Doherty et al 1 seem confident of their ability to distinguish emphysematous spaces from large cystic spaces of honeycomb lung on the basis of a wall thickness on HRCT scanning of greater or less than 1 mm. In cryptogenic fibrosing alveolitis (CFA) we think this is difficult unless an assessment of function (with V/Q scanning or expiratory CT scans) is made at the same time.2 The situation is complicated by the ability of fibrosis in mixed emphysematous-fibrotic areas to support the airways and mitigate the expected gas trapping.

“Emphysematous” changes were …