What is acute appendicitis and why does it happen?
Acute appendicitis is inflammation of the vermiform appendix that typically presents acutely within 24 hours. It is the leading cause of abdominal surgery in children and the most common abdominal surgical emergency worldwide. Incidence is about 100–223 per 100,000 people per year; it peaks between 5 and 45 years (mean age 28), and lifetime risk is 8.6% in males and 6.7% in females.
The core mechanism is obstruction of the appendiceal lumen. Pressure rises inside the lumen and wall, small vessels and lymphatics are occluded, the appendix fills with mucus and distends, and the wall becomes ischaemic and necrotic. Bacteria overgrow — first aerobes, then a mixed aerobic-anaerobic flora (E. coli, Bacteroides, Peptostreptococcus, Pseudomonas) — and the necrotic wall can perforate, forming a localised abscess or generalised peritonitis.
| Age group | Usual cause | Note |
|---|---|---|
| Children | Lymphoid hyperplasia | Overgrowth of lymphoid tissue causes inflammation and localised ischaemia |
| Adults | Faecolith (appendicolith), infection, tumour | Tumours that present as appendicitis: carcinoid (neuroendocrine), adenocarcinoma, mucocele |
| Any age | Worms (intestinal parasites), occasionally a gallstone | Less common mechanical causes |
Where is the appendix and what positions can it take?
The appendix is a true diverticulum (it has all colonic layers) arising from the posteromedial wall of the caecum, close to the ileocaecal valve. Its base is constant — found where the three taeniae coli converge — which is the surgeon's landmark at appendectomy. Its length varies from 5 to 35 cm (average 9 cm). It develops from the midgut.
- Blood supply: the appendicular artery, a terminal branch of the ileocolic artery (from the superior mesenteric artery). It is an end artery, so rising luminal pressure quickly causes ischaemia and gangrene.
- Lymph: to the ileocolic nodes, then superior mesenteric nodes.
- Nerves: visceral afferents enter the cord at T10 (umbilical dermatome) — hence early periumbilical pain.
| Position | Frequency / feature | Clinical clue |
|---|---|---|
| Retrocaecal (still intraperitoneal) | By far the most common | Right flank pain; pain on extending the right hip (psoas sign) |
| Pelvic | Recognised variant | Obturator sign is positive when the inflamed appendix lies below the pelvic brim against the obturator internus |
| Subcaecal, pre-ileal, post-ileal | Variable | Tip position changes where the pain localises |
| Hepatorenal recess | Rare, high-lying tip | Pain localises away from the right iliac fossa |
| Pregnancy | Uterus pushes the appendix upward | By late third trimester pain may be felt in the right upper quadrant |
What are the symptoms and classic clinical signs?
The typical story is vague periumbilical pain (visceral afferents, T8–T10) that migrates to the right lower quadrant once the parietal peritoneum is irritated. Anorexia, nausea and vomiting follow; diarrhoea, malaise and urinary frequency can occur. Only about 40% are febrile at presentation, and about 75% present within 24 hours of symptom onset. Pain may wake the patient or worsen on walking or coughing.
| Sign | How it is elicited / what it means |
|---|---|
| McBurney point tenderness | Maximal tenderness at the junction of the lateral one-third and medial two-thirds of a line from the right ASIS to the umbilicus (about 1.5–2 inches from the ASIS) |
| Rovsing sign | Pressure on the left lower quadrant produces pain in the right lower quadrant |
| Psoas sign | Right lower quadrant pain on extending the right hip (patient in left lateral position) or flexing the right thigh against resistance — irritated psoas, typical of a retrocaecal appendix |
| Obturator sign | Right thigh flexed, then the hip is rotated internally — pain means an inflamed appendix lying against the obturator internus (pelvic position) |
| Dunphy sign | Increased abdominal pain on coughing or anything that raises intra-abdominal pressure |
| Rebound tenderness (Blumberg) | Pain on sudden release of pressure — localised peritonitis |
How do the Alvarado and AIR scores work?
