Key Facts

Appendicitis remains the most common cause of an acute abdomen requiring surgery. Early recognition and surgery reduce the risk of perforation and its complications.

Epidemiology

Lifetime risk ~7-8%. Incidence ~100 per 100,000/year. Peak age 10-30 years. Slightly more common in males (M:F ~1.4:1). Perforation rate increases in children under 5 (~80-100%) and elderly (>50%).

Aetiology

• Luminal obstruction: Faecolith (~30-40%), lymphoid hyperplasia (children), tumour (elderly — caecal carcinoma), parasites
• Obstruction → mucus accumulation → distension → impaired venous drainage → bacterial invasion → inflammation → ischaemia → perforation

Pathophysiology

• Appendiceal obstruction → continued mucus secretion → raised intraluminal pressure
• Exceeds venous pressure → venous congestion → mucosal ischaemia
• Bacterial translocation (E. coli, Bacteroides) → transmural inflammation
• Periumbilical pain (visceral — T10 dermatome) → localises to RIF (somatic — parietal peritoneal irritation)
• If untreated: Gangrene → perforation → localised abscess or generalised peritonitis

Classic Presentation

• Periumbilical pain (visceral) migrating to RIF over 12-24 hours
• Anorexia (almost universal — absence should raise doubt)
• Nausea ± vomiting (usually after pain onset)
• Low-grade fever (37.5-38.5°C)

Examination Findings

• RIF tenderness — maximal at McBurney's point
• Guarding: Voluntary initially → involuntary with peritonitis
• Rovsing's sign: LIF palpation → RIF pain
• Psoas sign: Pain on passive extension of right hip (retrocaecal appendix)
• Obturator sign: Pain on internal rotation of flexed right hip (pelvic appendix)

Atypical Presentations

• Retrocaecal: Back/flank pain, minimal anterior signs, positive psoas sign
• Pelvic: Suprapubic pain, diarrhoea, urinary frequency
• Pregnancy: RUQ pain (displaced appendix in third trimester)
• Elderly: Late presentation, vague pain, higher perforation rate

Red Flags

• Generalised peritonism — likely perforation
• Mass in RIF — appendix abscess or mass
• Elderly with appendicitis — exclude caecal carcinoma (colonoscopy at follow-up)

Bedside

• Observations: Temperature, HR, BP
• Urine dipstick: Exclude UTI; mild pyuria can occur with pelvic appendicitis
• β-hCG: All women of reproductive age

Bloods

• FBC: Leucocytosis (WCC 10-15 × 10⁹/L typical; >15 suggests perforation/abscess)
• CRP: Raised (>10 in most; >100 suggests complicated appendicitis)
• U&Es: Dehydration assessment
• LFTs, amylase: Exclude biliary/pancreatic pathology

Imaging

• CT abdomen/pelvis: Investigation of choice in adults (sensitivity ~98%, specificity ~95%)
  • Findings: Dilated appendix >6mm, periappendiceal fat stranding, faecolith, abscess
• Ultrasound: First-line in children and pregnant women (non-compressible appendix >6mm, target sign)
• MRI: Alternative in pregnancy if US non-diagnostic

Non-pharmacological

• NBM, IV fluids, analgesia
• VTE prophylaxis: LMWH

Surgical (Definitive)

• Laparoscopic appendicectomy: Gold standard
  • Lower wound infection rate, faster recovery, diagnostic advantage in women
  • Histology of all specimens — exclude carcinoid, adenocarcinoma
• Open appendicectomy: If laparoscopic not available; Lanz incision (cosmetic) or gridiron incision
• Appendix mass/abscess: Consider initial conservative management (IV antibiotics, percutaneous drainage) → interval appendicectomy at 6-8 weeks

Pharmacological

• Antibiotics: Co-amoxiclav 1.2g IV (pre-operative prophylaxis); continue if complicated appendicitis
• Analgesia: IV paracetamol 1g + IV morphine titrated to effect
• Antiemetics: IV ondansetron 4mg

Referral Criteria

• All suspected appendicitis — surgical team
• Elderly — ensure caecal carcinoma excluded (colonoscopy within 6 weeks if >40 years or atypical)

• Simple appendicitis: Mortality <0.1%; morbidity ~5% (wound infection)
• Perforated appendicitis: Mortality ~1-2%; morbidity ~20-30% (abscess, wound infection, adhesions)
• Perforation risk: Increases after 36-48 hours of symptoms
• Negative appendicectomy rate: ~10-15% (acceptable; balanced against missing diagnosis)
• Appendiceal carcinoid: Found in ~0.5% of specimens; >2cm → right hemicolectomy

Modified Alvarado Score (MANTRELS)