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Thoracic differentials

thoracic ddx.png
thoracic ddx 2.png

Disease distribution

Upper lobe diseases

  • SET PARC mnemonic as above
  • The pathologies that have predilection for upper lobes is NOT because of increased oxygen tension in upper lobes, that is a myth
  • Upper lobes have 1/18th the perfusion of lower lobes and 1/3rd the ventilation
  • Inhaled toxins (eg. smoke) sits around in upper airway alveoli longer since less perfusion to absorb and whisk away
  • Lymphatic flow is poor in the upper lobe, particularly posterior which is why TB and other agents also have a predilection for upper lobe
  • Furthermore, upper lobe is more alkaline hence metastatic calcification tends to precipitate here

Bronchovascular

  • Tends to reflect a lymphatic spread

Nodules

Multiple nodules

  • Varying sizes more likely metastatic
  • Uniform and smaller size more likely granulomas