Acute appendicitis is an acute transmural inflammation of the vermiform appendix and represents the single most frequent indication for emergency abdominal surgery worldwide (lifetime risk 7–8%) 1,2. Prompt clinical stratification using the Alvarado Score or Appendicitis Inflammatory Response (AIR) Score combined with targeted cross-sectional imaging reduces both negative appendicectomy rates and perforation morbidity 1,3.

1. Etiology & Risk Factors

  • Luminal obstruction (primary trigger in >80% of cases) 1,2:
    • Lymphoid follicular hyperplasia (60%): predominant cause in children and young adults secondary to viral gastroenteritis, upper respiratory tract infection, Epstein-Barr virus, or measles.
    • Faecolith / Appendicolith (35%): inspissated calcified faecal concretion; predominant cause in adults and strongly associated with complicated/perforated appendicitis.
    • Neoplasms (1–2% in patients >40 years): appendiceal carcinoid (neuroendocrine tumour), appendiceal mucinous neoplasm (LAMN), or caecal adenocarcinoma obstructing the appendiceal orifice.
    • Parasites & Foreign bodies (<1%): Enterobius vermicularis (pinworm), Ascaris lumbricoides, ingested seeds, or barium inspissation.
  • Epidemiological Risk Factors: peak incidence at age 10–30 years; slight male predominance (1.4:1); low dietary fibre intake.

2. Pathophysiology

Obstruction of the narrow appendiceal lumen (normal capacity ~0.1 mL) creates a closed-loop obstruction while goblet cells continue secreting mucus. Rising intraluminal pressure exceeds venous and lymphatic outflow pressure, leading to mucosal ischaemia, bacterial translocation (Escherichia coli and Bacteroides fragilis), transmural neutrophilic infiltration of the muscularis propria (histopathological hallmark), and eventual infarction of the appendicular artery (a terminal branch of the ileocolic artery from the superior mesenteric artery) 1,2.

Pathophysiological Mechanism β€” Acute appendicitis 1 Luminal Obstruction of Vermiform Appendix Faecolith / appendicolith (adults), lymphoid hyperplasia (children/viral infection), parasite, or carcinoid tumour 2 Closed-Loop Mucus Secretion & Intraluminal Distension (>15–30 mmHg) Visceral afferent T10 nerve fibres stimulated β†’ poorly localised central periumbilical colicky pain & anorexia 3 Venous & Lymphatic Congestion β†’ Bacterial Translocation Polymicrobial invasion (Escherichia coli, Bacteroides fragilis, Pseudomonas) across mucosal barrier 4 Transmural Suppurative Inflammation & Parietal Peritoneal Irritation Somatic peritoneal pain shifts sharply to McBurney's point in Right Iliac Fossa (RIF) with guarding & Rovsing's sign 5 Arterial Compromise of Appendicular Artery (End-Artery of Ileocolic) Gangrenous necrosis within 24–48h β†’ Free perforation, periappendiceal abscess, or generalised peritonitis

3. Clinical Presentation & Classic Clinical Signs

  • Classic Migratory Pain Sequence (Murphy's sequence, 50–60% of patients):
    • Early visceral phase (0–12 hours): dull, poorly localised central periumbilical or epigastric colicky pain mediated by autonomic visceral afferents entering the spinal cord at T10, accompanied by profound anorexia ("hamburger sign"), nausea, and 1–2 episodes of vomiting (vomiting almost always follows pain onset; vomiting before pain suggests gastroenteritis) 1,2.
    • Late somatic phase (12–24 hours): as transmural exudate contacts the parietal peritoneum, pain localises sharply to the right iliac fossa (RIF) at McBurney's point (one-third of the distance along a line from the right anterior superior iliac spine [ASIS] to the umbilicus).
  • Named Physical Examination Signs 1,2:
    • McBurney's point tenderness & percussion rebound (Blumberg's sign): maximal localised tenderness and guarding in the RIF.
    • Rovsing's sign: deep palpation in the left iliac fossa (LIF) reproduces pain in the right iliac fossa due to retrograde displacement of colonic gas irritating the inflamed RIF peritoneum.
    • Psoas sign (Cope's psoas test): RIF pain elicited by passive extension of the right hip (patient in left lateral decubitus) or active right hip flexion against resistance β€” indicates a retrocaecal appendix overlying the iliopsoas muscle.
    • Obturator sign (Cope's obturator test): hypogastric/RIF pain upon passive internal rotation of the flexed right hip and knee β€” indicates a pelvic appendix in contact with the obturator internus muscle.
    • Dunphy's sign: sharp increase in RIF pain on coughing.

