CTICasesChronic Hypersensitivity Pneumonitis Mimicking UIP
Imaging findings
High-resolution CT shows extensive, asymmetric fibrotic disease predominating in the upper and mid lung zones, characterized by subpleural cystic spaces consistent with honeycombing, severe traction bronchiectasis, and reticular opacities. The lung bases are relatively spared of classic subpleural honeycombing, but demonstrate milder reticulation and traction bronchiectasis. Expiratory images show no significant air trapping, which can often be absent in advanced, severe stages of fibrosis. Surgical lung biopsy pathology shows fibrosis centered around the airways (bronchiolocentric) with chronic inflammation, fibroblast foci, and scattered interstitial granulomas.
Key takeaways
Chronic hypersensitivity pneumonitis (HP) can closely mimic a usual interstitial pneumonia (UIP) pattern on both CT and histopathology, presenting with subpleural honeycombing and traction bronchiectasis. A key distinguishing imaging feature of chronic HP is the relative upper lobe predominance of the fibrotic change and honeycombing compared to the basal-predominant distribution typical of idiopathic pulmonary fibrosis (IPF). Multidisciplinary correlation is essential, as the pathology of chronic HP typically shows airway-centered (bronchiolocentric) fibrosis and poorly formed non-caseating granulomas, even in the absence of a known environmental antigen exposure.
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