Emergency · Free article
Acute appendicitis for FRCS (Gen Surg): Alvarado, AIR and Adult Appendicitis scores, imaging by patient group, antibiotics or surgery, and the appendix mass.
The classic story is visceral periumbilical pain that moves to the right iliac fossa as the parietal peritoneum becomes involved, with anorexia, nausea and a low-grade fever. Tenderness is greatest near McBurney’s point, a third of the way from the anterior superior iliac spine to the umbilicus, with guarding and percussion tenderness. A retrocaecal appendix may cause flank pain and a positive psoas sign. A pelvic appendix may cause diarrhoea, urinary frequency and tenderness only on rectal examination, with few abdominal signs.
The differential is widest in women of reproductive age: ectopic pregnancy, ovarian cyst rupture or torsion, and pelvic inflammatory disease. A pregnancy test is mandatory. Mesenteric adenitis, Meckel’s diverticulitis, terminal ileal Crohn’s disease, right-sided diverticulitis, ureteric colic and pyelonephritis all mimic appendicitis, and in older patients so does a caecal carcinoma. Medical causes, such as diabetic ketoacidosis and lower lobe pneumonia, should be excluded before anyone is listed for theatre.
Scores do not make the diagnosis; they sort patients into groups. A low score identifies patients who can be observed, or discharged with safety-netting, without imaging. A high score in a young man may justify going straight to diagnostic laparoscopy. The intermediate group gains most from imaging. The 2020 WSES guidelines judge the Alvarado score not specific enough to diagnose appendicitis in adults, and recommend the AIR score and the Adult Appendicitis Score as the better clinical predictors.
| Feature (MANTRELS) | Points |
|---|---|
| Migration of pain to the right iliac fossa | 1 |
| Anorexia | 1 |
| Nausea or vomiting | 1 |
| Tenderness in the right iliac fossa | 2 |
| Rebound tenderness | 1 |
| Elevated temperature (37.3 °C or more) | 1 |
| Leucocytosis (white cell count above 10 × 10⁹/L) | 2 |
| Shift to the left (neutrophils above 75%) | 1 |
The Appendicitis Inflammatory Response (AIR) score adds C-reactive protein and grades the strength of peritoneal irritation. The Adult Appendicitis Score (AAS) weights the neutrophil count and interprets CRP according to how long symptoms have lasted. Both outperform the Alvarado score in validation studies.
The RIFT study (BJS 2020) validated 15 models in more than 5,000 patients aged 16–45 with right iliac fossa pain in UK hospitals. The AAS performed best for women, identifying low risk at a score of 8 or less, and the AIR score performed best for men, at 2 or less. Women were more than twice as likely as men to have a normal appendix removed, which is why validated scores and selective imaging matter most for them.
Supportive CT features are a non-compressible appendix wider than about 6 mm, wall thickening and enhancement, periappendiceal fat stranding and an appendicolith. Extraluminal gas, a fluid collection or a defect in the enhancing wall indicate complicated appendicitis.
Complicated appendicitis means gangrene, perforation, a phlegmon or an abscess. The distinction drives everything that follows: who can be offered antibiotics, whether antibiotics are needed after surgery and for how long. The American Association for the Surgery of Trauma (AAST) grades appendicitis on the same scale it uses for other emergency general surgery conditions.
| AAST grade | Findings |
|---|---|
| I | Acutely inflamed appendix, intact |
| II | Gangrenous appendix, intact |
| III | Perforated appendix with local contamination |
| IV | Perforated appendix with a periappendiceal phlegmon or abscess |
| V | Perforated appendix with generalised peritonitis |
Laparoscopic appendicectomy remains the standard treatment. An antibiotics-first strategy is an evidence-based option for selected adults with imaging-confirmed uncomplicated appendicitis. The choice is a shared decision: the patient trades a chance of avoiding an operation against a real chance of needing one later.
A reasonable candidate for antibiotics is an adult with CT-confirmed uncomplicated appendicitis, no appendicolith and no immunosuppression, who understands that the appendix may still need to come out. Older patients should know that a small proportion of apparent appendicitis is caused by an underlying neoplasm that antibiotics will not treat. The evidence in pregnancy and in children is more limited, and local policy applies.
A patient who presents late with a tender mass in the right iliac fossa usually has a phlegmon or an abscess walled off by omentum and bowel. Initial treatment is non-operative: intravenous antibiotics, with percutaneous drainage of an abscess large enough to drain. Operating in the inflammatory phase is difficult and more often ends in an ileocaecal resection, so surgery is kept for patients who fail to settle or develop generalised peritonitis.
Routine interval appendicectomy fell out of favour because recurrence is uncommon. However, the Peri-APPAC trial (Mällinen, JAMA Surgery 2019) was stopped early after finding a high rate of appendiceal neoplasm after periappendicular abscess, all in patients over 40. Patients over 40 therefore need the colon and appendix assessed once the episode settles, by colonoscopy and cross-sectional imaging or by interval appendicectomy.
Test yourself
A 23-year-old woman has 24 hours of vomiting and diffuse abdominal pain. She is drowsy, with respiratory rate 30/min, pulse 124 bpm and BP 96/58 mmHg; the abdomen is diffusely tender with guarding. Venous gas: pH 7.08, bicarbonate 7 mmol/L, glucose 27 mmol/L, lactate 2.1 mmol/L. WCC 22 × 10⁹/L, amylase 210 U/L.
What is the most appropriate next step?
In the RIFT study of UK patients aged 16–45, the Adult Appendicitis Score best identified low-risk women (a score of 8 or less) and the AIR score low-risk men (2 or less). The Alvarado score is widely known but less reliable for ruling appendicitis out.
Yes, in selected adults with imaging-confirmed uncomplicated appendicitis, after a shared decision. In CODA about three in ten patients needed an appendicectomy within 90 days, rising to 41% when an appendicolith was present.
Not routinely to prevent recurrence. Patients over 40 do need the colon and appendix assessed, because the Peri-APPAC trial found a high rate of neoplasm after periappendicular abscess in that age group.
Ultrasound first, then MRI without gadolinium if ultrasound is inconclusive. A negative or inconclusive MRI does not override strong clinical suspicion.
When it is larger than 2 cm, and for some tumours of 1–2 cm with adverse features such as mesoappendiceal invasion, an involved margin, vascular invasion or a higher grade.
Written for revision in the FRCS (Gen Surg) style under our editorial standards. It is not clinical advice: always confirm against current guidance. Spotted an error? Tell us.
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