Matched ventilation-perfusion defect from a pleural effusion: Prone positioning reveals normal perfusion

Pleural effusions in patients suspected of pulmonary thromboembolism can result in abnormalities on ventilation-perfusion scintigraphy. Often the cause of ventilation-perfusion scintigraphy abnormality is attenuation of lung activity by the effusion, which causes matched defects. Imaging in the prone position can move a free-flowing effusion, exposing true underlying perfusion. This useful maneuver has been reported previously to convert "indeterminate probability" to "low probability" scan. This report offers a more detailed description of the prone maneuver in a case where repositioning revealed underlying normal perfusion in an area with a previous matched defect-improving clinical usefulness of the scan.