Chronic subdural hematoma: concepts of physiopathogenesis. A review

From the present review it seems clear that the physiopathogenesis of the chronic subdural hematoma is far from being completely understood. However, an analysis of the known data can be summarized as follows: The development of subdural hematomas most likely occurs following minimal trauma in those patients with predisposing factors. Experimental data substantiates the fact that an accumulation of clotted blood in the subdural or subcutaneous space induced the formation of the fibroplastic neomembrane. The hypothesis that blood must come in contact with cerebrospinal fluid in order for the growth to occur, is still controversial. It has been virtually disproven that osmosis, referring to the electrolyte gradient as measured by freezing point depression, has any significance as a growth inducing factor. The protein oncotic gradient theory, having been the most widely accepted explanation as to the progressive enlargement of the subdural hematoma sac, has little experimental data supporting it. A larger body of clinical evidence exists supporting the concept that plasma and/or erythrocytes continuously penetrate into the subdural cavity, where enhanced fibrinolytic activity is present. However, this chronic rebleeding cannot fully explain the observed growth, because the composition of the hematoma fluid is smoewhat different from serum or plasma, and the protein content is also progressively diluted by fluid arising from an unknown source. There is some clinical and experimental evidence to suggest that a production-reabsorption balance may be a significant growth variable. No work has been done to define the role, if any, of local inflammatory mechanisms in the chronic subdural hematoma. Sound clinical evidence has shown that after the initial formation of the subdural clot, growth follows, than a slow, complete reabsorption usually occurs. Aside from the plausible production-reabsorption balance concept, it is not known why the evolution proceeds in this manner.