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IMAGE INTERPRETATION · LUNG V/Q IMAGING

Brain and Kidney MAA Uptake: Right-to-Left Shunt

Lung perfusion scintigraphy — Tc-99m MAA scan
Lung perfusion scintigraphy — Tc-99m MAA scan

CC BY-SA 4.0 · Wikimedia Commons · source file

Question

During a V/Q scan, uptake of Tc-99m MAA is unexpectedly visualized in the brain and kidneys on the perfusion images. What does this finding indicate?

  1. ARight-to-left cardiac or pulmonary shunt — MAA particles are crossing from the right to the left side of the circulation
  2. BFree pertechnetate contamination of the MAA preparation
  3. CNormal thyroid and salivary gland activity from free pertechnetate
  4. DBilateral PE with systemic embolization
Show the answer and explanation

A. Right-to-left cardiac or pulmonary shunt — MAA particles are crossing from the right to the left side of the circulation

Tc-99m MAA particles are normally too large (10–100 μm) to pass through the pulmonary capillaries (5–10 μm), so they lodge in the lungs. If MAA activity is seen in the brain and kidneys on perfusion images, it means the particles bypassed the pulmonary capillary bed by crossing through an intracardiac shunt (patent foramen ovale, ASD, VSD) or a pulmonary arteriovenous malformation (AVM) — a right-to-left shunt. This incidental finding on a V/Q scan is diagnostically important and can prompt further evaluation with echocardiography. The degree of systemic activity can quantify the shunt fraction.

More lung v/q imaging images

Lung perfusion scintigraphy — MAA preparation and injectionTc-99m MAA Injection Technique V/Q lung scan — high probability for PEPIOPED II: High-Probability V/Q with High Pretest Probability V/Q lung scan — wedge-shaped peripheral perfusion defectWedge-Shaped Pleural-Based Defect: Pulmonary Embolism Normal lung perfusion scintigraphy — standard 8 projectionsLung Perfusion Projections: Why Lateral Views Matter Ventilation-perfusion (V/Q) lung scan — 58-year-old maleHigh-Probability V/Q Scan: Mismatched Defects Ventilation/perfusion (V/Q) lung scan — multiple projectionsMatched V/Q Defects: Low Probability for PE
← Intermediate-Probability V/Q ScanTc-99m MAA Injection Technique →

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