5.3 Imaging examination

5.3.1 CT imaging (strong recommendation)
The imaging findings vary with the patient’s age, immunity status, disease stage at the time of scanning, underlying diseases, and drug interventions.
The imaging features of lesions show: (1) dominant distribution (mainly subpleural, along the bronchial vascular bundles); (2) quantity (often more than three or more lesions, occasional single or double lesions); (3) shape (patchy, large block, nodular, lumpy, honeycomb-like or grid-like, cord-like, etc.); (4) density (mostly uneven, a paving stones-like change mixed with ground glass density and interlobular septal thickening, consolidation and thickened bronchial wall, etc.); and (5) concomitant signs vary (air-bronchogram, rare pleural effusion and mediastinal lymph nodes enlargement, etc.).

5.3.2 Clinical data from Zhongnan Hospital of Wuhan University

Typical CT/X-ray imaging manifestation, including
Multiple, patchy, sub-segmental or segmental ground-glass density shadows in both lungs. They were classified as “paving stone-like” changes by fine-grid or small honeycomb-like thickening of interlobular septa. The thinner the CT scan layers, the clearer the ground-glass opacity and thickening of interlobular septa were displayed. A slightly high-density and ground-glass change with fuzzy edge in the fine-grid or small honeycomb-like thickening of interlobular septa were presented by the high-resolution computed tomography (HRCT), (Fig. 1: 45 cases, 54.2% in a total of 83 cases). The resolution of X-ray was worse lower than that of CT in the resolution, which was basically manifested as ground-glass opacities with fuzzy edge (Fig. 2: 9 cases, 10.8% in a total of 83 cases).
Fig. 1 Typical CT imaging manifestation (case 1). A 38 years old male with fever without obvious inducement (39.3 ℃), dry cough and shortness of breath for 3 days. Laboratory test: normal white blood cells (6.35 × 109/L), decreased lymphocytes percentage (4.1%), decreased lymphocytes count (0.31 × 109/L), decreased eosinophil count (0 × 109/L)), increased C-reaction protein (170.91 mg/L), increased procalcitonin (0.45 ng/ml). Imaging examination: multiple patches, grid-like lobule and thickening of interlobular septa, typical “paving stone-like” signs. a SL(Slice): 6 mm; b high-resolution computed tomography(HRCT). HRCT. high-resolution computed tomography
Fig. 2 Typical CT / X-ray imaging manifestation (case 2). A 51 years old male with general muscle ache and fatigue for 1 week, fever for 1 day (39.1 ℃), anemia. Laboratory test: normal white blood cells (9.24 × 109/L), lymphocytes percentage (5.1%), decreased lymphocytes (0.47 × 109/ L), decreased eosinophil count (0 × 109/L), increased C-reaction protein (170.91 mg/L), increased procalcitonin (0.45 ng/ml), increased erythrocyte sedimentation rate (48 mm/h). Imaging examination: a shows patchy shadows in the outer region of the left lower lobe, b shows large ground-glass opacity in the left lower lobe, and c shows subpleural patchy ground-glass opacity in posterior part of right upper lobe and lower tongue of left upper lobe, d shows large ground-glass opacity in the basal segment of the left lower lobe
(2) Multiple, patchy or large patches of consolidation in both lungs, with a little grid-like or honeycomb-shaped interlobular septal thickening, especially in the middle and lower lobes (Fig. 3: 26 cases, 31.3% in a total of 83 cases). It was more common in the elderly or severe condition patients.
Fig. 3 Typical CT / X-ray imaging manifestation (case 3). A 65 years old male with fever for 4 days (38.7 ℃). Laboratory test: normal white blood cells (3.72 × 109/L), decreased lymphocytes (0.9 × 109/ L), decreased eosinophil count (0 × 109/L), increased C-reaction protein (53.0 mg/L), increased procalcitonin (0.10 ng/ml), reduced liver function, hypoproteinemia, and mild anemia. Imaging examination: a and b showed large consolidation in the right middle lobe, patchy consolidation in the posterior and basal segment of the right lower lobe, with air-bronchogram inside, c showed patchy consolidation in the outer and basal segment of the left lower lobe, and a small amount of effusion in the right chest

Atypical CT/X-ray imaging manifestation, including
Single, or multiple, or extensive subpleural grid-like or honeycomb-like thickening of interlobular septum, thickening of the bronchial wall, and tortuous and thick strand-like opacity. Several patchy consolidations, occasionally with a small amount pleural effusion or enlargement of mediastinal lymph nodes, can be seen (Fig. 4: 6 cases, 7.2% in a total of 83 cases). This is mostly seen in the elderly.
Fig. 4 Atypical CT / X-ray imaging manifestation (case 1). An 83 years old female with fever for 4 days (maximum temperature of 38.8 ℃), cough, chills, sore throat, dry cough for 1 week, chest tightness and shortness of breath aggravating for 1 week. Laboratory test: normal white blood cells (4.6 × 109/L), normal neutrophil percentage (65.8%), decreased lymphocytes percentage (19.9%). Imaging examination: a and b showed diffuse interlobular septum thickening in both lungs to form a grid opacity, thickening of bronchial wall, and consolidation in the left sublobal lung. c showed diffused grid-like opacities in both lungs, especially in the left lung
(2) Single or multiple solid nodules or consolidated nodules in the center of lobule, surrounded by ground-glass opacities (Fig. 5: 5 cases, 6.2% in a total of 83 cases).
Fig. 5 Atypical CT / X-ray imaging manifestation (case 2). A 56 years old female with fever for 3 days. Laboratory test: decreased total protein (54.0 g/L),decreased albumin (35.5 g/L),decreased globulin (18.5 g/L), normal white blood cells (4.87 × 109/L), decreased lymphocytes percentage (10.1%), decreased lymphocytes (0.49 × 109/ L), decreased eosinophil count (0 × 109/L)), decreased eosinophil count percentage (0%). Imaging examination: a showed two consolidation nodulesat the center of the lateral segment of middle lobe of the right lung which was surrounded by ground-glass opacities; b showed patchy ground-glass opacity in the anterior segment of the right upper lung with patchy consolidation lesions in it; c showed patchy ground-glass opacities in both lungs with patchy consolidation lesions in it. d showed patchy consolidation in the ground-glass opacities in the middle lobe and dorsal segment of lower lobe of right lung

