[Histological study of the outer membrane of chronic subdural hematoma: possible mechanism for expansion of hematoma cavity].

Relationship between the histological features of the outer membrane of chronic subdural hematoma and computed tomography (CT) findings, and the period from trauma to surgery were studied, and the mechanism of hematoma enlargement was discussed. This study included 43 patients aged 16 to 84 years. The outer membranes collected during operation were examined by hematoxylin and eosin staining and elasticavan Gieson staining. Histological features were classified into 4 types according to maturity and intensity of the inflammatory reaction and hemorrhage. Type I: Noninflammatory membrane. This type of membrane was observed in 3 cases. This membrane, containing immature fibroblasts and collagen fibers, was associated with very slight or sparse cell infiltration and neocapillaries. Type II: Inflammatory membrane. This type of membrane was observed in 21 patients. The type, consisting of one layer of immature connective tissue, was associated with marked cell infiltration and vascularization throughout the entire thickness. Type III: Hemorrhagic-inflammatory membrane. This type of membrane was observed in 14 patients. This type had a structure of 2 or 3 layers, and was associated with capillaries with a large lumen on the side of the dura mater and marked cell infiltration and many thin new vessels on the side of the hematoma cavity. Some patients showed a layer consisting of only collagen fibers and fibroblasts between two such layers. In addition, hemorrhage into the membrane was often observed. Type IV: Scar-inflammatory membrane. This type of membrane was observed in 4 patients. This type showed inflammatory cell infiltration, neovascularization and hemorrhage in the outer membrane of cicatricial tissue.(ABSTRACT TRUNCATED AT 250 WORDS)