Many of these patients are comatose on admission. Presentation varies widely in acute subdural hematoma. However, subdural hematomas may be mixed in nature, such as when acute bleeding has occurred into a chronic subdural hematoma. Chronic subdural hematomas develop over the course of weeks and are hypodense compared with the brain. The subacute phase begins 3-7 days after acute injury. Generally, acute subdural hematomas are less than 72 hours old and are hyperdense compared with the brain on CT scans. These factors, as well as the neurologic and medical condition of the patient, determine the course of treatment and may also influence the outcome. When the inciting event is unknown, the appearance of the hematoma on neuroimaging studies can help determine when the hematoma occurred. Subdural hematomas are usually characterized by their size and location and the amount of time elapsed since the inciting event age (i.e., whether they are acute, subacute, or chronic). Rates of mortality and morbidity can be high, even with the best medical and neurosurgical care. Subdural hematoma may also be spontaneous or caused by a procedure, such as a lumbar puncture.
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Subdural hematoma occurs not only in patients with severe head injury but also in patients with less severe head injuries, particularly those who are elderly or who are receiving anticoagulants. Subdural hematoma is the most common type of traumatic intracranial mass lesion. A subdural hematoma (SDH) is a collection of blood below the inner layer of the dura but external to the brain and arachnoid membrane.