Radiology of pneumonia.

Infection of the lower respiratory tract, acquired by way of the airways and confined to the lung parenchyma and airways, typically presents radiologically as one of three patterns: (1) focal nonsegmental or lobar pneumonia, (2) multifocal bronchopneumonia or lobular pneumonia, and (3) focal or diffuse "interstitial" pneumonia. These patterns can be useful in identifying the etiological organism in the appropriate clinical setting. To serve the purpose of this article, these patterns are used as the primary method of classification of pulmonary infections caused by different organisms. Mycobacterial and fungal pulmonary infections are reviewed separately because of their wide range of radiographic appearance that depend on the stage of the disease at presentation. This article discusses the clinical and radiographic features of the most common causes of pneumonia, primarily in the adult population of the United States.