE has high sensitivity and specificity for detecting small bowel CD, and it has been validated against clinical, histologic and endoscopic assessments. The diagnostic accuracy of CTE in CD is comparable to that of MRE, and CTE yields higher-quality images because it is less susceptible to bowel motion artifacts
- Prognostication and Monitoring: CTE features that are consistently associated with active CD, including hyperenhancement and thickening of the bowel wall, have been shown to improve after successful treatment of the disease. This suggests a potential role for CTE in monitoring the efficacy of CD treatment
- Detection of Complications: CTE has high sensitivity and specificity for detecting small bowel stenosis and internal penetrating disease
Magnetic Resonance Enterography
MRE is a radiation-free technique optimized to image the small bowel, although it is also being studied for assessment of colonic inflammation.
- Assessment of Disease Activity: Similar to CTE, conventional MRE has high sensitivity and specificity for the diagnosis of active small bowel inflammation in CD. The recently developed MR Enterography Global Score (MEGS), detailed in the journal article, appears to be better than the Crohn's Disease MRI Index at capturing the full disease burden in patients with CD
- Prognostication and Monitoring: MRE-based scoring systems, including MEGS, have been validated to measure a response to therapy in CD
- Detection of Complications: MRE has high sensitivity and specificity for detecting strictures, small bowel fistulas and intra-abdominal abscesses. Findings of bowel wall thickening have been positively associated with small bowel fibrosis and negatively associated with response to medical therapy
Emerging Modalities: Contrast Ultrasonography
Contrast-enhanced ultrasonography (CEUS) analyzes tissue perfusion, using an intravenous contrast agent composed of innocuous microscopic gas bubbles that increase vascular contrast. Small intestine contrast ultrasonography (SICUS), which involves distending small bowel loops by having the patient ingest a hyperosmolar luminal contrast solution, results in enhanced sonographic images.
Few studies have investigated whether ultrasonography of any type can be used to monitor disease response in UC. However, in a prospective study of 67 patients, CEUS quantification of inflammation of the bowel wall correlated well with both endoscopic and clinical improvement.
- Assessment of Disease Activity: CEUS is useful in detecting disease activity in patients with CD. A recent meta-analysis put its sensitivity at 94% and its specificity at 79%. CEUS can also distinguish between fibrotic and inflammatory strictures
- Prognostication and Monitoring: SICUS has demonstrated high accuracy in assessing the progression of lesions, stenosis and penetrating complications. In one study it proved useful in evaluating postoperative recurrence of CD
- Detection of Complications: CEUS seems to be more accurate than standard ultrasonography for detecting abdominal abscesses
CTE or MRE or other forms of imaging may someday be combined with other biomarkers. A more comprehensive evaluation of UC and CD might facilitate more effective treatment and prevention of permanent damage.
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