Final answer:
Subdural hemorrhages usually originate from the tearing of bridging veins after a head injury, potentially involving major arterial damage at the pterion. They are seen on a CT scan as crescent-shaped areas of high density in acute cases, contrasting with chronic appearances that may display lower density due to blood breakdown.
Step-by-step explanation:
The likely origin of bleeding in subdural hemorrhages is typically due to the rupture or tearing of veins that bridge the dura mater and the arachnoid layer of the brain. A common cause for this is a head injury, which can stretch and tear these small veins. In some instances, a blow to the lateral side of the head may fracture the bones of the pterion, damaging major arterial branches and leading to a hematoma between the brain and the interior of the skull. This pooling blood contributes to increased intracranial pressure and can displace brain tissue.
In radiographic imaging, especially on a CT scan, a subdural hemorrhage will typically present as a crescent-shaped area of high density when acute, situated along the inner layer of the skull above the brain. This appears different from other types of hemorrhages, such as epidural hemorrhages, which tend to have a more lenticular or convex shape. Chronic subdural hemorrhages, which develop over time, may appear as lower density areas due to the breakdown of the blood products.