4. Diagnostic Workup & Interpretation

Laboratory & Bedside Investigations (2-Column Clinical Table)
Diagnostic Test Expected Clinical Finding & Diagnostic Significance
Full Blood Count (FBC / CBC) Leucocytosis (WCC 11,000–18,000/mmΒ³) with left-shift neutrophilia (>75% neutrophils). WCC >18,000/mmΒ³ suggests gangrenous/perforated appendicitis.
C-Reactive Protein (CRP) Elevated (>10 mg/L) after 6–12 hours of symptom onset. A normal WCC and normal CRP at >12 hours has a >98% negative predictive value against acute appendicitis.
Urine Ξ²-hCG (Mandatory) Mandatory in all females of childbearing age to exclude ruptured ectopic pregnancy prior to CT or theatre.
Urinalysis (Dipstick & Microscopy) Mild sterile pyuria or microscopic haematuria occurs in 20–30% due to ureteric/bladder irritation by an adjacent inflamed pelvic appendix; positive nitrites/bacteriuria point toward UTI.
Imaging & Radiology (Radiopaedia Standard)
  • Graded-Compression Ultrasound (First-line in children, young thin adults, and pregnant women) 1,3:
    • Non-compressible, blind-ending tubular structure in the RIF with outer-wall-to-outer-wall diameter >6 mm.
    • Target sign (bull's-eye sign) on axial view with mural wall thickness >2 mm.
    • Appendicolith: echogenic intraluminal focus with posterior acoustic shadowing.
    • Circumferential mural hyperaemia on colour Doppler ("ring of fire") and hyperechoic periappendiceal mesenteric fat stranding.
  • Contrast-Enhanced CT Abdomen & Pelvis (Gold standard in adults; sensitivity 96–98%, specificity 94–98%) 1,3:
    • Dilated appendix >6–7 mm in outer diameter that fails to fill with enteric contrast/gas.
    • Circumferential mural thickening (>2–3 mm) with hyperenhancement ("target sign") and periappendiceal fat stranding.
    • Arrowhead sign / Caecal bar sign: focal thickening of the caecal apex around the occluded appendiceal orifice.
    • Signs of perforation: extraluminal gas, extraluminal appendicolith, focal defect in the enhancing appendiceal wall, or rim-enhancing periappendiceal abscess.

5. Clinical Scoring Table β€” Alvarado Score (MANTRELS)

Clinical / Laboratory Parameter (MANTRELS Mnemonic) Score & Risk Stratification
M β€” Migration of pain to the right iliac fossa +1 point
A β€” Anorexia (or ketonuria) +1 point
N β€” Nausea or vomiting +1 point
T β€” Tenderness in the right iliac fossa (McBurney's point) +2 points
R β€” Rebound tenderness in the RIF +1 point
E β€” Elevated temperature (β‰₯37.3Β°C / 99.1Β°F) +1 point
L β€” Leucocytosis (WCC >10,000 /mmΒ³) +2 points
S β€” Shift of WBC count to the left (Neutrophils >75%) +1 point
Total Alvarado Interpretation (Max 10 points) 0–4 pts: Unlikely (discharge/observe) Β· 5–6 pts: Equivocal (Ultrasound / CT imaging) Β· 7–10 pts: High probability (Surgical consultation Β± CT)

