A 28-year-old woman presents with 18 hours of periumbilical pain that has migrated to the right lower quadrant, accompanied by anorexia and low-grade fever (38.2°C). On examination, she has rebound tenderness at McBurney's point and a positive Rovsing's sign. Her WBC is 12,500/μL with left shift. What is the investigation of choice to confirm the diagnosis?

## Investigation of Choice for Acute Appendicitis **Key Point:** Contrast-enhanced CT (CECT) abdomen and pelvis is the gold standard imaging modality for diagnosis of acute appendicitis in most clinical settings, with sensitivity and specificity both >95%. ### Why CT is Superior **High-Yield:** CT provides: - Direct visualization of the appendix (diameter >6 mm is abnormal) - Assessment of appendiceal wall enhancement and periappendiceal fat stranding - Detection of complications (perforation, abscess, peritonitis) - Evaluation of differential diagnoses (ovarian pathology, diverticulitis, mesenteric adenitis) - Ability to identify alternative diagnoses in atypical presentations ### Comparison of Imaging Modalities | Investigation | Sensitivity | Specificity | Advantages | Limitations | |---|---|---|---|---| | **CECT** | 94–98% | 95–98% | Gold standard; detects complications; rules out DDx | Radiation exposure; cost | | **Ultrasound** | 86–88% | 95–98% | No radiation; first-line in pregnancy/pediatrics | Operator-dependent; limited by bowel gas; cannot assess complications well | | **MRI** | 90–95% | 97–99% | Excellent for pregnant patients; no radiation | Time-consuming; cost; not readily available | | **Plain X-ray** | 5–15% | Variable | Rapid; no radiation | Non-specific; cannot visualize appendix directly | **Clinical Pearl:** In this case, the clinical diagnosis is highly likely (Alvarado score ~8/10: fever, RLQ tenderness, rebound, migration of pain, anorexia, elevated WBC with left shift). CECT is ordered to confirm diagnosis and assess for complications before surgery. **Mnemonic for CT findings in appendicitis — "WAFT":** - **W**all thickening (>2 mm) - **A**ppendix diameter (>6 mm) - **F**at stranding (periappendiceal) - **T**arget sign (cross-sectional appearance) ### When to Use Alternatives - **Ultrasound:** First-line in pregnant women, pediatric patients, and settings where CT unavailable - **MRI:** Reserved for pregnant patients (especially 2nd/3rd trimester) or when CT contraindicated - **Plain X-ray:** Only to rule out perforation (free air) in equivocal cases; not diagnostic for appendicitis **Warning:** Do not delay surgery waiting for imaging if clinical diagnosis is clear and patient is unstable or peritonitic — imaging is confirmatory, not mandatory before appendectomy in high-probability cases.