The appendix is a dead end hollow tube that can vary from 5 cm to 20 cm in length and is about 1cm in diameter. It is attached at its open end to the caecum, which is part of the large intestine.
The appendix serves no useful purpose in humans, and a small number of people are born without one, but in grazing animals it nurtures the bacteria that are necessary to digest the cellulose in grass. Rabbits have a huge appendix in proportion to the rest of their bowel.
The appendix floats relatively freely from its attachment, and may lie below, in front of, behind or beside the caecum. If the tube of the appendix becomes blocked by faeces or other material, it may become infected and cause appendicitis.
Appendicitis is a bacterial infection of the appendix. It is an almost unknown condition in poorer countries for dietary reasons, and the lack of fibre in Western diets is often blamed for the infection, although its incidence is steadily falling due to better dietary education.
If the narrow tube of the appendix becomes blocked by faeces, food, mucus or some foreign body, bacteria start breeding in the closed-off area behind the blockage. Pain develops around the navel, but soon moves to the lower right side of the abdomen just above the pelvic bone and steadily worsens. It is often associated with loss of appetite, slight diarrhoea and a mild fever. Depending on the position of the infected appendix, appendicitis can have variable symptoms, and sometimes, when it lies behind the caecum (retrocaecal appendicitis), its symptoms may be so misleading that the diagnosis is easily missed by a doctor. If untreated, the appendix becomes steadily more infected, full of pus, and eventually bursts to cause peritonitis.
There is no specific diagnostic test, but blood and urine tests and sometimes an ultrasound scan can be undertaken to exclude other causes of pain.