Figure Legend
Note In order to facilitate the reader’s recognition of pulmonary lobular signs, different arrows in figure2-6 in this manuscript represent the different signs (green arrow shows lobular size sign, green double-headed arrow shows fusion lobular sign, black arrow shows lobular septal thickening, white arrow shows lobular interstitial thickening sign , red arrow shows lobular vascular thickening sign).
Figure 1 Schematic of lobular structure of axial CT. The reticular structure of the left mimics the distribution of pulmonary lobules, and the larger one is the cortex lobule and the smaller one is the medullary lobule. The right is an enlarged simulated lobular structure. Letter a refers to the interlobular septum, b refers to intralobular vessel, and c refers to the intralobular interstitium.
Figure 2 Schematics of the lobular structural characteristics that include five categories: Lobular size (a), fusion lobules (b), interlobular septal thickening (c), intralobular interstitial thickening (d), intralobular vascular thickening (e). a1-e1images are the actual CT axial images corresponding to the schematics.
Figure 3 The combined picture (a-f) is composed of typical cases of COVID-19. All the cases are consistent with the three characteristics which include multiple GGOs or consolidations , pulmonary lobular or fusion lobule size and subpleural distribution.
Figure 4 Six COVID-19 cases are selected to represent the five atypical CT features. a-b represent single GGO or consolidation, c-d represent halo sign or reverse-halo sign, e-f represent bronchovascular bundle thickening with peripheral GGO or consolidation.
Figures 5 a-c Early, advanced and recovery stages of one COVID-19 patient are shown. a. The size of the lobule in the early stage. b. Fusion lobules in the advanced stage. The intralobular interstitial and interlobular vascular thickened. c. Lobular septal thickening in the recovery stage. d-f. Advanced, severe and recovery stages of another COVID-19 patient are depicted. d. During the advanced stage, the area of right pulmonary fusion lobule is increased, and the new leisons with lobular size are seen in the left lung. e. Diffuse mosaic sign (“white lung”) in severe stage. f. The interlobular septal thickening in the recovery stage.
Figure 6 a-f are differential diseases with COVID-19 in CT imaging respectively. Lobar pneumonia(a) is characterized by consolidation of lobar segments without obvious pulmonary lobular structure signs. Mycoplasma pneumonia (b) and Influenza pneumonia(c), both of them can be seen the sign of fusion lobule, but the mycoplasma pneumonia is distributed along the bronchovascular bundle. Pulmonary edema (d), there is obvious sign of interlobular septal thickening. Both traumatic wet lung (e) and pulmonary hemorrhage (f) show subpleural GGO, but there is no significant pulmonary lobular structure signs.