High-resolution computed tomography in the diagnosis of fibrotic hypersensitivity pneumonitis: A review

Aim. Assess the detection of rare computed tomographic features and their combination to detect cases of fibrotic hypersensitivity pneumonitis (HP). A retrospective analysis of data from high-resolution computed tomography of the lungs was performed in 52 patients with fibrotic hypersensitivity pneumonitis (fHP), in whom the clinical diagnosis was confirmed by morphological examination of lung biopsy. The analysis of the identified changes was carried out by qualitative and quantitative methods. The study included signs common to non-fibrotic and fibrotic hypersensitivity pneumonitis of HP, including ground glass symptom, mosaic density, centrilobular lesions, and emphysema. Separately, features related to pulmonary fibrosis in fHP, such as reticular changes, traction bronchiectasis, and honeycombing, were analyzed. In addition, the distribution parameters of these signs were determined separately in the cranio-caudal direction and in the axial plane. To search for combinations of tomographic features that are significant in the diagnosis, a correlation analysis of the identified changes was carried out.

Materials and methods. The revealed CT-signs of fHP in most cases correspond to the clinical recommendations for the diagnosis of HP. However, in fHP, signs were found with a high frequency that did not correspond to the typical picture of HP, in particular, the "ground glass" symptom. On the contrary, a relatively low percentage of occurrence was observed in relation to centrilobular lesions and "mosaic density", which were also an important part of the typical HP pattern. Emphysema, which is not included in any of the HP patterns, was noted with a relatively high frequency, and in some cases was combined with the "honeycomb lung" symptom. The greatest strength of the correlation was found in such combinations of signs as "frosted glass" + reticular changes; "frosted glass" + "mosaic density"; reticular changes + "mosaic density"; emphysema + centrilobular foci, as well as reticular changes + bronchiectasis. These combinations occurred with a relatively high frequency among the examined patients.

Results. Most of the identified changes correspond to current recommendations for the diagnosis of HP. A weak correlation between the signs does not allow us to identify combinations of signs with sufficient reliability that can help in the early diagnosis of HP.