1.Patient profiles
14 men and 10 women (mean age 48.0±18.1 years; range 14–87 years) had COVID–19 pneumonia, and 13 men and 15 women (mean age 49.5±21.5; age range 24–85year) had other CAP. No statistically significant differences in age or gender distribution between the two groups were identified (p>0.05). 16 (66.7%) cases of COVID–19 pneumonia had exposure to the source of transmission within the past 14 days, significantly higher than the cases of other CAP (n = 2, 7.1%) (p = 0.000). The most common symptoms of COVID–19 pneumonia were fever (n = 20, 83.3%), fatigue (n = 13, 54.2%) and cough (n = 12, 50%). While diarrhea (n = 4, 16.7%) was the less common symptom. The most common symptoms of CAP were fever (n = 22, 78.6%) and cough (n = 20, 71.4%). While fatigue (n = 8, 28.6%) and diarrhea (n = 2, 7.1%) were the less common symptoms. The differences in clinical symptoms between the two groups were not significant (p>0.05). The mean time of HRCT after the onset of symptoms was similar in two groups (COVID–19 vs. CAP, 4.3±2.9days vs. 4.2±3.5days, p = 0.969). Patients in group COVID–19 had significantly lower white blood cell count (5.29±1.53 ×109/L) than patients in group of other CAP (8.39±4.97×109/L) (p = 0.005), while the lymphocyte count did not significantly different among groups (1.28±0.66×109/L vs. 1.41±0.91×109/L, p = 0.576).
2.CT patterns
The thoracic CT manifestations of COVID–19 pneumonia and other CAP patients are summarized in Table 1. For 24 patients with COVID–19 pneumonia, pure GGA (n = 14, 58.3%) and mixed GGA with consolidation (n = 10, 41.7%) were the typical parenchymal abnormalities (Figure 1A). The main diseases were predominantly observed to be patches with long axis parallel to pleura (n = 14, 58.3%), followed by nodules with round morphology (n = 7, 29.2%), and patches with long axis along the bronchovascular (n = 6, 25.0%) (Figure 1B, 1C, 1D). No pure consolidation was detected in this retrospective case series. Air bronchogram (n = 13, 54.2%), vessels dilatation (n = 13, 54.2%) and crazy-paving appearance (n = 8, 33.3%) were the common findings (Figure 1E, 1F). Linear opacities (n = 5, 20.8%) and halo sign/reversed halo sign (n = 2, 8.3%) were also observed. No tree-in-bud sign, cavitary lesions, pleural effusion and lymphadenopathy was detected for any patients.
For the 28 patients with CAP, the parenchymal abnormalities were GGO with consolidation (n = 10, 35.7%), pure GGA (n = 9, 32.1%) and pure consolidation (n = 9, 32.1%) (Figure 2A, 2B). The main disease was predominantly observed to be patches with long axis parallel to bronchovascular (n = 14, 50.0%), followed by nodules with round morphology (n = 12, 42.9%), and patches with long axis parallel to pleura (n = 9, 32.1%). Air bronchogram (n = 16, 57.1%) and tree-in-bud sign (n = 12, 42.9%) were the most frequent findings (Figure 2C, 2D). Pleural effusion was presented in 6 of the patients with other CAP (21.4%). Crazy-paving appearance (n = 2, 7.1%), vessel dilatation (n = 2, 7.1%), linear opacities (n = 3, 10.7%), halo sign (n = 2, 7.1%) (Figure 2E, 2F)and lymphadenopathy (n = 2, 7.1%) were also observed. Cavitation was not detected in any patient.
The frequencies of crazy-paving appearance and vessel dilatation were significantly higher in patients with COVID–19 pneumonia compared with patients with other CAP (p = 0.031 and p = 0.000, respectively). Conversely, the frequencies of pure consolidation, tree-in-bud sign and pleural effusion were significantly higher in patients with CAP than those in patients with COVID–19 pneumonia (p = 0.002, p = 0.000 and p = 0.048, respectively). There were no significant differences in the shape of main lesions and other CT features, including pure GGA, mixed GGA with consolidation, air bronchogram, linear opacities, halo sign/reversed halo sign, cavitation and lymphadenopathy between the groups of COVID–19 pneumonia and other CAP.
3.Abnormality location and distribution
For the patients with COVID–19 pneumonia, main parenchymal abnormalities were noticed bilaterally in 17 patients (70.8%) and unilaterally in 7 patients (29.2%). Of the 24 patients, the predominant zonal distribution was the lower zone (n = 20, 83.3%), followed by the middle zone (n = 12, 50.0%) and the upper zone (n = 11, 45.8%). 17 patients (70.8%) had pulmonary parenchymal abnormalities predominantly distributed peripherally, and 7 patients (29.2%) had pulmonary parenchymal abnormalities distributed randomly. For patients with other CAP, main parenchymal abnormalities were observed to be bilaterally in 11 patients (39.3%) and unilaterally in 17 patients (60.7%). Of the 28 patients, middle zone was the predominant zonal distribution (n–18, 64.3%), followed by the lower zone (n = 16, 57.1%), and upper zone (n = 12, 42.9%). Main parenchymal abnormal findings were found to be randomly distributed in 11 patients (39.3%), peripherally distributed in 10 patients (35.7%), and centrally distributed in 7 patients (25.0%).
The frequency of bilaterally involvement and peripherally distribution was significantly higher in COVID–19 group than in the CAP group (p = 0.029, and p = 0.009, respectively). No significant differences in zonal involvement between the two groups were found.