Definition / Overview
- Appendicitis is acute inflammation of the vermiform appendix, representing one of the most common surgical emergencies worldwide.
- Lifetime risk is approximately 7-8% in the general population, with peak incidence in the second and third decades of life.
- The appendix arises from the posteromedial wall of the caecum, at the confluence of the three taeniae coli, approximately 2 cm below the ileocaecal valve.
- Despite its perceived simplicity, misdiagnosis remains frequent, negative appendectomy rates approach 15% in some series, and delayed diagnosis is among the leading causes of surgical malpractice claims.
Anatomy and Positional Variants
Position of the Appendiceal Tip
The tip position varies considerably and directly influences the clinical presentation:
| Position | Frequency | Characteristic Feature |
|---|---|---|
| Retrocaecal | ~64% | Psoas sign positive; RLQ guarding may be attenuated |
| Pelvic | ~32% | Obturator sign; may mimic gynaecological pathology |
| Subcaecal | ~2% | RLQ tenderness, may be atypical |
| Pre-ileal | ~1% | Central/periumbilical tenderness |
| Post-ileal | ~0.5% | Variable and easily confused with other pathology |
McBurney's Point
- Located one-third of the distance along a line drawn from the right anterior superior iliac spine (ASIS) to the umbilicus.
- Maximal tenderness at this point is a classical sign, though position-dependent.
Neurovascular Supply
- Arterial supply: appendicular artery, a branch of the ileocolic artery (from the superior mesenteric artery).
- Venous drainage: ileocolic vein → superior mesenteric vein → portal vein (relevant to pylephlebitis in complicated appendicitis).
- Lymphatic drainage: ileocolic nodes.
Pathophysiology
- The initiating event is luminal obstruction, most commonly by a faecolith (~35%), lymphoid hyperplasia (more common in children and young adults), or, rarely, tumour or foreign body.
- Obstruction leads to bacterial overgrowth within a closed loop, with rising intraluminal pressure.
- Mucosal ischaemia follows, progressing to transmural inflammation, necrosis, and ultimately perforation if untreated.
- The typical time course from symptom onset to perforation is 24-72 hours, though this is variable.
- Perforation leads to localised abscess formation (if the omentum walls off the process) or free peritonitis.
Microbiology
- Polymicrobial infection involving colonic flora:
- Gram-negative aerobes: Escherichia coli, Klebsiella spp.
- Anaerobes: Bacteroides fragilis, Fusobacterium spp.
- Gram-positive organisms: enterococci.
- Antibiotic choice should provide broad-spectrum coverage of these organisms (see Management below).
Clinical Features and Diagnosis
History
- Visceral pain phase: Early obstruction produces vague, poorly localised central or periumbilical pain, often cramping in character, mediated via T10 visceral afferents.
- Somatic pain phase: As parietal peritoneum becomes inflamed, pain migrates to the right iliac fossa (RIF/RLQ), this migration is among the most predictive historical features.
- Associated features: anorexia (highly consistent), nausea, vomiting (usually follows pain onset), low-grade fever, and constipation or diarrhoea.
Examination Signs
| Sign | Description | Clinical Utility |
|---|---|---|
| McBurney's point tenderness | Maximal pressure at McBurney's point | Sensitive but not specific |
| Rovsing's sign | RLQ pain elicited by LLQ palpation | Moderately specific for peritoneal irritation |
| Psoas sign | RLQ pain on extension of the right hip | Suggests retrocaecal appendix |
| Obturator sign | RLQ pain on internal rotation of right hip | Suggests pelvic appendix |
| Dunphy's sign | Worsening pain on coughing | Peritoneal irritation |
| Guarding / rigidity | Involuntary muscular resistance to palpation | Indicates peritonitis |
- The classical signs (psoas, obturator) are highly specific but poorly sensitive, their absence does not exclude appendicitis.
- Rectal examination has fallen out of routine use but may reveal right-sided pelvic tenderness, particularly with a pelvic appendix.
