Appendicitis: the appendix, its signs and the operation

1. The caecum and the appendix

The caecum is the blind lowest part of the large bowel, in the right iliac fossa, continuing upwards as the ascending colon. The appendix is a blind tube, usually 6 to 10 cm long, opening into the caecum about 2 cm below the ileocaecal valve. Its position varies, but its base never does: the three taeniae coli of the caecum converge exactly on it.

Surgeon’s corner: Lost in the right iliac fossa? Follow a taenia of the caecum down: it always leads to the base of the appendix, at open or laparoscopic surgery alike.

2. Where the tip can lie

The base stays put; the tip can point in different directions. Retrocaecal, behind the caecum, is the commonest; then pelvic, over the pelvic brim towards the bladder and the rectum; subcaecal; and pre- or post-ileal, towards the small bowel. The coloured arrows show these directions. The appendix of this model runs medially, towards the ileum.

Surgeon’s corner: The position changes the picture: retrocaecal gives flank pain and few signs in front; pelvic gives urinary symptoms, diarrhoea or pain on rectal examination; a pregnant uterus pushes the appendix up towards the right upper quadrant.

3. McBurney’s point

Draw a line from the anterior superior iliac spine (ASIS) to the umbilicus and take the point one third of the way along it from the spine. This is McBurney’s point, the surface marking of the base of the appendix, which lies just behind it.

Surgeon’s corner: Maximal tenderness at McBurney’s point is the classic local sign. The open gridiron incision is centred on it and splits the three flat muscles of the abdominal wall along their fibres.

4. The appendicular artery

The appendicular artery comes from the ileocolic artery, a branch of the superior mesenteric artery. It runs in the free edge of the mesoappendix to the tip. It is an end artery: no other vessel can take over.

Surgeon’s corner: Because it is an end artery, a swollen appendix quickly loses its blood supply. At appendicectomy, dividing the mesoappendix close to the appendix controls this artery.

5. What goes wrong: obstruction to perforation

The lumen is blocked (a faecolith, or swollen lymphoid tissue in the young). Mucus keeps being made, the pressure rises, the veins and then the end artery are compressed, the wall dies (gangrene) and finally bursts (perforation), giving a local abscess or generalised peritonitis.

Surgeon’s corner: Perforation risk climbs with time, especially after 36 to 48 hours and at the extremes of age (small children, the elderly), who also present late and atypically.

6. The pain and the peritoneal signs

The pain starts around the umbilicus: the inflamed appendix is felt as midgut pain (T10). Hours later it moves to the right iliac fossa, when the inflammation reaches the parietal peritoneum. Then the peritoneal signs appear: pain when the hand is released quickly (rebound, Blumberg) and pain in the right iliac fossa when you press on the left (Rovsing).

Surgeon’s corner: The Alvarado score (migration, anorexia, nausea, tenderness, rebound, fever, leucocytosis, left shift; out of 10) helps: ≤ 4 makes appendicitis unlikely, ≥ 7 makes it likely.

7. The psoas and obturator signs

An appendix lying on the psoas hurts when the muscle is stretched: extend the right hip with the patient on the left side (psoas sign, typical of a retrocaecal appendix). An appendix hanging into the pelvis touches the obturator internus: flex the right hip and knee and rotate the hip inwards (obturator sign, typical of a pelvic appendix).

Surgeon’s corner: A positive psoas or obturator sign tells you where the tip lies, and why a retrocaecal or pelvic appendicitis can have few signs in front.

8. Ultrasound: the first test

Ultrasound comes first in children, young women and pregnancy. The probe presses on the right iliac fossa: a normal appendix flattens, an inflamed one does not. Look for a blind-ending tube more than 6 mm across that does not compress, a target in cross-section, and bright inflamed fat around it. The panel shows a drawn example.

Surgeon’s corner: A normal appendix seen on ultrasound rules appendicitis out well; an unseen appendix does not. In pregnancy, MRI replaces CT.

9. CT: the appendix on the slice

CT with contrast is the most accurate test in adults. The CT box shows an axial slice through the appendix with the signs of appendicitis drawn in: a tube wider than 6 mm with a thick, enhancing wall, hazy (stranded) fat around it and a calcified appendicolith. Move the slider to follow it up and down.

Surgeon’s corner: CT also shows what changes the plan: an abscess (drain it first) or free air from a perforation.

10. Laparoscopic appendicectomy

Three ports (umbilicus, suprapubic, left iliac fossa). Find the appendix along the taeniae, open a window in the mesoappendix, seal or clip the appendicular artery, place two loops or a stapler at the base, divide and take the appendix out in a bag.

Surgeon’s corner: Antibiotics alone can treat selected uncomplicated cases, but about a third come back within five years; a faecolith or perforation means surgery.