Assessment of cardiomediastinal contours on chest x-ray (approach)

Described below is a systematic assessment (and associated pathology) of the cardiomediastinal contours on chest radiographs.

1. Mediastinum

Localize site of pathology by using silhouette signs:

• silhouette sign of right upper lobe: obscures right upper cardiomediastinal border
• silhouette sign of right middle lobe: obscures right heart/atrial border
• silhouette sign of right lower lobe: obscures right hemidiaphragm
• silhouette sign of left upper lobe: obscures left aortic knuckle, left heart border
• silhouette sign of left lingular lobe: obscures left heart border
• silhouette sign of left lower lobe: obscures left hemidiaphragm

Pathology:

• hiatus hernia: air-fluid level in the mediastinum
• thoracic aortic dissection: 12% of patients with dissection will have normal CXR; signs: 1. widened mediastinum (> 8cm), 2. abnormal aortic knuckle, 3. left pleural effusion, 4. pericardial effusion, 5. interval change
• unfolded aorta: normal process of aging, mimics aortic dissection in an asymptomatic patient
• pneumomediastinum: 1. lucent halo around the heart, 2. tubular aorta sign, 3. continuous diaphragm sign, 4. subcutaneous emphysema
• pectus excavatum: more apparent on the lateral view
• anterior mediastinal mass: increased density, displaces trachea, alteration of mediastinal contour

2. Heart

• assess position (frontal view): normally 1/3 right of midline & 2/3 left of midline
• assess borders (frontal view): normally right border - right atrium; left border - left ventricle & left auricle; inferior border - right ventricle & small portion of left
• pericardial fat pad (frontal view): normally one/both cardiophrenic angles
• on lateral X-ray: normally anterior border - right ventricle; posterior-superior border - left atrium; posterior-inferior border - left ventricle
• assess overall size: normally the cardiothoracic ratio < 50% on a PA CXR obtained in full inspiration

Pathology:

• cardiomegaly: 1. CTR > 50% implies cardiomegaly, 2. can be due to chamber enlargement or pericardial effusion
• pericardial effusion: 1. globular cardiac outline, 2. well-defined borders, 3. rapid alteration in heart size
• left ventricular aneurysm: rare but examinable! Localized, calcified bulge in mid part of the left heart border
• left ventricular failure: 1. cardiac enlargement (except in massive AMI), 2. increase in pulmonary vessel calibre, 3. Curly B lines, 4. pulmonary oedema-"bat's wing" appearance, 5. pleural effusion
• right atrial enlargement: 1. right border is enlarged, 2. filling of the retrosternal space on lateral X-ray
• left atrial enlargement: 1. causes widening of the sub-carinal angle (>100 degrees), 2. double heart border (the left atrium peeks behind the right atrium), 3. posterior bulge on lateral X-ray