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PH-GI06

Appendicitis

How blockage of the narrow appendix leads to rising pressure, ischaemia and infection of its wall, why the pain starts around the navel and moves to the right lower abdomen, and why a delay can lead to perforation and peritonitis.

By the end, you can

  • Describe the appendix, its blood supply and its nerve supply.
  • Explain how luminal obstruction leads to distension, ischaemia and bacterial invasion of the wall.
  • Explain why pain begins around the umbilicus and later localises to the right iliac fossa.
  • Explain how perforation occurs and leads to peritonitis or an abscess.
  • Explain why the presentation varies with the appendix’s position and the patient’s age.
  • Recognise the gross and microscopic stages, the Alvarado score and the key tests of appendicitis, and explain how surgery, antibiotics and drainage act on its mechanism.

What it is

Acute appendicitis is acute inflammation of the vermiform appendix, usually following obstruction of its lumen. It is the commonest abdominal surgical emergency, most frequent between 10 and 30 years of age, and can progress to gangrene and perforation if untreated.

2 types to tell apart
Uncomplicated
Inflamed but intact appendix.
Complicated
Gangrene, perforation, a walled-off abscess or an inflammatory mass, or generalised peritonitis.

Normal function

A narrow tube off the caecum

The is a narrow, blind-ending tube, usually 5–10 cm long, opening into the below the ileocaecal junction. Its wall contains abundant lymphoid tissue, especially in young people, and its lumen is only a few millimetres wide.

It hangs on a small mesentery, the , which carries the , an end artery with no alternative route of supply. The appendix may point downwards into the pelvis, behind the caecum (retrocaecal) or in other directions.

Its lining is supplied by visceral nerves from the midgut, which enter the spinal cord at about the tenth thoracic segment; the overlying parietal peritoneum is supplied by somatic nerves of the body wall.

Point to it on the model