Water lily sign on chest X-ray is seen in –
**Core Concept**
The water lily sign, also known as the "water lily" or "signet ring" sign, is a radiological finding seen on chest X-rays in patients with certain conditions. It is characterized by a rounded or oval-shaped opacity with a central lucency, resembling a water lily or a signet ring. This sign is typically associated with pneumopericardium, a condition where air enters the pericardial space around the heart.
**Why the Correct Answer is Right**
The water lily sign is seen in pneumopericardium due to the interaction between the air and the pericardium. The pericardium is a fibroserous sac that surrounds the heart, and when air enters this space, it causes a visible change on the chest X-ray. The air creates a rounded or oval-shaped opacity with a central lucency, which is the characteristic "water lily" appearance. This sign is often seen in conditions that cause air to enter the pericardial space, such as trauma, surgery, or certain medical procedures.
**Why Each Wrong Option is Incorrect**
**Option A:** Not applicable.
**Option B:** The "egg on a string" sign is seen in pneumomediastinum, not pneumopericardium.
**Option C:** The "double density" sign is seen in pericardial effusion, not pneumopericardium.
**Clinical Pearl / High-Yield Fact**
The water lily sign is a key radiological finding in pneumopericardium, and it is often seen in conjunction with other signs such as the "cardiac crescent" sign. Recognizing this sign is crucial for diagnosing pneumopericardium and guiding further management.
**Correct Answer: D. Pneumopericardium. Pneumopericardium is a condition where air enters the pericardial space around the heart.**