Vermiform appendix

At a glance

English

Vermiform appendix

Latin (TA2)

Appendix vermiformis

System

Digestive

Region

Abdomen

Side

Single, on the midline

About the vermiform appendix

The vermiform ('worm-shaped') appendix is a slender tube, usually 6 to 9 cm long though very variable, that arises from the back and inner side of the caecum, a couple of centimetres below the ileocaecal valve. Its base has a fixed position: it lies where the three taeniae coli of the caecum converge, which lets surgeons find it by following any taenia down. The tip, in contrast, can point in many directions. The commonest position is behind the caecum (retrocaecal); it may also hang over the pelvic brim, lie below the caecum, or sit in front of or behind the end of the ileum.

It is held by its own small mesentery, the mesoappendix, which hangs from the lower end of the small bowel mesentery and carries the appendicular artery. The base corresponds on the surface to McBurney's point, a third of the distance from the right anterior superior iliac spine towards the navel. The lumen is narrow and is often partly or completely closed in older adults.

Its wall has the same layers as the colon, but the longitudinal muscle forms a complete coat rather than taeniae. The submucosa contains masses of lymphoid follicles, most abundant in childhood and young adulthood and declining with age. It is now thought to play a part in gut immunity and perhaps to act as a reservoir from which normal gut bacteria can repopulate the colon after illness.

Appendicitis is the commonest surgical emergency of the abdomen. Blockage of the lumen, often by a hard plug of faeces or swollen lymphoid tissue, lets bacteria multiply; the swelling cuts off the single end artery and the wall may perforate. Pain typically starts around the umbilicus, because the appendix shares the midgut's nerve supply, and then shifts to the right iliac fossa once the parietal peritoneum is irritated. Treatment is usually removal of the appendix, often by keyhole surgery.

Function and supply

Begins at

Opens from the posteromedial wall of the caecum, below the ileocaecal junction, where the taeniae coli meet.

Ends at

Ends blindly at a free tip whose position varies: retrocaecal, pelvic, subcaecal or beside the terminal ileum.

Function

Contributes lymphoid tissue to gut immunity and may store helpful gut bacteria.

Nerve supply

Sympathetic and vagal fibres from the superior mesenteric plexus; visceral pain is referred to the umbilical region.

Blood supply

The appendicular artery, a branch of the ileocolic artery running in the mesoappendix; veins drain through the ileocolic vein to the portal system.