Yes, a subdural hematoma is a type of traumatic brain injury. It is one of the most serious forms of TBI, caused by bleeding between the brain and its outer protective covering. The severity can range from mild to life-threatening depending on how much blood collects and how quickly.
How a Subdural Hematoma Happens
Your brain is surrounded by layers of protective tissue. Small veins called bridging veins stretch between the brain’s surface and the tough outer membrane (the dura). When your head experiences a sudden impact or rapid acceleration and deceleration, these veins can tear. Blood then leaks into the inner layer of the dura and pools between the membrane and the brain.
What makes this injury particularly dangerous is a feedback loop. As blood accumulates, pressure inside the skull rises. That increased pressure actually forces more blood out of the torn veins and into the growing collection, causing the hematoma to enlarge on its own. This is why some subdural hematomas expand rapidly even after the initial injury.
Acute, Subacute, and Chronic Types
Subdural hematomas are classified by how quickly symptoms develop after the injury:
- Acute: symptoms within 4 days of injury. These are the most dangerous and typically result from significant trauma like car accidents or serious falls.
- Subacute: symptoms appear between 4 and 21 days after injury.
- Chronic: symptoms develop after 21 days, sometimes weeks or months later. These often follow a minor bump to the head that the person barely remembers.
Chronic subdural hematomas are especially common in older adults. As people age, the brain naturally shrinks slightly, which stretches the bridging veins and makes them more vulnerable to tearing from even mild impacts. Blood-thinning medications dramatically increase the risk. Patients taking warfarin, for example, have a 42.5-fold increase in the incidence of chronic subdural hematoma compared to those not on blood thinners. In some studies, over 40% of elderly patients with chronic subdural hematomas were taking anticoagulant or antiplatelet medications.
How Severity Is Measured
Like all traumatic brain injuries, subdural hematomas are graded using the Glasgow Coma Scale, which scores a person’s ability to open their eyes, speak, and move on command. The scale runs from 3 to 15:
- Mild TBI: GCS score of 13 to 15
- Moderate TBI: GCS score of 9 to 12
- Severe TBI: GCS score of 3 to 8
A small chronic subdural hematoma in someone who is fully alert might qualify as a mild TBI. A large acute subdural hematoma in someone who is unconscious would be classified as severe. The same type of bleeding can sit anywhere on the spectrum depending on how much blood has collected and how much pressure it puts on the brain.
Symptoms and Diagnosis
Acute subdural hematomas typically cause a sudden, severe headache, confusion, weakness on one side of the body, slurred speech, or loss of consciousness. Chronic subdural hematomas are more subtle. They can mimic dementia in older adults, with gradually worsening confusion, difficulty walking, personality changes, or persistent headaches over weeks.
A CT scan without contrast dye is the standard diagnostic tool. On imaging, a subdural hematoma appears as a bright, crescent-shaped collection hugging the inner surface of the skull. This crescent shape distinguishes it from an epidural hematoma, which appears lens-shaped and is caused by arterial bleeding rather than torn veins. A subdural hematoma can cross the lines between skull bones, while an epidural hematoma cannot.
Treatment and Surgery Thresholds
Not every subdural hematoma requires surgery. Current guidelines recommend surgical removal when the blood collection is thicker than 10 millimeters or when it pushes the brain more than 5 millimeters off center (called midline shift), regardless of the patient’s level of consciousness. Smaller hematomas that aren’t causing significant pressure may be monitored with repeat imaging to ensure they don’t grow.
For chronic subdural hematomas, surgery is typically less invasive. A small opening in the skull allows the older, liquefied blood to drain. For acute cases, a larger opening may be needed to remove the clotted blood and stop active bleeding.
Survival and Recovery Outcomes
Historically, mortality rates for acute traumatic subdural hematoma ranged from 22% to 66%. More recent data from a Level I trauma center found in-hospital mortality of 14% across a large cohort of adult patients, a meaningful improvement likely driven by faster diagnosis and better intensive care. Survival rates were similar whether patients underwent surgery or were managed without it, though the surgical and nonsurgical groups had different injury characteristics.
Among survivors, recovery prospects are encouraging in many cases. At discharge, 94% of surviving patients had a GCS score of 13 or higher, meaning they were alert and oriented. About 81% could feed themselves independently, and 92% could communicate independently. Walking was harder to recover quickly: only 43% were moving independently by the time they left the hospital, though this figure improves with rehabilitation over the following months.
Long-Term Risk of Seizures
Epileptic seizures are a recognized complication after subdural hematoma, and the risk differs sharply between acute and chronic types. In acute subdural hematomas, about 28% of patients develop seizures in the early period after injury, and 43% experience seizures within two to three years. For chronic subdural hematomas, those numbers drop to around 5% early and 10% over two to three years.
The strongest predictor of seizures after an acute subdural hematoma is a very low level of consciousness after surgery (a GCS below 9 at 24 hours). For chronic subdural hematomas, alcohol use, prior stroke, and changes in mental status are the main risk factors. Interestingly, the size of the hematoma, which side of the head it’s on, and the patient’s age and sex do not significantly predict seizure risk in either type.
Subdural Hematomas in Children
In infants and children under two, subdural hematomas carry a unique significance. A subdural hematoma is the most common brain imaging finding in cases of suspected abusive head trauma (sometimes called shaken baby syndrome). The infant skull is thinner, the brain is proportionally larger, and the neck muscles are weaker, all of which make the bridging veins more susceptible to tearing from shaking or impact forces. No single finding confirms abuse on its own, but a subdural hematoma in an infant with no clear accidental cause raises immediate concern and typically triggers a full evaluation including CT and MRI of the brain and spine.