Differentiation of bacterial and non-bacterial community-acquired pneumonia by thin-section computed tomography

Abstract

Background and objective: The management of community-acquired pneumonia (CAP) depends, in part, on the identification of the causative agents. The objective of this study was to determine the potential of thin-section computed tomography (CT) in differentiating bacterial and non-bacterial pneumonia.

Patients and methods: Thin-section CT studies were prospectively examined in hospitalized CAP patients within 2 days of admission, followed by retrospective assessment by two pulmonary radiologists. Thin-section CT findings on the pneumonias caused by each pathogen were examined, and two types of pneumonias were compared. Using multivariate logistic regression analyses, receiver operating characteristic (ROC) curves were produced.

Results: Among 183 CAP episodes (181 patients, 125 men and 56 women, mean age+/-S.D.: 61.1+/-19.7) examined by thin-section CT, the etiologies of 125 were confirmed (94 bacterial pneumonia and 31 non-bacterial pneumonia). Centrilobular nodules were specific for non-bacterial pneumonia and airspace nodules were specific for bacterial pneumonia (specificities of 89% and 94%, respectively) when located in the outer lung areas. When centrilobular nodules were the principal finding, they were specific but lacked sensitivity for non-bacterial pneumonia (specificity 98% and sensitivity 23%). To distinguish the two types of pneumonias, centrilobular nodules, airspace nodules and lobular shadows were found to be important by multivariate analyses. ROC curve analysis discriminated bacterial pneumonia from non-bacterial pneumonia among patients without underlying lung diseases, yielding an optimal point with sensitivity and specificity of 86% and 79%, respectively, but was less effective when all patients were analyzed together (70% and 84%, respectively).

Conclusion: Thin-section CT examination was applied for the differentiation of bacterial and non-bacterial pneumonias. Though showing some potential, this examination at the present time would not be applicable for patients with underlying lung diseases, severe conditions of pneumonia, or immunocompromised conditions.

Fig. 1

Mycoplasmal pneumonia in a 30-year-old woman. A transverse thin-section CT scan (1-mm collimation) through the level of the ventriculi of the heart shows ground-glass attenuation combined with centrilobular nodules (arrows) and thickened bronchial walls (arrowheads) in the left lower lobe.

Fig. 2

Mycoplasmal pneumonia in a 27-year-old woman. A transverse thin-section CT scan (2-mm collimation) through the level of the dome of the right diaphragm demonstrates dominant centrilobular nodules in this patient. A small area of airspace consolidation with air-bronchogram is visible (arrow).

Fig. 3

Mycoplasmal pneumonia in a 28-year-old man. A transverse thin-section CT scan (2-mm collimation) through the level of the ventriculi of the heart shows centrilobular nodules with poorly defined margins (arrows) located in the outer lung zone, focal areas of airspace consolidation, and ground-glass opacities. Airspace nodules more than 3 mm in size are also seen in this field.

Fig. 4

Pneumococcal pneumonia in a 76-year-old man. A transverse thin-section CT scan (3-mm collimation) of the left lung at the level of the carina demonstrates ground-glass attenuation around airspace consolidation. Thickening of bronchovascular bundles were also observed in bacterial pneumonias (arrows).

Fig. 5

Pneumococcal pneumonia in a 60-year-old man. A transverse thin-section CT scan (1-mm collimation) of the right lung at the level of the carina shows an ill-defined cluster of airspace nodules with obscured vessels located in the outer third of the right upper lobe (arrows).

Fig. 6

Pneumococcal pneumonia in a 29-year-old woman. A transverse thin-section CT scan (1-mm collimation) of the right lung at the level of the ventriculi of the heart shows airspace consolidations and interlobular septal thickenings (arrows) within ground-glass attenuation. Thickening of bronchial walls is also noted (arrowheads).

Fig. 7

Receiver operating characteristic (ROC) curves from six-variable logistic regression models of the dependent variables “bacterial pneumonia” (models 1 and 2) and “mycoplasmal pneumonia” (model 3). Model 1 includes 125 cases with or without underlying lung disease (ULD) and model 2 includes 90 cases without ULD. Model 3 includes 56 cases diagnosed as either pneumococcal or mycoplasmal pneumonia without ULD. Sensitivity indicates the proportion of correctly classified patients as bacterial pneumonia in models 1 and 2 (pneumococcal pneumonia in model 3), and specificity indicates the proportion of correctly classified patients as non-bacterial pneumonia in models 1 and 2 (mycoplasmal pneumonia in model 3). The areas under the ROC curves for models 1, 2, and 3 were 0.837, 0.885 and 0.953, respectively.