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Radiologic Findings: Upper GI and Small bowel follow through: There is abnormal wall thickening, luminal narrowing, and cobblestoning involving a long segment of the distal ileum including the terminal ileum. There is also involvement of the cecum. Slight separation of bowel loops is also demonstrated. Marked duodenal fold thickening is also seen. CT Findings: There is a wall thickening of the terminal ileum and cecum. Stranding of the surrounding mesenteric fat adjacent to the cecum is present. Fat proliferation within the mesenteric fat surrounding the cecum is also demonstrated.

Diagnosis:Crohn's disease.

Discussion: Crohn's disease, also termed regional enteritis, is a transmural (involving all layers of the bowel and the serosal surface) granulomatous disease that may involve any area of the GI tract from the mouth to the anus. The small bowel is involved by Crohn's disease in 80% of patients with the terminal ileum being the most frequently involved segment. In 30% of patients, disease is confined to the small bowel, and in 50% of patients there is also colonic involvement with the small bowel. Esophageal, gastric, and duodenal involvement is seen in 30% of patients. The etiology remains unknown; however, possible factors include infection, altered immunity, and genetic predisposition.

The peak incidence o Crohn's disease is between the ages of 20 and 40, and approximately 25% of patients present in childhood, adolescence, or teen-age years. Most children with Crohn's disease present with an insidious onset of GI symptoms particularly nonspecific abdominal pain (75%) and diarrhea (70%). Extra-intestinal manifestation may accompany or precede clinical presentation in as many as 40% of affected children. These non-GI manifestations include failure to thrive with delayed puberty, fever of unknown origin, anorexia, arthritis, chronic infection, aphthous stomatitis, and erythema nodosum.

Crohn's disease may be localized to one segment of bowel or involve several segments of bowel with intervening normal bowel. The normal bowel is known as skip areas. The earliest changes seen is granularity of the mucosa likely reflecting mucosal edema. Small mucosal edema then progresses to more prominent mural edema and increased mucosal secretions resulting in thickening of mucosal folds and effacement of the mucosal pattern. Nodular irregularity with linear and transverse ulcerations may develop lending the mucosa a cobblestone appearance. Deeper ulcerations can extend into the mesentery and adjacent organs to form fistulae. With transmural and even mesenteric involvement, inflamed loops of bowel may become adherent to each other or to adjacent organs resulting in palpable masses, fistulae, or obstruction. The inflamed, thickened, and fibrotic mesentary can cause separation and retraction of bowel loops. Edema and fibrosis eventually leads to marked narrowing of the lumen. The segment of stenotic bowel produces the "string sign" on small bowel follow-through. The so-called thumbprinting results from thickening of the submucosa which is due to edema, blood, or inflammatory cells within the bowel wall. Major intra-abdominal complications include enteroenteric fistulae, sinus tracts, and abscesses.

References:
1. Blickman JG. Pediatric Radiology: The Requisites. St. Louis: Mosby, 1994, pp 92- 94.

2. Caffey's Pediatric X-Ray Diagnosis, 9th Ed. St. Louis: Mosby, 1993, pp 1069-1071.

3. Gore RM, Levine MS, Laufer I. Textbook of Gastrointestinal Radiology. Philadelphia:
W. B. Saunders, 1994, pp 824-843.

4. Harrison's Principles of Internal Medicine, 12th Ed. New York: McGraw-Hill, 1991, pp 1268-1281.

5. Kirks DR. Practical Pediatric Imaging, 2nd Ed. Boston: Little/Brown, 1991, pp 793- 796.

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