The Hidden Pneumothorax—Unmasking the Deep Sulcus Sign: A Case Report

Iatrogenic pneumothorax is a well-recognized complication of percutaneous transthoracic procedures such as computed tomography (CT)-guided lung biopsy.However, its diagnosis can be challenging, especially on supine radiographs, where classical findings of apical air may be absent.Instead, subtle signs such as the "deep sulcus sign" may be the only clue.We report the case of an elderly male who developed pneumothorax following a CT-guided biopsy of a pulmonary lesion.The pneumothorax was identified on a supine chest radiograph by the presence of a deep costophrenic sulcus.Early recognition of this subtle sign helped avoid progression to a tension pneumothorax, and the patient was successfully managed with conservative therapy.This case highlights the importance of clinical suspicion, awareness of imaging subtleties, and timely intervention in the prevention of iatrogenic pneumothorax.