Approach Considerations
Crohn disease radiologic evaluation
In 2017, an expert panel, which included contributors from the Society of Abdominal Radiology Crohn’s Disease–Focused Panel, the Society of Pediatric Radiology, and the American Gastroenterological Association, issued the following guidelines on the use of computed tomography enterography (CTE) and magnetic resonance enterography (MRE) in patients with small bowel Crohn disease [17, 18] :
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The number of involved bowel segments and their location, as well as the length and degree of upstream dilatation of Crohn strictures, should be reported by radiologists to help gastroenterologists and surgeons determine the best therapeutic plan.
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Radiologists should state if mural inflammation is present when describing areas with stricture or penetrating disease.
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Cross-sectional enterography should be performed at Crohn disease diagnosis.
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Consider cross-sectional enterography for disease monitoring in patients with small bowel disease or penetrating complications.
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While a dedicated pelvic magnetic resonance (MR) study is needed in patients with perianal disease, all CTEs and MREs should also include imaging of the anus.
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Radiologists should comment on and describe intramural T2 hyperintensity, restricted diffusion, perienteric stranding, wall thickness, and mural ulcerations seen on imaging, because they typically correlate with disease severity.
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MRE is preferred over CTE to estimate response to medical treatment in patients with asymptomatic disease.
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Noncontrast MRE with T2-weighted and diffusion-weighted imaging is an “acceptable alternative” when intravenous contrast agents cannot be used.
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Radiologists should evaluate CTE and MRE examinations for signs of mesenteric venous thrombosis, occlusions, or small bowel varices.
Laboratory Studies
Laboratory data for Crohn disease are nonspecific. The complete blood count (CBC) may reveal evidence of hypochromic microcytic anemia due to the iron deficiency anemia secondary to gastrointestinal (GI) blood loss, or it may reveal normocytic anemia due to the anemia of chronic disease.
levels of acute-phase reactants, the erythrocyte sedimentation rate (ESR), and C-reactive protein (CRP) levels are often elevated in patients with Crohn disease. However, a normal ESR or CRP level should not deter further evaluation in a suspicious case.
Hypoalbuminemia is a common laboratory finding in patients with Crohn disease. Additional common deficiencies include iron and micronutrients (eg, folic acid, vitamin B-12, serum iron, total iron binding capacity, calcium, and magnesium).
Stool studies should be obtained to rule out bacterial or parasitic infection.
Serologic testing for inflammatory bowel disease (IBD) is available. Immunoglobulin A (IgA) and immunoglobulin G (IgG) antibodies to anti– Saccharomyces cerevisiae (ASCA) have been associated with Crohn disease, whereas perinuclear antineutrophil cytoplasmic antibody (p-ANCA) has been associated with ulcerative colitis (UC).
Although these tests might assist in differentiating between Crohn disease and UC, they are not good screening tests. In a retrospective review, serologic screening that included ASCA, pANCA, and antibody to Escherichia coli outer membrane porin (anti-OmpC) demonstrated a sensitivity of 60%, a specificity of 91%, and a positive predictive value of 60%. [19]
Excretion of fecal calprotectin, a protein derived from neutrophils, is increased with colorectal inflammation. [1] Enzyme-linked immunosorbent assay (ELISA) for fecal calprotectin is available; the cutoff level is 50 µg/g feces.
Radiography, MRI, CT, US, and PET
A single-contrast upper GI radiologic series with small-bowel follow-through (SBFT) can be used to evaluate the small intestine, which cannot be reached during endoscopy (see the image below).
Image obtained during upper gastrointestinal series with small-bowel follow-through shows narrowing and irregularity in distal ileum in 16-year-old male adolescent with Crohn disease.
Magnetic resonance enterography (MRE) [2] and computed tomography enterography (CTE) are increasingly being used for evaluation of the small bowel. Both modalities are as sensitive and specific as SBFT for detection of small bowel inflammation and may be more accurate for detection of extraenteric complications, including fistulae and abscesses. [3] MRE is a particularly attractive option because of the lack of radiation exposure.