Atypical Presentations
- Children: Variable and less localised findings; higher perforation rate at presentation due to diagnostic delay; omentum is less developed and less able to contain perforation.
- Elderly: Blunted inflammatory response, attenuated pain, and later presentation; higher perforation rate.
- Pregnancy: Appendix displaced superiorly and laterally by the gravid uterus; RLQ tenderness may be less reliable; high fetal loss risk with perforation.
- Immunocompromised: Attenuated signs and symptoms; lower threshold for imaging.
Investigation
Laboratory
| Test | Finding in Appendicitis | Comment |
|---|---|---|
| WBC | Leukocytosis $>10{,}000\,\text{cells/mm}^3$ | Present in ~80%; non-specific |
| Neutrophilia | Left shift, $>75\%$ neutrophils | More specific than WBC alone |
| CRP | Elevated (especially $>75\,\text{mg/L}$) | Rises later than WBC; strong predictor of perforation |
| Urinalysis | Sterile pyuria or microscopic haematuria | Adjacent inflammation; does not exclude appendicitis |
| Urine $\beta$-hCG | Must be checked in all women of childbearing age | Excludes ectopic pregnancy; guides imaging choices |
| Serum amylase/lipase | Normal in appendicitis | Useful to exclude pancreatitis |
| LFTs | Normal in appendicitis | Useful to exclude biliary pathology |
- No single laboratory test reliably confirms or excludes appendicitis, combinations of clinical findings with inflammatory markers have greater discriminatory value.
- Highly elevated CRP combined with marked leukocytosis should raise suspicion for perforation.
Imaging
Ultrasound (USS)
- First-line in children and pregnant women to avoid ionising radiation.
- A non-compressible, aperistaltic, tubular structure with outer diameter $>6\,\text{mm}$ is diagnostic.
- Sensitivity ~75-86%; specificity ~81-98%.
- Operator-dependent; limited by body habitus and bowel gas; non-visualisation of the appendix is not reassuring.
Computed Tomography (CT)
- Gold standard imaging modality in adults with diagnostic uncertainty.
- Sensitivity ~94-98%; specificity ~95%.
- Findings: appendiceal diameter $>6\,\text{mm}$, periappendiceal fat stranding, appendicolith, free fluid, pneumoperitoneum (if perforated).
- CT has significantly increased pre-operative diagnostic accuracy but has not reduced perforation rates at a population level.
- Radiation exposure must be considered, particularly in children and pregnant women, use only when USS is non-diagnostic.
MRI
- Preferred when USS is inconclusive in pregnancy, or in paediatric patients where CT radiation is a concern.
- Sensitivity ~91-96%; specificity ~97%.
- Availability and time constraints may limit use in acute settings.
Plain Abdominal X-Ray
- Very limited role in modern practice.
- An appendicolith on plain film (~11% of appendicitis cases) is not sufficiently specific to be considered pathognomonic.
- May demonstrate free air if perforation has occurred.
Clinical Scoring Systems
Alvarado Score (MANTRELS)
Derived from retrospective analysis of patients presenting with abdominal pain suspicious for appendicitis; assigns points to clinical and laboratory variables:
| Feature | Points |
|---|---|
| Migration of pain to RLQ | 1 |
| Anorexia | 1 |
| Nausea / vomiting | 1 |
| RLQ tenderness | 2 |
| Rebound tenderness | 1 |
| Elevated temperature ($>37.3°C$) | 1 |
| Leukocytosis ($>10{,}000$) | 2 |
| Left shift (neutrophilia) | 1 |
| Total | 10 |
Interpretation:
- Score $\leq 4$: Low probability; appendicitis unlikely
- Score $5$-$6$: Equivocal; consider imaging or observation
- Score $\geq 7$: High probability; operative intervention appropriate
- A score of $\geq 9$ in males or $\geq 9$ in females has been considered equivalent to CT-confirmed appendicitis in some studies
Limitations:
- Derived from a retrospective single-centre cohort
- Insufficient sensitivity/specificity to be used in isolation
- Has been largely superseded by readily available CT in adults
- Score does not eliminate the need for clinical judgment
Appendicitis Inflammatory Response (AIR) Score
- Developed as a refinement to the Alvarado score in adult populations.
