Silhouette Sign

Case 44

Malignancy / , , , , ,

This radiograph demonstrates left upper lobe collapse. This is one of the more challenging lobar collapse patterns to recognize on AP or PA radiographs as the left upper lobe collapses anteriorly and superiorly and ends up superimposed over the inflated left lower lobe. Other than the increased opacity over the left hemithorax, other notable features present on this radiograph are a left juxtaphrenic peak sign and silhouetting of the left heart border and hilum by the collapsed left upper lobe.

When this finding is identified, the cause of the collapse should be further investigated with CT. This case was post-obstructive collapse secondary to a central obstructing mass. The mass is not well visualized on this radiograph.

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Case 32

Infectious/Inflammatory / , ,

This radiograph demonstrates a lingular consolidation concerning for pneumonia. The location of the consolidation can be localized to the lingula even without a lateral radiograph using silhouette sign. There is a loss of sharpness and definition, or “silhouetting,” of the left heart border at the location of the consolidation, indicating that the consolidated lung makes direct contact with the left heart. Anatomically the pulmonary lobe that has the greatest area of contact with the left heart is the left upper lobe, specifically the inferior left upper lobe (the lingula), making the silhouette sign a reliable method of localization. The lingula is a relatively common location for pneumonia.

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