Hypersensitivity pneumonitis, or HP, is caused by exposure to inciting antigens that induce the body to mount an immune response.38 It may present as acute, subacute, or chronic, characterized by the duration of exposure and different clinical and radiographic features.39 There is variability in the literature as to what constitutes acute, subacute, and chronic HP.39
Here we have images from 4 patients with HP, which can present with a wide range of abnormalities, some of which may mimic pulmonary fibrosis. Image A shows peribronchovascular septal thickening with patchy areas of ground glass opacification and consolidation with traction bronchiectasis and architectural distortion, in keeping with fibrosis. Importantly, the subpleural is not involved, and the abnormalities have a more central involvement than we see with classic UIP. In image B, there are more extensive, multifocal areas of reticular abnormalities, traction bronchiectasis, and architectural distortion with more severe scarring. There is architectural distortion with reticulation, peribronchovascular subpleural sparing, and areas suggestive of air trapping. Image C demonstrates another hallmark of HP in addition to the reticular architectural changes of fibrosis. Notice that multiple, small micronodules are seen, which is very typical for this disease. The presence of micronodules excludes definite UIP.5 In the final image, there is a more diffuse abnormality with ground glass, areas of architectural distortion and traction bronchiectasis, in addition to honeycombing, indicated by the arrow.
