Chest x-ray

Two Views

Frontal View

Assess Quality

• May be PA (preferred, taken at a standard 1.8 m distance) or AP (done for patients who are unable to go to imaging department or to position for PA)
  • PA will magnify the mediastinum
  • AP more often done at an upward angle, which can blunt the left dome of the diaphragm
• Inspiration: at least 6 anterior ribs should be above the left dome of the diaphragm
  • Shallow inspiration can result in enlarged cardiac diameter, crowding of lung vessels, and basal atelectasis
• Rotation: spine of the vertebral bodies should be midline between the heads of the clavicles
  • Can make one lung appear lighter/darker compared to the other
  • PA rotated right can result in prominent aortic arch on the right, simulating mediastinal mass
  • AP rotated left can also make aortic arch more prominent

Assess Pathology

• Cardiothoracic ratio: should be less than 50% on a PA x-ray
  • If greater, it suggests cardiomegaly
• Domes of the diaphragm: they should be clear and well-defined
  • If obscured, it suggests pathology of the adjacent lower lung
• Heart borders: they should be clear and well-defined
  • If obscured, it suggests pathology of the adjacent lung
• Hila:
  • Should be similar density bilaterally, with left hilum never lower than the right
  • Look for the "little fingers" of the pulmonary arteries bilaterally; when lost, can suggest atelectasis of adjacent lower lobe
• Bones
• Overlooked sites: lung apex, superimposed on the heart, around each hilum, under the diaphragm

Lateral View

• Vertebral bodies: should become more transparent as they descend
  • If they fail to do so (i.e. become whiter, or stay the same density), it suggests lower lobe disease
• Domes of the diaphragm: they should be clear and well-defined
  • The right dome is visible front to back, while the left dome delineation fades anteriorly, where it merges with the cardiac shadow
  • If obscured, it suggests pathology of the adjacent lower lung
• Hila: assess the size/density (should be normal) and the borders (should be well-defined rather than bumpy or irregular)
• Cardiac shadow: any well-defined or abrupt change could suggest pathology
• Lungs: assess for lung densities, paying particular attention to the cardiac shadow, posterior to heart, and in the costophrenic recess

Parenchymal Changes

Alveolar and Interstitial Changes

• Something radiodense (pus, blood, water, protein, debris) can fill the alveoli, or the interstitial tissue that supports and surrounds the alveoli can become radiodense (from edema, inflammation, fibrosis)
• However, it can be very difficult to categorize into one or the other category

	Alveolar	Interstitial
Common findings	Fluffy or blobby opacity with ill-defined edges May be coalescent May follow segmental or lobar distribution	May have small nodules or linear/reticular/reticulonodular opacities
Occasional findings	Air bronchograms may be seen	Honeycombing (in advanced disease) Decreased lung volumes (in advanced disease)