Q. Explain Left Atrial Enlargement ?

This chamber is oval in the frontal projection and flattened in lateral projection. On the PA view, its appendage makes a small contribution to the left heart border. The left atrium (LA) may enlarge in many directions. Rightward enlargement is seen as increased density, producing a convex border overlying or to the right of the right heart border. This could mimic a dilated aortic root. When the chamber enlarges to the left, it causes straightening or convexity of the left heart border in the region of the left atrial appendage. Posterior enlargement of the LA is seen as increased central heart density on a PA view and as posterior displacement of the left atrial border and the pulmonary veins on the lateral view. Superior enlargement is manifested as widening of the carinal angle, which is usually less than 90 degrees. Occasionally, the LA may be aneurysmally dilated. On the PA view, the right border may approach the right chest wall, with a markedly enlarged appendage on the left, and splaying of the carinal angle to 180 degrees. On the lateral view, the massively enlarged LA is convex posteriorly, forming the entire heart border. Fig. 4.9 shows the changes in cardiac contour that result from LA enlargement on four views.