Appendix Positions

Mnemonic

Positions of the appendix tip, in rough order of frequency:

• Retrocaecal, about 65 per cent, which is why the psoas sign is positive and why tenderness may be minimal anteriorly
• Pelvic, about 30 per cent, giving diarrhoea, urinary symptoms and a positive obturator sign, and tenderness best found on rectal examination
• Subcaecal, preileal and postileal, the remainder

“The base is constant, the tip is not.” The base always lies at the convergence of the three taeniae coli, which is the reliable way to find it at operation, and it projects to McBurney’s point on the surface.

Its midgut origin gives the classic periumbilical to right iliac fossa shift of pain, and a retroileal appendix may cause almost no abdominal signs at all.

Expansion

• Retrocaecal / retrocolic - about 65 per cent
• Pelvic - about 30 per cent
• Subcaecal, preileal and postileal - the remainder

The base is constant, at the convergence of the taeniae coli on the caecum, but the tip can lie anywhere on a 360-degree arc. Presentation varies accordingly:

• Retrocaecal - pain may be poorly localised; abdominal tenderness can be mild because the caecum shields the parietal peritoneum. Irritation of psoas gives a positive psoas sign and a flexed hip
• Pelvic - irritates the bladder and rectum, giving urinary frequency, diarrhoea and tenderness on rectal examination; abdominal signs may be minimal. A positive obturator sign
• Preileal or postileal - may cause vomiting and diarrhoea from ileal irritation

This variability is why appendicitis remains a clinical diagnosis with a substantial negative appendicectomy rate.