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Portrait of Appendix

Anatomy · Organs & viscera

Appendix

Vermiform appendix

Abdomen · right iliac fossa

The appendix, or vermiform appendix, is a narrow, blind-ended tube about 9 cm long that arises from the posteromedial wall of the caecum, roughly 2 cm below the ileocaecal valve. Its tip can lie in several places, most often behind the caecum or dipping into the pelvis. It is best known for appendicitis, which classically causes pain that moves from around the navel to the right lower abdomen.

How to spot them

  • ▸A thin worm-like tube hanging from the caecum in the right lower abdomen
  • ▸Its base is fixed where the three taeniae coli converge on the caecum, but its tip is mobile
  • ▸Attached to the ileum by a small triangular fold of peritoneum, the mesoappendix, which carries its artery
  • ▸Surface marking: McBurney's point, one third of the way along the line from the right anterior superior iliac spine to the navel

What to know

A narrow, worm-shaped tube averaging about 9 cm long, with a lumen that often becomes obstructed by a hard faecal pebble

Appendix — the vermiform appendix.

The spot one third of the way from the right hip bone to the umbilicus where tenderness is classically greatest

McBurney's point, the surface marking for the base of the appendix.

A blind tube whose tip may lie behind the caecum in about two in three people, or dip down into the pelvis in most of the rest

Appendix — retrocaecal and pelvic positions.

A structure supplied by a single end artery in its own fold of peritoneum, so its blood supply is easily cut off when swollen

The appendicular artery, in the mesoappendix, from the ileocolic artery.

Pain that begins around the navel then shifts to the right lower abdomen; named in 1886 by Reginald Fitz

Appendicitis — inflammation of the appendix.

Darwin thought it a useless relic of a herbivorous ancestor, but modern work suggests it may store gut bacteria

The appendix, once called a vestigial organ.

Removed in 1735 by Claudius Amyand from a boy's inguinal hernia, the first recorded operation of its kind

The first appendicectomy (Amyand's hernia).

Key ideas

  • Its wall is rich in lymphoid tissue, so it acts like a small gut-associated immune organ, particularly in young people.
  • Appendicitis begins with visceral pain felt at the umbilicus (T10), and only when the inflamed appendix irritates the parietal peritoneum does pain move to the right iliac fossa.

Quick-fire facts

  • •It averages about 9 cm long, with a range from 2 to 20 cm, and a narrow lumen a few millimetres wide.
  • •It arises from the posteromedial wall of the caecum about 2 cm below the ileocaecal valve.
  • •Its tip is variable: retrocaecal (about 65 per cent) and pelvic (about 30 per cent) are the commonest positions, though published percentages vary.
  • •McBurney's point is named after the New York surgeon Charles McBurney, who described it in 1889.
  • •Lanz's point, two thirds of the way along the interspinous line from left to right, is another surface marking used for its base.
  • •Appendicitis is one of the commonest causes of emergency abdominal surgery, with a lifetime risk of roughly 7 to 8 per cent.
  • •Rovsing's sign is pain in the right iliac fossa when the left iliac fossa is pressed.
  • •The term 'appendicitis' was coined by the Boston pathologist Reginald Fitz in 1886.
  • •The three taeniae coli of the colon converge at its base, which surgeons follow to find it.

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