Kerley lines are a sign seen on chest x-rays with interstitial pulmonary eema. They are thin linear pulmonary opacities caused by fluid or cellular infiltration into the interstitium of the lungs. They are suggestive for the diagnosis of congestive heart failure, but are also seen in various non-cardiac conditions such as pulmonary fibrosis, interstitial deposition of heavy metal particles or carcinomatosis of the lung. Chronic Kerley B lines may be caused by fibrosis or hemosiderin deposition caused by recurrent pulmonary oedema.