Alvarado (1986) found eight predictive factors and turned them into a 10-point score, remembered as MANTRELS. The modified Alvarado score drops the left shift and totals 9; a score of 7 or more is significantly associated with appendicitis.
| Item | Points |
|---|---|
| Migration of pain to the right iliac fossa | 1 |
| Anorexia | 1 |
| Nausea / vomiting | 1 |
| Tenderness in the right iliac fossa | 2 |
| Rebound tenderness | 1 |
| Elevated temperature | 1 |
| Leukocytosis | 2 |
| Shift to the left of neutrophils | 1 |
| Interpretation | 0–4 low probability; 5–6 possible; 7–8 probable; 9–10 very probable |
The Appendicitis Inflammatory Response (AIR) score (Andersson, 2008) uses eight variables — vomiting, right lower quadrant pain, rebound tenderness or muscular defence, temperature, neutrophil proportion, WBC count and CRP — and grades the inflammatory ones, totalling 12.
| Item | Points |
|---|---|
| Vomiting | 1 |
| Pain in the right lower quadrant | 1 |
| Rebound tenderness or muscular defence — light / medium / strong | 1 / 2 / 3 |
| Body temperature > 38.5 °C | 1 |
| Polymorphonuclear leukocytes 70–84% / ≥ 85% | 1 / 2 |
| WBC 10.0–14.9 / ≥ 15.0 × 109/L | 1 / 2 |
| CRP 10–49 / ≥ 50 | 1 / 2 |
| Interpretation | 0–4 low probability; 5–8 indeterminate; 9–12 high probability |
Which investigations are used — ultrasound or CT?
Blood tests: leukocytosis is present in about two-thirds; most patients have WBC > 10,000/mm³, and ≥ 17,000/mm³ is associated with complicated appendicitis. A normal WBC and normal CRP together have a high negative predictive value. Rising WBC and CRP increase the likelihood of complicated disease. A urinalysis helps exclude a urinary tract infection.
| Modality | Findings / role | Preferred in |
|---|---|---|
| Ultrasound (graded compression) | Non-compressible appendix, AP diameter > 6 mm, appendicolith, echogenic periappendiceal fat; diameter < 5 mm with compressibility helps exclude | Children and pregnant women (no radiation); WSES recommends point-of-care US as first-line in adults and children when imaging is needed |
| CT abdomen-pelvis with IV contrast | Diameter > 6 mm, wall > 2–3 mm, fat stranding, wall enhancement, appendicolith; > 95% accuracy in adults | Preferred modality in adults when diagnosis is uncertain; non-contrast CT if renal function is poor |
| MRI | Distended, thick-walled appendix with periappendiceal fluid | Pregnancy after an inconclusive ultrasound; children with inconclusive US |
How is acute appendicitis managed?
- Resuscitate: nil by mouth, IV crystalloids, analgesia, consent.
- Antibiotics covering gram-negative aerobes and anaerobes — for example a third-generation cephalosporin (ceftriaxone or cefotaxime) plus metronidazole, or a beta-lactam/beta-lactamase inhibitor.
- Appendectomy is the gold standard. Laparoscopic appendectomy is preferred: fewer wound infections, less pain, shorter stay; its main drawback is longer operating time.
- Timing: WSES recommends operating on uncomplicated appendicitis on the next available list within 24 hours; delays beyond 24 hours from admission raise adverse outcomes.
- After surgery: no antibiotics are needed for uncomplicated appendicitis; complicated appendicitis gets a short postoperative course (StatPearls cites 4 days).
| Situation | Approach |
|---|---|
| Periappendiceal abscess without peritonitis | Antibiotics + CT- or US-guided percutaneous drainage |
| Phlegmon or abscess | Non-operative management is a reasonable first line (WSES); early laparoscopic surgery is a safe alternative in experienced hands |
| Interval appendectomy | Classically 6–10 weeks after recovery, but WSES recommends against routine interval appendectomy in adults under 40 and children; reserve it for recurrent symptoms |
| Recurrence after non-operative treatment of perforated appendicitis | Reported at 12–24% |
Can appendicitis be treated with antibiotics alone?
