CTICasesHypersensitivity Pneumonitis Progressing to Fibrosis
Imaging findings
CT from 2012 demonstrates extensive mosaic attenuation with geographic ground-glass opacity, consistent with active hypersensitivity pneumonitis. No expiratory images were available at that time. CT from 2017 shows marked progression with extensive peribronchial fibrosis, ground-glass opacity with reticulation particularly at the bases, and a pattern now resembling NSIP with some features suggesting UIP progression. Expiratory imaging confirms true air trapping with lobules that fail to deflate on exhalation, documenting the air trapping component of the disease.
Key takeaways
Hypersensitivity pneumonitis can progress over years from an active exudative/inflammatory phase with mosaic attenuation and ground-glass opacity to a fibrosing phase characterized by peribronchial fibrosis, reticulation, and traction bronchiectasis. The peribronchial rather than purely peripheral distribution of fibrosis is a clue that helps distinguish fibrosing HP from UIP/IPF. Air trapping on expiratory imaging is a characteristic feature of HP at all stages. Despite the dramatic CT progression in this case, the antigen was never identified.
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