6. Differential Diagnosis (2-Column Comparison Table)

Condition Distinguishing Clinical, Biochemical & Imaging Features
Mesenteric Adenitis Children/adolescents following recent viral pharyngitis/URTI; high fever (>38.5Β°C) early; US/CT shows normal appendix (<6 mm) with clustered enlarged RIF mesenteric lymph nodes (>8–10 mm).
Ruptured Ectopic Pregnancy / Ovarian Torsion Positive Ξ²-hCG in ectopic pregnancy with amenorrhoea and vaginal bleeding; sudden severe unilateral pelvic pain with adnexal whirlpool sign and absent Doppler flow in ovarian torsion.
Meckel's Diverticulitis Clinically indistinguishable from acute appendicitis; located on the antimesenteric border of the distal ileum within 2 feet (60 cm) of the ileocaecal valve; look for Meckel's diverticulum if appendix is normal at laparoscopy!
Terminal Ileitis (Crohn's Disease / Yersinia enterocolitica) Prolonged diarrhoea, weight loss, mouth ulcers, or erythema nodosum; CT shows long-segment circumferential wall thickening and creeping fat of the terminal ileum.
Right Ureteric Colic Colicky loin-to-groin pain (patient cannot lie still, unlike peritonitis where patient lies completely still), microscopic/macroscopic haematuria, hyperattenuating calculus on non-contrast CT KUB.

7. Management & Treatment Protocol

  • Initial Stabilization & Resuscitation:
    • Keep patient nil by mouth (NPO), establish IV access, administer isotonic crystalloid resuscitation (Hartmann's solution / 0.9% NaCl), and provide prompt IV analgesia (IV paracetamol + titrated opioids β€” clinical trials confirm analgesia does not mask peritoneal signs) and antiemetics (ondansetron 4 mg IV) 1,2.
    • Pre-operative IV Antibiotics: administer within 60 minutes prior to skin incision covering Gram-negative bacilli and anaerobes β€” e.g. Cefuroxime 1.5 g IV + Metronidazole 500 mg IV (or Co-amoxiclav 1.2 g IV; Piperacillin-tazobactam 4.5 g IV in perforated cases) 1,3.
  • Surgical Management (Laparoscopic Appendicectomy β€” Gold Standard):
    • 3-port laparoscopy (umbilical camera port, suprapubic port, left iliac fossa port) offers lower wound infection rates, less post-operative pain, faster return to work, and diagnostic visualization of the pelvis/terminal ileum compared to open McBurney/Lanz incision 1,3.
    • Intra-operative rule: if the appendix appears macroscopically normal at diagnostic laparoscopy and no alternative pathology (Meckel's diverticulum, tubo-ovarian pathology, Crohn's ileitis) is found, remove the appendix to prevent future diagnostic confusion.
    • Post-operative antibiotics: simple non-perforated appendicitis requires no post-operative antibiotics; perforated/gangrenous appendicitis requires 3–5 days of IV/oral broad-spectrum antibiotics until afebrile and WCC normalises 1,3.
  • Appendiceal Mass / Phlegmon (Ochsner-Sherren Regimen):
    • For late presentation (>5 days) with a localised RIF mass/abscess and no generalised peritonitis: treat with IV antibiotics + CT/US-guided percutaneous drainage of collections >3–4 cm, followed by colonoscopy and CT at 6–8 weeks in patients aged β‰₯40 years to exclude caecal/appendiceal malignancy 1,3.

8. Complications & Prognosis

  • Perforation (15–20% overall; higher in children <5 years and elderly >65 years): leads to localised periappendiceal abscess, pelvic abscess (presenting days post-op with swinging pyrexia and mucous diarrhoea), or generalised four-quadrant peritonitis.
  • Surgical Site Infection (SSI) & Intra-abdominal Abscess: most common post-operative complications.
  • Stump Appendicitis: recurrent appendicitis in a residual appendiceal stump left >5 mm long during initial appendicectomy (always ligate the appendiceal base flush with the caecal pole where the taeniae coli converge).
  • Pylephlebitis: rare, life-threatening septic thrombophlebitis of the superior mesenteric and portal vein presenting with high rigors, jaundice, and hepatic abscesses.