Kerley's lines

Kerley A lines (red arrows): are a coarse network of essentially straight, linear opacities about 2 to 6 cm long and 1 mm thick within the lung substance usually situated in the upper zone and pointing toward the hilum centrally and directed toward but not extending to the pleural surface peripherally. The orientation of these lines does not conform to the distribution of the bronchovascular bundles; they represent edema of the central pulmonary septa and perilymphatic connective tissue. They are seen in pneumoconiosis, lymphangitic carcinoma, and pulmonary edema (in which case they may be reversible).

Kerley B lines (blue arrow): represent edema of the interlobular septa and are straight linear opacities approximately 1.5 to 2 cm in length and 1 to 2 mm in width situated at the lung base and oriented at right angles to the pleural surface.They are reversible and transient in pulmonary edema. They may be permanent and irreversible in chronic pulmonary venous hypertension, pneumoconiosis, sarcoidosis, and lymphangitic carcinoma.

Kerley C lines (green arrows): are reticular opacities at the lung base, representing Kerley’s B lines en face.These are usually septal lines and a specific feature suggesting lymphatic involvement.