ObjectiveTo explore the differential diagnosis value of airspace consolidation in thoracic CT between organizing pneumonia (OP) and acquired community pneumonia (CAP).MethodsA retrospective study was taken by retrieving the patients CT database from October 2010 to August 2016. Fifty-six consecutive patients with OP and 99 consecutive patients with CAP whose CT showed airspace consolidation were enrolled and their clinical characteristics and radiological characteristics were analyzed.ResultsThe percentage of patients whose CT image showed various amount of air bronchogram (ABG) with different shapes is higher in OP group than that in CAP group (87.5% and 72.7% respectively, χ2=4.558, P=0.033). The median and interquartile range amount of ABG in the OP patients were significantly higher than those in CAP group [4 (ranged from 2 to 8) and 2 (ranged from 0 to 4) respectively, z=3.640, P=0.000]. Morphologically, 58.9% of the OP patients showed entire air bronchogram (EABG) on the thoracic CT, significantly higher than that in CAP group (21.2%) (χ2=22.413, P=0.000). Interrupted ABG was found in 26.3% of CAP patients, while 16.1% of OP patients shared same features and the difference was not statistically significant (χ2=2.125, P=0.148). Traction bronchiectasis and ground glass opacity (GGO) were more likely to be found in the OP patients rather than CAP patients with 26.8% and 39.3% respectively, while they were found in 1.0% and 11.1% in the CAP patients (P<0.05). Reversed halo sign was found only 1.0% of the CAP patients, significantly lower than that in OP group, 26.8% (χ2=25.671, P=0.000). Pleural effusion and bronchial wall thickening were more commonly found in the CAP group with 56.6% and 35.4% respectively. By multivariate logistic analysis, EABG (OR=5.526, P=0.000), traction bronchiectasis (OR=21.564, P=0.010), GGO (OR=4.657, P=0.007) and reversed halo sign (OR=13.304, P=0.023) were significantly associated with OP, while pleural effusion (OR=0.380, P=0.049) and bronchial wall thickening (OR=0.073, P=0.008) were significantly associated with CAP. Other features in thoracic CT coexisting with ABG all reach significance statistically between the OP and CAP group (all P<0.05).ConclusionsAirspace consolidation in thoracic CT may be valuable for the differential diagnosis between OP and CAP. EABG is more commonly found in OP patients than in CAP patients. When EABG exists or ABG coexists with traction bronchiectasis, GGO and reversed halo sign, a diagnose of OP should be considered.