A supine portable chest radiograph of a trauma patient shows increased lucency at the right costophrenic angle extending inferiorly, with unusually sharp demarcation of the right hemidiaphragm. No pleural line is seen at the apex. What does this represent?

• A Deep sulcus sign of anterior basal pneumothorax ✓
• B Free intraperitoneal air beneath the diaphragm
• C Right lower lobe collapse with compensatory hyperlucency
• D Diaphragmatic rupture with herniated bowel

Explanation

In a supine patient, intrapleural air rises to the anterior and anteromedial pleural space rather than the apex, producing the deep sulcus sign: abnormal deepening and lucency of the costophrenic angle with sharp diaphragmatic outline. Recognising this prevents missing a pneumothorax that lacks the classic apical visceral pleural line seen on erect films. Free intraperitoneal air collects under the central diaphragm and does not deepen the costophrenic sulcus, and lobar collapse produces volume loss with opacity, not localised lucency.

Reference: Brant and Helms' Fundamentals of Diagnostic Radiology, 5th ed.

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Written and medically reviewed by the StethoPrep medical team.