February 12, 2010

Insidious Hypersensitivity Pneumonitis

Axial CT image shows bilateral numerous centrilobular groundglass opacities (arrows) and areas of air trapping (heterogeneous low attenuation in lung parenchyma) in this 57-year-old nonsmoker.

Facts: Hypersensitivity Pneumonitis
  • Numerous etiology: exposure to microbes, animal protein, plant protein, low-molecular-weight chemicals
  • Clinical features depend on the amount of allergen, duration of exposure, nature of antigen and host factors
  • Clinical syndromes divided into three types: 1. acute (or episodic) with improvement between attacks, 2. insidious with superimposed acute attack, 3. insidious without acute attacks
  • Histology shows cellular bronchiolitis, diffuse chronic interstitial infiltrates, nonnecrotizing granulomas or giant cells in alveoli/interstitium
  • Much more common in nonsmokers
Imaging Appearance
  • Usually not seen on chest radiograph. Bilateral groundglass opacities and fine reticulations can be seen (similar appearance to pulmonary edema). If fibrosis occurs, reticular opacities and honeycombing is visualized
  • On CT: centrilobular ground glass opacities (less than 5 mm ill-defined nodules in centrilobular distribution), air trapping and diffuse groundglass opacities
  • Usually symmetric in the mid/lower lungs
  • Clinical history + lab test (Antibody testing) + bronchoalveolar lavage finding + imaging
  • In BAL, there is increased lymphocytes with CD4:CD8 ratio of less than 1

Our case: insidious hypersensitivity pneumonitis due to unknown etiology, the diagnosis was confirmed with BAL and lung biopsy. The main differential diagnosis based on imaging in this case was NSIP.

Hirschmann JV, Pipavath SNJ, Godwin JD. Hypersensitivity pneumonitis: a historical, clinical and radiologic review. RadioGraphics 2009;29:1921-1938.

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