Pulmonary Aspiration Syndromes: An Imaging-based Review.

The term "aspiration" describes lung injury that results from unintentional passage of contents other than air into the lungs and bronchial tree, commonly from the gastrointestinal and upper respiratory tracts. Only a small proportion of aspiration-related events are symptomatic, especially in predisposed individuals such as patients with diminished consciousness, impaired swallowing, oesophageal motility disorders, and reflux disease. Aspiration-related syndromes can be classified based on the onset of presentation, composition of the aspirated substance, and anatomic site of injury. When considering the injury site, the aspirated material can either obstruct the airways, thereby presenting with obstructive features (eg, atelectasis on radiographs); it can alternatively affect the lung parenchyma. Lung injury due to aspiration of noxious agents such as acid or lipids is termed chemical aspiration pneumonitis. The aspirated contents can alternatively lead to lung parenchymal infection when the contents are infected, which is termed aspiration pneumonia. We have reviewed the imaging manifestations of various entities related to aspiration and have classified the abnormalities based on the site of injury and the nature of the culprit agent. Differences between "aspiration pneumonitis" and "aspiration pneumonia" are also explored. This is followed by an illustration of a few specific situations related to aspiration in pediatric and adult patients.