Stage based on CT image
The CT imaging demonstrates 5 stages according to the time of onset and the response of body to the virus, including: Ultra-early stage. This stage usually refers to the stage of patients without clinical manifestation, negative laboratory test but positive throat swab for 2019-nCoV within 1–2 weeks after being exposed to a virus-contaminated environment (history of contact with a patient or patient-related family members, unit, or medical staff in a cluster environment). The main imaging manifestations are single, double or scattered focal ground-glass opacity, nodules located in central lobule surrounded by patchy ground-glass opacities, patchy consolidation and sign of intra-bronchial air-bronchogram, which was dominant in the middle and lower pleura (Fig. 6: 7 cases, 8.4% in a total of 83 cases).
Fig. 6 CT imaging of ultra-early stage. a A 33 years old female with patchy ground-glass opacities after occupational exposure. b A 67 years old male with a history of contact with infected patients, showing large ground-glass opacity. c A 35 years old female exhibiting large consolidated opacity with air-bronchogram inside after occupational exposure
(2) Early stage.This stage refers to the period of 1–3 days after clinical manifestations (fever, cough, dry cough, etc.). The pathological process during this stage is dilatation and congestion of alveolar septal capillary, exudation of fluid in alveolar cavity and interlobular interstitial edema. It showed that single or multiple scattered patchy or agglomerated ground-glass opacities, separated by honeycomb-like or grid-like thickened of interlobular septa (Fig. 7: 45 cases, 54.2% in a total of 83 cases).
Fig. 7 CT imaging of early stage. Male, 38 years old, fever without obvious inducement (39.3 ℃), dry cough and shortness of breath for 3 days. Laboratory test: decreased white blood cells (3.01 × 109/L), decreased lymphocytes (0.81 × 109/ L), increased C-reaction protein (60.8 mg/L), increased procalcitonin (0.16 ng/ml). Imaging examination: a (thin layer CT) and b (high-resolution CT) showed multiple patchy and light consolidation in both lungs and grid-like thickness of interlobular septa
(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
(4) Consolidation stage. This stage refers to the period around 7–14 days after clinical manifestations appeared. The main pathological features in this stage are the fibrous exudation of the alveolar cavity and the disappearance of capillary congestion in the alveolar wall. CT imaging showed the multiple patchy consolidations in slighter density and smaller range than that of the previous stage. (Fig. 9: 26 cases, 31.2% in a total of 83 cases).
Fig. 9 CT imaging of consolidation stage. A 65 years old male with fever (maximum temperature of 39 ℃). Laboratory test: hypoproteinemia (decreased total protein (62.20 g/L), decreased albumin (35.70 g/L)), abnormal liver function (increased alanine aminotransferase (79 U/L), increased aspartate aminotransferase (72 U/L)), increased procalcitonin (0.10 ng/ml), increased C-reaction protein (53 mg/L), decreased white blood cells (3.72 × 109/L), decreased lymphocytes (0.9 × 109/ L), mildanemia (decreased red blood cells (4.10 × 1012/L), decreased hemoglobin (131.10 g/L), decreased hematocrit (39.0%). Imaging examination: a (thin layer CT) and b (high-resolution CT) showedmultiple patchyand large consolidation in right middle lobe, posterior and basal segment of right lower lobe and outer and basal segment of left lower lobe, with air-bronchogram inside
(5) Dissipation stage. This stage refers to the period roughly between 2 and 3 weeks after the onset of clinical manifestations. The range of lesions was further reduced. CT imaging showed patchy consolidation or strip-like opacity. As time goes on, it showed grid-like thickening of interlobular septum, thickening and strip-like twist of bronchial wall and a few scattered patchy consolidations (Fig. 10: 17 cases, 20.5% in a total of 83 cases).
Fig. 10 CT imaging of dissipation stage. A 79 years old female with intermittent fever. Laboratory test after 3 days of comprehensive treatment: decreased red blood cells (3.73 × 1012/L), hemoglobin (107 g/L), decreased hematocrit (31.8%), decreased lymphocytes percentage (13.9%), decreased lymphocytes (0.62 × 109/ L), decreased eosinophil count percentage (0%), decreased eosinophil count (0 × 109/L), increased alanine aminotransferase (46 U/L), deceased total protein (56.8 g/L), decreased albumin (33.5 g/L), normal C-reaction protein and procalcitonin. Imaging examination: a patchy ground-glass opacity and grid-like thickening of interlobular septa in the tongue-like segment of left upper lobe, and patchy consolidation in the posterior segment of right middle and lower lobe. b 9 days after admission to hospotial, CT scan showed absorption of lesions in the middle lobe, narrowing of lesions in the lower lobe of the right lung, and absorption of lesions in the tongue-like segment of left upper lobe which exhibited a cord-like change