If a Computed Tomography Angiography (CTA) chest shows a possible nonocclusive thrombus versus a mixed artifact, should I order further tests to confirm?

From the Guidelines

You should order further tests to confirm a possible nonocclusive thrombus versus a mixed artifact on a CTA chest, as the clinical implications of missing a true thrombus are significant and can impact morbidity, mortality, and quality of life. The most appropriate next step would be a dedicated pulmonary angiogram or a ventilation-perfusion (V/Q) scan to definitively characterize the finding, as suggested by the high sensitivity and specificity of CTA in diagnosing acute aortic dissection and other conditions 1. If clinical suspicion for pulmonary embolism remains high, you might consider starting therapeutic anticoagulation with low molecular weight heparin (such as enoxaparin 1mg/kg twice daily) or direct oral anticoagulants (like apixaban 10mg twice daily for 7 days followed by 5mg twice daily) while awaiting confirmatory testing.

Some key points to consider in this decision include:

• The accuracy of CTA in diagnosing conditions such as acute aortic dissection, with sensitivities of 90% to 100% and specificities ranging from 87% to 100% 1
• The importance of clinical context, including the patient's symptoms, risk factors for thromboembolism, and vital signs, in guiding the urgency of additional testing and whether to initiate empiric treatment while awaiting results
• The potential for artifacts on CTA, particularly in areas with cardiac motion or beam hardening, which can lead to false positives or negatives
• The use of other diagnostic tests, such as D-dimer testing and ultrasound of the lower extremities, to help confirm or rule out deep vein thrombosis as a source of the possible thrombus

Given the most recent evidence from 2023, CTA is an effective method for diagnosis of pulmonary embolism in patients presenting with symptoms suspicious for pulmonary embolism 1. Therefore, a dedicated pulmonary angiogram or a ventilation-perfusion (V/Q) scan is the most appropriate next step to confirm the diagnosis, and empiric treatment should be considered based on clinical suspicion and risk factors.

From the Research

Diagnostic Approach for Possible Nonocclusive Thrombus vs Mixed Artifact

If a Computed Tomography Angiography (CTA) chest shows a possible nonocclusive thrombus versus a mixed artifact, the next steps in diagnosis can be guided by understanding the strengths and limitations of CTA in detecting pulmonary embolism (PE) and the role of other diagnostic tools like ventilation-perfusion (V/Q) scanning.

Comparison of CTA and V/Q Scanning

• CTA is considered the most sensitive test for diagnosing pulmonary embolism 2, 3.
• V/Q scanning is another diagnostic tool, with its use and preference varying based on patient factors and institutional practices 4.
• Studies have compared the sensitivity and specificity of CTA and V/Q scanning in detecting PE, with CTA showing higher sensitivity for central PE and equivalent or higher specificity compared to high-probability V/Q scans 5.

Considerations for Further Testing

• Given the high sensitivity of CTA for pulmonary embolism, a negative multidetector CTPA study result can essentially rule out the diagnosis of pulmonary embolism without the need for further testing like deep vein thrombosis exclusion 2.
• However, if the CTA result is inconclusive, such as in the case of a possible nonocclusive thrombus vs mixed artifact, further evaluation may be necessary.
• V/Q scanning could be considered as an alternative or additional diagnostic tool, especially in patients where CTA is not feasible or in cases where the suspicion of PE remains high despite a negative or inconclusive CTA 3, 4.
• The choice between CTA and V/Q scanning may also depend on patient factors such as renal function, given the contrast requirements for CTA, and the availability of V/Q scanning facilities 4.

Specific Diagnostic Scenarios

• For chronic thromboembolic pulmonary hypertension (CTEPH), both V/Q scanning and CTPA have been shown to be accurate methods for detection, with high sensitivity and specificity 6.
• The diagnostic approach should be tailored to the individual patient's presentation, risk factors, and the specific clinical scenario, considering the strengths and limitations of each diagnostic modality.

Decision for Further Testing

• If the initial CTA chest shows a possible nonocclusive thrombus vs mixed artifact, the decision to order further tests should be based on clinical judgment, considering the pre-test probability of PE, patient risk factors, and the potential risks and benefits of additional testing.
• Consultation with a specialist or further review of imaging by a radiologist may also be helpful in determining the next steps in management.