Tiny veins called bridging veins run between the dura and the surface of the brain. A subdural hematoma develops when these veins tear and leak blood, usually as the result of a head injury. A collection of blood then forms over the surface of the brain. In a chronic subdural collection, the problem is not discovered immediately and blood leaks from the veins slowly over time. A subdural hematoma is more common in the elderly because normal brain shrinkage occurs with aging that stretches and weakens the bridging veins. Thus, these veins are more likely to break in the elderly, even after a minor head injury. Rarely, a subdural hematoma can occur spontaneously (i.e., not from an accident or injury). Risks include head injury, old age, chronic use of aspirin, anti-inflammatory drugs such as Ibuprofen or blood thinning (anti-coagulant) medication, chronic heavy alcohol use, or many diseases associated with blood clotting problems.
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