Primary TB

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Primary TB

  • There are no radiological features which are in themselves diagnostic of primary mycobacterium tuberculosis infection (TB) but a chest X-ray may provide some clues to the diagnosis
  • This image shows consolidation of the upper zone with ipsilateral hilar enlargement due to lymphadenopathy
  • These are typical features of primary TB
  • Note: The chest X-ray may be normal in primary TB, in fact most patients infected are never unwell enough to require a chest X-ray

Healed primary TB

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Healed primary TB

  • Following an immune response to primary infection, a caseating granuloma forms which calcifies over time – this is known as a ‘Ghon focus’ – TB has gone!
  • A Ghon focus is a rounded, well-defined focus of calcific density (as dense as bone) usually located in the periphery of the lung
  • This chest X-ray shows a large, rounded calcified focus near the right hilum
  • The CT (not usually necessary) shows it is located in the lung peripherally
  • This is a particularly large Ghon focus

Post-primary TB

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Post-primary TB

  • Post-primary TB (secondary TB or reactivation TB) is more common in immunocompromised individuals – for example those with HIV/AIDS, those on immunosuppressing drugs, or those with malnutrition or diabetes
  • The upper lobes are more commonly affected
  • Consolidation often extends to the hilum
  • The hilar structures may be distorted due to volume loss of the upper lobe

Post-primary TB – Lung cavity

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Post-primary TB – Lung cavity

  • (Same patient as image above – 4 months later)
  • Cavities are a common finding in mycobacterial infection

Healed post-primary TB

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Healed post-primary TB

  • Following an immune response to post-primary infection, the affected area often becomes scarred (fibrotic) and calcified
  • The combined fibrosis and calcification can be described as ‘fibro-calcific change’

Miliary TB

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Miliary TB

  • Miliary TB is due to disseminated spread of mycobacterial infection
  • It can occur either at the time of primary infection or on disease reactivation – prognosis is poor
  • Very fine nodules are typically seen scattered throughout the lungs