What are the recommended diagnostic approaches for suspected cholecystitis and pulmonary embolism?

Recommended Diagnostic Approaches for Suspected Cholecystitis and Pulmonary Embolism

Diagnostic Approach for Suspected Cholecystitis

Abdominal ultrasound (US) is the recommended initial imaging modality for suspected acute cholecystitis due to its cost-effectiveness, wide availability, lack of invasiveness, and absence of radiation exposure. 1

Initial Evaluation with Ultrasound

• Abdominal US has variable sensitivity (50-100%) and specificity (33-100%) for detecting acute cholecystitis, with summary sensitivity of 81% and specificity of 83% 1, 2
• Key findings to evaluate include:
  • Presence of gallstones (96% sensitivity for cholelithiasis) 2, 3
  • Gallbladder wall thickness (>3mm suggests inflammation) 2
  • Sonographic Murphy sign (pain when probe presses on gallbladder) 2
  • Pericholecystic fluid 2
  • Common bile duct diameter (normal <6mm, or <8-10mm in elderly) 2

Follow-up Imaging When Ultrasound is Inconclusive

• If clinical suspicion remains high but US is equivocal:
  • CT scan is suggested as the subsequent imaging modality for non-pregnant adults and children 1
  • CT can identify complications and rule out other etiologies 1
  • If CT is also equivocal and acute cholecystitis is still suspected, MRI/MRCP or HIDA scan are reasonable options 1
  • HIDA scan (cholescintigraphy) has the highest diagnostic accuracy with sensitivity of 96% and specificity of 90% 4

Special Considerations

• For pregnant patients with suspected acute cholecystitis, US or MRI should be used as the initial diagnostic imaging modality to avoid radiation exposure 1, 5
• Technical limitations of US such as bowel gas or body habitus should be documented as they may affect diagnostic accuracy 2

Diagnostic Approach for Suspected Pulmonary Embolism

A diagnostic algorithm combining clinical probability assessment, D-dimer testing, and appropriate imaging is recommended for suspected pulmonary embolism (PE). 1, 6

Initial Evaluation

• Assess clinical probability of PE using validated prediction rules 1, 6
• Perform chest radiography to exclude alternative diagnoses such as pneumonia, heart failure, pneumothorax, or tumor 1
• Measure D-dimer level using ELISA method 1
  • A normal D-dimer (<500 μg/L) by ELISA assay can safely exclude PE in patients with low clinical probability 1
  • D-dimer is most useful in emergency ward patients but less useful in elderly or hospitalized patients 1

Imaging Selection Based on Initial Evaluation

• If D-dimer is elevated or clinical suspicion remains high:
  • CT pulmonary angiography is currently the most widely used imaging modality 6
  • Ventilation/perfusion (V/Q) scanning is recommended as an alternative in:
    • Patients with contraindications to CT contrast 6
    • Young patients to reduce radiation exposure 6
    • Patients with a normal chest X-ray (higher proportion of diagnostic scans) 6

V/Q Scan Interpretation

• V/Q scans should be reported as normal, high probability, or non-diagnostic/indeterminate 6
• A normal V/Q scan effectively rules out PE 1, 6
• A high probability V/Q scan confirms PE 1, 6
• Non-diagnostic scans require further evaluation 6

Additional Testing

• Lower limb venous compression ultrasonography (US) can be useful:
  • US shows a proximal deep vein thrombosis (DVT) in 50% of patients with proven PE 1
  • Finding a DVT in a patient with suspected PE is sufficient to initiate anticoagulation 1
  • A normal US exam of the leg veins does not rule out PE 1

Common Pitfalls to Avoid

• Relying solely on clinical assessment without objective testing 1
• Using traditional latex and whole agglutination D-dimer tests, which have low sensitivity for PE 1
• Interpreting V/Q scans without considering clinical probability 1
• V/Q scan interpretation may be difficult in patients with previous PE, heart failure, COPD, lung fibrosis, or lung cancer 6

By following these evidence-based diagnostic approaches, clinicians can effectively evaluate patients with suspected cholecystitis and pulmonary embolism while minimizing unnecessary testing and optimizing patient outcomes.