Rapid development of extensive alveolar infiltrates, usually involving a whole lobe or even several lobes. Air bronchograms are infrequent because the acute inflammatory exudate fills the airways, leading to segmental collapse and a loss of volume.
Most frequently occurs in children, especially during the first year of life. In adults, usually affects hospitalized patients with lowered resistance or as a complication of a viral respiratory infection. A characteristic finding in childhood disease is the development of pneumatoceles, thin-walled cystic spaces in the parenchyma that typically disappear spontaneously within several weeks. Pleural effusion (or empyema) often occurs.