Proximal small bowel Crohn disease is present in up to 35% of children with this chronic inflammatory bowel disorder. It is also regarded as a more severe clinical phenotype that is associated with significant morbidity, including poor growth. MRE has now become the radiological procedure of choice in identifying proximal small bowel disease in children with Crohn disease. Moreover, the increased sensitivity of MRE to detect early-onset disease may allow physicians to tailor therapy more effectively. [20]
MRI is especially useful in the evaluation of pelvic and perianal disease (see the images below). Abdominal ultrasonography (US) can be used to investigate intestinal disease and to rule out gallbladder and kidney stones. Positron emission tomography (PET) is an experimental diagnostic tool.
Small abscess on right side of anal sphincter in 9-year-old boy with Crohn disease.
Endoscopy
The development of flexible, small-caliber endoscopes has allowed colonoscopic evaluation of pediatric patients of all ages, including infants. Colonoscopy with several colonic and terminal ileal biopsies is invaluable and considered a standard in the diagnosis of Crohn disease (see the image below).
Colonoscopic image of large ulcer and inflammation of descending colon in 12-year-old boy with Crohn disease.
Upper endoscopy, or esophagogastroduodenoscopy (EGD), should be part of the first-line investigation in all new cases of suspected Crohn disease. It is useful in planning therapy and in differentiating between Crohn disease and UC, especially if granulomas are present. Clinically significant upper GI inflammation can be present in the absence of upper GI symptoms.
Video capsule endoscopy is increasingly being used to evaluate for small-bowel Crohn disease in children. [4] Before the procedure is initiated, a dissolvable patency capsule should be placed or small bowel imaging performed to ensure that there are no areas of narrowing or stricture where the video capsule might create an obstruction.
Histologic Findings
The microscopic findings in intestinal biopsy samples from pediatric patients with Crohn disease consist of edema, inflammation (mononuclear and polymorphonuclear), cryptitis and crypt abscesses, architectural crypt changes, and transmural extension of the inflammation (see the image below).
Histologic features of chronic colitis with crypt atrophy and branching and lymphocytic infiltrate. Hematoxylin-eosin staining. Image courtesy of Dr E Ruchelli.
The presence of granulomas may be helpful in differentiating between UC and Crohn disease (see the image below), but granulomas are present in only about 30% of biopsy specimens obtained from patients with Crohn disease.
Colonic granuloma in patient with Crohn disease. Hematoxylin-eosin staining. Image courtesy of Dr E Ruchelli.
Staging
Multiple scoring systems incorporating the patient’s history, physical findings, and laboratory data have been developed to assess disease activity in adults with Crohn disease.
The Pediatric Crohn Disease Activity Index (PCDAI) was developed and validated in 1990. Its results are correlated with the physician’s global assessment and with the modified Harvey-Bradshaw index, and it has significant interobserver reliability. The important difference between this index and the Crohn Disease Activity Index (CDAI), which was developed for use in adults with Crohn disease, is the inclusion of growth parameters in the score.
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Colonoscopic image of large ulcer and inflammation of descending colon in 12-year-old boy with Crohn disease.
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Histologic features of chronic colitis with crypt atrophy and branching and lymphocytic infiltrate. Hematoxylin-eosin staining. Image courtesy of Dr E Ruchelli.
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Colonic granuloma in patient with Crohn disease. Hematoxylin-eosin staining. Image courtesy of Dr E Ruchelli.
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Image obtained during upper gastrointestinal series with small-bowel follow-through shows narrowing and irregularity in distal ileum in 16-year-old male adolescent with Crohn disease.
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Inflamed terminal ileum in 10-year-old girl with Crohn disease.
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Small abscess on right side of anal sphincter in 9-year-old boy with Crohn disease.
Tables
|
Crohn Disease |
Ulcerative Colitis |
Characteristic |
||
Distribution |
Entire GI tract |
Colon only, although gastritis recognized |
Skip lesions |
Continuous involvement proximally from rectum |
|
Pathology |
Full thickness |
Mucosa only |
Granulomas (30%) |
No granulomas |
|
Radiology |
Entire GI tract |
Colon only |
Skip lesions |
Continuous involvement proximally from rectum |
|
Fistulas, abscesses, fibrotic strictures |
Mucosal disease only |
|
Cancer risk |
Increased |
Estimated 1%/y, starting 10 y after diagnosis |
Presentation |
||
Bleeding |
Common |
Very common |
Obstruction |
Common |
Uncommon |
Fistula |
Common |
None |
Weight loss |
Common |
Uncommon |
Perianal disease |
Common |
Rare |
GI = gastrointestinal. |
||
