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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 edema. Alveolar edema manifests as ill-defined nodular opacities tending to confluence. Interstitial edema can be seen as peripheral septal lines – Kerley B lines.

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 carcinomatosa; pneumoconioses; sarcoidosis; and pulmonary lymphoma.

Reference: Chapman S, Nakielny R. Aids to Radiological Differential Diagnosis 4th edition. Saunders 2003

Credit: Dr Laughlin Dawes