Earliest sign of Left Atrial enlargement is:

Left atrial enlargement usually occurs in mitral valve disease (either stenosis or insufficiency). The earliest signs of left atrial enlargement are: Straightening of the upper left border of the cardiac silhoutte Prominence of the main pulmonary aeries Dilatation of the upper lobe pulmonary veins Posterior displacement of the esophagus by an enlarged LA which can only be demonstrated using barium swallow The earliest sign is perhaps the straightening of the upper left border of the hea. Since posterior displacement of the oesophagus is the only choice given of the above features it is the correct answer. Ref: Harrison's Principles of Internal Medicine, 16th Edition, Page 1392