Is transabdominal ultrasound (US) the first-line imaging modality for acute cholangitis?

Transabdominal Ultrasound as First-Line Imaging for Acute Cholangitis

Yes, transabdominal ultrasound (US) is the recommended first-line imaging modality for acute cholangitis according to the most recent clinical practice guidelines. 1

Evidence Supporting Ultrasound as Initial Imaging

• The 2024 Infectious Diseases Society of America (IDSA) guidelines suggest abdominal ultrasound as the initial diagnostic imaging modality for nonpregnant adults with suspected acute cholangitis (conditional recommendation, very low certainty of evidence) 1
• Transabdominal ultrasound serves as the first imaging test in initial evaluation due to its wide availability, despite its relatively low sensitivity (25-63%) for common bile duct stone detection 1
• Ultrasound has high diagnostic accuracy in demonstrating biliary dilatation, which is a key imaging finding in the diagnosis of acute cholangitis 1
• The American College of Radiology recommends ultrasound as first-line imaging due to several practical advantages including shorter examination time, ability to evaluate gallbladder morphology, and no radiation exposure 2, 3

Diagnostic Approach for Acute Cholangitis

• The diagnosis of acute cholangitis should include:

  • Clinical signs: jaundice, fever, chills, and right upper quadrant abdominal pain
  • Laboratory findings: indicators of inflammation and biliary stasis
  • Imaging findings: biliary dilatation or evidence of an etiology (e.g., stricture, stone, obstructing mass) 1

• Key ultrasound findings to evaluate include:

  • Presence of biliary dilatation (normal bile duct diameter should be less than 8 mm) 1
  • Evidence of obstructing etiology (stones, strictures, masses) 2, 3
  • Assessment of gallbladder if cholecystitis is also suspected 2

Subsequent Imaging When Initial US is Inconclusive

• If initial ultrasound is equivocal or non-diagnostic and clinical suspicion persists, the IDSA guidelines suggest obtaining an abdominal CT scan with IV contrast as subsequent imaging (conditional recommendation, very low certainty of evidence) 1
• Other secondary imaging options include:
  • Magnetic resonance cholangiopancreatography (MRCP): has an accuracy of detecting CBD stones surpassing 90%, though with weakness in detecting small stones 1
  • Endoscopic ultrasound (EUS): minimally invasive procedure with high sensitivity (93%) and specificity (96%) for CBD stone detection 1

Special Populations

• For pregnant patients with suspected acute cholangitis, both ultrasound and MRI are appropriate initial imaging options, with no clear recommendation favoring one over the other (knowledge gap) 1
• For children, although evidence was not systematically reviewed due to the uncommon nature of acute cholangitis in this population, it would be reasonable to follow the same imaging pathway as for adults 1

Potential Pitfalls

• Operator experience significantly impacts the diagnostic accuracy of ultrasound for biliary pathology, with experienced examiners achieving much higher sensitivity (82% vs. 46%) 4
• Biliary dilatation may not always be present at the early stage of bile duct obstruction 5
• Ultrasound alone may miss small stones in the common bile duct 1, 5
• CT with IV contrast is preferable when used as subsequent imaging after inconclusive ultrasound 1