Overview
Acute Appendicitis
1. Clinical Overview
Summary
Acute appendicitis is inflammation of the vermiform appendix, most commonly caused by luminal obstruction from faecolith, lymphoid hyperplasia, or rarely tumour. It is the most common surgical emergency worldwide, with lifetime risk of 7-8%. The classic presentation is periumbilical pain migrating to the right iliac fossa, but atypical presentations are common and delay in diagnosis increases perforation risk. Early appendicectomy remains the gold standard treatment, though antibiotics-first strategies are emerging for uncomplicated cases.
Key Facts
- Definition: Acute inflammation of the vermiform appendix
- Lifetime Risk: 7-8% (peaks age 10-30)
- Perforation Rate: 20-30% at presentation; higher in extremes of age
- Mortality: Less than 1% for uncomplicated; 5% for perforated
- Key Management: Laparoscopic appendicectomy within 24 hours
- Critical Investigation: CT abdomen/pelvis (sensitivity greater than 95%)
Clinical Pearls
The Migration Pattern: Classic visceral to somatic pain migration (periumbilical → RIF) occurs in only 50-60% of cases. Atypical presentations are the rule, not the exception.
The 24-Hour Rule: Risk of perforation increases significantly after 36 hours of symptoms. Aim for appendicectomy within 24 hours of diagnosis.
Retrocaecal Appendix: 30% of appendices are retrocaecal, causing back pain, flank pain, or psoas irritation rather than classic RIF tenderness.
Why This Matters Clinically
Appendicitis is the most common cause of acute abdomen requiring surgery. Delayed diagnosis leads to perforation, abscess formation, peritonitis, and increased morbidity/mortality. Recognition of atypical presentations in elderly, pregnant, and immunocompromised patients is critical.
2. Epidemiology
Incidence & Prevalence
- Incidence: 100 per 100,000 per year in developed countries
- Lifetime Risk: 7-8%
- Peak Age: 10-30 years
- Trend: Stable; slight decrease in high-income countries
Demographics
| Factor | Details |
|---|---|
| Age | Peak 10-30 years; bimodal peak in elderly |
| Sex | Male:Female ratio 1.4:1 |
| Ethnicity | Higher in Western populations |
| Geography | Higher in developed countries (dietary factors) |
Risk Factors
Non-Modifiable:
- Age 10-30 years
- Male sex
- Family history of appendicitis
- Cystic fibrosis (mucus inspissation)
Modifiable:
| Risk Factor | Relative Risk |
|---|---|
| Low fibre diet | 1.5x |
| Smoking | 1.2x |
| Recent GI infection | 2x |
3. Pathophysiology
Mechanism
Step 1: Luminal Obstruction
- Faecolith (most common in adults)
- Lymphoid hyperplasia (most common in children/young adults)
- Foreign body, parasites, or tumour (rare)
Step 2: Mucosal Inflammation
- Obstruction leads to mucus accumulation and distension
- Intraluminal pressure rises, compressing mucosal blood vessels
- Bacterial overgrowth (Bacteroides, E. coli, Streptococcus)
- Mucosal ulceration and inflammation
Step 3: Transmural Inflammation
- Inflammation extends through appendiceal wall
- Visceral peritoneal irritation causes vague periumbilical pain
- As parietal peritoneum involved, pain localises to RIF
Step 4: Perforation
- Continued ischaemia leads to necrosis
- Perforation typically at antimesenteric border (watershed zone)
- Results in localised abscess or generalised peritonitis
Classification
| Type | Definition | Clinical Features |
|---|---|---|
| Simple/Uncomplicated | Inflamed appendix, no perforation | Classic presentation, responds to surgery |
| Gangrenous | Necrotic appendix wall | Higher complication rate |
| Perforated | Free or contained rupture | Peritonitis, abscess, sepsis |
| Appendix Mass | Walled-off inflammation | Palpable RIF mass, may need interval surgery |
| Appendix Abscess | Localised pus collection | Requires drainage (percutaneous or surgical) |
Anatomical Considerations
- Appendix position varies: retrocaecal (30%), pelvic (30%), subcaecal (20%), pre/post-ileal (20%)
- Retrocaecal appendicitis may present with back/flank pain and no RIF tenderness
- Pelvic appendicitis may cause diarrhoea, urinary symptoms, or rectal tenderness
- In pregnancy, appendix displaced superiorly by gravid uterus
4. Clinical Presentation
Symptoms
Typical Presentation (50-60%):
Atypical Presentations:
Signs
Red Flags
[!CAUTION] Red Flags — Seek immediate surgical input if:
- Generalised peritonitis (rigid abdomen, absent bowel sounds)
- Signs of sepsis (temperature greater than 38.5°C, HR greater than 100, hypotension)
- Palpable RIF mass (appendix mass or abscess)
- Elderly or immunocompromised with any RIF pain
- Pregnant woman with right-sided abdominal pain
Periumbilical pain migrating to RIF (visceral to somatic transition) — 50%
Common presentation.
