Kerley B lines are linear opacities seen on the chest radiograph. They are 1-2 cm long horizontal lines which meet the pleura at right angles. They are typically seen as a ladder up the side of the lungs beginning at the costophrenic angle.

Kerley B lines represent interlobular lymphatics which have been distended by fluid or tissue.

Kerley B lines are usually an indication of raised pulmonary venous pressure due to:

• left ventricular failure
• mitral stenosis

Other causes include:

• lymphangitis carcinomatosa
• pulmonary fibrosis
• parasitic infection