## **Core Concept**
Pleural effusion refers to the accumulation of fluid in the pleural space of the lungs, which can result from various pathological processes. The question focuses on identifying a common cause of pleural effusion that occurs without evident lung infiltration on imaging. This requires understanding the different mechanisms leading to pleural effusion, such as heart failure, malignancy, and liver cirrhosis.

## **Why the Correct Answer is Right**
The correct answer, **Congestive Heart Failure (CHF)**, is a leading cause of pleural effusion without lung infiltration. CHF leads to increased hydrostatic pressure in the pulmonary veins, causing fluid to leak into the pleural space. This type of effusion is typically a transudate, characterized by low protein and lactate dehydrogenase (LDH) levels. The pathophysiology involves the imbalance between the forces driving fluid into the pleural space and those removing it, primarily due to elevated pulmonary venous pressure.

## **Why Each Wrong Option is Incorrect**
- **Option A:** While pulmonary embolism can cause pleural effusion, it is often associated with lung infarction or infiltration, making it less likely to be the correct answer in the context of "without evident lung infiltration."
- **Option B:** Tuberculosis can cause pleural effusion, but it usually presents with lung infiltration or other signs of pulmonary involvement.
- **Option C:** Pneumonia typically presents with lung infiltration, making it an incorrect choice for a scenario without evident lung infiltration.

## **Clinical Pearl / High-Yield Fact**
A key clinical pearl is that **exudative pleural effusions** (e.g., due to pneumonia, malignancy) are often associated with lung infiltration or other abnormalities on chest imaging, whereas **transudative pleural effusions** (e.g., due to CHF, liver cirrhosis) are less likely to have concomitant lung infiltration. This distinction can guide the diagnostic approach to pleural effusions.

## **Correct Answer: D. Congestive Heart Failure.**