What causes a box-shaped heart in the cardiac silhouette on chest radiograph?
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Answer:
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A box-shaped heart on chest X-ray is caused by Ebstein anomaly, a congenital malformation of the tricuspid valve characterized by downward (apical) displacement of the septal and posterior leaflets into the right ventricle. This leads to atrialization of a portion of the right ventricle, resulting in a markedly enlarged right atrium. The clinical consequences of Ebstein anomaly include right atrial enlargement with tricuspid regurgitation, cyanosis, arrhythmias, and symptoms of right heart failure. The box-shaped heart reflects these structural abnormalities on imaging.
Why is it called so?
The term “box-shaped heart” derives from the radiographic cardiac silhouette’s appearance, which resembles a rectangular or box-like shape. This shape results from the massively enlarged right atrium filling the right hemithorax, combined with a shelved or flattened left cardiac border caused by the dilated right ventricular outflow tract or residual right ventricle, and a small calibre aorta and main pulmonary artery.
Pathophysiology
The pathological displacement of the tricuspid valve leaflets reduces functional right ventricular volume, causing blood to flow backward (tricuspid regurgitation) and enlarge the right atrium significantly. The atrialized portion of the right ventricle contributes to the altered contour. The expansion of the right atrium, along with remodeling of the right ventricle and outflow tract, changes the cardiac silhouette to a box-like shape on frontal chest radiographs.
Alternative names: None
Other associated named signs: None
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