Definition of Chronic subdural hematoma:

A chronic subdural hematoma is an "old" collection of blood and blood breakdown products between the surface of the brain and its outermost covering (the dura). The chronic phase of a subdural hematoma begins several weeks after the first bleeding.

Causes, incidence, and risk factors:

A subdural hematoma develops when the tiny veins that run between the dura and surface of the brain (bridging veins) tear and leak blood. This is usually the result of a head injury.

A collection of blood then forms over the surface of the brain. In a chronic subdural collection, blood leaks from the veins slowly over time, or a fast hemorrhage is left to clear up on its own.

A subdural hematoma is more common in the elderly because of normal brain shrinkage that occurs with aging. This shrinkage stretches and weakens the bridging veins. These veins are more likely to break in the elderly, even after a minor head injury. Rarely, a subdural hematoma can occur without known cause (i.e., not from an accident or injury).

Risks include:

• Long term, heavy alcohol use
• Long-term use of aspirin, anti-inflammatory drugs, such as ibuprofen, or blood thinning (anticoagulant) medication
• Diseases associated with reduced blood clotting
• Head injury
• Old age