Should we proceed with CT pulmonary angiography (CTPA) in a 16-year-old suspected of pulmonary hypertension where the initial CT thorax did not show arterial thrombosis?

Should You Proceed with CTPA in This Case?

No, you should not proceed with CTPA if the initial contrast-enhanced CT thorax adequately visualized the pulmonary arteries and excluded thrombosis, but you should instead obtain a V/Q scan to evaluate for chronic thromboembolic pulmonary hypertension (CTEPH), which is the critical next step in the diagnostic workup for suspected pulmonary hypertension. 1, 2

Understanding the Diagnostic Algorithm for Pulmonary Hypertension

Why V/Q Scan is the Preferred Next Step

• V/Q scanning is the examination of choice for evaluating CTEPH and differentiating it from other causes of pulmonary hypertension, with sensitivity of 90-100% and specificity of 94-100% 1
• The American College of Cardiology and European Society of Cardiology both recommend V/Q scanning in all patients with unexplained pulmonary hypertension, primarily to assess for CTEPH 1, 2
• A normal or low-probability V/Q scan essentially excludes the diagnosis of CTEPH with sensitivity of 90-100% and specificity of 94-100% 1

The Role of CT vs CTPA in Your Case

• If your initial "CECT thorax" was performed with adequate contrast timing and included evaluation of the pulmonary arteries (essentially functioning as a CTPA), then repeating it would provide minimal additional value 1
• CTA chest with IV contrast is rated as "usually appropriate" (rating 8) for suspected pulmonary hypertension, but it is considered equivalent to CT chest with IV contrast when properly timed 1
• Modern multidetector CTPA demonstrates sensitivities of 99-100% and specificities of 100% for detecting chronic thromboembolic disease, but V/Q scanning remains more sensitive than CTPA in detecting chronic thromboembolic pulmonary disease amenable to surgery 1, 3

Critical Distinction: Acute vs Chronic Thromboembolic Disease

This is a crucial pitfall to avoid: Your question states the artery "didn't show anything thrombosis," but you need to distinguish between:

• Acute thrombosis (which CTPA excels at detecting) 1
• Chronic thromboembolic disease (which V/Q scan is superior for detecting) 1

The absence of acute thrombosis on CT does not exclude CTEPH, which presents with different findings including:

• Eccentric thrombus within pulmonary arteries
• Recanalized thrombus with or without calcification
• Abrupt cutoff and narrowing of affected pulmonary arteries
• Thin linear webs within affected arteries
• Mosaic attenuation of lung parenchyma 1

Recommended Diagnostic Pathway for This 16-Year-Old

Immediate Next Steps

1. Obtain V/Q scan (or perfusion scan) as the priority imaging study 1, 2
2. Ensure echocardiography has been performed to assess right ventricular function and estimate pulmonary artery pressures 1, 2
3. Complete basic workup including chest X-ray, ECG, and pulmonary function tests with DLCO 2

Interpretation of V/Q Results

• If V/Q shows multiple segmental perfusion defects: Suspect CTEPH and proceed with right heart catheterization and selective pulmonary angiography 2
• If V/Q is normal or shows only small peripheral non-segmental defects: Consider other causes of pulmonary hypertension (idiopathic PAH, connective tissue disease-associated PAH, etc.) 1
• If V/Q is abnormal, then CTPA or formal pulmonary angiography may be indicated for surgical planning 2

When CTPA Would Be Appropriate

CTPA would be indicated in this patient if:

• The V/Q scan shows abnormalities suggesting CTEPH, requiring detailed anatomic mapping for potential surgical intervention 1, 2
• There is clinical suspicion of acute pulmonary embolism superimposed on chronic disease 4
• Detailed assessment of parenchymal lung disease is needed that wasn't adequately evaluated on the initial CT 1

Important Considerations for Pediatric Patients

• Radiation exposure is a significant concern in a 16-year-old patient 1
• V/Q scan has lower radiation exposure (☢☢☢) compared to CTPA (☢☢☢), though both are in the same category 1
• The cumulative radiation from multiple CT studies should be avoided when V/Q scan can provide the necessary diagnostic information 1

Additional Workup Considerations

Beyond imaging, ensure comprehensive evaluation includes:

• Screening for connective tissue disease (particularly scleroderma spectrum) 1, 2
• Evaluation for congenital heart disease with potential shunts 1, 2
• Assessment for hereditary hemorrhagic telangiectasia if family history suggests it 1
• Genetic testing for BMPR2, ACVRL1, and ENG mutations if heritable PAH is suspected 1, 2

The definitive diagnosis of pulmonary hypertension requires right heart catheterization, which should be performed at a pulmonary hypertension expert center once non-invasive testing suggests the diagnosis 1, 2