English: This patient presented with acute onset of dyspnoea. The frontal chest radiograph is the key to diagnosis. It shows evidence of both interstitial and alveolar oedema. Alveolar oedema manifests as ill-defined nodular opacities tending to confluence (see image with arrows). Interstitial oedema 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. Radiopedia