- Incorporates CRP more prominently and uses a slightly different weighting of variables.
- Demonstrated superior discrimination compared to the Alvarado score in prospective evaluations.
- Three risk strata: low (observation), intermediate (further imaging), high (operative).
Paediatric Appendicitis Score (PAS)
- Developed specifically for children using eight clinical and laboratory variables.
- Useful in the paediatric emergency setting to stratify risk and guide imaging decisions.
- Score $\leq 2$: low risk; Score $3$-$6$: intermediate; Score $\geq 7$: high risk.
Key Principle for GSSE
- Scoring systems perform better than individual symptoms or signs in isolation but remain insufficient as standalone diagnostic tools.
- Their primary utility is in risk stratification, determining who requires imaging versus who can proceed directly to theatre or be discharged.
Differential Diagnosis
The differential is broad and position-dependent:
- Gynaecological: Ectopic pregnancy, ovarian torsion, ruptured ovarian cyst, pelvic inflammatory disease, endometriosis
- GI: Meckel's diverticulitis, Crohn's disease (terminal ileum), mesenteric adenitis, caecal carcinoma, perforated caecal diverticulitis
- Urological: Ureterolithiasis, urinary tract infection, pyelonephritis
- Vascular: Ruptured aortic aneurysm (elderly)
- Musculoskeletal: Psoas abscess, iliopsoas haematoma
Management
General Principles
- Nil by mouth, IV access, IV fluid resuscitation (if dehydrated).
- Analgesia, early adequate analgesia does not impair diagnostic assessment and should not be withheld (strong evidence contradicts historical dogma).
- Antibiotic therapy, initiate pre-operatively; covers gram-negative aerobes and anaerobes.
- Determine: uncomplicated vs. complicated appendicitis (perforation, abscess, peritonitis).
Antibiotic Regimens
- Uncomplicated: Single agent, e.g. co-amoxiclav IV, or cefazolin + metronidazole.
- Complicated (perforation/peritonitis): Broader spectrum, e.g. piperacillin-tazobactam IV, or gentamicin + metronidazole + ampicillin (empiric triple therapy).
- Duration: 24-hour prophylaxis for uncomplicated; 3-5 days minimum for complicated.
Non-operative Management
- Emerging evidence supports antibiotics-alone as an initial treatment strategy for uncomplicated (non-perforated, non-faecolith) appendicitis:
- Short-term success rates of ~70-80%.
- Approximately 25-30% will recur within 1 year and require appendectomy.
- Patient counselling and shared decision-making are essential.
- Not appropriate for complicated appendicitis, faecolith, or diagnostic uncertainty.
Operative Management, Appendectomy
Timing
- Uncomplicated appendicitis: Appendectomy within 24 hours of diagnosis is safe; a short delay (overnight) for optimisation does not increase perforation risk.
- Complicated appendicitis: Urgent appendectomy for free perforation with peritonitis. Contained abscess may be managed initially with antibiotics ± percutaneous drainage, followed by interval appendectomy at 6-8 weeks.
Laparoscopic vs. Open Appendectomy
| Parameter | Laparoscopic (LA) | Open (OA) |
|---|---|---|
| Wound infection | Reduced | Higher |
| Intra-abdominal abscess | Slightly increased (in some series) | Lower |
| Return to work | Faster | Slower |
| Hospital costs | Higher (theatre costs) | Lower |
| Diagnostic benefit | Can inspect entire peritoneal cavity | Limited visualisation |
| Preferred population | Women of childbearing age, obese, elderly | Resource-limited; prior abdominal surgery |
- Laparoscopic appendectomy is the preferred approach in most modern units.
