[Hypersensitivity pneumonitis : S2K guideline from a radiological perspective]

Hypersensitivity pneumonitis (HP, also known as extrinsic allergic alveolitis [EAA]) is a rare disease which is limited to the lungs and caused by an immunological inflammatory reaction of the lung parenchyma and terminal bronchioli. The first German guideline on the diagnosis and treatment of HP was published in 2024. The imaging method of choice is high-resolution computed tomography (HRCT). Radiologically, a distinction is made between purely inflammatory and fibrotic HP. If there are signs of fibrotic HP in the HRCT, the relation between the extent of inflammation and fibrosis should be determined and given in the report. The prognosis depends significantly on the extent of fibrosis and the proportion of so-called honeycombs.