Immunohistochemical localization of tissue-type plasminogen activator in the lining wall of chronic subdural hematoma.

Capsules of chronic subdural hematoma were immunohistochemically stained with monoclonal antibody against tissue-type plasminogen activator. Endothelial cells of sinusoids and capillaries in the outer membrane showed strong immunostaining. Endothelial cells of veins and arteries in the dura mater showed moderate and weak staining. No cells other than the endothelial cells were stained. In the inner membrane, tissue-type plasminogen activator immunoreactivity was not seen. The mean concentration of tissue-type plasminogen activator in the hematoma content was higher than that in the plasma. The more the sinusoids in the outer membrane were developed, the higher the concentration of tissue-type plasminogen activator contained in the hematoma fluid. In chronic subdural hematoma, overproduction and oversecretion of tissue-type plasminogen activator from the sinusoidal and capillary endothelial cells in the outer membrane cause increased fibrinolysis, which in turn impairs hemostasis, and hemorrhage from the capillaries recurs, resulting in enlargement of the chronic subdural hematoma.