Object. Thrombomodulin is a thrombin receptor on vascular endothelial cells that is highly expressed when these cells are injured, and it has anticoagulating activity. The authors investigated thrombomodulin expression to clarify why chronic subdural hematomas (CSDHs) continue to grow slowly, like a tumor, and are liquefied. Methods. Burr hole craniotomy and drainage were performed in all 35 patients with CSDH who were included in the study. The plasma-soluble thrombomodulin and blood clotting factor values were determined in the hematoma and in peripheral blood. In the seven most recent cases, the plasma-soluble thrombomodulin values were determined in the residual hematoma collected from the drainage tube the day after surgery. The outer membranes of the CSDH that were obtained as specimens at operation were stained with monoclonal antibody against thrombomodulin for immunohistochemical studies. The plasma-soluble thrombomodulin values were higher (p < 0.0001), and conversely the values for factors V and VIII were lower in the hematoma than in peripheral blood (p < 0.0001). The plasma-soluble thrombomodulin values were lower in the residual hematomas than in the same lesions at operation (p= 0.018). The endothelial cells on the sinusoidal vessels exhibited immunoreactivity with thrombomodulin antibody in 28 (93%) of 30 cases. Conclusions. The thrombomodulin is expressed on the sinusoidal vessels, and the blood coagulation system is inhibited in the hematoma. These findings indicate that these vessels are continuously injured and fail to heal. As a result, the bleeding from the sinusoidal vessels may persist, and the hematoma may grow slowly and fail to coagulate. It is suspected that transmitted pulsation variations in the hematoma cavity generate sinusoidal vessel injury.
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