Non-fibrotic hypersensitivity pneumonitis is distinguished from fibrotic hypersensitivity pneumonitis by the absence of fibrosis. This classification supersedes the previous division into acute, subacute and chronic.
Radiographic features
CT
Described features include 1:
mosaic attenuation pattern: typically three density sign with areas of normal lung interspersed with areas of increased attenuation and multilobar areas of lobular air trapping
ill-defined centrilobular or diffuse ground glass opacity which may be upper zone predominant
lobular air trapping
Differential diagnosis
Depending on the time course and the amount of exposure to the antigen (e.g., single but massive exposure vs. recurring exposure) the imaging findings may differ and can be quite nonspecific. In general consider differentials for:
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