Histologic sections (routine H&E stain) of lung reveal the alveoli to be filled with pale, nongranular pink fluid. Neither leukocytes nor erythrocytes are present within this fluid. What is the most likely (i.e., most common) cause of this abnormality?
**Core Concept**
The histological finding described in the question is indicative of an alveolar edema, characterized by the accumulation of fluid in the alveoli, leading to a pale and nongranular appearance on routine H&E staining. This condition is often associated with an imbalance in the Starling forces, which regulate fluid movement across the capillary-alveolar interface.
**Why the Correct Answer is Right**
The most likely cause of this abnormality is pulmonary edema, which occurs when the hydrostatic pressure in the pulmonary capillaries exceeds the oncotic pressure, leading to fluid leakage into the alveolar space. This can be caused by various factors, including left ventricular failure, high altitude, or increased capillary permeability due to inflammation or infection. The absence of leukocytes or erythrocytes in the fluid suggests that it is a transudate rather than an exudate.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is not relevant to the histological finding described. Although it is a cause of respiratory distress, it would not typically result in the accumulation of pale, nongranular fluid in the alveoli.
**Option B:** This option is a possible cause of respiratory failure, but it would not typically result in the histological finding described. It is more commonly associated with the presence of leukocytes and erythrocytes in the alveolar fluid.
**Option C:** This option is a cause of respiratory distress, but it is not typically associated with the accumulation of pale, nongranular fluid in the alveoli. It would more likely result in the presence of leukocytes and erythrocytes in the alveolar fluid.
**Option D:** This option is not relevant to the histological finding described. Although it is a cause of respiratory distress, it would not typically result in the accumulation of pale, nongranular fluid in the alveoli.
**Clinical Pearl / High-Yield Fact**
In cases of pulmonary edema, the presence of a "batwing" pattern on chest radiography can be a useful diagnostic clue, indicating the presence of fluid in the dependent portions of the lungs.
**Correct Answer:** C.