Normal lung; no fibrotic burden at the flimsiest small fibers in some alveolar walls
1
Lung structure: alveoli partly enlarged and rarefied, but no fibrotic masses was present; alveolar septa: isolated gentle fibrotic changes (septum ≤ 3× thicker than normal)
2
Lung structure: alveoli partly enlarged and rarefied, but no fibrotic masses; alveolar septa: clearly fibrotic changes (septum > 3× thicker than normal) with knot-like formation but not connected to each other
3
Lung structure: alveoli partly enlarged and rarefied, but no fibrotic masses; alveolar septa: contiguous fibrotic walls (septum > 3× thicker than normal) predominantly in the whole microscopic field
4
Lung structure: single fibrotic masses (≤10% of microscopic field); alveolar septa: variable
5
Lung structure: confluent fibrotic masses (>10% and ≤50% of microscopic field), lung structure severely damaged but still preserved; alveolar septa: variable
6
Lung structure: large contiguous fibrotic masses (>50% of microscopic field), lung architecture mostly not preserved; alveolar septa: variable, mostly not exist
7
Lung structure: alveoli nearly obliterated with fibrous masses but still up to five air bubbles; alveolar septa: nonexistent
8
Lung structure: alveoli nearly obliterated with fibrous masses but still up to five air bubbles; alveolar septa: nonexistent
