Understand 1st year medicine

Made by a (former) student for students!

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Know your anatomy before interpreting.

  • Lung Fields: any lesion should not be defined in lobes but as ZONES.

Horizontal fissure usually extends from the oblique fissure along the border of the 4th rib. Horizontal fissure runs roughly horizontally from the edge of the lung towards the right hilum.

Lateral chest x-rays are helpful in demonstrating the oblique fissures (also known as the major fissures).


  1. Tracheal Air Column
  2. Carina
  3. 1st Rib
  4. Scapula
  5. Minor or Horizontal Fissure
  6. Right Hemidiaphram
  7. Left Hemidiaphram
  8. Ascending Aorta
  9. Clavicle
  10. Superior Vena Cava Shadow
  11. Region of Azygos Vein
  12. Right Pulmonary Artery
  13. Left Atrial Appendage
  14. Border of Right Atrium
  15. Inferior Vena Cava
  16. Aortic Arch
  17. Left Pulmonary Artery
  18. Border of Left Ventricle
  19. Descending Aorta


 Aspects of CXR


AP (Anterior Posterior) or PA (Posterior Anterior?

  • PA (chest facing detector, beam from back to chest) view for the more anterior structures - lungs and heart.
  • AP (back facing detector, beam from chest to back) view for the more posterior structures - scapula. The disadvantage to this is that the heart, being a more anterior structures, gets magnified as it is further from the detector plate.

Good inspiration?
Inspiration expands lung fields
A good CXR will have a good view of the lung fields (i.e. inspiration with view of the 9th posterior rib).
If only up to the 7th posterior rib is seen - hypoinflation! Do not confuse this with cardiomegaly or lower zone pneumonia!

Good exposure?
Vertebral column faintly visible only
Over-exposure - too black so you can’t really discern the lung! Spinous process clearly visible
Under-exposure - too white


How to interpret CXR

Use the "PIER" mnemonic to assess for adequacy of the film. Ask yourself is the film worth "pier-ing" into? <-- to remember the mnemonic

  1. Position: Typically, upright PA and lateral. Sick patients will have the fuzzier supine AP (because the film is slid under their chest as they are lying down).
  2. Inspiration: Count the visible ribs. Lung fields should extend to about the 10th or 11th rib.
  3. Exposure: If the film is penetrated enough, you should be able to make out the spinous processes "inside" the vertebrae. If the film is underexposed/too white, you won't be able to see them. If the film is overexposed/too black, bony details will be lost.
  4. Rotation: Evaluate the clavicals. They should appear symmetric and equal in length. Now systematically work through the x-ray.

Evaluate the film. Here is one popular pneumonic. See the links at the bottom of the post for more CXR guides with images.
  • A = Airway: are the trachea and mainstem bronchi patent; is the trachea midline?
  • B = Bones: are the clavicles, ribs, and sternum present and are there fractures, lytic lesions?
  • C = Cardiac silhouette: is the diameter of the heart > ½ thoracic diameter (enlarged)?
  • D = Diaphragm: are the costophrenic and costocardiac margins sharp? is one hemidiaphragm enlarged over another? is free air present beneath the diaphragm?
  • E = Effusion/empty space: is either present?
  • F = Fields (lungs): are there infiltrates, increased interstitial markings, masses, air bronchograms, increased vascularity, or silhouette signs?
  • G = Gastric bubble: is it present and on the correct (left) side?
  • H = Hilar region: is there increased hilar lymphadenopathy?
  • Now check the places you forgot to look:
    • Soft Tissue - Breast shadows, supraclavicular regions, axillae, chest wall. Look for thickness, subcutaneous emphysema (air bubbles-dark spots), calcifications (bright spots).
    • Behind the heart
    • The apices
    • Under the clavicles
    • The costophrenic angle and the cardiophrenic angle and interface
  • alveolar patchy, poorly marginated. Represents material other than air in the airspaces. May see "air bronchograms"-black lines representing air-filled bronchi amidst water-density alveoli. May note "silhouette signs"-organs' margins blurred by dense material in alveoli of nearby lung tissue.
  • interstitial: thickening of bronchi, septae. Linear or finely granular patterns of abnormal shadows. "Kerley's B-lines" (not "curly" B-lines) are thickening of interlobular septae and are small, bright, horizontal lines seen esp. towards the bases of the lungs. They are associated with CHF. The interstitial pattern is seen in CHF, interstitial fibrosis, cancer, inflammation.
  • atelectasis: loss of volume leads to a shift of interlobar fissures & mediastinum towards the collapsed region.
  • nodules: one or more dense, bright, round lesions. Adenoma, granuloma, cancer, cyst, lymph node, etc.
  • other: abscess (lucency within density, air-fluid level); pneumatoceles (air-containing spaces seen with some pneumonias); honeycombing (airspaces w/thick septae)

Pathology and Anomalies

Heart failure

  • Alveolar oedema (bat’s wings)
  • Kerley B lines (interstitial oedema)
  • Cardiomegaly
  • Dilated prominent upper lobe vessels
  • Effusionpleural)
Azygous fissure

If there is an azygous fissure, the vein appears to run within the lung, but is actually surrounded by both parietal and visceral pleura. The azygous fissure therefore consists of four layers of pleura, two parietal layers and two visceral layers, which wrap around the vein giving the appearance of a tadpole.