Fig. 1

Hexagonal pattern in the HRCT. a, b Hexagonal pattern is an interlobular septal thickening expanding from the subpleural region to two or more inner layers of the secondary pulmonary lobules. c When there is subpleural collapse such that the structure of the secondary pulmonary lobules is no longer recognizable, hexagonal pattern was defined as interlobular septal thickening that expands to two or more inner layers of the secondary pulmonary lobules from the collapsed area