Appendicitis

Epidemiology

Pathophysiology

1. Luminal distension and mucosal ischemia
2. Bacterial overgrowth and invasion
3. Edema, vasocongestion, inflammation
4. Infarction and necrosis
5. Perforation

Clinical Features

Classic Presentation

• Abdominal pain - begins as vague, crampy, periumbilical pain, then migrates to the right lower quadrant (RLQ) over 24 hours as parietal peritoneum becomes involved
• Anorexia (almost universal)
• Nausea and vomiting (typically follow pain onset)
• Low-grade fever (usually later in the course)

Physical Examination

Laboratory Studies

• WBC: Leukocytosis (>10,000/µL) present in ~90% of cases; normal WBC in 10% - does not exclude appendicitis
• CRP / Procalcitonin: CRP is the most sensitive biomarker but lacks specificity
• Urinalysis: Mild sterile pyuria (<5-10 WBC/hpf) occurs due to proximity to the ureter - does not indicate UTI
• Pregnancy test: Mandatory in all females of childbearing age to exclude ectopic pregnancy

Clinical Scoring Systems

• Score ≤3: Low probability; consider discharge with return precautions
• Score 4-6: Moderate probability; imaging recommended
• Score ≥7: High probability; surgical consultation

Imaging

Ultrasound (US)

• First-line in children and pregnant women (no ionizing radiation)
• Graded compression technique: sensitivity 74-94%, specificity 85-93%
• US findings of appendicitis: non-compressible tubular structure >6mm in diameter, increased periappendiceal echogenicity (fat stranding), appendicolith (echogenic focus with shadowing)
• Key limitation: the appendix is frequently not visualized (non-diagnostic study) due to body habitus, bowel gas, or atypical position

CT Abdomen/Pelvis (with or without contrast)

• Preferred modality in adults - sensitivity/specificity ≥94%
• Findings: dilated appendix (>6mm), appendiceal wall thickening, periappendiceal fat stranding, appendicolith, pericecal fluid
• Low-dose CT (2 mSv) is comparable in accuracy to standard-dose CT
• Reduces negative appendectomy rate from ~12% to ~6%

CT abdomen: axial and coronal views showing a thickened inflamed appendix (arrow) - classic "target sign." - Sabiston Textbook of Surgery

MRI

• Accuracy comparable to CT, but more expensive and time-consuming
• Preferred in pregnancy when US is non-diagnostic (avoids radiation)

Differential Diagnosis

Treatment

Uncomplicated Appendicitis

• Laparoscopic: fewer wound infections (50% lower), shorter hospital stay (~1.1 days), less postoperative pain, faster return to activity
• Open appendectomy: preferred when there is evidence of perforation or when laparoscopy is not feasible

• Cefotetan 2 g IV, OR
• Cefoxitin 2 g IV (followed by 3 postoperative doses), OR
• Ticarcillin-clavulanic acid

• IV antibiotics can resolve symptoms in the majority of patients in the short term
• However, a meta-analysis of 5 RCTs found a 40% treatment failure rate, mostly due to recurrent appendicitis
• Cannot currently identify "self-limiting" cases prospectively
• Waiting risks perforation, which increases mortality from 0.0002% to 3% and morbidity from 3% to 47%
• Current practice in the USA: surgery remains the initial treatment of choice

Complicated Appendicitis (Perforated / Abscess / Phlegmon)

CT findings of complicated appendicitis with periappendiceal abscess (arrows). - Sabiston Textbook of Surgery

• Early perforation: appendectomy is still the treatment
• Well-formed abscess/phlegmon (symptoms >5 days): percutaneous drain placement (IR-guided) + IV antibiotics, followed by interval appendectomy in 6-8 weeks
• Broad-spectrum antibiotics required; duration based on clinical response

Special Populations

Pediatric

• Laparoscopic appendectomy is the standard of care
• Ultrasound and MRI are preferred over CT to avoid long-term radiation risks
• Nonoperative management with antibiotics is viable in uncomplicated cases (80-90% symptom resolution in 24-48h), but recurrence rates may reach 40% at medium-term follow-up
• Most pediatric surgeons still prefer operative management within 12-24h of diagnosis - Current Surgical Therapy, 14e
• A 2026 JAMA Pediatrics meta-analysis re-evaluated nonoperative management for pediatric uncomplicated appendicitis

Pregnancy

• Appendicitis is the most common surgical emergency in pregnancy (incidence same as non-pregnant)
• Delays in diagnosis contribute to increased perforation rates and fetal mortality
• The appendix is displaced in less than 25% of pregnant patients even in the 3rd trimester - atypical pain location is possible
• Physiologic leukocytosis in pregnancy can confuse the picture
• Imaging: US first; if non-diagnostic, MRI is the preferred follow-up (not CT)

Complications

Key Pearls

• A normal WBC does not exclude appendicitis (10% of confirmed cases have normal WBC)
• Right lower quadrant pain is the single best predictor (LR+ 7.3-8.5 in adults)
• Use the AIR or AAS score rather than Alvarado for modern risk stratification
• In women of childbearing age, always order a pregnancy test and consider pelvic pathology
• Appendicitis is a surgical urgency, not an emergency - brief preoperative optimization is appropriate; prolonged delay increases perforation risk
• The negative appendectomy rate with imaging is ~3.7% in children and ~6% in adults (vs. 12-13.5% without imaging)