Appendicitis is inflammation and infection of the appendix, a small tube-shaped piece of tissue attached to the large intestine. The appendix is located in the right lower abdomen (belly). Appendicitis results from blockage in the appendix caused by dried mucus, hard stool, parasites or other foreign bodies. Mucus, which is secreted by the inner lining of the appendix, builds up behind the blockage when it can no longer drain into the large intestine. As the mucus builds up, the patient may complain of belly pain, loss of appetite and nausea. The blockage and build-up of mucus can impair blood flow through the appendix, and cause swelling and infection. Over time, this swelling and infection can cause the appendix to perforate (burst or rupture). If untreated, the infection can then spread and lead to peritonitis, an infection of other tissues in the abdomen.
Appendicitis is the most common cause of emergency abdominal surgery in children. It is slightly more common in boys and is rare in babies less than 1 year of age. Most cases occur between 8-16 years of age. The rate of perforation is higher in younger children (less than 5 years) because of their difficulty describing symptoms and difficulty examining them.