Ventilation perfusion scan (pulmonary scintigraphy)
The ventilation/perfusion lung scan should be performed in patients with PH to look for potentially treatable CTEPH. The ventilation/perfusion scan remains the screening method of choice for CTEPH because of its higher sensitivity than CT .
A normal- or low-probability ventilation/ perfusion scan effectively excludes CTEPH with a sensitivity of 90–100% and a specificity of 94–100%. While in PAH the ventilation/ perfusion lung scan may be normal, it may also show small peripheral unmatched and nonsegmental defects in perfusion. Contrast-enhanced CT may be used as a complementary investigation but does not replace the ventilation/perfusion scan or traditional pulmonary angiogram. A caveat is that unmatched perfusion defects are also seen in PVOD.
The V/Q scan in CTEPH typically shows multiple segmental or larger perfusion defects in areas of normal ventilation. Since there is often only partial vascular obstruction in CTEPH, there may be grey zones, and the lung perfusion scan can underestimate the degree of vascular obstruction. On the other hand, a normal or low probability V/Q scan virtually excludes surgical accessible CTEPH.