Basilar pneumothorax in the supine adult.

A pneumothorax in a supine patient may outline the anterior costophrenic sulcus, resulting in an abrupt curvilinear change in density projected over the right or left upper quadrant, which is normally convex inferiorly. The upper quadrant will also appear relatively lucent. In a small pneumothorax these may be the only radiographic findings when the patient is supine. This can be easily identified on mobile-unit radiographs of limited technical quality. Either finding should lead to a prompt cross-table lateral or decubitus study to confirm the diagnosis and allow estimation of the size of the pneumothorax.