Non-fibrotic hypersensitivity pneumonitis
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Non-fibrotic hypersensitivity pneumonitis is a phenotypical form of hypersensitivity pneumonitis and one of the main two subtypes under the newer classification systems.
Described features include 1
mosaic attenuation pattern: typically reflects coexistent lobules affected by pneumonitis (increased attenuation) interspersed with lobules of normal or slightly decreased attenuation (due to bronchiolar obstruction).
usually bilateral and symmetric with a diffuse distribution, both axially and craniocaudally
combination of parenchymal abnormalities and features of small airway disease: considered highly suggestive features in the appropriate clinical context
isolated air trapping is another pattern that may be seen with non-fibrotic hypersensitivity pneumonitis
Additional non-specific HRCT features which can be suggestive in the appropriate clinical context include:
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: