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Pneumonia of the Right Middle Lobe With Silhouette Sign


This chest x-ray shows an infiltrate that appears to blend with the right heart border (silhouette sign). The silhouette sign indicates contiguous positioning of the 2 structures that have similar radiodensity; the part of the lung contiguous with the right heart border is the right middle lobe, so that is the part with the infiltrate and pneumonia.

SCIENCE PHOTO LIBRARY