A small portion of each lung normally reaches into the costophrenic angle.
2.
In an upright x-ray, 75 mL of fluid blunts the posterior costophrenic angle.
3.
The costophrenic angle is abnormally deepened when the pleural air collects laterally, producing the deep sulcus sign.
4.
Patients with chronic obstructive pulmonary disease ( COPD ) may exhibit deepened lateral costophrenic angles due to hyperaeration of the lungs and cause a false deep sulcus sign.
5.
Pleural thickening may cause blunting of the costophrenic angle, but is distinguished from pleural fluid by the fact that it occurs as a linear shadow ascending vertically and clinging to the ribs.
6.
Each costophrenic angle can normally be seen as on chest x-ray as a sharply-pointed, downward indentation ( dark ) between each hemi-diaphragm ( white ) and the adjacent chest wall ( white ).
7.
Blunting of the lateral costophrenic angle usually requires about 175 mL but may take as much as 500 mL . Larger pleural effusions opacify portions of the hemithorax and may cause mediastinal shift; effusions > 4 L may cause complete opacification of the hemithorax and mediastinal shift to the contralateral side.
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