Deep Sulcus Sign.
There is a supine pneumothorax on the right as evidenced by a deep sulcus sign. Other findings are – ETT which is abutting the right main bronchus (needs to be pulled back a bit), a right sided subclavian line & a right pleural line visible all the way up to the apex.
Deep sulcus sign is said to be present on a supine chest x-ray when the costophrenic angle is radiolucent and dips into the hypochondrium. It indicates the presence of a pneumothorax. It may be the only sign of abnormal pleural air.
Reference – https://pubs.rsna.org/doi/abs/10.1148/radiol.2282020524?journalCode=radiology