Pathophysiology:  The commonest cause of a large left atrium is mitral regurgitation, usually due to rheumatic heart disease.

CXR Findings:

Measuring size of the left atrium:

There are many plain film "signs" of left atrial enlargement.  The best one is direct measurement of a diagonal of the anatomic left atrium.  The left atrium "lives" in the subcarinal position, tagged onto the posterior upper cardiac border. Measure the double contour of the left atrium from its outermost convex point to the inner halfway point of the left main stem bronchus (X-Y in CXR).

Normal XY in male: < 7.0 cm

Normal XY in female: < 6.5 cm

“Aunt Sophies”:  Other causes of large left atria.

1. Mitral stenosis
2. Heart failure and cardiomyopathies
3. Left atrial myxoma
4. Left to right shunts and congenital cardiac abnormalities