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Cardiac Silhouette on Chest X‑Ray: Normal Anatomy, Measurements, and Pathologic Clues

The cardiac silhouette is the heart's radiographic shadow on a frontal chest X‑ray. Its size, shape, and borders reflect underlying cardiac and pericardial anatomy.

Border Anatomy (PA View)

Border	Structures
Right heart border	Right atrium (upper), IVC/SVC entry (lower)
Left heart border	Aortic knob, pulmonary artery, left atrial appendage, left ventricle (apex)
Superior border	Aortic arch, main pulmonary artery
Inferior border	Right ventricle (left portion), diaphragm interface

Normal Parameters

Cardiothoracic ratio (CTR): < 0.50 (heart width / thoracic width) on PA film.
Shape: Oval/pear; right border straight/concave, left border convex.
Borders: Sharp, distinct; no obscuration by lung disease.

Common Abnormalities

Finding	Suggests
CTR > 0.50 (cardiomegaly)	Heart failure, valvular disease, cardiomyopathy, pericardial effusion
Left atrial enlargement	Double density sign, straightening of left border, splaying of carina
Right ventricular enlargement	Filling of retrosternal space on lateral; elevated apex
"Boot‑shaped" heart	Tetralogy of Fallot (upturned apex, concave pulmonary bay)
"Water‑bottle" silhouette	Pericardial effusion (large, globular)

Limitations

AP portable films exaggerate CTR (magnification).
Rotation, inspiration depth, obesity affect appearance.
Cannot assess chamber volumes/function directly—echo, CMR, CT needed.

The cardiac silhouette is a rapid, low‑cost screening tool; abnormalities trigger targeted advanced imaging.

Offene Herz-Chirurgie

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