What is the next step for a patient with a questionable filling defect vs artifact within the proximal right upper lobe segment pulmonary artery on a Computed Tomography (CT) chest with contrast?

Management of Questionable Filling Defect in Proximal Right Upper Lobe Pulmonary Artery

For a questionable filling defect versus artifact in the proximal right upper lobe segment pulmonary artery on CT chest with contrast, further imaging with a repeat dedicated CT pulmonary angiogram (CTPA) should be performed to definitively characterize the finding.

Diagnostic Algorithm for Questionable Pulmonary Artery Filling Defects

Step 1: Evaluate Clinical Probability of Pulmonary Embolism (PE)

• Assess clinical probability using validated prediction rules (Wells score or Geneva score)
• Consider patient's risk factors for thromboembolism
• Evaluate symptoms (dyspnea, chest pain, hemoptysis)

Step 2: Imaging Approach Based on Initial CT Finding

1. Repeat Dedicated CTPA

   • When standard CT with contrast shows questionable filling defect, a dedicated CTPA is the first-line follow-up test 1
   • CTPA is highly sensitive and specific for PE detection (sensitivity >90%, specificity >95%)
   • Optimized contrast timing and acquisition parameters improve visualization of pulmonary vasculature

2. Alternative Imaging Options (if CTPA contraindicated):

   • V/Q Scan: Consider if patient has renal insufficiency or contrast allergy
   • Lower Extremity Compression Ultrasound: May help identify DVT as source of potential PE
   • Pulmonary Angiography: Rarely needed, reserved for cases where non-invasive tests remain indeterminate 1

Step 3: Interpretation of CTPA Results

• Definite PE: Filling defect in segmental or more proximal pulmonary artery confirms PE diagnosis 1
• No PE: Normal CTPA in a patient with low/intermediate clinical probability excludes PE 1
• Persistent Uncertainty: Consider additional imaging tests if subsegmental filling defects remain questionable 1

Important Considerations

Differential Diagnosis for Pulmonary Artery Filling Defects

• True pulmonary embolism
• Technical artifacts (motion, beam hardening, partial volume averaging)
• Pulmonary artery stump thrombosis (in patients with prior lobectomy) 2
• Pulmonary artery sarcoma or other intrinsic vascular tumors 3, 4
• Pulmonary artery dissection 5

Common Pitfalls to Avoid

1. Misinterpreting artifacts as PE

   • Respiratory motion artifacts can mimic filling defects
   • Suboptimal contrast timing may lead to false positives

2. Overlooking alternative diagnoses

   • Non-thrombotic causes of filling defects may require different management
   • Malignant processes may mimic PE but require oncologic rather than anticoagulant therapy 3

3. Premature anticoagulation

   • Initiating anticoagulation before confirming diagnosis can lead to unnecessary bleeding risk
   • Some conditions mimicking PE (like pulmonary artery dissection) may worsen with anticoagulation 5

Clinical Pearls

• Questionable filling defects in proximal pulmonary arteries warrant further investigation due to high mortality risk if PE is missed
• Dedicated CTPA protocols with optimized contrast timing significantly improve diagnostic accuracy
• Unsuspected PE can be detected on routine contrast-enhanced CT scans, highlighting the importance of careful evaluation of the pulmonary vasculature on all chest CTs 6
• For persistent diagnostic uncertainty after CTPA, consider multidisciplinary discussion with radiology and pulmonology

By following this systematic approach, the true nature of the questionable filling defect can be determined, allowing for appropriate management decisions that will optimize patient outcomes in terms of morbidity and mortality.