Acute abdomen and emergencies
Right iliac fossa pain and appendicitis
Overview and approach
Right iliac fossa pain includes appendicitis and gastrointestinal, urinary and gynaecological emergencies.
- Appendicitis is the commonest surgical emergency of the abdomen; diagnosis combines clinical scoring, labs and selective imaging1.
- Approach: stratify risk (score), image the intermediate-risk group, then operate or treat with antibiotics1.
- Peak incidence is in the teens and twenties; perforation and death are most common at the extremes of age2.
- How it develops: the lumen is blocked, most often by a faecolith, but also by lymphoid swelling after viral illness, worms or a tumour (e.g. carcinoid). Pressure rises, bacteria multiply and invade the wall, venous congestion is followed by arterial compromise, and gangrene and perforation follow2.
- Slow vs fast: if it evolves slowly, the terminal ileum, caecum and omentum wall it off and an abscess or mass forms; rapid vascular compromise gives free perforation into the peritoneal cavity2.
- The clock: perforation is rare in the first 24 hours but may reach 80% after 48 hours2.
Assessment and clinical features
Assess pain migration, vomiting, bowel/urinary symptoms, fever, last menstrual period and pregnancy possibility; examine for peritonism.
- Classic: periumbilical pain migrating to the RIF, anorexia, nausea, low-grade fever, RIF tenderness (McBurney point), guarding, rebound; Rovsing, psoas and obturator signs are supportive. Presentation is atypical in children, older adults, pregnancy and retrocaecal appendix.
- Alvarado score (migration, anorexia, nausea/vomiting, RIF tenderness, rebound, fever, leucocytosis, left shift): a score under 5 is highly sensitive for excluding appendicitis but should not be used to confirm it1.
- Why the pain moves: early pain comes from the distended appendix and travels on slow visceral C fibres, so it is vague and central. Once the parietal peritoneum is inflamed, fast somatic A-delta fibres localise it to the RIF, and it becomes constant and worse with movement or coughing. The classic sequence occurs in only about two-thirds2.
- Anorexia is almost always present: a hungry patient rarely has appendicitis. Vomiting occurs in about half and is usually brief2.
- Position changes the signs: a retrocaecal or pelvic appendix may cause little abdominal tenderness, with tenderness only in the flank or on rectal or pelvic examination. A pelvic appendix can cause diarrhoea or urinary frequency and dysuria2.
- Temperature is usually normal or only slightly raised; a fever above about 38.3 °C suggests perforation2.
- A mass usually takes about 3 days to form. A mass earlier than this suggests caecal cancer or Crohn's disease2.
Why appendicitis is missed in some groups2.
| Group | What makes it hard | Consequence |
|---|---|---|
| Infants under 2 | Non-specific vomiting, diarrhoea, fever; distension may be the only sign | Perforation in 70-80% |
| Over 70 | Pain and tenderness blunted; may present with a mass or adhesive obstruction days later | Perforation in about 30% |
| Pregnancy | Nausea and discomfort are common anyway; appendix pushed up towards the RUQ in later pregnancy | Fetal loss about 1.5% with a normal appendix vs 20-35% with perforation |
Differentials and investigations
FBC/CRP, urine and pregnancy testing where relevant; ultrasound or CT selected for patient/context. Consider ectopic pregnancy, torsion, Crohn’s and ureteric stone.
- Differentials: mesenteric adenitis, terminal ileitis/Crohn’s, caecal diverticulitis, right ureteric colic, ovarian torsion/cyst, ectopic pregnancy, PID, testicular torsion, UTI.
- Bloods/urine: FBC, CRP, urinalysis, beta-hCG in women of reproductive age.
- Imaging for intermediate-risk patients: ultrasound/POCUS first; if non-diagnostic, CT (low-dose, contrast-enhanced preferred) or repeat ultrasound; MRI is preferred in pregnancy1.
- White cell count: a moderate rise10–18 is typical; above 20 suggests perforation; a normal count does not exclude appendicitis2.
- An appendix lying against the ureter or bladder can put a few white or red cells in the urine without bacteria, so do not stop at a diagnosis of UTI2.
- In an older patient, anaemia or blood in the stool should raise caecal cancer2.
- CT: shows a thickened appendix with fat stranding, often a faecolith; positive predictive value 95-97%. Free gas is uncommon even after perforation. A plain X-ray rarely helps (faecolith visible in only about 5%)2.
- Telling the mimics apart2:
- PID: sexual history, vaginal discharge, cervical motion tenderness.
- Mittelschmerz: mid-cycle, more diffuse and milder; a ruptured corpus luteum cyst behaves the same but near menstruation.
- Mesenteric adenitis: usually children, higher fever, more diffuse pain, abdomen relaxed between cramps; sometimes Yersinia.
- Crohn's disease: longer history of similar episodes, often a palpable inflammatory mass.
Management and follow-up
Analgesia, hydration, surgical review and management directed by diagnosis; do not withhold analgesia to preserve signs.
- Analgesia, IV fluids, nil by mouth, early surgical review. Antibiotics per eTG/local guideline.
- Laparoscopic appendicectomy is the preferred operation. For selected uncomplicated appendicitis without an appendicolith, antibiotics-first treatment can be discussed (IV then oral antibiotics), with recurrence up to about 39% at five years1.
- Complicated appendicitis (perforation, abscess, phlegmon) needs resuscitation, antibiotics and surgical or percutaneous source control.
Red flags and clinical pearls
Peritonitis, shock, pregnancy with concerning pain/bleeding or a deteriorating child needs urgent escalation.
- Always check pregnancy status; ectopic pregnancy and torsion mimic appendicitis.
- Generalised peritonitis or sepsis suggests perforation: resuscitate and expedite theatre.
- A normal CRP/WCC does not exclude early appendicitis; re-examine serially.
- Viva: Alvarado score, role of imaging, antibiotics-first option and its recurrence rate.
- Mortality is about 0.1% for non-perforated appendicitis but about 3% once perforated, and up to 15% in older patients2.
- Pain lasting weeks or months is rarely due to chronic appendicitis, although recurrent acute attacks do occur2.
References
- WSES Jerusalem guidelines 2020 update: acute appendicitis (PMC)
- Longo DL, Fauci AS, Kasper DL, Hauser SL, Jameson JL, Loscalzo J, editors. Harrison's Principles of Internal Medicine. 18th ed. New York: McGraw-Hill; 2012. Chapter 300, Acute appendicitis and peritonitis.
Last updated from Sen’s notes on 22 October 2026.