Anorexia (most consistent symptom) — 80%
Common presentation.
Nausea and vomiting (after pain onset) — 60%
Common presentation.
Low-grade fever — 40%
Common presentation.
5. Clinical Examination
Structured Approach
General:
- Vital signs: Temperature, HR, BP
- Signs of dehydration or sepsis
- Patient positioning (often lying still, knees flexed)
Abdominal Examination:
- Inspection: Reduced movement with respiration
- Palpation: Start away from RIF, assess for tenderness, guarding, rigidity
- Percussion: Percussion tenderness (peritonism)
- Auscultation: Reduced or absent bowel sounds (ileus)
Special Tests
| Test | Technique | Positive Finding | Sensitivity/Specificity |
|---|---|---|---|
| McBurney's Point | Palpate 1/3 from ASIS to umbilicus | Maximal tenderness | 50-80% / 75-90% |
| Rovsing's Sign | Press LIF, pain felt in RIF | RIF pain on LIF palpation | 22-68% / 58-96% |
| Psoas Sign | Extend R hip with patient on left side | Pain on hip extension | 13-42% / 79-97% |
| Obturator Sign | Flex and internally rotate R hip | Pain on internal rotation | 8-22% / 94-98% |
| Rebound Tenderness | Release pressure quickly from abdomen | Pain on release | 63% / 69% |
6. Investigations
First-Line (Bedside)
- Observations — Temperature, HR, BP, RR
- Urinalysis — Exclude UTI (mild pyuria may occur with pelvic appendix)
- Pregnancy test — All women of childbearing age
Laboratory Tests
| Test | Expected Finding | Purpose |
|---|---|---|
| FBC | WCC 10-18 × 10⁹/L, neutrophilia | Inflammatory marker |
| CRP | Elevated (greater than 10 mg/L) | Inflammatory marker, higher in perforation |
| U&Es | May show dehydration | Baseline, pre-operative |
| LFTs | Usually normal | Baseline |
| Amylase/Lipase | Normal (if elevated, consider pancreatitis) | Differential diagnosis |
| Lactate | Elevated if septic | Severity marker |
Imaging
| Modality | Findings | Indication |
|---|---|---|
| CT Abdomen/Pelvis | Appendix greater than 6mm, periappendiceal fat stranding, faecolith | Gold standard in adults |
| Ultrasound | Non-compressible appendix greater than 6mm, target sign | First-line in children and pregnancy |
| MRI | Similar to CT without radiation | Pregnancy if USS inconclusive |
| Plain X-ray | Faecolith (10%), free air (perforation) | Not routinely indicated |
Diagnostic Criteria
Alvarado Score (MANTRELS):
- Migration of pain (1)
- Anorexia (1)
- Nausea/Vomiting (1)
- Tenderness in RIF (2)
- Rebound tenderness (1)
- Elevated temperature (1)
- Leukocytosis (2)
- Shift to left (neutrophilia) (1)
Score Interpretation:
- 0-4: Appendicitis unlikely
- 5-6: Possible appendicitis (imaging recommended)
- 7-10: Probable appendicitis (surgery likely)
7. Management
Management Algorithm
SUSPECTED APPENDICITIS
↓
┌─────────────────────────────────────────┐
│ CLINICAL ASSESSMENT │
│ Alvarado Score + Vital Signs │
└─────────────────────────────────────────┘
↓
┌─────────────────────────────────────────┐
│ RISK STRATIFICATION │
├─────────────────────────────────────────┤
│ LOW RISK (0-4) → Observe/Discharge │
│ MODERATE (5-6) → CT Imaging │
│ HIGH RISK (7-10) → Surgical Consult │
└─────────────────────────────────────────┘
↓
┌─────────────────────────────────────────┐
│ CT CONFIRMS DIAGNOSIS │
├─────────────────────────────────────────┤
│ UNCOMPLICATED → Laparoscopic │
│ Appendicectomy │
│ APPENDIX MASS → Antibiotics +/- │
│ Interval Surgery │
│ ABSCESS → Percutaneous Drainage + │
│ Interval Surgery │
│ PERFORATED → Emergency Surgery │
└─────────────────────────────────────────┘
