Diagnosis of Appendicitis

1. Pathophysiology Basis for Symptoms

• Luminal distension and bacterial proliferation
• Visceral inflammation (causing diffuse, poorly localised pain)
• Progression to mural ischaemia and perforation if untreated

• Bailey and Love's Short Practice of Surgery, p. 1358

2. History and Symptoms

Classic sequence:

1. Periumbilical or central colicky pain - the initial visceral pain from appendiceal distension (midgut origin - referred to the umbilicus via T10)
2. Anorexia - present in virtually all cases; a highly constant feature
3. Nausea and 1-2 episodes of vomiting - vomiting follows the onset of pain (important: pain before vomiting differentiates appendicitis from gastroenteritis)
4. Pain migration to the right iliac fossa (RIF) - as parietal peritoneum becomes inflamed, pain shifts and becomes constant, more intense, and localised to the RIF
5. Low-grade fever - temperature of 37.2-37.7°C with pulse 80-90 bpm; typically appears after the first 6 hours. In 20% of patients there is no pyrexia or tachycardia in early stages

• The classic visceral-somatic pain sequence occurs in only ~50% of cases
• Atypical presentation is more common in the elderly
• A pelvic appendix may cause suprapubic pain, tenesmus, and urinary frequency without classical RIF tenderness
• Retrocaecal appendix may present with loin pain, with absent anterior tenderness
• Bailey and Love's Short Practice of Surgery, pp. 1360-1361

3. Physical Examination Signs

Retrocaecal appendix: Rigidity may be absent; deep pressure may not reach the appendix (the "silent appendix"). Deep loin tenderness and quadratus lumborum rigidity may be more prominent.

Pelvic appendix: Complete absence of abdominal rigidity. Tenderness elicited on rectal examination (rectovesical pouch or pouch of Douglas). Rectal examination is mandatory in all patients with lower abdominal pain.

• Bailey and Love's Short Practice of Surgery, pp. 1360-1361
• Fischer's Mastery of Surgery, p. 7854

4. Laboratory Investigations

Novel biomarkers (e.g. calprotectin, PCT) have not yet demonstrated sufficient utility for routine use.

• Tintinalli's Emergency Medicine, p. 565-566
• Fischer's Mastery of Surgery, p. 7854

5. Scoring Systems

Modified Alvarado Score (MANTRELS):

• Score 1-4: Low risk
• Score 5-9: Possible or probable appendicitis
• Score ≥7: Probable appendicitis

Other Scoring Systems:

• Appendicitis Inflammatory Response (AIR) score - currently the best-performing in adults
• Adult Appendicitis Score (AAS) - comparable performance
• Pediatric Appendicitis Score (PAS) / Samuel score - used in children

• Tintinalli's Emergency Medicine, p. 565
• Current Surgical Therapy 14e, p. 3459

6. Imaging

Plain Radiography

• Generally not helpful; findings are nonspecific
• May show a non-specific bowel gas pattern, localised ileus, or an appendicolith (visible in up to 50% of children)

Ultrasound (US)

• Non-compressible appendix >6 mm in diameter
• Wall thickening and periappendiceal fluid
• Appendicolith with posterior acoustic shadowing
• Colour Doppler: periappendiceal hyperaemia

CT Abdomen/Pelvis

• Dilated appendix >6 mm with wall thickening
• Periappendiceal fat stranding
• Appendicolith
• Periappendiceal abscess or free fluid
• In perforation: loss of appendix wall continuity, pneumoperitoneum

MRI

1. Graded-compression US first
2. MRI if US non-diagnostic
3. CT as last resort if MRI also non-diagnostic

Ultrasound (A) and CT (B) demonstrating acute appendicitis - note the non-compressible appendix with appendicolith (white arrow) and posterior acoustic shadowing on US, confirmed on CT with periappendiceal inflammation

Perforated appendicitis: US showing appendicolith with shadowing; CT confirming appendicolith and pelvic fluid collection indicating perforation

• Tintinalli's Emergency Medicine, pp. 566-567
• Roberts and Hedges' Clinical Procedures, p. 1708

7. Differential Diagnosis

In females of reproductive age, PID and ovarian pathology must always be considered.

