Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Arooj Naz, M.B.B.S

Although CT scans are not a primary modality of testing for bacterial pneumonia, they may be utilized in complex cases where the underlying cause is unknown^[1] and/or when empiric antibiotic use yields no symptomatic relief in the patient. CT scans may be very informative and assist in differentiating infectious and noninfectious pneumonia.^[2] Similar to chest x-rays, CT findings can also be described according to the type of pneumonia including lobar or focal nonsegmental pneumonia, lobular or multifocal bronchopneumonia, and diffuse or interstitial (atypical) pneumonia.

Type of Pneumonia	Common Organisms	CT Scan	Findings
Lobar/ Focal non-segmental[3]	Klebsiella pneumoniae Legionella pneumophila Haemophilus influenzae		Focal dense opacification of the majority of an entire lobe Relative sparing of the large airways Ground glass opacity appearance in a lobar or segmental pattern
Lobular/ Multifocal Bronchopneumonia[4]	Staphylococcus aureus Klebsiella pneumoniae Haemophilus influenzae Pseudomonas aeruginosa Escherichia coli		Multiple foci of opacity in a lobular pattern “Tree in Bud” appearance Larger areas of consolidation may appear as ‘patchwork quilt’
Diffuse/ Interstitial (Atypical)[5]	Mycoplasma Chlamydophila pneumoniae Chlamydophila psittaci Legionella		Focal ground glass opacity appearance (in a centrilobular pattern) Diffuse and bilateral (in most cases) Bronchial wall thickening Segmental atelectasis from small airway obstruction may occur Radiological findings are often more pronounced than the patients appearance Mycoplasma pneumoniae: airspace consolidation Legionella pneumophila: residual scarring may persist

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