The extrapleural fat sign on postmortem computed tomography may differentiate acute from chronic extrapleural hematomas

Abstract

Extrapleural fat sign is currently regarded as a CT finding that is useful in detecting Extrapleural hematoma (EH). The EH is caused by bleeding between parietal pleura and fascia endothoracica. The incidence of EH is low and thus the opportunity to study EH with both postmortem computed tomography (PMCT) and autopsy remains rare. Here we report two autopsy cases of EH that were also studied with PMCT. Case 1, acute EH case, was 90-year-old male, knocked down by a car. Two days after, he died. On PMCT, clear extrapleural fat sign was found in EH. On autopsy, his EH was shown to be mainly made by fresh clot. Fracture of the ribs was found under the EH. Hematoxylin-eosin (HE)-stained section revealed vacuoles, implying the existence of fatty tissue, between EH and pleura. Case 2, chronic EH case, was 76-year-old male, found dead in bathtub. On PMCT, EH without extrapleural fat sign was demonstrated. On autopsy, EH made by organized clot, was found. HE stained sections revealed heavy proliferation of fibroblasts lacking vacuoles in this clot. Thus it seems likely that extrapleural fat sign on PMCT reflects the time elapse after EH formation: Fat layer is present in acute EH, causing fat sign on image. Then, the fat layer is replaced by fibroblasts along with the development of inflammation reaction, causing disappearance of fat sign. Thus, evaluation of fat sign may be used to know if the HE is acute or chronic in forensic medicine as well as in clinical medicine. Keywords: Extrapleural hematoma, Postmortem computed tomography, Extrapleural fat sign, Autopsy