• Goldman-Cecil Medicine, p. 2191

8. Special Populations

Children

• Difficult to assess; presentation is often atypical especially in infants
• Perforation rate is much higher due to delayed diagnosis (thin omentum unable to wall off inflammation)
• US preferred as initial imaging (avoids radiation)
• PAS score used

Elderly

• Pain localisation to RIF is unusual
• Symptoms may be blunted; leukocytosis may be absent
• Higher perforation rate at presentation

Pregnant Patients

• Appendix displaced superiorly and laterally by gravid uterus
• Peritoneal signs may be reduced
• Most common non-obstetric surgical emergency in pregnancy
• Imaging algorithm: US → MRI → CT

9. Summary: Diagnostic Approach

Suspected Appendicitis
        │
        ▼
Clinical assessment (history + examination)
+ Lab work (WBC, CRP, urinalysis, βhCG in females)
+ Apply scoring system (AIR/Alvarado)
        │
   ┌────┴────┐
High suspicion    Diagnostic uncertainty
(adult, clear     (atypical, pregnancy,
 presentation)     child, obese)
        │                │
  Surgical              Imaging
consultation     ┌───────┴──────────┐
        │        US (first-line in   CT (adults,
        ▼        children/pregnant)  not pregnant)
   Appendectomy         │            │
                    Non-diagnostic   │
                        └─────────MRI/CT

Key principle: Clinical judgment of an experienced clinician remains the most accurate diagnostic tool. Scoring systems and imaging are adjuncts - they should not override strong clinical suspicion.

• Fischer's Mastery of Surgery, p. 7854
• Bailey and Love's Short Practice of Surgery, p. 3007

Treatment Protocol for Appendicitis

Step 1: Classify the Appendicitis

Step 2: Initial Resuscitation (all patients)

• IV fluid resuscitation (crystalloid)
• IV antibiotics - start promptly (preoperative dose; repeat intraoperatively if surgery is prolonged)
• Analgesia - opioid-sparing multimodal approach preferred
• NBM (nil by mouth)
• VTE prophylaxis for admitted patients
• Urinalysis, FBC, CRP, βhCG (if female)
• Surgical consultation

Step 3: Definitive Treatment - Decision Tree

Acute Appendicitis Confirmed
         │
    ┌────┴────────────────┐
    │                     │
UNCOMPLICATED         COMPLICATED
    │                     │
    ├── Operative          ├── With diffuse peritonitis/
    │   (standard)        │   sepsis → Emergency surgery
    │                     │
    └── Non-operative      └── With phlegmon/abscess →
        (select patients)      Non-operative first

A. UNCOMPLICATED APPENDICITIS

Option 1: Appendectomy (Standard of Care)

• Lower superficial wound infection rate (~50% lower)
• Shorter hospital stay (~1.1 days shorter)
• Less postoperative pain, faster return to normal activity
• Better for obese patients, young women, diagnostically uncertain cases
• Allows full abdominal survey

• Fischer's Mastery of Surgery, p. 7844
• Sleisenger and Fordtran's GI & Liver Disease, p. 2442
• Mulholland and Greenfield's Surgery, p. 458

Option 2: Non-operative Management (Antibiotics Alone)

Key Evidence

Antibiotic Regimen for Non-operative Management (APPAC-style):

• IV: Ertapenem 1g daily for 3 days (hospital)
• Oral step-down: Levofloxacin 500 mg daily + metronidazole 500 mg TDS for 7 days

Criteria for Non-operative Management (Uncomplicated Only):

• CT-confirmed uncomplicated appendicitis
• No appendicolith
• Clinically stable, no signs of peritonitis
• Able to comply with follow-up
• Patient preference after informed consent

• Appendicolith present (significantly higher failure/complication rate)
• Perforation, abscess, phlegmon
• Diffuse peritonitis
• Immunocompromised patients
• Children (antibiotics shown inferior in 2025 Lancet RCT)
• Failure to improve within 24-48h of antibiotics

