Bottom Line: In patients with pericardial effusion, the water bottle sign appears when the chest x-ray’s cardiac silhouette has a globular shape that looks like a water bottle as the result of slowly accumulating fluid. In the screenshot from YouTube below, the four images show a normal chest x-ray (top left corner), a patient with cardiomegaly (lower right corner), and a chest x-ray with a water bottle sign (lower right corner). The water bottle shape appears in the upper right corner.
Reference for Image: Hammadshams. Chest X-Ray – Cardiomegaly or No Cardiomegaly – Water Bottle Sign. https://www.youtube.com/watch?v=oG_bE2x5LG8. Accessed January 23, 2018.