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Describe the positions, blood supply and applied anatomy of the vermiform appendix.

Anatomy · 1st Professional — Pre-Clinical

Position and Features

The vermiform appendix is a narrow blind-ended muscular tube arising from the posteromedial wall of the caecum, about 2 cm below the ileocaecal junction.

Length varies from 2 to 20 cm, averaging 9 cm
It has a complete peritoneal covering and a small mesentery, the mesoappendix, which carries the appendicular artery
The three taeniae coli of the caecum converge on its base — the surest way to find it at operation

Positions of the Appendix

Position	Frequency	Clinical note
Retrocaecal / retrocolic	About 65% — commonest	Rigidity may be absent; psoas spasm gives a positive psoas test
Pelvic	About 30%	Irritates the bladder and rectum — diarrhoea and urinary frequency; tenderness on rectal examination
Subcaecal	About 2%	—
Pre-ileal / post-ileal	About 1–2% each	Post-ileal is the most difficult to diagnose

Blood Supply and Surface Marking

Appendicular artery — a branch of the ileocolic artery, itself from the superior mesenteric; it runs in the free margin of the mesoappendix
It is an end artery — thrombosis in appendicitis therefore causes gangrene and perforation rapidly
McBURNEY'S point — the junction of the lateral one-third and medial two-thirds of a line from the right anterior superior iliac spine to the umbilicus; the point of maximum tenderness
Lymph drains to the ileocolic nodes

The Pain of Appendicitis

Clinical Signs

Sign	Method	Indicates
Rovsing sign	Pressure in the left iliac fossa causes pain on the right	Peritoneal irritation
Psoas sign	Pain on extending the right hip	Retrocaecal appendix
Obturator sign	Pain on internal rotation of the flexed thigh	Pelvic appendix
Blumberg sign	Rebound tenderness	Parietal peritonitis
Pointing sign	The patient points to McBurney's point	Localised parietal irritation

Applied Aspects

Acute appendicitis is the commonest abdominal surgical emergency
Gridiron (McBurney) incision — muscle-splitting at right angles to the spino-umbilical line; the Lanz incision is a transverse variant with a better cosmetic result
The ilioinguinal nerve is at risk in these incisions, and its injury weakens the conjoint tendon, predisposing to inguinal hernia
Appendicular abscess or mass — the greater omentum walls off the infection; usually treated conservatively at first
Differential diagnosis — mesenteric adenitis in children, ruptured ectopic pregnancy and ovarian torsion in women, ureteric colic, Meckel diverticulitis, and in India, ileocaecal tuberculosis
The appendix is rich in lymphoid tissue ("the abdominal tonsil"), maximal in adolescence — which is why appendicitis peaks in that age group

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