Appendicitis is an inflammation of the vermiform appendix, a finger-like appendage to the cecum, the first part of the large intestine. The inflammation results from a bacterial infection that causes the appendix to swell and fill with pus. An early symptom of appendicitis is intermittent pain in the navel region. This becomes more severe and, within hours, localizes to the lower, right-hand corner of the abdomen. The abdominal muscles tighten, and the person loses his or her appetite and becomes nauseated. A slight fever is usual, as is constipation.