This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: All India exam, Subject name: Pathology
Earliest sign of left atrial enlargement 
Select and explain. 
A. Elevation of the left main bronchus, B. Double cardiac shadow, C. Widening of carina, D. Cephalization of the blood flow
A: Elevation of the left main bronchus
Answer: A: Elevation of the left main bronchus 
Explanation: .Left atrial enlargement refers to dilation of the left atrium which occurs from multiple disease states that can chronically increase the left atrial pressure. These include congestive hea failure, cardiomyopathies, congenital hea defects and valvular hea disease In rheumatic mitral valve disease, there may be left atrial enlargement with specific enlargement of the left atrial appendage, first seen as a straightening of the left hea border below the left main bronchus, then as a discrete bulge on the left, immediately below the pulmonary bay and left main bronchus. Ref Robbins 9/e pg 345