Should an abdominal ultrasound be performed in patients with acute abdominal symptoms?

Abdominal Ultrasound in Acute Abdominal Pain

The decision to perform abdominal ultrasound depends critically on the specific clinical presentation and suspected diagnosis—ultrasound is the preferred initial imaging for right upper quadrant pain (suspected cholecystitis), children with suspected appendicitis or intra-abdominal abscess, and pregnant patients, while CT with IV contrast is preferred for most other acute abdominal presentations in non-pregnant adults. 1

Clinical Presentation-Based Imaging Algorithm

Right Upper Quadrant Pain (Suspected Cholecystitis/Cholangitis)

• Abdominal ultrasound is the initial diagnostic imaging modality of choice for non-pregnant adults with suspected acute cholecystitis or cholangitis 1
• Ultrasound achieves high diagnostic accuracy without radiation exposure and is readily available 1
• If ultrasound results are equivocal or non-diagnostic, proceed to CT with contrast, MRI/MRCP, or HIDA scan for subsequent imaging 1

Right Lower Quadrant Pain (Suspected Appendicitis)

Non-pregnant adults:

• CT abdomen/pelvis with IV contrast is the preferred initial imaging, with sensitivity 96-100% and specificity 93-95% 2, 3
• Ultrasound is NOT recommended as first-line in adults due to lower sensitivity (76%) and operator-dependence 2
• IV contrast increases CT sensitivity to 96% compared to unenhanced CT; oral contrast is unnecessary and delays diagnosis 2

Children and adolescents:

• Ultrasound is the recommended initial imaging modality to avoid radiation exposure, with sensitivity 76% and specificity 95% 2, 1
• Point-of-care ultrasound by emergency physicians shows higher accuracy (sensitivity 91%, specificity 97%) 2
• If ultrasound is negative/equivocal but clinical suspicion persists, proceed to CT or MRI 1, 2

Pregnant patients:

• Ultrasound is the initial imaging modality of choice 2
• If ultrasound is inconclusive, MRI without IV contrast is preferred over CT 2

Left Lower Quadrant Pain (Suspected Diverticulitis)

• CT abdomen/pelvis with IV contrast is the initial imaging modality for non-pregnant adults with suspected acute diverticulitis 1
• Ultrasound or MRI may be considered only if CT is unavailable or contraindicated 1
• In pregnant adults, ultrasound or MRI can be considered, though evidence is insufficient to recommend one over the other 1

Suspected Intra-Abdominal Abscess

Adults:

• CT with contrast is generally preferred for initial imaging 1

Children:

• Ultrasound or CT are both acceptable as initial imaging, though ultrasound is preferred when feasible to avoid radiation 1
• Ultrasound is operator-dependent and may yield equivocal results; MRI is reasonable but not always readily available and may require sedation 1
• If initial ultrasound is negative/equivocal but clinical suspicion persists, proceed to CT or MRI 1

Pregnant patients:

• Ultrasound or MRI can be considered as initial imaging, though no clear recommendation exists for one over the other 1

General Principles for Resource-Limited Settings

• A step-up diagnostic approach is recommended: begin with clinical and laboratory examination, then proceed to imaging as needed and available 1
• In settings where CT is unavailable, plain X-ray and ultrasound can help identify surgical emergencies cost-effectively 1
• Ultrasound is increasingly available, portable, and less expensive, though highly user-dependent 1

Key Diagnostic Considerations

When Ultrasound is Appropriate First-Line:

• Right upper quadrant pain (cholecystitis/cholangitis) in any patient 1
• Pediatric patients with suspected appendicitis or intra-abdominal abscess 1, 2
• Pregnant patients with any acute abdominal presentation 1, 2
• Resource-limited settings where CT is unavailable 1

When CT is Preferred Over Ultrasound:

• Non-pregnant adults with suspected appendicitis 2, 3
• Suspected diverticulitis in non-pregnant adults 1
• Generalized or non-localized acute abdominal pain in adults 1, 3, 4
• Left upper quadrant pain 1
• When ultrasound is negative/equivocal but clinical suspicion remains high 1, 5

Critical Pitfalls to Avoid

Operator dependence: Ultrasound accuracy is highly operator-dependent and may yield equivocal results in 25-50% of cases for certain conditions like pancreatitis 1, 2

Missed perforated appendicitis: Both ultrasound and MRI may incorrectly classify up to half of perforated appendicitis cases as simple appendicitis 2

Radiation concerns in children: While radiation exposure is a valid concern, it should be balanced against the need for accurate diagnosis—CT remains appropriate when ultrasound is non-diagnostic and clinical suspicion is high 1, 2

Delayed diagnosis: Avoid ordering oral contrast with CT as it delays diagnosis without improving accuracy; IV contrast alone is sufficient 2

Clinical assessment limitations: Clinical evaluation alone has insufficient diagnostic accuracy to identify the correct diagnosis, though it can discriminate between urgent and non-urgent causes 5