Pulmonary inflammatory hyperinflation in infants.

In infants less than 3 years old pulmonary hyperinflation can be a clinical and radiological sign of acute pneumonitis. It is an early, nonspecific occurrence in the presence of inflammation. The most reliable radiologic signs include flattening and undulation of the diaphragm, mediastinal elongation and narrowing, and a cardiac outline completely visualized above the diaphragm.