Reverse pulmonary edema | Radiology Signs

Answer:

Reverse pulmonary edema (the “photographic negative of pulmonary edema”) is the classic radiographic pattern of chronic eosinophilic pneumonia (CEP), in which peripheral and nondependent pulmonary opacities occupy the lung periphery while sparing the central, perihilar lung. The same peripheral, nondependent distribution can also be seen in re-expansion pulmonary edema following rapid re-expansion of a chronically collapsed lung, such as after drainage of a pneumothorax or large pleural effusion.

Why is it called so?

Named “Reverse pulmonary edema” because its peripheral, nondependent distribution of opacities is the opposite (or photographic negative) of the typical central, perihilar, dependent bat-wing pattern seen in cardiogenic hydrostatic pulmonary edema. The term was coined by Gaensler and Carrington in 1977 to describe this pattern in chronic eosinophilic pneumonia.

Pathophysiology

In chronic eosinophilic pneumonia, eosinophilic infiltration of the alveolar septa and airspaces occurs preferentially in the lung periphery, producing dense subpleural opacities that spare the central lung. In re-expansion pulmonary edema, rapid re-expansion of a chronically collapsed lung after relief of obstruction generates high negative intrapleural pressure, reperfusion injury, and endothelial permeability changes, leading to fluid leakage into peripheral, nondependent alveolar spaces and interstitium; hydrostatic factors may contribute secondarily, producing unilateral or bilateral nondependent opacities sparing central regions.

Alternative names: Photographic negative of pulmonary edema, reverse batwing sign

Other associated named signs: Reversed halo sign / atoll sign (a distinct CT ring pattern occasionally also seen in eosinophilic pneumonia, but most characteristic of organizing pneumonia)

References

1. Gaensler EA, Carrington CB. Peripheral opacities in chronic eosinophilic pneumonia: the photographic negative of pulmonary edema. AJR Am J Roentgenol. 1977.