When should a CT (Computed Tomography) chest be repeated after a pulmonary embolism (PE)?

When to Repeat CT Chest After Pulmonary Embolism

CT chest should not be routinely repeated after a pulmonary embolism diagnosis unless there are new or recurrent symptoms suspicious for PE, as there is no risk-free period after an initial negative CT, and clinical evaluation with validated tools should guide the decision for reimaging. 1, 2

Approach to Suspected Recurrent PE After Initial Diagnosis

Clinical Assessment First

• Use validated clinical prediction tools (Wells score or Geneva score) to assess pretest probability
• Evaluate for symptoms similar to initial presentation:
  • Dyspnea
  • Chest pain
  • Tachycardia
  • Tachypnea
  • Hypoxemia

D-dimer Testing

• For patients with low or intermediate clinical probability, obtain D-dimer testing first
• Use age-adjusted D-dimer thresholds (age × 10 ng/mL) for patients over 50 years 1
• If D-dimer is negative in low-risk patients, PE can be safely excluded without imaging 1

Alternative Imaging Strategies to Consider

For patients with history of multiple CT scans for PE, consider alternative approaches:

1. Lower-extremity venous ultrasonography:

   • Particularly useful in patients with lower extremity symptoms
   • Positive proximal DVT can establish need for anticoagulation without CT 1
   • Especially valuable in pregnant patients or those with contraindications to CT

2. V/Q scanning:

   • Consider in patients without contraindications (COPD, pneumonia, pulmonary edema)
   • Normal perfusion scan effectively excludes PE 1
   • Particularly useful for patients with renal failure or contrast allergies

Important Considerations

Radiation Exposure Concerns

• Clinicians should educate patients about radiation risks from multiple CTs 1
• Research shows 5% of patients evaluated for PE had 5 or more CTs within 5 years 1
• Develop institutional protocols for patients with history of multiple CTs

No "Risk-Free" Period

• Evidence shows there is no risk-free period after a negative CTPA 2
• Even within 2 weeks after a negative CTPA, there is a 5% positive rate on repeat scanning 2
• Patients with clinical suspicion should be rescanned even after a recent negative study

Risk Stratification for Repeat Imaging

• Patients with RV strain on both CT and echocardiography have higher risk of clinical deterioration 3
• Consider echocardiography as a complementary assessment in high-risk patients

Common Pitfalls to Avoid

1. Overreliance on previous negative CT results

   • Multiple prior negative CTPAs do not eliminate risk of subsequent PE 2
   • Clinical suspicion should always guide decision-making

2. Failure to use clinical prediction rules

   • Always use established clinical prediction scoring systems to determine need for repeat imaging 2

3. Ignoring alternative diagnostic approaches

   • For patients with multiple prior CTs, consider alternative diagnostic strategies like ultrasound or V/Q scan 1
   • Shared decision-making with patients regarding radiation exposure risks is essential

4. Missing clinically unsuspected PE

   • Incidental PE findings on routine chest CT should not be ignored, as they may require treatment 4
   • Review all chest CTs thoroughly, even when obtained for other indications

In summary, the decision to repeat CT chest after PE should be based on clinical assessment, D-dimer testing when appropriate, and consideration of alternative imaging strategies to minimize radiation exposure while ensuring appropriate diagnosis of recurrent PE.