of honey combing or other lung comorbidities (Figure 1 ). Echo cardio graphy may also be useful. When early undiagnosed IPF presents with fulminant respiratory insufficiency and ARDS [3, 29] , honeycombing with bibasilar and subpleural distribution on HRCT [1] can establish the diagnosis of IPF exacerbation and diff eren tiate defi nitely from AIP [49] . In IPF exacerbations, HRCT reveals new bilateral ground-glass abnormalities or consolidations (or both) upon UIP pattern [6] . A ground-glass pattern, especially if extensive, is not a feature of stable IPF, and its rapid development away from areas of fi brosis heralds DAD. Akira and colleagues [18, 56] have proposed a classifi cation of acute exacer bations of IPF on the basis of three ground-glass and consolidation computed tomography patterns that appear to have prognostic implications: (a) peripheral, (b) multifocal, and (c) diff use, though others did not confi rm a similar assumption [57] .