Whereas most patients who develop hydrostatic pulmonary edema will develop interstitial edema first, followed by alveolar edema, some patients will present first with alveolar edema.

In contrast, however, as alveolar edema resolves, it does not clear by forming interstitial edema.

100-1A), perihilar indistinctness and vascular haze (see Fig. At higher left atrial pressures, frank alveolar edema occurs, with spillage of fluid into the air spaces.

In these patients, the chest radiograph will show an air space consolidation pattern (see Fig.

These findings are all more reliably distinguishable on posteroanterior (PA) and lateral chest radiographs than on portable radiographs, but commonly patients with the greatest likelihood of hydrostatic pulmonary edema will be imaged using an anteroposterior technique (AP).

AP techniques can make the diagnosis of hydrostatic pulmonary edema difficult because heart magnification, resulting from the considerably shorter focus-film distance as well as projectional magnification, can render determination of cardiac size unreliable, particularly in patients with low lung volumes.

Other potential causes include left atrial, mitral valvular, or pulmonary venous obstruction and volume overload in patients with renal failure or iatrogenic hypervolemia.

Less commonly, low intravascular oncotic pressure resulting from hypoalbuminemia, typically in patients with liver failure or nephrotic syndrome, may produce interstitial fluid accumulation.

Interstitial edema may change or clear within hours of treatment, whereas alveolar edema may require a longer time to clear.Kerley B lines are most readily visible in the inferior and lateral aspects of the thorax, near the lateral costophrenic sulcus (see Fig. The regular appearance of Kerley B lines in the lung bases is the result of the regular organization of pulmonary lobules at the lung bases.Kerley A lines also represent interlobular septal thickening but are relatively uncommon compared with Kerley B lines.Finally, pleural effusions often appear only as hazy attenuation projecting over lungs in patients imaged in a supine or semierect position.However, this appearance is not specific for pleural effusion and can be seen with extensive posterior atelectasis because anterior aerated lung superimposes on the increased opacity of the posteriorly located atelectatic lung.

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