<prompt> A patient with breathlessness shows Kerley B-lines in chest X-ray. These lines represents:Linear fibrosisHaemosiderin depositsSmall focal atelectasisThickened interlobular septa  <response>: In pulmonary edema, as the pulmonary venous pressure increases, fluid leaks from the pulmonary capillaries into the adjacent interstitium. This interstitial pulmonary edema may be identified by peribronchial cuffing, indistinctness of the perivascular margins, perihilar haziness, and thickening of the interlobular septa and interlobar fissures. Septal thickening results in Kerley A arrow and Kerley B arrowhead lines on chest radiograph. Ref: Chiles C., Gulla S.M. 2011. Chapter 4. Radiology of the Chest. In M.Y. Chen, T.L. Pope, D.J. Ott Eds, Basic Radiology, 2e. 