The supine chest radiograph shows a deep sulcus sign on the right side indicative of right pneumothorax. There are also multiple rib fractures on the right and an endotracheal tube which is directed towards the right main bronchus. There is also an appropriately positioned right subclavian line.

The deep sulcus sign can be observed on supine chest x-rays and represents a deep costophrenic angle extending towards the hypochondrium. In a supine patient, the pneumothorax collects anteriorly and basally, thus causing this sign.

Following resuscitation or the placement of a central line in an unwell patient, it is important to investigate the deep sulcus sign by including lateral costophrenic angles in a supine chest x-ray.

Reference: https://pubs.rsna.org/doi/10.1148/radiol.2282020524