Earliest CXR feature of left atrial enlargement is
A i.e. Elevation of the left main bronchus Left atrial enlargment presents radiologically with elevation of left main bronchus (earliest feature)Q, splaying or widening of carinaQ (to right or obtused angle), indentation & displacement of oesophagus posteriorly, double contour/shadow/density or double right hea borderQ, and prominent left atrial appendage. Left Atrial Enlargement LA does not form any pa of cardiac border in normal subjects (on PA view) because it lies in midline & posteriorly. It usually, enlarges postriorly & to the right causing indentation & displacement of oesophagus posteriorly (on barium swallow) . Elevation of left main bronchusQ is the earliest evidence (feature) of left atrial enlargmentQ. Subequently there is splaying of carina (i.e. carinal angle widens and become right or obtused angled as compared to normal 51-71 degree). The right border of an enlarged left atrium is visible as double contour (shadow/density) adjacent to the right hea border usually within the main cardiac shadow. Double right hea border is formed d/t bulging of left atrium into right lung & eventually forming right hea border. The borders of left & right atria are differentiated by the fact that left atrial border passes medially towards spine & border of right atrium is limited below by entry of IVC (inf. venacava). With massive enlargment LA can form the most pa of right cardiac border - Left border of LA is rarely visible, although left atrial appendage, when dilated, is seen as a bulge below the main pulmonary aery. - On lateral view postero-superior pa of cardiac shadow becomes prominent. Right Atrium Enlargement - In early stage, only RA appendage fills the space b/w front of heat & back of sternum (prominent anterosuperior pa on lateral view). - It causes an increase in the curvature of right hea border, which becomes more convex, prominent and also protudes to the right away from midline (>3cm beyond right lateral veebral border). It is often accompanied by enlargment of superior venacava and increase in RA height (most reliable sign). In normal individuals, the distance b/w top of aoic arch and the junction of SVC & RA is more than the distance between the later & right cardiophrenic angle. When the reverse happens (i.e. SVC/RA to RCPA distance >AA to SVC/RA distance), the RA is said to be enlarged. Left Ventricle Enlargment On PA view, there is prominent left hea border with rounding. Hyperophy produces rounding of cardiac apex whereas dilatation causes elongation/displacement of cardiac apex to the left or to the left & downwards Lateral view shows prominent postero-inferior pa of cardiac shadow Right Ventricle Enlargement RV enlarges mainly to the left & anteriorly, so there is prominence of left hea border on PA view and prominence of anterior pa of cardiac shadow with encroachment of retrosternal space in upper pa on lateral view. Pulmonary conus (outflow tract) becomes prominent. It may form left cardiac border and can rotate LV to the left with elevation of cardiac apex. This rotation tends to swing the aoa to right, so that aoic knukle becomes less prominent.
Elevation of the left main bronchus
Double cardiac shadow
Widening of carina
Pericardial effusion