Findings: PA and lateral chest radiographs demonstrate bilateral parahilar infiltrates, resembling "bats-wing" or "butterfly" in which the hilum or "medulla" of the lungs are mainly involved with sparing of the periphery or "cortex."
Diagnosis: The "bats-wing" pattern of pulmonary edema.
Discussion: Although it was believed that the "bats-wing" pattern of edema is commonly associated with uremia, there has been increasing evidence that the lesion is the result of acute left ventricular failure and that there is no specific relationship to uremia.
Several proposed theories for the mechanism of this unusual anatomic distribution of pulmonary edema include that the arterials of the cortex may be particularly adapted for vasoconstriction or vasodilation, much the same as in the kidney. Vasoconstriction into "cortex" would result in shunting of the blood to the perihilar or "medullary" zones of the lungs, those protecting the cortex from the insult of edema. Another theory proposes that the accumulation of fluid is dependent upon deficiency with which the lymphatics can remove excess fluid. Since the cortical portions of the lungs undergo greater volumetric change than those of the medulla, this stimulates increased lymphatic clearance of the excess fluid.
The clinical manifestations, however, may not be as impressive as the roentgenographic appearance. Even when there is evidence of massive consolidation of the medial two thirds of the lungs, the clinical presentation may be unremarkable. This may be due to minimal amount of parenchyma in the "medullary" portion of the lungs where gas change occurs.
References:
RG Fraser, Pare JA Peter, Pare PD, Fraser RS, Genereux GP.
Diagnosis of Diseases of the Chest, 3rd Edition. W.B. Saunders Co.,
Philadelphia; 1990:1917-1920.
Freundlich IN, Bragg DG. A Radiographic Approach to Diseases of the Chest,
2nd Edition, Williams and Wilkins' Baltimore; 1997: 659.
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