## Imaging Modalities in Obstructive Jaundice Workup **Key Point:** Endoscopic Ultrasound (EUS) has the **highest sensitivity** for detecting choledocholithiasis (>95–98%), including small stones (<5 mm) that may be missed by MRCP or CT. ### Sensitivity Comparison | Imaging Modality | Sensitivity for CBD Stones | Specificity | Advantages | Limitations | |---|---|---|---|---| | **Ultrasound** | 50–70% | Moderate–High | Non-invasive, no radiation, cheap, first-line | Operator-dependent, limited by bowel gas | | **MRCP** | 85–95% | >90% | Best non-invasive modality, excellent biliary tree visualization, no contrast | Contraindicated in metallic implants, misses very small stones | | **CT abdomen** | 65–90% | High | Fast, good for complications | Less sensitive than MRCP/EUS for small stones, radiation exposure | | **EUS** | >95–98% | >95% | **Highest sensitivity overall**, excellent for small stones, real-time imaging, therapeutic potential | Semi-invasive, operator-dependent, requires sedation, not universally available | **High-Yield:** EUS has consistently demonstrated the **highest sensitivity and specificity** for choledocholithiasis detection in meta-analyses, outperforming MRCP particularly for stones <5 mm. Multiple studies (including those cited in Bailey & Love's Short Practice of Surgery and Blumgart's Surgery of the Liver) confirm EUS sensitivity of 95–98% vs. MRCP sensitivity of 85–95%. **Clinical Pearl:** While MRCP is the preferred **non-invasive** first-line modality after ultrasound (due to its non-invasive nature and wide availability), EUS is the most sensitive modality **overall**. When the question asks for the "highest sensitivity," EUS is the correct answer. MRCP is preferred when therapeutic intervention is not immediately planned. ### Workup Algorithm ``` Suspected obstructive jaundice ↓ Ultrasound abdomen (first-line) ↓ CBD dilated / stones suspected? Yes → MRCP (non-invasive confirmation) ↓ Inconclusive or small stones suspected? → EUS (highest sensitivity, therapeutic option) ↓ Stone confirmed → ERCP ± sphincterotomy ``` **Mnemonic:** **EUS = Extremely Ultra-Sensitive** — for choledocholithiasis, EUS tops the sensitivity chart, especially for tiny stones that fool MRCP. **Reference:** Bailey & Love's Short Practice of Surgery (27th ed.); Blumgart's Surgery of the Liver, Biliary Tract and Pancreas (6th ed.) — EUS sensitivity for CBD stones: 95–98%; MRCP sensitivity: 85–95%. 
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