Acute Appendicitis
Surgery · GI Surgery · lean revision notes
Acute Appendicitis
Acute appendicitis is the inflammation of the vermiform appendix and remains the most common surgical emergency of the abdomen and the single most frequently examined GI-surgery topic in NEET PG. Master the pathophysiology, the Alvarado score, atypical positional presentations, and the modern operative debate, and you have a near-guaranteed mark.
Definition & relevant anatomy
The vermiform appendix is a blind-ending tubular diverticulum arising from the posteromedial wall of the caecum, about 2 cm below the ileocaecal valve, where the three taeniae coli converge. This convergence is the surgical landmark used to locate the appendix at operation — follow the anterior taenia (taenia libera) down to its base.
- Length: 6–9 cm (range 2–20 cm); it is a vestigial organ rich in gut-associated lymphoid tissue (GALT), peaking in adolescence.
- Blood supply: appendicular artery, a branch of the ileocolic artery (which itself arises from the superior mesenteric artery). It is an end artery running in the mesoappendix — hence early ischaemia, gangrene and perforation when the lumen obstructs.
- The base of the appendix is constant; the tip is variable, and its position dictates the clinical picture.
| Appendix position | Approx. frequency | Clinical clue |
|---|---|---|
| Retrocaecal / retrocolic | ~65% (commonest) | Pain poorly localised; rigidity may be absent; positive psoas sign |
| Pelvic | ~30% | Suprapubic pain, diarrhoea, tenesmus; positive obturator sign; tenderness on PR |
| Subcaecal / paracaecal | small % | Mimics RIF tenderness classically |
| Pre-ileal / post-ileal | small % | Post-ileal may cause diarrhoea; signs masked by bowel |
High-yield: The retrocaecal position is the commonest (~65%); the pelvic appendix is the next commonest and is the classic cause of "appendicitis presenting with diarrhoea and a normal abdomen but tender rectum."
Etiology & pathophysiology
The central event is luminal obstruction, which raises intraluminal pressure, impairs venous and lymphatic drainage, causes mucosal ischaemia and bacterial invasion → inflammation → gangrene → perforation.
Causes of obstruction (vary by age):
- Faecolith / faecalith — commonest overall in adults; a calcified faecal concretion. Strongly associated with gangrenous and perforated appendicitis.
- Lymphoid hyperplasia — commonest in children/adolescents, often post-viral (e.g., after URTI, measles, mononucleosis); GALT peaks 10–20 years, matching peak incidence.
- Foreign body, parasites — Enterobius vermicularis (pinworm), Ascaris, barium; rare.
- Tumours — carcinoid (neuroendocrine) tumour is the commonest appendiceal tumour and a recognised cause of obstruction; also mucinous neoplasm.
Bacteriology: polymicrobial — Escherichia coli and Bacteroides fragilis predominate (gram-negative aerobe + anaerobe). This dictates antibiotic choice.
Stepwise progression (flow):
Luminal obstruction → mucus accumulation & rising intraluminal pressure → lymphatic/venous congestion (oedematous/catarrhal appendicitis) → arterial compromise + bacterial transmural invasion (phlegmonous/suppurative) → ischaemic infarction (gangrenous) → perforation → localised abscess/appendicular mass (if walled off by omentum) OR generalised peritonitis (if free).
High-yield: Perforation is most likely at the tip (most ischaemic, end-artery territory) or at the site of a faecolith. Children and the elderly perforate earlier and more often because of thin/atrophic walls, atypical presentation and delayed diagnosis.
Clinical features
The classic sequence (present in only ~50–60%, but heavily tested):
- Periumbilical colicky pain (visceral, referred to T10 dermatome via midgut innervation).
- Anorexia, nausea, then vomiting — anorexia is so consistent that a genuinely hungry patient should make you doubt the diagnosis.
- Pain shifts to the right iliac fossa (RIF) and becomes constant and sharp (somatic, parietal peritoneum irritation) — the Murphy's triad / classic migration of pain.
- Low-grade fever (37.5–38.5 °C). High spiking fever suggests perforation/abscess.
High-yield: Shifting of pain from umbilicus to RIF + anorexia is the most discriminating history. Vomiting that precedes pain argues against appendicitis (think gastroenteritis).
Examination signs (memorise these — directly asked):
| Sign | How elicited | Significance |
|---|---|---|
| McBurney's point tenderness | 1/3 of the way along a line from ASIS to umbilicus (i.e., ~5 cm from ASIS) | Maximal tenderness; localised parietal inflammation |
| Rovsing's sign | Pressure in LIF causes pain in RIF | Peritoneal irritation |
| Psoas sign | Pain on passive hip extension (or active flexion against resistance) | Retrocaecal appendix irritating psoas |
| Obturator sign | Pain on internal rotation of flexed right hip | Pelvic appendix irritating obturator internus |
| Blumberg's sign | Rebound tenderness | Localised peritonitis |
| Dunphy's sign | Increased RIF pain on coughing | Peritoneal irritation |
| Markle (heel-drop) sign | Pain on jarring/heel strike | Peritoneal irritation |
| Baldwin / Cope | Flank pain on flexing right thigh | Retrocaecal |
High-yield: McBurney's point = junction of the lateral 1/3 and medial 2/3 of the spino-umbilical line (ASIS to umbilicus). This exact wording is a repeat MCQ.