Acute/Emergency Management
Immediate Actions:
- IV access and fluid resuscitation
- Analgesia (opioid — does not mask signs)
- Antiemetics (ondansetron 4mg IV)
- Keep nil by mouth
- Surgical referral within 1 hour if high clinical suspicion
- Antibiotics if septic or perforated (cefuroxime + metronidazole)
Conservative Management
- Observation with serial examinations if diagnosis uncertain
- Antibiotics-first strategy (emerging for uncomplicated cases in select patients)
- ~70% success rate, 20-30% recurrence at 1 year
Medical Management
| Drug Class | Drug | Dose | Duration |
|---|---|---|---|
| IV Fluids | 0.9% Saline or Hartmann's | Titrate to resuscitation | Until surgery |
| Analgesia | Morphine | 5-10mg IV PRN | Until control |
| Antiemetic | Ondansetron | 4mg IV | PRN |
| Antibiotic (Sepsis) | Cefuroxime + Metronidazole | 1.5g + 500mg IV | Until surgery |
| Antibiotic (Perf) | Piperacillin-Tazobactam | 4.5g IV TDS | 5-7 days post-op |
Surgical Management
Indications:
- All confirmed appendicitis (unless appendix mass/abscess with planned interval surgery)
Procedures:
- Laparoscopic Appendicectomy — Gold standard; 3 ports; shorter recovery
- Open Appendicectomy — If laparoscopic not available or converted; Lanz/Gridiron incision
- Interval Appendicectomy — 6-8 weeks after resolution of mass/abscess
Disposition
- Admit if: Clinical appendicitis, awaiting surgery or imaging
- Discharge if: Appendicitis excluded, reliable follow-up arranged
- Follow-up: Post-operative review at 2 weeks; histology review
8. Complications
Immediate (Minutes-Hours)
| Complication | Incidence | Presentation | Management |
|---|---|---|---|
| Perforation | 20-30% | Sudden worsening, peritonitis | Emergency surgery |
| Sepsis | 5-10% | Fever, hypotension, tachycardia | Antibiotics, resuscitation |
Early (Days)
- Wound infection: 5-10% (higher if perforated) — antibiotics, open wound
- Intra-abdominal abscess: 2-5% — CT-guided drainage or reoperation
- Ileus: 5-15% — conservative management, NG tube if vomiting
- Stump appendicitis: Rare — incomplete resection; requires completion appendicectomy
Late (Weeks-Months)
- Adhesive small bowel obstruction: 1-3% — conservative or surgical
- Incisional hernia: 1-2% (higher with open surgery)
- Infertility (females): Increased risk with perforated appendicitis
9. Prognosis & Outcomes
Natural History
- Untreated appendicitis progresses to perforation in 24-72 hours
- Perforation rate increases 5% every 12 hours after 36 hours of symptoms
- Appendix mass may resolve with antibiotics or require interval surgery
Outcomes with Treatment
| Variable | Outcome |
|---|---|
| Mortality (uncomplicated) | Less than 0.1% |
| Mortality (perforated) | 1-5% |
| Morbidity (uncomplicated) | 3-5% |
| Morbidity (perforated) | 15-30% |
| Recurrence after antibiotics | 20-30% at 1 year |
Prognostic Factors
Good Prognosis:
- Young, healthy patient
- Early presentation (less than 24 hours)
- Uncomplicated appendicitis
- Laparoscopic surgery
Poor Prognosis:
- Extremes of age (less than 5, greater than 65)
- Delayed presentation
- Perforation or abscess
- Significant comorbidities
- Immunocompromised state
10. Evidence & Guidelines
Key Guidelines
- WSES Jerusalem Guidelines (2020) — Diagnosis and treatment of acute appendicitis in adults and children. WSES
- NICE CKS Appendicitis — Clinical Knowledge Summary for primary care. NICE CKS
- AAST Guidelines — American Association for the Surgery of Trauma management recommendations.
