This patient presented with acute onset of dyspnea. The frontal chest radiograph is the key to diagnosis of acute pulmonary edema.
It shows evidence of both interstitial and alveolar edema. Alveolar edema manifests as ill-defined nodular opacities tending to confluence (see image with arrows). Interstitial edema can be seen as peripheral septal lines - Kerley B lines (arrowheads).
Peripheral septal lines are due to thickening of the interlobular septa. They are 1-3cm long and extend to the pleural surface. They may be due to pulmonary venous hypertension, as in this case. Other causes are: lymphangitis carcinomatosis; pneumoconioses; sarcoidosis; and pulmonary lymphoma.