CTEPH & V/Q in Pulmonary Hypertension⁹⁹ᵐTc-MAA (Q) · ⁹⁹ᵐTc-Technegas / ¹³³Xe (V)

Quick Answer

Chronic thromboembolic pulmonary hypertension (CTEPH) is pulmonary hypertension caused by organized, unresolved thromboembolic material obstructing the pulmonary arteries (WHO Group 4 PH). It matters enormously because it is the one potentially curable form of pulmonary hypertension — by pulmonary endarterectomy (PEA) or balloon pulmonary angioplasty (BPA). The V/Q scan is the guideline-recommended screening test: a normal (or very-low-probability) V/Q effectively excludes CTEPH, and V/Q is more sensitive than CT pulmonary angiography for the chronic, organized disease.

Why V/Q, not CTPA, is the screen

In the workup of pulmonary hypertension, a normal V/Q scan effectively excludes CTEPH, and V/Q is more sensitive than CTPA for it — so V/Q is the recommended screening test whenever CTEPH is possible. This is the reverse of acute PE, where CTPA is usually first-line: chronic organized clot lines and recanalizes vessels, producing perfusion defects that CTPA can miss but that show as mismatched segmental defects on V/Q. Missing CTEPH matters because, unlike other PH, it is potentially surgically curable.

The pattern

CTEPH produces multiple bilateral segmental (or larger) mismatched perfusion defects — perfusion loss with preserved ventilation, like acute PE but chronic and often more extensive. A normal or near-normal perfusion scan makes CTEPH very unlikely and redirects the PH workup toward other groups (pulmonary arterial hypertension, left-heart disease, lung disease).

V/Q vs CTPA for CTEPH

The two are complementary: V/Q screens (high sensitivity, excludes disease), then CTPA / conventional pulmonary angiography and right-heart catheterization characterize and assess operability. A positive V/Q mandates referral to a CTEPH center.

Why the diagnosis is high-stakes

CTEPH is under-recognized — it can follow acute PE (a fraction of patients fail to fully resolve) or arise without a clear prior PE. Because PEA can be curative and BPA helps inoperable/residual disease, establishing the diagnosis changes the entire trajectory from chronic medical PH management to a potential surgical cure. This is the core reason any PH evaluation should include a V/Q scan rather than relying on CTPA alone.

High-Yield Pearls

• Normal V/Q excludes CTEPH; V/Q is more sensitive than CTPA for it — the recommended PH screen.
• CTEPH is the only potentially curable PH (pulmonary endarterectomy; BPA for inoperable/residual disease).
• Pattern: bilateral segmental mismatched perfusion defects (chronic, often extensive).

Common Pitfalls

• Relying on a negative CTPA to exclude CTEPH — it can miss distal organized disease.
• Reading matched defects from coexisting lung disease as CTEPH (correlate with CT/ventilation).
• Failing to refer a positive screen to a CTEPH/PEA center for operability assessment.

Related Pages

• Base study: V/Q scan & pulmonary embolism; perfusion agent: ⁹⁹ᵐTc-MAA.

Differential Diagnosis

• Acute PE — also produces mismatched segmental defects, but these should resolve on follow-up; CTEPH defects are chronic and persistent.
• Non-thromboembolic causes of mismatched defects that mimic CTEPH — pulmonary artery sarcoma, extrinsic vascular compression (mediastinal fibrosis, tumor, adenopathy), large-vessel vasculitis (Takayasu), congenital pulmonary-artery stenosis, and pulmonary veno-occlusive disease.
• Pulmonary arterial hypertension (Group 1) — perfusion is typically normal or patchy and non-segmental; a normal V/Q redirects the workup here.
• Matched defects from parenchymal/airway disease (COPD/emphysema, fibrosis, effusion, prior resection) — Group 3 PH, not CTEPH; correlate ventilation and CT.

Reporting Checklist

• State the ventilation agent and whether SPECT/SPECT-CT was performed (improves sensitivity and specificity over planar).
• Report defect number, size, distribution, and mismatched-vs-matched character (segmental vs non-segmental).
• Give a screening-level conclusion: a normal/near-normal perfusion scan effectively excludes CTEPH.
• Correlate with CT/ventilation to separate CTEPH mismatch from parenchymal matched defects.
• If mismatched segmental defects are present, recommend referral to a CTEPH/PEA center with CTPA/pulmonary angiography and right-heart catheterization for confirmation and operability.

Self-Check

Key References

• ESC/ERS pulmonary hypertension guidelines — V/Q scanning as the recommended screening test for CTEPH.
• Tunariu N, et al. Ventilation–perfusion scintigraphy is more sensitive than multidetector CTPA in detecting chronic thromboembolic pulmonary disease.