A 45-year-old Indian woman presents with progressive dyspnea and orthopnea. On examination, she has an opening snap and a diastolic murmur at the apex. A posteroanterior chest X-ray is obtained. The structure marked **B** (left heart border) shows straightening of the left heart border with a double density sign on the right side of the mediastinum and splayed carina. Which of the following cardiac conditions best explains these radiological findings?

Explanation

## Why "Mitral stenosis with left atrial enlargement" is right The clinical presentation (opening snap, diastolic murmur at apex) combined with the specific radiological triad of straightening of the left heart border, double density on the right mediastinum, and splayed carina are pathognomonic for left atrial (LA) enlargement. The structure marked **B** includes the LA appendage and left heart border; when the LA enlarges (as in mitral stenosis), it straightens the normally concave left heart border, creates a double density as the enlarged LA projects behind the right atrium, and splays the carina by posterior displacement. Mitral stenosis is endemic in India due to high prevalence of rheumatic heart disease, making this a high-yield diagnosis. (Sutton Radiology: Cardiac chamber enlargement patterns on CXR) ## Why each distractor is wrong - **Left ventricular hypertrophy with lateral apex displacement**: LV enlargement displaces the apex laterally and downward, but does NOT produce straightening of the left heart border, double density, or splayed carina. These findings are specific to LA enlargement, not LV. - **Aortic regurgitation with aortic root dilatation**: While aortic regurgitation may cause LV enlargement and aortic root dilatation, it does not produce the characteristic straightening of the left heart border or splayed carina seen with LA enlargement. The double density sign is not a feature of aortic root disease. - **Right atrial enlargement with increased right heart border bulge**: RA enlargement increases the right heart border bulge but does NOT cause straightening of the left heart border, double density on the right, or splayed carina. These are features of LA, not RA, enlargement. **High-Yield:** LA enlargement on CXR = straightened left border + double density + splayed carina; classic in mitral stenosis (rheumatic heart disease endemic in India). [cite: Sutton Radiology — Cardiac chamber enlargement patterns; NEET-PG standard CXR interpretation]