The etiology of Crohn's is not understood, but it appears to be more frequent in some families and is probably some sort of autoimmune type disease. Crohn's leads to inflammation and thickening of the bowel wall. It often effects the anus with ulcers and draining tracts. Untreated, these inflammatory areas thicken and narrow the lumen or opening of the bowel. They often lead to penetrating ulcers which cause fistulas or abscesses around the bowel.
Treatment is usually medical since surgery is only pursued as a last resort.
Initial treatment is usually Prednisone or some other strong anti-inflammatory to decrease the ulcers, bowel thickening, and fistula production. After the inflammation is under control, other medications are used to minimize the quantity of steroids necessary. These may be steroid enemas, oral anti-inflammatory drugs which are not absorbed, etc. This can be a debilitating disease and needs aggressive management to avoid the potential serious consequences of untreated inflammation of the bowel. I have had 2 resections and gall bladder removal.