Rare findings in high resolution computed tomography (HRCT) in interstitial lung diseases

High resolution computed tomography (HRCT) is an imaging method, achieving an optimal resolution of lung interstitium images. HRCT enables more accurate diagnosis of interstitial lung diseases, in which it is a diagnostic method of choice. A lot of pathological findings specific only for HRCT were described. Some of them are relatively rare, and therefore not well known. In some cases good knowledge of them is essential in making a correct diagnosis based on HRCT results. The aim of the study was assessment of rare findings on HRCT, their morphology and diagnostic value in interstitial lung disease. The tram track sign and signet-ring sign visible on HRCT are very specific findings in bronchiectases. The tree-in-bud pattern is a specific finding for diseases of small airways, especially involving small bronchioles. The differences in sizes of vessels in hyper-lucent and hyper-dense lung areas enable differentiation of mosaic perfusion from other reasons for inhomogeneous lung density. Rounded atelectasis and comet tail sign are specific findings for asbestosis. The angiogram sign is a very specific finding for bronchoalveolar carcinoma.