Blunting of the costophrenic angle

Last revised by Daniel J Bell on 16 Jun 2021

Blunting of the costophrenic angle (also known as blunting of the costophrenic sulcus) is a chest radiograph sign usually indicative of a small pleural effusion. It may be seen on either frontal or lateral erect projections. It has been found that approximately 200 mL pleural fluid needs to be present for blunting of a costophrenic angle to be visible on a lateral chest radiograph.

It is important to recognize that this sign is far from pathognomonic of a pleural effusion. Causes include 1:

In a study of 600 chest radiographs, which had been performed as a "routine" screening study in well, male, military recruits, Ben Felson (1913-1988) found that incidental costophrenic angle blunting was present in 1.2% cases. He put the appearances down to old pleural disease 2.

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