Water lilly sign is seen in chest X-ray of :
**Core Concept**
The "water lily sign" is a radiological finding seen on chest X-ray, referring to the appearance of air trapped within the interlobar fissure, resembling a water lily pad. This occurs due to an obstruction of the airway, leading to air trapping and subsequent displacement of the fissure.
**Why the Correct Answer is Right**
The water lily sign is typically seen in patients with an obstructive process, such as a foreign body or tumor, which prevents the normal flow of air through the airway. The trapped air within the interlobar fissure creates a characteristic "water lily" appearance, which is a diagnostic clue for the healthcare provider. The interlobar fissure is a thin membrane that separates the lobes of the lung, and its displacement indicates an airway obstruction.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the water lily sign is not typically associated with a pleural effusion, which would present as a homogenous opacity on chest X-ray.
**Option B:** This option is incorrect because the water lily sign is not a normal variant of the chest X-ray, and its presence indicates an underlying pathology.
**Option C:** This option is incorrect because the water lily sign is not a feature of a normal lung silhouette, and its presence suggests an airway obstruction.
**Clinical Pearl / High-Yield Fact**
The water lily sign is a classic radiological finding that should prompt the healthcare provider to investigate for an airway obstruction, such as a foreign body or tumor.
**Correct Answer: D. A foreign body in the airway.**