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IMAGE INTERPRETATION · LUNG V/Q IMAGING

Matched V/Q Defects: Low Probability for PE

Ventilation/perfusion (V/Q) lung scan — multiple projections
Ventilation/perfusion (V/Q) lung scan — multiple projections

CC BY 3.0 · Myohan / Wikimedia Commons · source file

Question

On a V/Q lung scan, both the ventilation and perfusion images show defects in the SAME region (a 'matched' defect). By PIOPED II criteria, a matched ventilation-perfusion defect in the setting of a normal or near-normal chest X-ray is most consistent with:

  1. AHigh probability for pulmonary embolism
  2. BLow probability for pulmonary embolism
  3. CCertain diagnosis of pulmonary embolism
  4. DNormal study
Show the answer and explanation

B. Low probability for pulmonary embolism

A matched V/Q defect — where both ventilation and perfusion are reduced in the same lung region — is characteristic of parenchymal lung disease (COPD, pneumonia, mucus plug), not PE. PE causes perfusion loss without ventilation loss (mismatch). According to PIOPED II criteria, matched defects with a normal or near-normal CXR are LOW probability for PE. Low probability does not mean zero risk — clinical probability must be integrated.

More lung v/q imaging images

Lung perfusion scintigraphy — normal study (standard projections)Normal Lung Perfusion Scan and Pulmonary Embolism Lung perfusion scintigraphy — multiple viewsHow Tc-99m MAA Lung Perfusion Imaging Works V/Q lung scan showing ventilation-perfusion mismatchReducing MAA Particles in Pulmonary Hypertension Lung perfusion scintigraphy — multiple projectionsStripe Sign on a Lung Perfusion Scan V/Q lung scan — matched ventilation and perfusion defectsV/Q Scan in COPD: Matched Defects Lung perfusion scintigraphy — normal study in a young female patientV/Q Scan vs CTPA for Pulmonary Embolism in Pregnancy
← High-Probability V/Q Scan: Mismatched DefectsNormal Lung Perfusion Scan and Pulmonary Embolism →

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