Key Facts

Acute appendicitis is the most common surgical emergency, accounting for >40,000 appendicectomies per year in the UK. Early diagnosis and treatment are essential to prevent perforation and peritonitis.

Epidemiology

Lifetime risk is approximately 7% (8.6% males, 6.7% females). Peak incidence is 10-30 years. Rare in under-2s and over-70s (but higher complication rates at extremes of age). Incidence is higher in Western countries.

Aetiology

• Luminal obstruction: faecolith (most common in adults), lymphoid hyperplasia (most common in children — often viral-triggered), foreign body, tumour (carcinoid, adenocarcinoma — rare), parasites
• Obstruction → increased intraluminal pressure → venous congestion → bacterial invasion → ischaemia → perforation

Pathophysiology

Luminal obstruction causes continued mucosal secretion against a closed loop, raising intraluminal pressure. This compresses mucosal veins, causing oedema, ischaemia, and bacterial translocation (E. coli, Bacteroides fragilis). Inflammation progresses from mucosal (catarrhal) to transmural (suppurative) to gangrenous to perforated. Perforation may be contained (appendix mass/phlegmon, peri-appendicular abscess) or free (generalised peritonitis). The progression from symptom onset to perforation typically takes 24-72 hours.

Classic Presentation

• Periumbilical pain (visceral, poorly localised — T10 dermatome) → migrates to RIF over 12-24 hours (somatic, well-localised as parietal peritoneum inflamed)
• Anorexia (almost universal — absence should prompt diagnostic reconsideration)
• Nausea ± vomiting (usually follows pain onset — important: pain precedes vomiting in appendicitis, opposite in gastroenteritis)
• Low-grade fever (37.5-38.5°C; higher suggests perforation)

Clinical Signs

• McBurney's point tenderness: 2/3 from umbilicus to ASIS
• Guarding and rebound tenderness (peritoneal irritation)
• Rovsing's sign: palpation of LIF causes RIF pain
• Psoas sign: pain on hip extension (retrocaecal appendix)
• Obturator sign: pain on internal rotation of flexed hip (pelvic appendix)

Atypical Presentations

• Retrocaecal (~65%): flank/back pain, less peritonism
• Pelvic: suprapubic pain, diarrhoea, urinary frequency
• Elderly: vague symptoms, delayed presentation → higher perforation rate
• Pregnancy: pain displaced superiorly by gravid uterus
• Children: less typical history, rapid progression to perforation

Red Flags

• Generalised peritonism (perforation)
• Sepsis (tachycardia, hypotension, fever >38.5°C)
• Palpable RIF mass (appendix mass — usually >48 hours symptoms)
• Very young (<5 years) or elderly — higher perforation rates

Bedside

• Observations: pulse, BP, temperature, RR
• Urinalysis: exclude UTI, haematuria (ureteric colic); sterile pyuria may occur with pelvic appendix adjacent to ureter
• Pregnancy test (β-hCG): mandatory in all women of childbearing age

Bloods

• FBC: leucocytosis (WCC >10 × 10⁹/L in ~80%; neutrophilia)
• CRP: raised (>10 in most; >100 suggests complicated appendicitis)
• U&Es: dehydration, baseline
• Lactate: if concern for sepsis

Imaging

• CT abdomen/pelvis with IV contrast: first-line in adults — sensitivity >95%, specificity >95%; shows appendiceal dilatation (>6 mm), wall thickening, periappendiceal fat stranding, appendicolith, abscess, free fluid
• USS abdomen: first-line in children and pregnant women; sensitivity ~85% (operator-dependent); non-compressible appendix >6 mm
• MRI: alternative in pregnancy if USS inconclusive

Special Tests

• Alvarado (MANTRELS) score: Migration, Anorexia, Nausea/vomiting, RIF Tenderness, Rebound, Elevated temperature, Leucocytosis, Shift to left; score 0-10; ≥7 = operate; 5-6 = CT; <5 = observe
• Appendicitis Inflammatory Response (AIR) score: alternative scoring system

Non-pharmacological

• NBM: preparation for potential surgery
• IV fluids: resuscitation
• Analgesia: IV paracetamol + IV morphine (do NOT withhold analgesia — historical practice of withholding is outdated and unethical)

Pharmacological

• IV antibiotics (pre-operative): co-amoxiclav 1.2 g IV or cefuroxime 1.5 g + metronidazole 500 mg IV; continue post-operatively for 5 days if complicated/perforated
• Antibiotic-only treatment: emerging option for uncomplicated appendicitis — CODA trial showed ~70% avoided surgery at 90 days with antibiotics alone; APPAC II — 7-day moxifloxacin course; ~25-30% eventually need appendicectomy within 5 years; appropriate discussion of options with patient

Surgical/Interventional

• Laparoscopic appendicectomy: gold standard; lower wound infection rate, faster recovery, better cosmesis than open; diagnostic advantage (can visualise pelvis/other pathology)
• Open appendicectomy: if laparoscopy unavailable or converted
• Appendix mass: if >48 hours symptoms with contained mass — initial conservative management (IV antibiotics) with interval appendicectomy at 6-8 weeks (debated — some centres now advocate early surgery)
• Peri-appendicular abscess: CT-guided drainage + IV antibiotics; interval appendicectomy

Referral Criteria

• All suspected appendicitis: urgent surgical review
• Diagnostic uncertainty: CT imaging
• Appendix mass/abscess: surgical team for conservative vs interventional management
• Histology: always send appendix specimen (carcinoid tumour found in ~1%)

Uncomplicated appendicitis treated with appendicectomy has near-zero mortality and <5% complication rate. Perforation rate is ~20% overall (higher in children <5 and elderly >70). Perforation increases morbidity (wound infection, abscess, ileus) but mortality remains <1% with modern care. Negative appendicectomy rate with CT usage is <5% (previously ~15-20% without imaging). After antibiotic-only treatment, ~25-30% require appendicectomy within 5 years. Incidental carcinoid tumour: if <10 mm and appendiceal, appendicectomy is curative.

Alvarado (MANTRELS) Score