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?

) Pulmonary edema refers to excess accumulation of fluid in the extravascular spaces of the lung. Pulmonary edema can be classified based on the etiology into cardiogenic pulmonary edema and noncardiogenic pulmonary edema. Cardiogenic pulmonary edema results from abnormalities of hemodynamic (Starling) forces, while noncardiogenic pulmonary edema results from cellular injury. Causes of cardiogenic pulmonary edema include increased hydrostatic forces, as seen with congestive hea failure (the most common cause of pulmonary edema); decreased oncotic pressure, such as resulting from decreased albumin levels; and lymphatic obstruction. Noncardiogenic edema may be the result of either endothelial injury (infections, disseminated intravascular coagulopathy, or trauma) or alveolar injury (from inhaled toxins, aspiration, drowning, or near drowning). Microscopically, pulmonary edema reveals the alveoli to be filled with pale pink fluid. Cardiogenic edema may lead to alveolar hemorrhages and hemosiderin-laden macrophages (hea failure cells). Where cardiogenic edema is present, chest x-rays show an increase in the caliber of the blood vessels in the upper lobes, perivascular and peribronchial fluid ("cuffing"), and Kerley B lines (fluid in the interlobular septa). Noncardiogenic edema produces a "whiteout" of the lungs. Reference: Robbins & Cotran Pathologic Basis of Disease, 9edition.