Diagnostic scoring — Alvarado (MANTRELS) score
The Alvarado score is the most examined clinical scoring system. Mnemonic MANTRELS, total 10 points.
| Feature | Component | Points |
|---|---|---|
| M – Migration of pain to RIF | Symptom | 1 |
| A – Anorexia | Symptom | 1 |
| N – Nausea/vomiting | Symptom | 1 |
| T – Tenderness in RIF | Sign | 2 |
| R – Rebound tenderness | Sign | 1 |
| E – Elevated temperature (≥37.3 °C) | Sign | 1 |
| L – Leucocytosis (>10,000) | Lab | 2 |
| S – Shift of WBC to left (>75% neutrophils) | Lab | 1 |
Interpretation:
- 1–4 → appendicitis unlikely (discharge/observe).
- 5–6 → compatible; observe / image.
- 7–8 → probable appendicitis.
- 9–10 → very probable → surgery.
High-yield: The two components scoring 2 marks each are Tenderness in RIF and Leucocytosis. A score ≥7 usually warrants surgical intervention. Note: in modern practice Alvarado is most useful for ruling out (low scores) rather than confirming.
Other scores worth a line: AIR (Appendicitis Inflammatory Response) score and RIPASA score (better validated in Asian populations and women).
Investigations & investigation of choice
Appendicitis is fundamentally a clinical diagnosis; investigations support and triage.
- Blood: Neutrophilic leucocytosis (WBC 10,000–18,000); WBC >18,000 suggests perforation/abscess. CRP rises later — a normal WBC and normal CRP makes appendicitis unlikely. β-hCG mandatory in women of childbearing age to exclude ectopic.
- Urinalysis: To exclude UTI/calculus; mild pyuria/haematuria can occur with a pelvic/retrocaecal appendix irritating the ureter/bladder — do not be misled.
Imaging:
| Modality | Best for | Key findings | Notes |
|---|---|---|---|
| USG (graded compression) | Children, pregnant women, thin patients (investigation of choice here) | Non-compressible, blind-ending tube >6 mm, target sign, probe tenderness, faecolith | Operator dependent; avoids radiation |
| CT abdomen (contrast) | Adults, obese, equivocal, suspected abscess/mass | Diameter >6 mm, wall thickening, periappendiceal fat stranding, appendicolith | Most sensitive & specific (~95%); investigation of choice in adults |
| MRI | Pregnant women if USG inconclusive | Avoids ionising radiation |
High-yield: USG is the imaging investigation of choice in children and pregnant women; CT is the most accurate in adults and the best for diagnosing complications (abscess, appendicular mass). A diameter >6 mm is the cut-off on both USG and CT.
Management & drug of choice
Uncomplicated acute appendicitis → appendicectomy (appendectomy) remains the gold standard.
Preoperative: Nil by mouth, IV fluids, analgesia (analgesia does not mask diagnosis — old teaching is obsolete), and prophylactic IV antibiotics covering gram-negatives and anaerobes.
- Antibiotic of choice: a second-/third-generation cephalosporin + metronidazole, or a beta-lactam/beta-lactamase inhibitor (e.g., co-amoxiclav, piperacillin-tazobactam). Single prophylactic dose for simple cases; therapeutic course (5–7 days) for perforation/peritonitis.
Operative options — laparoscopic vs open:
| Feature | Laparoscopic appendicectomy | Open (Lanz/McBurney grid-iron incision) |
|---|---|---|
| Wound infection | Lower | Higher |
| Postoperative pain & hospital stay | Less / shorter | More |
| Return to work | Faster | Slower |
| Diagnostic value | Superior — allows full pelvic survey (key in women & obese) | Limited exposure |
| Intra-abdominal abscess | Slightly higher in some studies | Lower |
| Cost / operating time | Higher / longer | Lower / shorter |
High-yield: Laparoscopic appendicectomy is preferred in women of reproductive age and obese patients because it permits inspection of the pelvis and the contralateral side, and reduces wound infection. The classic open incision is the grid-iron (McBurney) — muscle-splitting; the cosmetic transverse version is the Lanz incision.
Non-operative management (NOM) — antibiotics alone: Increasingly evidence-based for uncomplicated appendicitis (CODA, APPAC trials). ~70% avoid surgery at 1 year, but recurrence/failure is significant and an appendicolith predicts failure. NOM is contraindicated if there is an appendicolith, perforation, or a suspected tumour.
