The split pleura sign is seen with pleural empyemas and is considered the most reliable CT sign helping to distinguish an empyema from a peripheral pulmonary abscess (see empyema vs pulmonary abscess) 1,2.
The sign results from fibrin coating both the parietal and visceral surfaces of the pleura with resulting ingrowth of blood vessels with accompanying enhancement. Both layers of the pleura can then be visualized as linear regions of enhancement that come together at the margins of the collection 1.
Other causes of split pleura sign include 3:
malignancy including mesothelioma
hemothorax
talc pleurodesis
lobectomy
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