For imaging-confirmed uncomplicated appendicitis, antibiotics alone are now an accepted option to discuss with selected patients — but appendectomy remains the standard. Two trials anchor the evidence:
| Trial | Design | Main findings |
|---|---|---|
| APPAC (Finland; JAMA 2018, 5-year follow-up) | 530 adults aged 18–60 with CT-confirmed uncomplicated appendicitis; IV ertapenem 3 days then oral levofloxacin + metronidazole 7 days vs open appendectomy | 27.3% of the antibiotic group had appendectomy within 1 year; cumulative recurrence 39.1% at 5 years; complications lower than after surgery |
| CODA (USA; NEJM 2020) | 1,552 adults; 10-day antibiotic course vs appendectomy (96% laparoscopic) | Antibiotics non-inferior on 30-day health status; 29% had appendectomy by 90 days — 41% with an appendicolith vs 25% without; complications higher with an appendicolith |
What are the complications of appendicitis and appendectomy?
Delay drives complications: about 2% rupture around 36 hours from symptom onset, and the risk rises by roughly 5% for every further 12 hours without treatment. Global mortality in one observational study was 0.28%, higher in under-resourced countries (1–4%), in patients over 80 years and in the immunosuppressed.
- Perforation → localised abscess or generalised peritonitis and sepsis.
- Pylephlebitis (septic thrombophlebitis of the portal vein) and pylethrombosis.
- Hydroureteronephrosis, bowel obstruction, internal fistulae (bladder, vagina, uterus, skin).
- After appendectomy: surgical site infection is the most common complication; intra-abdominal abscess (3–4% after open, 9–24% after laparoscopic), prolonged ileus, enterocutaneous fistula, small-bowel obstruction.
- Stump appendicitis — inflammation of a long residual stump; keeping the stump ≤ 5 mm minimises the risk.
| Tumour size | Surgery |
|---|---|
| < 1 cm | Appendectomy with negative margins |
| 1–2 cm | Undefined; right hemicolectomy if mesenteric invasion, enlarged nodes or equivocal margins |
| > 2 cm | Right hemicolectomy |
How is mesenteric lymphadenitis told apart from appendicitis?
Mesenteric adenitis is inflammation of the mesenteric lymph nodes — usually near the terminal ileum — causing sudden right lower quadrant pain that classically gets mistaken for appendicitis. In one case series, 16% of 70 children clinically diagnosed with appendicitis turned out to have mesenteric adenitis.
| Feature | Mesenteric adenitis | Acute appendicitis |
|---|---|---|
| Typical patient | Child under 10 or young adult | Any age; peak 5–45 years |
| Preceding illness | Recent upper respiratory infection or gastroenteritis | Usually none |
| Causes | Viral; Yersinia enterocolitica and Y. pseudotuberculosis; Salmonella, E. coli, streptococci | Luminal obstruction |
| Tenderness | Notably less on palpation | Localised RIF tenderness, guarding, rebound |
| Ultrasound | Enlarged hypoechoic nodes (≥ 8 mm short axis) with a normal appendix | Non-compressible appendix > 6 mm |
| Treatment | Self-limiting — fluids, NSAIDs; pain settles within about 4 weeks | Appendectomy (or selected antibiotic-first) |
- Other differentials: Crohn ileitis, complicated caecal diverticulum, Yersinia or Campylobacter ileitis, gastroenteritis, right-sided colitis, renal colic and kidney stones.
- In women: ectopic pregnancy, ruptured ovarian cyst, ovarian torsion, salpingitis / pelvic inflammatory disease (severe cervical motion tenderness), mittelschmerz, tubo-ovarian abscess.
- In men: testicular torsion, epididymitis.