This 3 1/2-inch-long tube of tissue extends from your large intestine on the lower right side of your body.

In the U.S., 1 in 20 people will get appendicitis at some point in their lives. Although it can strike at any age, appendicitis is rare in children younger than 2. It’s most likely to affect people between the ages of 10 and 30.   Appendicitis happens when the appendix gets blocked, often by poop, a foreign body (something inside you that isn’t supposed to be there), or cancer. Blockage may also result from infection, since the appendix can swell in response to any infection in the body.

Diagnosing appendicitis can be tricky. Symptoms  are often unclear or similar to those of other illnesses, including gallbladder problems, bladder or urinary tract infection, Crohn's disease, gastritis, kidney stones, intestinal infection, and ovary problems.   These tests can help diagnose appendicitis:   Examination of your abdomen to look for inflammation Urine (pee) test to rule out a urinary tract infection Rectal exam Blood test to see whether your body is fighting an infection CT scans Ultrasound

Left untreated, an inflamed appendix will burst, spilling bacteria and debris into the abdominal cavity, the central part of your body that holds your liver, stomach, and intestines. This can lead to peritonitis, a serious inflammation of the abdominal cavity's lining (the peritoneum). It can be deadly unless it is treated quickly with strong antibiotics.   Sometimes, an abscess forms outside an inflamed appendix.  Scar tissue then "walls off" the appendix from the rest of your organs. This keeps the infection from spreading. But an abscessed appendix can tear and lead to peritonitis.

On occasion, a person may not see their doctor until appendicitis with rupture has been present for many days or even weeks. In this situation, an abscess usually has formed, and the appendiceal perforation may have closed over. If the abscess is small, it initially can be treated with antibiotics; however, an abscess usually requires drainage. A drain (a small plastic or rubber tube) usually is inserted through the skin and into the abscess with the aid of an ultrasound or CT scan that can determine the exact location of the abscess. The drain allows pus to flow from the abscess out of the body. The appendix may be removed several weeks or months after the abscess has resolved. This is called an interval appendectomy and is done to prevent a second attack of appendicitis.

Recovery from an appendectomy depends on the severity of the inflammation. If inflammation is mild, recovery can take a few days to a week.  If there has been more extensive inflammation such as an abscess or localized perforation of the appendix, recovery might take several weeks.  Free rupture of the appendix into the peritoneal cavity (abdomen) may require even longer.  Recovery has become much faster with the substitution of laparoscopic for “open” surgery.

There is a small group of patients in whom the inflammation and infection of appendicitis remain mild and localized to a small area. The body is able not only to contain the inflammation and infection but to resolve them as well. These patients usually are not very ill and improve during several days of observation. This type of appendicitis is referred to as "confined appendicitis" and may be treated with antibiotics alone. The appendix may or may not be removed later. There is still some controversy, however, about leaving the healed appendix in place since appendicitis can recur.

When the appendix is removed surgically, a small portion may be left behind. This piece of appendix may become inflamed and is prone to develop all of the complications of appendicitis. Thus, it is possible for individuals who have had their appendix "removed" to develop another episode of appendicitis. Stump appendicitis is treated similarly to appendicitis with an intact (surgically unremoved) appendix. It is important to consider early and diagnose stump appendicitis since inadequate diagnosis and treatment can result in a rupture of the inflamed stump.

Recently, it has been hypothesized that some episodes of appendicitis-like symptoms, especially recurrent symptoms, may be due to an increased sensitivity of the intestine and appendix from a prior episode of inflammation. That is, the recurrent symptoms are not due to recurrent episodes of inflammation. Rather, prior inflammation has made the nerves of the intestines and appendix or the central nervous system that innervate them more sensitive to normal stimuli, that is, with stimuli other than inflammation. This will be a difficult, if not impossible, hypothesis to confirm.