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CXR interpretation

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Bones
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Gavin Joynt

The "normal" CXR

The appearance of the chest radiograph in ICU or in any acutely ill patient is affected by the necessity for AP positioning, supine or sitting position, and the variable degree of inspiration. When the radiograph is taken make sure that ECG cables and other radio-opaque objects are removed from the radiographic field, when reasonable.

The AP view results in the magnification of anterior structures - the clavicle, sternum, and heart and a 15% increase in the width of the mediastinum can be expected. In addition, supine positioning widens the mediastinum and heart due to gravitational effects. The supine position also diverts more pulmonary blood flow to the upper lobes and redistributes pleural fluid. Similarly pneumothorax may be more difficult to detect.

Ideally, radiographs should be taken at the peak of inspiration. Critically ill patients are usually unable to maintain inspiratory hold positions. Poor inspiratory film alter the apparent size of the heart and mediastinum, which may appear 10-40% larger or wider. Crowding of lung markings may lead to over-diagnosis of basal atelectasis, lung edema etc.

The radiograph can sometimes be taken with the patient in the lateral decubitus position. This is used to determine the presence of a pleural effusion and can distinguish whether it is mobile or loculated.

Reading the CXR

  1. Dim room lighting
  2. Check patient information - name, age, sex, date of radiograph and if multiple images arrange them in chronological order
  3. Identify radiographic technique - AP/PA film, exposure, rotation, patient position (supine, sitting or erect)
  4. Soft tissues – thickness, contours, presence of gas, masses
  5. Bones – density, lesions or fractures
  6. Identify and check position of lines, tubes and other invasive devices
  7. Lungs -  look for abnormal densities (opacity or lucency) or pneumothorax
  8. Pleura - thickening, calcification, effusion or pneumothorax
  9. Trachea - midline or deviated, wall, lumen diameter
  10. Mediastinum - width and contour, discreet masses
  11. Heart - size and shape
  12. Pulmonary vessels - artery or vein enlargement
  13. Hila - position, masses or lymphadenopathy
  14. Check review areas - apices, especially right upper lobe, retrocardiac area, the peripheral lung margins, posterior costophrenic sulci, and the diaphragm.

Technique tips

  • Sometimes the film may have been taken at an angle. It may make one side of the CXR look generally lighter than the other. This may artificially make lung fields look different and suggest pathology such as pleural effusion or pulmonary oedema when it does not exist. To exclude this effect establish the baseline density of the film - look at the four comers of the film (where the x-rays have not passed through tissues). These areas should be equally black and uniform. Baseline density can be estimated by assessing the axillary soft tissues which should also be of equal density.
  • The silhouette sign - We are best able to distinguish anatomical margins when two structures of different density abut one another. These margins are lost when two structures of similar density abut one another. Pathology that changes the density of one, or both, of the two structures may be responsible for loss of normal anatomical margins (eg loss of the right heart border in right middle lobe consolidation)
  • To identify PA or AP film – in an AP radiograph, observe the medial border of the scapula, which is projected well into the lung fields.

  • Lung volume can be estimated by observing the point where a posterior rib crosses the dome of the diaphragm. Normal for PA film - 9th or 10th posterior rib. This point is at the 8th or 9th ribs in older patients.

© Gavin Joynt, June 2005


©Charles Gomersall, February, 2015 unless otherwise stated. The author, editor and The Chinese University of Hong Kong take no responsibility for any adverse event resulting from the use of this webpage.
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