in the early stages crohn's disease causes small scattered shallow crater-like areas (erosions) on the inner surface of the bowel. these erosions are called aphthous ulcers. with time the erosions become deeper and larger ultimately becoming true ulcers (which are deeper than erosions) and causing scarring and stiffness of the bowel. as the disease progresses the bowel becomes increasingly narrowed and ultimately can become obstructed. deep ulcers can puncture holes in the wall of the bowel and bacteria from within the bowel can spread to infect adjacent organs and the surrounding abdominal cavity. when crohn's disease narrows the small intestine to the point of obstruction the flow of the contents through the intestine ceases. sometimes the obstruction can be caused suddenly by poorly digestible fruit or vegetables that plug the already narrowed segment of the intestine. when the intestine is obstructed digesting food fluid and gas from the stomach and the small intestine cannot pass into the colon. the symptoms of small intestinal obstruction then appear including severe abdominal cramps nausea vomiting and abdominal distention. obstruction of the small intestine is much more likely since the small intestine is much narrower than the colon to begin with. deep ulcers can puncture holes in the walls of the small intestine and the colon and create a tunnel between the intestine and adjacent organs. if the ulcer tunnel reaches an adjacent empty space inside the abdominal cavity a collection of infected pus (an abdominal abscess) is formed. patients with abdominal abscesses can develop tender abdominal masses high fevers and abdominal pain. when the ulcer tunnels into an adjacent organ a channel (fistula) is formed. the formation of a fistula between the intestine and the bladder (enteric-vesicular fistula) can cause frequent urinary tract infections and the passage of gas and feces during urination. when a fistula develops between the intestine and the skin (enteric-cutaneous fistula) pus and mucous emerge from a small painful opening on the skin of the abdomen. the development of a fistula between the colon and the vagina (colonic-vaginal fistula) causes gas and feces to emerge through the vagina. the presence of a fistula from the intestines to the anus (anal fistula) leads to a discharge of mucous and pus from the fistula's opening around the anus.
how does crohn's disease affect the intestines?