This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Radiology
Earliest radiological sign of Pulmonary Venous Hypeension in Chest X-ray is: 
Select and explain. 
A. Cephalization of pulmonary vascularity, B. Pleural effusion, C. Kerley B lines, D. Alveolar pulmonary edema
A: Cephalization of pulmonary vascularity
Answer: A: Cephalization of pulmonary vascularity 
Explanation: The first radiographic sign of pulmonary venous hypeension is cephalization of the pulmonary vessels due to pulmonary vein and aery dilatation. In the normal individual, there is continuous passage of fluid from the pulmonary veins into adjacent interlobular lymphatics that return the fluid to the central mediastinal veins. If the lympatic reserve is overcome by increased transudate as a result of elevated pulmonary venous pressure, the interlobular septa are thickened and become visible radiographically. The first radiologic sign of pulmonary venous hypeension is cephalization of the pulmonary vessels. Ref: Atlas of Pulmonary Vascular Imaging By Conard Wittram, Page 51; Textbook of Radiology and Imaging By David Sutton, 5th Edition, Pages 288-89