The appendix is a hollow, wormlike structure attached to the intestines. It lies in the lower part of right abdomen at the belt line. In early life the appendix produces immune cells, but later on what it does seems causing trouble. Several different mechanisms begin a process of inflammation that usually progresses to rupturing of the appendix and spilling of its toxic contents into the abdomen, if it is not treated. Appendicitis is most common in the teens and twenties, but anyone can have it at any age.

Of a hundred people with a ruptured appendix, somewhere between three and fifteen will die, depending upon their general state of health. The rest will be very sick for a while and need hospital treatment. But if it is surgically removed before it ruptures, less than one in a thousand will die.

Most of the time the tiny channel inside the appendix gets plugged up with a food particle, causing it to swell, get infected, and fill up with pus. At other times an infection seems to start things off. Typically the swelling reaches its limit in less than a day, after which the appendix will burst and spills its contents into the abdomen.

The standard sequence of events begins with four to six hours of generalized abdominal pain, followed by nausea and vomiting, followed by localization of the pain at the appendix in the lower right abdomen. That area becomes very tender to the touch. Just before the appendix ruptures, the symptoms will generally ease off for a while. Pain from appendicitis actually gets better when the appendix ruptures and before peritanitis has a chance to set in.

Appendicitis requires immediate medical attention. The standard treatment is emergency surgery. Because there are many variations to the typical history, also many other possible diseases that produce similar symptoms, and often the surgeon is not exactly sure what is going on. From the patient's history, the clinical examination and the laboratory tests the doctor will decide the safest course of action. In questionable cases, CT scans or ultrasounds are frequently used to look at the appendix. Unnecessary surgery then can be avoided. Surgeons feel that it is better occasionally to remove a normal appendix than to miss a sick one by not operating.