HRCT features of idiopathic interstitial pneumonias

Some lung diseases are just confusing. What’s UIP? What’s NSIP? Here I hope to shed some light into the interstitial pneumoniae and their HRCT features.

UIP (Usual interstitial pneumonia)

  • Also known as IPF (idiopathic pul.fibrosis)
  • Commonly associated with collagen vascular diseases. Other associations include drug toxicity or asbestosis.
  • Clue:
    #1: reticular patterns with honeycombing at basal lung; apical-basal gradient.
    – Others: GGO (at initial stages), traction bronchiectasis
  • Prognosis: bad. Despite treatment, areas of GGO will tend to progress to fibrosis.

NSIP (non-specific interstitial pneumonia)

  • Is also associated with collagen vascular diseases, drug toxicity, environmental exposure
  • Two types: fibrotic (which is more common but poorer prognosis) and cellular type (less common)
  • Clue: #1 UIP like(reticular patterns, GGO which can progress to fibrosis at advanced stages) but lacking the apical-basal gradient

    Above: Traction bronchiectasis and GGO in upper and lower lobe
    Below:GGO with reticular patterns, honeycombing at lower lobe
  • Treatment: respond to steroids and cessation of the inciting factors

LIP (lymphocytic interstitial pneumonitis)

  • Associated with Sjogren’s syndrome (and other collagen vascular diseases), AIDS, Castleman disease
  • Clue: #1 GGO with large scattered cysts, mid-lower lobe predominance
  • Treatment: underlying disorder. The natural history is variable, from near complete resolution to progressive disease.

COP (Cryptogenic organizing pneumonia)

  • Histologic pattern of alveolar inflammation with varied aetiology (including pulmonary infection). The idiopathic form of OP is called cryptogenic organizing pneumonia (COP).
  • Clue: #1 Patchy peripheral consolidation (reversed bat wing sign), Atoll sign (reversed halo sign of GGO)

    ** Atoll sign: denser consolidation of crescentic (forming more than three fourths of a circle) or ring (forming a complete circle) shape of at least 2 mm in thickness
    – Other ddx are invasive aspergillosis, pulmonary mucormycosis (fungal lung infections), TB, autoimmune diseases eg WG and sarcoidosis.

  • Treatment: corticosteroids

RB-ILD and DIP (Resp.bronchiolitis interstitial lung disease, desquamative interstitial pneumonia)

  • Smoking related lung disorders
  • DIP is thought to represent the final progression of RB-ILD.
  • Other predisposing factors include collagen vascular diseases & infection eg HIV.
  • Clue: #1 : GGO with upper lobe predominance (smokers), centrilobular nodules, presence of centrilobular/paraseptal emphysema
    Presence of GGO and paraseptal empysema in a smoker suggestive of RB-ILD

AIP (acute interstitial pneumonitis)

  • Acute onset; the only interstitial pneumonitis with acute onset
  • ARDS-like but no typical inciting factors
    #1: extensive GGO (crazy paving) with evidence of lung fibrosis
  • Can be fatal. Typically treated with corticosteroids and mechanical ventilation. prognosis is poor.

** Smoking related lung diseases

  • Smoking related ILD
    – RB, RB-ILD, DIP
    – Pulmonary LCH
    – Combined pul.fibrosis and emphysema (UIP pattern + upper lobe emphysema)
  • Lung tumours
  • COPD

So in conclusion

  • We know that many interstitial lung diseases have overlapping predisposing factors (most commonly collagen vascular disease, but can be infection eg HIV, exposure to drugs or environment) and CT features (all can have GGO, traction bronchiectasis etc).





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