• ~1 in 3 patients will still need appendectomy within 1 year
• If appendicitis recurs, definitive surgery is recommended
• Risk of delayed diagnosis of neoplasm (colonoscopy recommended in patients >40 years after non-operative management)
• Fischer's Mastery of Surgery, p. 7854
• Mulholland and Greenfield's Surgery, pp. 457-458

B. COMPLICATED APPENDICITIS

1. Perforated Appendicitis with Diffuse Peritonitis / Sepsis

• Urgent source control is mandatory
• Lavage and suction of the peritoneal cavity
• Intraoperative cultures
• IV antibiotics continued postoperatively for 4 days after source control
• Longer duration if source control is inadequate or patient is immunosuppressed

• Single agent: Piperacillin-tazobactam 4.5g IV Q8h OR Ertapenem 1g IV daily
• Combination: Cephalosporin (3rd-gen) or fluoroquinolone + metronidazole
• Avoid: Ampicillin-sulbactam (high E. coli resistance), tigecycline (increased mortality vs comparators)

• Cefepime or ceftazidime + metronidazole OR
• Piperacillin-tazobactam monotherapy OR
• Imipenem / meropenem / doripenem
• Add vancomycin if MRSA suspected
• Alternative for beta-lactam allergy: Vancomycin + aztreonam + metronidazole
• Current Surgical Therapy 14e, p. 1255

2. Appendiceal Abscess or Phlegmon (Without Diffuse Peritonitis)

1. Bowel rest + IV fluids + IV antibiotics
2. CT-guided percutaneous drainage if abscess ≥3 cm is present (single abscess, accessible)
3. Monitor closely for clinical response (fever, WBC, pain trend)
4. Step down to oral antibiotics when improving; typically 7-14 days total
5. Interval appendectomy: NOT routinely recommended (recurrence risk only ~7.4%)
6. Colonoscopy or repeat CT in patients >40 years to exclude underlying neoplasm (found in ~1.2-17% in some series, increasing with age)

• Failure to respond within 48-72 h
• Clinical deterioration
• Rupture/spreading peritonitis
• Mulholland and Greenfield's Surgery, pp. 458-459

C. SPECIAL POPULATIONS

Pregnancy

• Laparoscopic appendectomy is safe throughout pregnancy (including 2nd/3rd trimester)
• Recommended as first-line definitive treatment
• Second trimester preferred if timing allows
• Non-operative management may be considered but carries higher risk of fetal loss with perforation
• Open appendectomy as alternative; debate continues regarding which approach carries lower fetal risk in late pregnancy
• Postoperative tocolysis: only if uterine irritability is documented

Children

• Appendectomy remains the standard - 2025 Lancet RCT showed antibiotics were inferior to appendectomy (34% vs. 7% failure rate at 1 year)
• Laparoscopic approach preferred
• Thin, poorly developed omentum means faster progression to perforation
• Perforation rates up to 90% in infants <2 years

Elderly

• Higher perforation rate at presentation
• More comorbidities increase surgical risk - may favour initial non-operative management in select cases
• Lower threshold for broad-spectrum antibiotics

D. POST-APPENDECTOMY CARE

• Same-day discharge or next day
• Diet as tolerated post-operatively
• Oral analgesia (paracetamol ± NSAIDs ± short course opioid)
• Return to normal activity within 1-2 weeks

• Continue IV antibiotics for 4 days after source control
• Monitor for:
  • Wound infection (most common complication) - open wound if superficial
  • Intra-abdominal abscess (higher with laparoscopic approach) - usually requires percutaneous drainage
  • Stump appendicitis (rare, 1/50,000) - re-operation required
  • Enterocutaneous fistula (rare) - conservative initially; ileocecectomy if persistent

Summary Treatment Algorithm

Confirmed Appendicitis
        │
   Uncomplicated?
     YES    NO (complicated)
      │           │
   Surgical?  Peritonitis?
   preference   YES    NO
      │          │      │
 Laparoscopic  Urgent  Abscess/
 appendectomy surgery  phlegmon
  (preferred) (emer-     │
      │       gency)   Non-op
   OR if     + broad    Abx +
   patient    Abx      drain if
   prefers               ≥3cm
 Antibiotics-             │
 first if NO          Interval
 appendicolith     appendectomy
   + informed         NOT
   consent          routine

