Findings: Plain film of the chest demonstrates diffuse, bilateral alveolar infiltrates with scattered air bronchograms. The cardiac silhouette and pulmonary vascularity are within normal limits. No pleural effusion is seen.

Diagnosis: Lung injury pulmonary edema

Discussion: The differential diagnosis of pulmonary edema is extensive, and correctly distinguishing between the various causes relies upon both clinical and radiographic clues. Note should be made that there is some overlap in the radiographic findings between the different causes. The three main categories of causes of pulmonary edema include cardiogenic, nephrogenic, and lung injury.

Cardiogenic causes include congestive heart failure, cardiac tamponade, and cardiomyopathies, among others. Pulmonary edema may also be nephrogenic or caused by fluid overload. Lung injury pulmonary edema may be seen in near-drowning, toxic inhalation, and in neurogenic shock.

Heart size is usually enlarged in cardiogenic pulmonary edema, but normal in lung injury. The pulmonary vascularity is usually engorged and cephalized in cardiogenic causes, balanced to cephalized in fluid overload, and normal in lung injury. Pleural effusion may be seen in all three causes. Septal lines indicative of interstitial edema are more frequent in cardiogenic causes. The infiltrates of cardiogenic pulmonary edema are usually diffuse, and air bronchograms are rare. Those of nephrogenic pulmonary edema are classically described as bat-wing in distribution, whereas those of lung injury tend to be more peripheral. While the peripheral infiltrate is fairly specific for lung injury, the diffuse variety is equally commonly seen in lung injury. The presence of air bronchograms is also fairly specific for lung injury.

References:
Aberle DR, Wiener-Kronish JP, Webb WR, et al. Radiology 1988;168:73-79.
Hydrostatic versus Increased Permeability Pulmonary Edema: Diagnosis Based
on Radiographic Criteria in Critically Ill Patients.

Milne ENC, Pistolesi M, Miniati M, et al. The Radiologic Distinction of Cardiogenic
and Non-cardiogenic Edema. AJR 1985;144:879-894.

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