Special situations:
- Appendicular mass (phlegmon) presenting >3–5 days: treat with Ochsner–Sherren regimen — conservative management (IV fluids, antibiotics, monitor pulse/temperature/mass size) followed by interval appendicectomy after 6–8 weeks. Surgery during the acute mass phase is hazardous.
- Appendicular abscess: image-guided percutaneous drainage + antibiotics, then interval appendicectomy.
- Pregnancy: Commonest non-obstetric surgical emergency in pregnancy. Pain may localise higher (RUQ) in later trimesters (gravid uterus displaces caecum upward — though recent data dispute the classic upward shift). Appendicectomy is indicated; delay increases foetal loss.
- Normal-looking appendix at surgery: still remove it (to prevent diagnostic confusion later), and search for other pathology — Meckel's diverticulum, mesenteric adenitis, ovarian/tubal pathology, terminal ileitis (Crohn's). If frank Crohn's of the caecal base — do not remove to avoid fistula.
High-yield: Ochsner–Sherren conservative regimen is for the appendicular mass; the chief sign that mandates abandoning conservative management and operating is a rising pulse, spreading tenderness, or an enlarging mass (signs of spreading peritonitis/abscess).
Complications
- Perforation → generalised peritonitis (commonest serious complication; higher in extremes of age).
- Appendicular mass / phlegmon and appendicular abscess.
- Pylephlebitis — septic thrombophlebitis of the portal vein; presents with high fever, rigors, jaundice → may cause liver abscesses. Rare but classically asked.
- Subphrenic / pelvic abscess postoperatively (pelvic abscess → swinging fever + diarrhoea/mucus PR; drain via rectum).
- Faecal fistula, adhesive intestinal obstruction, wound infection, stump appendicitis (recurrence in a retained long stump).
- Mucocoele / pseudomyxoma peritonei if an underlying mucinous neoplasm ruptures.
Key differentials
| Differential | Distinguishing pointer |
|---|---|
| Mesenteric adenitis | Children, post-viral, higher fever, tenderness shifts with position, generalised |
| Meckel's diverticulitis | Identical picture; "rule of 2s" — 2 ft from ileocaecal valve, 2% population |
| Ureteric colic | Loin-to-groin pain, haematuria, restless patient (vs lying still) |
| Ectopic pregnancy / ovarian torsion / ruptured follicle | Female; β-hCG, USG; sudden onset |
| PID | Bilateral, cervical motion tenderness, vaginal discharge |
| Acute terminal ileitis (Crohn's / Yersinia) | Diarrhoea, weight loss, chronicity |
| Right-sided diverticulitis, cholecystitis, perforated peptic ulcer, gastroenteritis | Site, sequence of symptoms, history |
High-yield: In a child with RIF pain, mesenteric adenitis is the top mimic; in a woman, always exclude ectopic pregnancy and ovarian pathology with β-hCG and USG before labelling appendicitis.
Recently asked / exam angle
- McBurney's point location — junction of lateral 1/3 and medial 2/3 of ASIS–umbilicus line (perennial single-best-answer).
- Commonest position of appendix = retrocaecal; commonest cause of obstruction in adults = faecolith; in children = lymphoid hyperplasia.
- Alvarado score — which two parameters carry 2 points (RIF tenderness + leucocytosis); MANTRELS expansion.
- Investigation of choice — USG in child/pregnancy, CT in adult (>6 mm cut-off).
- Commonest tumour of appendix = carcinoid (neuroendocrine), usually at the tip; if <2 cm → appendicectomy suffices, >2 cm or base involvement → right hemicolectomy.
- Ochsner–Sherren regimen and interval appendicectomy timing (6–8 weeks).
- Laparoscopic preferred in women/obese; image-and-treat trials (NOM, appendicolith predicting failure).
- Pylephlebitis as a cause of post-appendicitis liver abscess.
Rapid revision
- Appendicitis = luminal obstruction → ischaemia → gangrene → perforation; bacteria E. coli + B. fragilis.
- Commonest appendix position = retrocaecal (~65%); commonest mimic-by-diarrhoea = pelvic.
- Obstruction cause: faecolith (adults), lymphoid hyperplasia (children).
- Classic sequence: periumbilical pain → anorexia → vomiting → pain shifts to RIF. Anorexia is near-universal.
- McBurney's point = lateral 1/3–medial 2/3 of ASIS-to-umbilicus line.
- Psoas sign = retrocaecal; obturator sign = pelvic appendix.
- Alvarado/MANTRELS out of 10; RIF tenderness and leucocytosis = 2 points each; ≥7 → operate.
- β-hCG mandatory in reproductive-age women; USG diameter cut-off >6 mm.
- Imaging: USG in children/pregnancy, CT most accurate in adults & for abscess.
- Appendicular mass → Ochsner–Sherren + interval appendicectomy at 6–8 weeks.
- Laparoscopic appendicectomy preferred in women and obese; open = grid-iron (McBurney) / Lanz.
- Watch for pylephlebitis → portal pyaemia/liver abscess; commonest appendiceal tumour = carcinoid at the tip.