Radiology of severe acute respiratory syndrome (SARS): the emerging pathologic-radiologic correlates of an emerging disease.

Severe acute respiratory distress syndrome (SARS) caused by SARS-associated coronavirus (SARS-CoV) is a systemic infection that clinically manifests as progressive pneumonia. During the initial phases of infection the virus causes pauci-inflammatory alveolar and interstitial edema that result in imaging abnormalities dominated by ground glass opacities (GGO). Severe SARS cases can develop radiologic and pathologic findings of diffuse alveolar damage. Although radiologic evidence of acute bronchiolitis is absent, SARS-CoV also infects ciliated airway epithelium, probably accounting for respiratory transmissibility of the virus. Radiologic recovery from SARS can be complete, but computed tomography images often show persistent GGO and reticular opacities, some of which reflect pathologic findings of fibrosis. Long-term follow-up imaging of survivors shows gradual decrease of GGO and reticulation with persistent air trapping in some patients. The latter is evidence of small airway disease that is not radiologically evident at the onset of the disease.