- In women of childbearing age, laparoscopy offers the advantage of identifying and treating gynaecological pathology, when a normal appendix is found at laparoscopy, gynaecological pathology is identified in ~73% of cases, compared to ~17% at open exploration.
- For obese patients, laparoscopy significantly reduces wound-related morbidity.
Open Appendectomy, Key Steps
- Gridiron (McBurney's) incision or Lanz (transverse) incision in RIF.
- Split external oblique in the direction of its fibres; split internal oblique and transversus; open peritoneum.
- Identify the appendix by following the taeniae coli to their convergence at the base.
- Ligate and divide the mesoappendix (containing the appendicular artery).
- Crush, ligate, and divide the base of the appendix; mucosal stump treated with diathermy.
- Purse-string invagination of stump is optional (not mandated by evidence).
Laparoscopic Appendectomy, Key Steps
- Three-port approach: umbilical (10-12 mm camera), suprapubic or LIF, and RIF or LIF.
- Trendelenburg positioning with left tilt to shift bowel medially.
- Identify appendix, dissect mesoappendix, clip and divide appendicular artery.
- Staple or loop-ligate the appendicular base; divide.
- Retrieve specimen in an endoscopic bag to prevent wound contamination.
Complications and Special Considerations
Complications of Appendicitis
- Perforation: Most common complication; risk increases significantly after 48-72 hours of symptoms; higher in elderly and children.
- Pericaecal abscess: Contained perforation; managed initially with IV antibiotics ± image-guided percutaneous drainage.
- Pylephlebitis: Septic portal vein thrombosis, rare but life-threatening; presents with swinging fevers, right upper quadrant pain, and jaundice.
- Faecal fistula: Post-operative; may close spontaneously if distal obstruction excluded.
Post-operative Complications
- Wound infection: Reduced with laparoscopic approach and appropriate antibiotic prophylaxis.
- Intra-abdominal collection: More reported with laparoscopic approach in complicated appendicitis; may require radiological drainage.
- Stump appendicitis: Recurrence if stump is too long ($>5\,\text{mm}$).
Incidental Findings
- If a macroscopically normal appendix is found intra-operatively, it should still be removed (removed for histology; avoids future diagnostic confusion).
- Always inspect the terminal ileum (Crohn's, Meckel's), caecum (tumour), and in women the pelvis (ovarian/tubal pathology).
Perioperative Considerations for GSSE
- Anaesthesia: General anaesthesia is standard; consider RSI in acute abdomen (full stomach risk/aspiration).
- DVT prophylaxis: Compression stockings and chemical prophylaxis per institutional protocol; sepsis and immobility increase VTE risk.
- Pregnancy: If appendicitis confirmed or highly suspected, operate regardless of gestational age, fetal loss from untreated perforation exceeds operative risk. MRI is preferred imaging; laparoscopy is safe up to ~28 weeks with appropriate positioning.
- Fluid balance: Dehydrated patients (especially children) require pre-operative fluid resuscitation; avoid hyponatraemia with appropriate fluid selection.
- Paediatric considerations: Weight-based dosing for analgesics and antibiotics; involve paediatric surgical team; higher baseline heart rate and respiratory rate must be interpreted accordingly when assessing clinical severity.
High-Yield Summary for GSSE MCQ/Viva
- Migration of pain to the RLQ + anorexia + inflammatory markers = most predictive combination.
- Sterile pyuria on urinalysis does not exclude appendicitis.
- Alvarado score $\geq 7$ warrants operative consideration; score alone is insufficient to replace clinical judgment.
- CT is gold standard in adults; USS is first-line in children and pregnant women.
- Laparoscopy preferred: especially in women of childbearing age, obese patients, and elderly.
- Non-operative management of uncomplicated appendicitis is evidence-based but carries a ~25-30% one-year recurrence rate.
- Elevated CRP + leukocytosis = high predictor of perforation.
- Always check urine $\beta$-hCG in women of reproductive age before imaging or operating.
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