Deep sulcus sign (chest)
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The deep sulcus sign on a supine chest radiograph raises suspicion of a pneumothorax.
On a supine chest radiograph (common in intensive care units or as part of a trauma radiograph series), it may be the only suggestion of a pneumothorax because air collects anteriorly and basally, within the non-dependent portions of the pleural space, as opposed to the apex when the patient is upright.
The costophrenic angle is abnormally deepened when the pleural air collects laterally, producing the deep sulcus sign.