Which sign on a chest X-ray may indicate pulmonary congestion?

Kerley B-lines are short, thin lines seen on a chest X-ray that indicate interstitial edema, which is often associated with pulmonary congestion. They are typically a sign of increased pulmonary vascular pressure and reflect fluid accumulation in the interstitial spaces of the lungs. Kerley B-lines appear in the peripheral regions of the lungs and are particularly indicative of heart failure and other conditions contributing to pulmonary congestion.

In contrast, other signs such as mediastinal shift may indicate a mass effect or large pleural effusion, but they do not specifically point to pulmonary congestion. Lobar lung collapse reflects atelectasis rather than fluid overload in the lungs, and diaphragmatic elevation can be due to various factors, including phrenic nerve paralysis or subdiaphragmatic processes, but again, it is unrelated to the presence of pulmonary congestion. Thus, among the options, Kerley B-lines most directly signify the presence of fluid in the lungs due to congestion.