[Natural history of intestinal lesions in inflammatory bowel disease]

Crohn's disease may involve any part of the digestive tract from mouth to anus, but affects mainly the distal ileum and the,colon. At diagnosis, perianal lesions are observed in 20% of the cases. During the disease course, strictures develop in the majority of patients with ileal disease, while penetrating lesions (fistulas and abscesses) develop in half of the patients. Only one third of patients with colonic involvement will develop structuring or penetrating lesions. Intestinal lesions of ulcerative colitis involve constantly the rectum and may extend continuously throughout the colon. At diagnosis, lesions involve the rectum, the left colon and most of the colon in similar proportions. Subsequent extension of the lesions over 20 years is observed in half of the patients. In Crohn's disease, 40%-50% of the patients require intestinal resection at 10 years. The risk of colectomy in ulcerative colitis is about 1% per year Dysplasia and cancer may complicate longstanding extensive colonic lesions in Crohn's disease and ulcerative colitis. Malignant transformation of chronic inflammatory lesions may also occur in patients with longstanding lesions of the small bowel in Crohn's disease.