Crohn Disease, also known as Regional Enteritis, is a prolonged inflammatory bowel disease of unknown etiology and upredictable course. The disease may affect the entire GI tract and does so in a characteristic discontinuous and asymmetric pattern. Males and females are affected equally and usually present between ages 15 and 30. Symptoms vary but most commonly include abdominal pain with diarrhea, which may be bloody. Other symptoms include low-grade fever, anorexia and weight loss, anemia, perianal abscess/fistula and malabsorption.

The small bowel is most frequently involved followed by the colon. The terminal ileum alone or in combination with other sites is involved in 95% of cases. Typical findings on small bowel follow-through include fold thickening with nodularity, aphthous ulcers and cobblestone mucosa and ulceration. Crohn or granulomatous colitis occurs most frequently on the right side with sparing of the rectosigmoid. Often small nodular filling defects are seen with aphthous ulcers. Discontinuous involvement or "skip lesions" throughout the bowel are characteristic. Complications include fistulae, sinus tracts, abscesses, perforation, toxic megacolon and increased risk for bowel lymphoma and adenocarcinoma.

Findings on CT include thickened bowel wall potentially with skip areas, "creeping fat" due to mesenteric fat proliferation, vascular dilation and tortuosity, mesenteric adenopathy, fistula, stricture or abscess. Although complications may be treated surgically, primary therapy is medical as recurrence rate after resection is up to 39%.

There are many extraintestinal manifestations including gallstones, urolithiasis, uveitis and arthritis. Also, Crohn Disease is associated with pyoderma gangrenosum and erythema nodosum.