A 32-year-old woman presents with acute onset severe right upper quadrant pain and vomiting for 6 hours. She has a history of multiple episodes of similar pain over the past 2 years. On examination, she is febrile (38.2°C), tachycardic, and has positive Murphy's sign. Serum bilirubin is 1.8 mg/dL, ALT 120 IU/L, and WBC 14,500/μL. What is the imaging modality of choice to confirm the diagnosis?

Explanation

## Clinical Scenario Analysis This patient presents with classic acute cholecystitis: fever, right upper quadrant pain, Murphy's sign, elevated inflammatory markers, and a history of biliary colic. The diagnosis requires imaging confirmation. ## Investigation of Choice: Ultrasonography **Key Point:** Real-time ultrasonography is the **first-line imaging modality** for suspected acute cholecystitis and cholelithiasis. It is the gold standard for initial assessment. ### Why Ultrasound is Optimal | Feature | Advantage | |---------|----------| | **Sensitivity for stones** | 95–99% for gallstones ≥2 mm | | **Sensitivity for cholecystitis** | 88–95% when combined with clinical signs | | **Real-time assessment** | Direct visualization of Murphy's sign under probe | | **Cost & accessibility** | Inexpensive, widely available, no contrast needed | | **Radiation** | None (no ionizing radiation) | | **Time** | Rapid (15–20 minutes) | **High-Yield:** Sonographic Murphy's sign (maximal tenderness over the gallbladder fossa during inspiration) has 80–90% specificity for acute cholecystitis when stones are present. ### Ultrasound Findings in Acute Cholecystitis 1. Gallstones (echogenic foci with posterior acoustic shadow) 2. Gallbladder wall thickening (>3 mm) 3. Pericholecystic fluid 4. Sonographic Murphy's sign 5. Dilated common bile duct (if obstruction) **Clinical Pearl:** In acute cholecystitis, the gallbladder is often distended and tender. Ultrasound can be performed at the bedside and allows dynamic assessment during the examination. ## Why Other Modalities Are Secondary **Contrast-enhanced CT:** Useful for complications (perforation, abscess, pancreatitis) or when ultrasound is inconclusive, but not first-line due to radiation exposure and cost. **HIDA scan:** Indicated for suspected acute acalculous cholecystitis or cystic duct obstruction when ultrasound is equivocal; has lower sensitivity for stones and is time-consuming. **MRCP:** Reserved for suspected choledocholithiasis or biliary obstruction; not needed for uncomplicated acute cholecystitis. **Mnemonic:** **USOUND FIRST** — Ultrasound is the Screening Observation Useful for Noting Ductal and gallbladder Findings In Routine Testing. [cite:Harrison 21e Ch 308]