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D. CXR-CARDIOMEDISTINAL CONTOURS

D. CXR-CARDIOMEDISTINAL CONTOURS

1. Mediastium

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, minimcs 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 lateral view.
  • Anterior mediastinal mass: increased density, displaces trachea, alteration of mediastinal contour.

2. Heart

  • Assess position (frontal view): 1/3 right of midline + 2/3 left of midline.
  • Assess borders (frontal view): right border = right atrium; left border = left ventricle + left auricle; inferior border = right ventricle + small portion of left.
  • Pericardial fat pad (frontal view): one/both cardiophrenic angles.
  • On lateral xray: anterior border = right ventricle; posterior-superior border = left atrium; posterior-inferior border = left ventricle.
  • Assess overall size: 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 left heart border.
  • Left ventricular failure: 1. cardiac enlargement (except in massive AMI), 2. increase in pulmonary vessle caliber, 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.


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REFERENCES

1. Goodman, L. and Felson, B. (2015). Felson's principles of chest roentgenology. 3rd ed. Philadelphia, PA: Elsevier, Saunders.
2. Dähnert W. Radiology Review Manual. LWW. (2011) ISBN:1609139437. Read it at Google Books - Find it at Amazon
3. Elizabeth Puddy, Catherine Hill; Interpretation of the chest radiograph, Continuing Education in Anaesthesia Critical Care & Pain, Volume 7, Issue 3, 1 June 2007, Pages 71–75, https://doi.org/10.1093/bjaceaccp/mkm014

Ⓒ A. Manickam 2018

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