Imaging of community-acquired pneumonia: Roles of imaging examinations, imaging diagnosis of specific pathogens and discrimination from noninfectious diseases

Table 1 Specific imaging findings¹ of representative pathogens for community-acquired pneumonia

Pathogens	Specific imaging appearances
Streptococcus pneumoniae	Alveolar/lobar pneumonia
Mycoplasma pneumoniae	Bronchopneumonia with bronchial wall thickening affecting central bronchi
Chlamydophila pneumoniae	Infectious bronchiolitis with bronchial dilatation
Legionella pneumophila	Sharply marinated peribronchial consolidations within ground-glass opacities
varicella-zoster	Scattered nodules with a random distribution
Tubercle bacillus	Tree-in-bud appearance with finer and denser branching opacities than bronchopneumonia of common bacteria (postprimary tuberculosis)
Cryptococcus neoformans	Multiple nodules/masses with or without cavities in the same pulmonary lobe
Pneumocystis jirovecii	Bilateral patchy ground-glass opacities with a geographic distribution

¹Note that these imaging findings may be fairly specific but are not sensitive (i.e., other imaging findings are also not uncommon.) for these pathogens.

Table 2 Particular clinical conditions related to community-acquired pneumonia

Pathophysiological conditions	Imaging findings
Aspiration pneumonia	Bronchopneumonia or patchy ground-glass opacities at dorsal parts of the lung (S2, S1+2, S6 and S10) intrabronchial materials
Sinobronchial syndrome	Centrilobular or peribronchial nodules with bronchial wall thickening with bronchiectasis and mucus in the bronchi findings of paranasal sinusitis
Pneumonia on a background of pulmonary emphysema	Consolidation with pseudocavities or pseudohoneycombing, delayed resolution

Table 3 Representative differential diagnoses of community-acquired pneumonia

	Discriminators from community-acquired pneumonia
Non-infectious pneumonia
Cryptogenic organizing pneumonia	Relatively chronic clinical course (often for more than one month), evidences of organization (concavity of the opacities, traction bronchiectasis, clear visualization of peripheral air bronchograms, or mild parenchymal distortion), reversed halo sign
Chronic eosinophilic pneumonia	Bilateral nonsegmental consolidations with peripheral predominance
Lipoid pneumonia	Presence of fat within the consolidation on both visual assessment and computed tomography value measurement
Neoplasm	Lack of inflammatory response on laboratory data, chronic clinical course
Mucinous invasive adenocarcinoma	bulging contour, stretching or thinning of bronchi, cavities
Malignant lymphoma	Infiltrative spread around the consolidation (halo sign, galaxy sign, or thickening of surrounding vessels, etc.)