A hematoma in the brain is a collection of blood that pools inside or around the brain, usually after an injury or a burst blood vessel. Unlike a bruise on your arm that fades on its own, blood trapped inside the skull has nowhere to go. As it accumulates, it presses against brain tissue, and because the skull is rigid, even a small amount of blood can create dangerous pressure. Brain hematomas range from slow-developing collections that build over weeks to sudden, life-threatening bleeds that require emergency surgery.
Four Types Based on Location
The brain is wrapped in several protective layers called meninges, and where blood collects relative to those layers determines the type of hematoma and how it behaves.
- Epidural hematoma: Blood pools between the skull and the outermost membrane. This is almost always caused by a blow to the head that tears an artery running along the inside of the skull. Because arterial blood flows under high pressure, epidural hematomas can expand rapidly.
- Subdural hematoma: Blood collects just beneath the outer membrane, on the surface of the brain. These typically result from torn veins and can develop quickly after major trauma or slowly over days to weeks, especially in older adults.
- Subarachnoid hemorrhage: Bleeding occurs in the fluid-filled space that cushions the brain. Head injuries are the most common cause, though a ruptured aneurysm can trigger one without any trauma at all.
- Intraparenchymal hemorrhage: Blood leaks directly into the brain tissue itself. This type is closely linked to high blood pressure and is essentially a form of hemorrhagic stroke.
What Causes Brain Hematomas
Head trauma is the leading cause across all types. Falls, car accidents, sports injuries, and any forceful impact to the head can rupture blood vessels inside the skull. But not every brain hematoma starts with an injury.
High blood pressure is the single most common non-traumatic cause, responsible for roughly 37% of spontaneous bleeding inside the brain in one study of younger adults. Chronically elevated blood pressure weakens small arteries deep in the brain over time, and eventually one gives way. The resulting bleeds tend to occur in the brain’s deep structures rather than near the surface.
Structural abnormalities in blood vessels, such as arteriovenous malformations (tangles of abnormal vessels) and cavernomas (clusters of thin-walled vessels), account for about 29% of non-traumatic cases. These are typically present from birth and may go undetected for years until they bleed. Cocaine and amphetamine use can also trigger bleeding by causing sudden, extreme spikes in blood pressure.
Blood-thinning medications add risk as well. People taking anticoagulants or antiplatelet drugs bleed more easily, and when bleeding happens inside the skull, it can be harder to stop. Overall, modern oral anticoagulants carry a roughly 0.5% risk of intracranial bleeding over about 17 months of use, which is low in absolute terms but meaningful because the consequences are severe.
Symptoms to Recognize
Symptoms depend on the type, size, and speed of bleeding. A fast-growing epidural hematoma can cause loss of consciousness within minutes. In some cases, roughly 14% to 21% of epidural hematomas, the person initially loses consciousness, then appears to recover and feel fine for a period of minutes to hours. This “lucid interval” is dangerously misleading because it’s followed by sudden, rapid deterioration as pressure builds.
Subdural hematomas are classified by how quickly they develop: acute (under 4 days), subacute (4 to 21 days), or chronic (over 21 days). Acute subdural hematomas produce severe headache, confusion, and often one-sided weakness soon after injury. Chronic subdurals, common in older adults, can develop so gradually that the original head bump is forgotten. Weeks later, subtle changes appear: mild cognitive decline, slight weakness on one side of the body, personality shifts, or increasing drowsiness.
Across all types, warning signs include worsening headache, nausea or vomiting, confusion, slurred speech, weakness or numbness on one side, seizures, unequal pupil sizes, and decreasing consciousness. Any combination of these after a head injury, or appearing suddenly without explanation, warrants emergency evaluation.
How a Brain Hematoma Causes Damage
The immediate danger comes from what doctors call mass effect. The growing pocket of blood takes up space inside the skull, compressing the brain tissue next to it. As pressure rises, the brain can shift out of its normal position. If it shifts far enough, structures get pushed across the midline of the skull or downward toward the base, compressing the brainstem, the part of the brain that controls breathing and heart rate. This process, called herniation, is the most life-threatening complication.
Even when herniation doesn’t occur, the pressure can cut off blood flow to surrounding tissue, causing additional injury beyond the original bleed. Swelling around the hematoma compounds the problem over the first several days. This is why a person can appear stable initially and then worsen: the secondary swelling adds to the pressure created by the blood itself.
Diagnosis
A non-contrast CT scan of the head is the gold standard for detecting brain hematomas. It takes only minutes, clearly shows fresh blood as a bright white area, and pinpoints the location and size of the bleed. CT is the first imaging test performed in emergency rooms when a brain hematoma is suspected.
MRI may be used afterward to provide more detail, particularly for smaller or older bleeds that CT might miss. For chronic subdural hematomas that have been developing for weeks, the blood changes in appearance over time and can be harder to spot on CT alone.
Treatment Options
Small hematomas that aren’t causing significant pressure may be managed without surgery. The patient is monitored closely, usually in an intensive care unit, with repeat CT scans to track whether the bleed is growing. Medications to control blood pressure and reduce swelling are part of this approach.
Surgery becomes necessary when the hematoma is large enough to push brain structures out of alignment. The general threshold is a midline shift of more than 5 millimeters on imaging. For bleeds within the brain tissue specifically, research suggests surgery provides a clear survival benefit when the blood volume reaches 60 milliliters or more. Below about 45 milliliters, non-surgical management tends to work well. Volumes in between require judgment based on the patient’s overall condition.
The type of surgery depends on the hematoma. Epidural and acute subdural hematomas often require a craniotomy, where a section of skull is temporarily removed to drain the blood and relieve pressure. Chronic subdural hematomas can sometimes be drained through one or two small holes drilled in the skull, a less invasive procedure. In-hospital death rates for surgically treated chronic subdural hematomas are low, under 1%, though the 30-day mortality rate rises to about 4% and the one-year rate is approximately 15%, reflecting the fact that many patients are elderly with other health conditions.
Recovery and Long-Term Outlook
Recovery depends heavily on the severity of the initial injury, the size of the bleed, and how quickly treatment was received. The fastest gains typically happen in the first three to six months. During this window, the brain is most actively reorganizing and compensating for damaged areas.
But recovery doesn’t stop at six months. Longitudinal research tracking patients for up to five years after brain injury shows that functional improvement continues well beyond the initial period, particularly for people with moderate to severe injuries. Survivors demonstrated increasing odds of regaining independence over time, though elevated rates of lingering symptoms, including fatigue, memory difficulties, and mood changes, persisted across all severity levels up to five years out.
Rehabilitation typically involves physical therapy to rebuild strength and coordination, occupational therapy to relearn daily tasks, and sometimes speech therapy. The specific program depends on which areas of the brain were affected. Younger patients and those with smaller bleeds that were treated quickly tend to have the best outcomes, while large hematomas that caused herniation or prolonged unconsciousness carry a more guarded prognosis.