Eosinophil degranulation in the capsule of chronic subdural hematomas.

A previously unrecognized role of eosinophils in chronic subdural hematomas is described. Outer membranes of hematomas with marked infiltration by eosinophils were studied ultrastructurally with particular attention to the degranulation of these cells. In all of the five cases studied, degranulation was observed. Disintegration of the cells contributed to the release of granules. The free granules, the matrix of which has been demonstrated to contain plasminogen, were often circulating in the vascular lumen and trapped among the aggregated platelets. They were also found within the fragile vascular wall surrounded by fibrinoid material and in the edematous perivascular interstitium. Some of the perivascular eosinophils showed frank solubilization of granule matrix contents in spite of unaltered crystalloids. These findings suggest a role of eosinophils in the development of local hyperfibrinolysis within the outer membranes, which might contribute to the fluidity of chronic subdural hematomas and the resultant leakage of blood from the vessels in the capsules.