Landmark Trials
APPAC Trial (2015) — Antibiotics vs Appendicectomy for uncomplicated appendicitis
- 530 patients randomised
- Key finding: 73% success with antibiotics alone at 1 year; 27% required surgery
- Clinical Impact: Antibiotics-first may be option in select uncomplicated cases
CODA Trial (2020) — Comparison of Outcomes of Antibiotic Drugs and Appendectomy
- 1552 patients randomised
- Key finding: Antibiotics non-inferior for 30-day health status; 29% required surgery at 90 days
- Clinical Impact: Shared decision-making for uncomplicated appendicitis
CROSS Trial (2021) — CT versus Clinical Diagnosis
- 518 patients
- Key finding: Routine CT reduced negative appendicectomy rate from 16% to 3%
- Clinical Impact: Supports liberal use of CT in equivocal cases
Evidence Strength
| Intervention | Level | Key Evidence |
|---|---|---|
| Laparoscopic over open | 1a | Multiple RCTs, Cochrane review |
| CT for diagnosis | 1b | CROSS Trial |
| Antibiotics for uncomplicated | 1b | APPAC, CODA Trials |
| Surgery within 24h | 2a | Cohort studies |
11. Patient/Layperson Explanation
What is Appendicitis?
Your appendix is a small finger-shaped pouch attached to your large bowel, in the lower right side of your tummy. Appendicitis happens when this pouch gets blocked and becomes inflamed and infected. Think of it like a blocked drain that becomes swollen and painful.
Why does it matter?
If appendicitis is not treated, the appendix can burst (perforate), spilling infection into your tummy. This is very serious and can make you very unwell. The good news is that with prompt surgery, appendicitis is easily treated and most people recover completely.
How is it treated?
- Surgery (most common): A keyhole operation (laparoscopic appendicectomy) to remove the appendix. You usually go home the next day.
- Antibiotics: In some mild cases, antibiotics alone may be tried, but about 1 in 4 people will still need surgery later.
- Drainage: If there is an abscess (collection of pus), it may be drained first, with surgery later.
What to expect
- Most people have keyhole surgery and go home after 1-2 days
- You can usually return to normal activities in 1-2 weeks
- Full recovery takes 2-4 weeks
- You do not need your appendix to live normally
When to seek help
Go to A&E or call 999 if you have:
- Severe tummy pain, especially if it moves to the lower right side
- Pain that gets suddenly worse
- Fever with tummy pain
- Vomiting and unable to keep fluids down
- Tummy becomes hard or rigid
12. References
Primary Guidelines
- Di Saverio S, et al. Diagnosis and treatment of acute appendicitis: 2020 update of the WSES Jerusalem guidelines. World J Emerg Surg. 2020;15(1):27. PMID: 32295644
Key Trials
- Salminen P, et al. Antibiotic Therapy vs Appendectomy for Treatment of Uncomplicated Acute Appendicitis: The APPAC Randomized Clinical Trial. JAMA. 2015;313(23):2340-8. PMID: 26080338
- CODA Collaborative. A Randomized Trial Comparing Antibiotics with Appendectomy for Appendicitis. N Engl J Med. 2020;383(20):1907-1919. PMID: 33017106
- Bhangu A, et al. Safety of short, in-hospital delays before surgery for acute appendicitis: multicentre cohort study. Ann Surg. 2014;259(5):894-903. PMID: 24509193
- van Rossem CC, et al. Randomized clinical trial of routine preoperative computed tomography vs clinical decision rules in patients suspected of acute appendicitis. Br J Surg. 2016;103(10):1313-21. PMID: 27479251
Further Resources
- NHS Appendicitis Information: nhs.uk/conditions/appendicitis
- Patient.info: patient.info/digestive-health/appendicitis
Last Reviewed: 2025-12-24 | MedVellum Editorial Team
Medical Disclaimer: MedVellum content is for educational purposes and clinical reference. Clinical decisions should account for individual patient circumstances. Always consult appropriate specialists for emergency situations.