Liberation of eosinophil granules in the inner capsule of chronic subdural hematomas

The role of eosinophilic infiltration in the inner capsule was studied in 35 consecutive cases of chronic subdural hematomas. The eosinophilic infiltration in the inner capsule was microscopically observed in 10 of the 22 cases which were associated with the infiltration in the outer capsule. The majority of eosinophils were ultrastructurally fully granulated and contained numerous glycogen granules. In contrast, some eosinophils were undergoing marked cellular disruption or necrosis with a resultant liberation of secretion granules. This was confirmed in all of the 10 cases. The free granules were closely apposed to fibrin strands which were interwoven with a number of disintegrating inflammatory cells. The inner capsule was usually adhered by massive fibrinous clot and the remaining liquified hematoma contained low levels of fibrinogen and high levels of FDP. Secretion granules of the eosinophils were previously demonstrated to contain plasminogen or cytotoxic material. Accordingly, the eosinophils conceivably contribute to both the fluidity of subdural clot and the disruption of inflammatory cells in chronic subdural hematomas.