Key signs	Distribution	Ancillary signs	Non-parenchymal signs	Acute alveolar disease
GGO with possible patchy consolidations	GGO often bilateral and diffuse, consolidations with multifocal and peripheral basal distribution	Signs of fibrosing lung disease (UIP pattern)	Lymph node enlargement, pulmonary arterial hypertension	Acute Exacerbation of IPF (AE-IPF)
GGO, smooth interlobular septal thickening	Bilateral, patchy without zonal predominance	Possible crazy paving and consolidations	Small pleural effusion	Acute Eosinophilic Pneumonia (AEP)
First week: GGO and/or consolidations	Bilateral extensive GGO, mainly gravity-dependent consolidations	Second week: associated sign of fibrosis	Absent	Acute Interstitial Pneumonia (AIP)
First week: GGO and/or consolidations	Bilateral extensive GGO, mainly gravity-dependent consolidations	Second week: associated sign of fibrosis	Small pleural effusion	Acute Respiratory Distress Syndrome (ARDS)
GGO and/or patchy consolidations	Bilateral extensive GGO, patchy consolidations, possible perihilar (butterfly distribution)	Scattered feeding-vessels low-density (subsolid) nodules, solid and often cavitated macronodules	Hilar or mediastinal adenopathy, tracheal concentric wall thickening	Diffuse Alveolar Hemorrhage in Wegener’s granulomatosis (DAH in WG)
DAD pattern: GGO, possible consolidations	Bilateral diffuse GGO, possible gravity-dependent consolidations	Possible crazy paving	Possible pleural effusion	Drug toxicity (amiodarone)
GGO and consolidations, also lobular	GGO and lobular consolidation prevail in the upper zones, while extended consolidations are gravity dependent	Nodules, often subsolid, possible ginkgo biloba sign	Possible pleural effusion	Fat Embolism Syndrome (FES)
GGO	Symmetric bilateral, diffuse, or patchy, mainly the upper lobes and perihilar regions (butterfly sign)	Possible cysts, consolidations in patients with more severe disease	Small hilar or mediastinal lymph nodes	Infection, acute (PJP)
GGO, peribronchial cuffing and vessel enlargement, smooth septal thickening	Bilateral, central, and gravitational, possible perihilar regions (butterfly sign)	Possible crazy paving	Bilateral pleural effusion, cardiomegaly, dilatation of arteries and veins, mediastinal lymph nodes	Pulmonary edema (PE), alveolar