Fig. 1

a–g COVID-19 pneumonia phases. HRTCs of patients showing the different phases and possible evolutions of COVID-19 pneumonia. In a, two subpleural, sharply demarked ground-glass opacities (white arrows in a) indicate phase 1. There is evidence of concomitant widening of peripheral vessels (black arrow in a). In b and c, subpleural extensive areas of ground glass (white arrow in c) and crazy paving pattern (black bordered white arrows in b, c) are referable to phase 2. Black arrows in b indicate dilatated segmental and subsegmental vessels. Phase 2 may also be characterised by extensive areas of crazy paving (black bordered white arrow in d), in which small consolidative foci are evident (black circle in d); In e, dependent and non-dependent consolidations (black circles in e) are hallmarks of phase 3. Phase 4 (f) presents as irregular consolidative foci (black circle in f) coexisting with confluent ground-glass opacities (white arrow in f) and crazy paving pattern (black bordered white arrow in f), whereas ARDS, which represents a possible complication COVID-19 pneumonia, is characterised by dependent consolidations (black asterisk in g) and widespread ground-glass attenuation