Pathogenesis and epidemiology of chronic subdural hematoma

Background: Chronic subdural hematoma (SDH) is a common condition encountered in neurosurgical practice; however, its pathogenesis remains controversial. Current Concepts: SDH refers to blood accumulation inside the dura and is classified into acute, subacute, and chronic types. Histopathologically, acute SDH shows no neomembrane formation and the hematoma is a clot, in contrast to chronic SDH characterized by a neomembrane surrounding the liquefied hematoma. SDH is usually categorized into acute and chronic types, with subacute SDH being more similar to chronic SDH. Posttraumatic subdural lesions include acute and chronic SDH, subdural hygroma (SDG), or effusion. SDG is a blood-tinged fluid accompanied by neomembrane formation in some cases. These lesions are pathologically different from each other but may change depending on the situation. Discussion and Conclusion: Chronic SDH mainly originates from an SDG and acute SDH. SDG is usually triggered by trauma but only occurs in patients in whom sufficient potential space is available and may occur spontaneously in such cases. Therefore, SDG frequently occurs in children and in elderly patients, in men with a larger skull size, and on the left side of the body, which usually shows a wider hemisphere. Separation of the dural border cell layer causes inflammation, indicated by fibroblast proliferation and neovascularization. Conversion of an SDG into a chronic SDH or enlargement of a chronic SDH is attributable to formation of neomembranes, neovascularization, and repeated microhemorrhages from fragile capillaries. Chronic SDH is treated with removal of the hematoma to relieve the mass effect and embolization of the feeding artery for the bleeder. Outcomes of chronic SDH depend on the absorptive-expansion capacity dynamics.