• 2024 Cochrane Review confirms antibiotics are a viable alternative to surgery for uncomplicated appendicitis in adults, with ~69% avoiding surgery at 1 year and fewer wound complications, but lower overall treatment success
• 2025 Lancet IPD meta-analysis shows appendicolith presence is a strong contraindication to antibiotic-first management (OR 2.82 for complications)
• 2024 SAGES guidelines give conditional recommendations for operative management as first-line but acknowledge antibiotics as an acceptable alternative with shared decision-making
• 2025 Lancet pediatric RCT definitively showed antibiotics inferior to appendectomy in children - appendectomy remains the standard in pediatric patients

Oral Medications and IV Fluids in Uncomplicated Appendicitis

1. Pre-operative / perioperative (patient going to surgery)
2. Non-operative management (antibiotics-first strategy, no surgery)

I. IV FLUIDS

Goal

Choice of IV Fluid

How Much?

• Give 500 mL - 1 L IV crystalloid bolus initially in a euvolaemic adult presenting with mild-moderate dehydration
• Reassess: HR, BP, urine output, mucous membranes
• Target urine output ≥0.5 mL/kg/hr
• Maintain IV fluids while NBM (nil by mouth)
• In uncomplicated appendicitis without sepsis, aggressive fluid loading is not required - the goal is simply euvolemia, not resuscitation

"Euvolemia should be established with IV access and crystalloid administration" before proceeding to surgery.

• Fischer's Mastery of Surgery, p. 7839

II. ANTIBIOTICS

Context A: Going to Surgery (Perioperative Prophylaxis)

Recommended IV Antibiotic (Single Preoperative Dose):

• Ciprofloxacin 400 mg IV + metronidazole 500 mg IV
• Or clindamycin + gentamicin (less preferred; potential nephrotoxicity)

Duration: For confirmed uncomplicated (non-perforated) appendicitis, a single preoperative dose is sufficient. No prolonged postoperative antibiotics are needed.

• Fischer's Mastery of Surgery, p. 3412; Current Surgical Therapy 14e

Context B: Non-Operative Management (Antibiotics as Definitive Treatment)

Standard Two-Phase Regimen (APPAC Trial Protocol)

Ertapenem is a carbapenem with excellent gram-negative and anaerobic coverage, once-daily dosing, and good tolerability. Used in APPAC (n=530) with 72.7% success at 1 year.

• Ciprofloxacin 500 mg BD + Metronidazole 500 mg TDS for 7 days

Do NOT use:

• Ampicillin-sulbactam alone (high E. coli resistance)
• TMP-SMX alone (high local resistance to E. coli in many regions)
• Metronidazole alone (no gram-negative cover)

CODA Trial Regimen (USA, n=1,552)

• IV ertapenem for 24 hours (inpatient), then
• Oral ciprofloxacin + metronidazole to complete a 10-day total course
• Demonstrated antibiotics were non-inferior at 90 days; 40% required appendectomy at 1 year

Fully Oral Regimen (Outpatient-Only Protocol)

• Ciprofloxacin 500 mg BD + Metronidazole 500 mg TDS x 7 days (90% of patients in that series)
• 76% avoided appendectomy at 1 year
• Suitable only for clinically stable, reliable patients who can return immediately if symptoms worsen

III. SUMMARY TABLE

IV Phase (24-72 hours, inpatient)

Oral Step-Down Phase (7 days, outpatient)

IV Fluids

IV. CRITERIA TO STEP DOWN FROM IV TO ORAL (before discharge)

• Afebrile (<38°C) for >24 hours
• Pain controlled without IV analgesia
• Return of bowel function / tolerating oral intake
• WBC trending down (<12,000)
• Clinically improving (reduced RIF tenderness)

If the patient fails to meet these criteria within 48-72 hours, re-evaluate - consider CT reassessment and escalation to surgery.