Pulmonary Edema (28200-36500)
In this section of lung, septal capillaries are congested and the alveoli are filled with pink-staining proteinaceous edema fluid. Within the edema fluid there are macrophages, many of which contain hemosiderin pigment. These changes result from increased hydrostatic pressure in the pulmonary circulation, as is seen in left-sided heart failure or mitral stenosis.

Chronic Passive Congestion of Lung (28200-36140)
The alveolar septa appear thickened, and the alveolar spaces contain numerous pigment-laden macrophages. A few alveolar spaces contain pink edema fluid. Note the thick-walled pulmonary vessel.