(3) Rapid progression stage. This stage refers to the period about 3–7 days after clinical manifestations started, the pathological features in this stage are the accumulation of a large number of cell-rich exudates in the alveolar cavity, vascular expansion and exudation in the interstitium, both of which lead to further aggravation of alveolar and Interstitial edema. The fibrous exudation connects each alveolus through the inter-alveolar space to form a fusion state. The CT manifested a fused and large-scale light consolidation with air-bronchogram inside (Fig. 8: 17 cases, 20.5% in a total of 83 cases).
Fig. 8 CT imaging of rapid progression stage. A 50 years old female with anorexia, fatigue, muscle soreness, nasal congestion and runny nose for 1 week, sore and itching throat for 2 days. Laboratory test: increased erythrocyte sedimentation rate (25 mm/h), normal white blood cells (4.08 × 109/L), decreased lymphocytes (0.96 × 109/ L), increased C-reaction protein (60.8 mg/L). Imaging examination: a (thin layer CT) and b (high-resolution CT) showed multiplepatchy and light consolidation in both lungs and grid-like thickness of interlobular septa