Fig. 4

a–d COVID-19 pneumonia differential diagnoses: hypersensitivity pneumonia and eosinophilic pneumonia. HRTCs of a patient affected by hypersensitivity pneumonia at baseline (a) and after two years (b): acute/subacute hypersensitivity pneumonia is characterised by diffuse ground-glass opacities clearly demarcated from air trapping areas (white arrows in a); chronic hypersensitivity pneumonia presents with architectural distortions and traction bronchiectases (black arrow in b). The triad of mosaic oligemia (1 in b), ground-glass opacities (2 in b) and normal pulmonary parenchyma (3 in b) is defined as “headcheese sign” (black oval in b). HRTC of acute eosinophilic pneumonia (c, d) showing confluent crazy paving opacities (white bordered black arrows in c, d) coexisting with consolidations (black asterisk in c) and slight bilateral pleural effusions