In a patient with right upper quadrant pain, should the initial imaging be a focused abdominal ultrasound rather than a contrast‑enhanced CT scan?

Initial Imaging for Right Upper Quadrant Pain

Ultrasound should be the initial imaging modality for patients presenting with right upper quadrant pain, not CT scan. 1

Primary Recommendation

The American College of Radiology rates abdominal ultrasound as 9/9 (usually appropriate) for right upper quadrant pain evaluation, making it the clear first-line imaging choice. 1, 2 This recommendation is based on multiple advantages that make ultrasound superior to CT as the initial test:

• No ionizing radiation exposure, which is particularly important for young patients and those requiring repeat imaging 1, 3
• Rapid availability and shorter examination time compared to CT 4
• 96% accuracy for detecting gallstones, the most common cause of RUQ pain 3
• Ability to identify alternative diagnoses including hepatic abnormalities, bile duct dilatation, and other organ pathology 1, 5
• Real-time assessment with sonographic Murphy's sign, adding functional information to anatomic findings 2

When to Escalate to CT

CT with IV contrast (rated 6/9 - may be appropriate) should be reserved for specific scenarios 1:

• Ultrasound findings are nondiagnostic or equivocal 1
• Patient presentation is atypical for standard biliary disease 1
• Patient is critically ill requiring comprehensive evaluation 1
• Complications are suspected, such as perforation, abscess, or gangrenous cholecystitis 2
• Alternative diagnoses need evaluation after negative or inconclusive ultrasound 3

Comparative Performance Data

While one retrospective study of 2,859 emergency department encounters found CT and ultrasound had similar sensitivity (55% vs 61%) and specificity (92% vs 91%) for cholecystitis 6, this does not override guideline recommendations because:

• CT detected acute nongallbladder abnormalities missed by ultrasound in 32% of cases 6, but this advantage only matters when ultrasound is truly negative or equivocal
• Ultrasound remains the appropriate first test due to radiation concerns, cost-effectiveness, and ability to guide immediate clinical decisions 1, 4
• The guideline approach of ultrasound-first with selective CT escalation balances diagnostic accuracy with patient safety 1

Critical Pitfalls to Avoid

• Never order CT without IV contrast for suspected cholecystitis - critical findings like gallbladder wall enhancement and adjacent liver parenchymal hyperemia cannot be detected without contrast 2
• Do not assume negative CT excludes gallstones - CT has only 75% sensitivity for cholelithiasis, while ultrasound approaches 96% 2, 3
• Do not skip ultrasound and proceed directly to CT unless the patient is hemodynamically unstable 2
• Recognize that critically ill patients commonly have gallbladder abnormalities on ultrasound without true acute cholecystitis (acalculous cholecystitis) 2

Alternative Second-Line Options

If ultrasound is equivocal and clinical suspicion remains high 1:

• Cholescintigraphy (HIDA scan) has 96% sensitivity and 90% specificity for acute cholecystitis, superior to ultrasound's 81% and 83% 1
• MRI with MRCP provides 85-100% sensitivity for biliary pathology and is preferred in pregnant patients 2, 3