A chronic subdural hematoma is a slow-building collection of blood between the brain and its outer protective covering, developing over weeks to months rather than all at once. It most commonly affects older adults after a minor head injury they may not even remember. The condition is increasingly common as the population ages and more people take blood-thinning medications, with incidence rates climbing sharply after age 65.
How It Forms
The space where blood collects sits between the brain itself and the dura, a tough membrane lining the inside of the skull. The traditional explanation was simple: a bump to the head tears small veins that bridge this space, and blood slowly pools. But that theory doesn’t fully hold up. A slow venous bleed would cause noticeable symptoms within days, yet chronic subdural hematomas typically take four to seven weeks after an injury to become symptomatic.
What actually happens is more complex. After an initial small bleed, the body forms a membrane around the blood collection. That membrane becomes the real problem. It grows its own fragile blood vessels, which leak easily, adding fresh blood to the collection over time. Meanwhile, the body’s normal clot-repair process works against itself: substances that break down clots are unusually active inside the hematoma, preventing the bleeding from sealing off. Inflammatory cells gather in the membrane walls, fueling a cycle of membrane growth, new leaky vessels, and continued fluid accumulation. The hematoma essentially becomes self-sustaining.
Who Is Most at Risk
Age is the single biggest factor. As the brain naturally shrinks with age, it pulls away slightly from the skull, stretching those bridging veins and leaving more space for blood to accumulate. Among men 85 and older, the incidence reaches roughly 355 cases per 100,000 people per year. For women in the same age group, it’s about 115 per 100,000. In the 65-to-74 range, rates are much lower: around 28 per 100,000 in men and 8 per 100,000 in women.
Men are more than twice as likely as women to develop the condition after a mild head injury. Other established risk factors include kidney failure and the use of blood-thinning medications, including both traditional blood thinners and newer direct oral anticoagulants. Between 50% and 77% of patients have a documented head injury in the weeks before symptoms appear, though the initial trauma can be as minor as bumping a doorframe or a low-impact fall.
Symptoms to Recognize
Because the blood builds up gradually, symptoms creep in rather than arriving all at once. This is what makes a chronic subdural hematoma different from an acute one, where severe symptoms like sudden unconsciousness develop within hours of a major injury. With the chronic form, the warning signs can look like normal aging or even dementia, which often delays diagnosis.
Common symptoms include:
- Cognitive changes: increasing confusion, memory problems, difficulty paying attention
- Physical symptoms: persistent headache, problems with balance or walking, weakness or numbness in the arms, legs, or face
- Speech and vision changes: trouble speaking or swallowing, visual disturbances
- Behavioral shifts: personality changes, unusual drowsiness, or in rare cases psychosis
- Severe cases: seizures, nausea and vomiting, or loss of consciousness
Some people have no symptoms at all, with the hematoma discovered incidentally on a brain scan done for another reason. The key red flag is any new neurological symptom appearing weeks or months after a head injury in an older adult.
How It’s Diagnosed
A CT scan of the head is the standard diagnostic tool. On imaging, a chronic subdural hematoma appears as a crescent-shaped collection pressed against the brain surface. Its appearance varies depending on the age and composition of the blood. Older, fully liquefied blood shows up darker than the surrounding brain tissue, while collections with a mix of old and new bleeding show a layered or mixed-density pattern. In a study of 242 cases, nearly half appeared as a uniform gray density similar to brain tissue, which can make detection trickier. About a third showed mixed density, suggesting repeated episodes of bleeding at different times.
When a CT scan is unclear, particularly when the blood collection blends in with the brain’s density, MRI provides a more detailed picture.
Surgical Treatment Options
Most symptomatic chronic subdural hematomas require some form of surgical drainage. The three main approaches are twist-drill craniostomy, burr hole drainage, and craniotomy, each involving a progressively larger opening in the skull.
Burr hole drainage is the most widely used technique. The surgeon drills one or two small holes in the skull and flushes out the liquefied blood, often leaving a temporary drain in place for a day or two. It’s less invasive than a full craniotomy and can be done under local anesthesia, which matters for elderly patients who may not tolerate general anesthesia well.
A craniotomy involves removing a larger section of skull bone temporarily. Proponents argue that the wider exposure allows surgeons to break up internal compartments within the hematoma and open the surrounding membranes more thoroughly, potentially reducing the chance of re-accumulation. In practice, the choice between procedures often comes down to the surgeon’s experience and preference rather than strict clinical criteria.
Nonsurgical and Newer Approaches
For patients with mild symptoms or those too frail for surgery, watchful monitoring with repeat imaging is sometimes an option. Steroids like dexamethasone have been used to try to reduce inflammation and shrink the hematoma without surgery. However, a major trial published in the New England Journal of Medicine found that among patients managed without surgery, 100% of those receiving a placebo had favorable outcomes compared to 82% of those receiving dexamethasone. The steroid did not show a clear benefit and carries its own risks, particularly for elderly patients prone to infection or stomach problems.
A newer technique called middle meningeal artery embolization has shown more promise. This minimally invasive procedure, performed through a catheter threaded from the groin to the head, blocks the artery that feeds the problematic membranes surrounding the hematoma. By cutting off the blood supply to those leaky membrane vessels, it disrupts the cycle that keeps the hematoma growing. A meta-analysis of six randomized controlled trials found that embolization cut the recurrence rate in half compared to standard management alone. The procedure-related complication rate was about 1%, though rare serious events including stroke and nerve injury have been reported.
Recovery and Recurrence
After surgical drainage, most patients experience noticeable improvement in their symptoms within days to weeks. Follow-up CT scans are typically done within the first few days after surgery, then repeated at intervals until the collection has resolved and the patient returns to their baseline function.
Recurrence is a well-known challenge. In one study of 150 surgical patients, 12% experienced a recurrence, with most happening within three months. Recurrence usually means the hematoma re-accumulates before the previous collection has fully resolved, and it may require a repeat procedure.
Long-Term Outlook
Short-term survival after a chronic subdural hematoma is generally good. The 30-day mortality rate is about 9.4%. But the one-year mortality rate is considerably higher at roughly 33%, which largely reflects the age and overall health of the population affected rather than the hematoma itself. The typical patient is 76 years old with other medical conditions, and those comorbid illnesses drive much of the longer-term risk.
Some patients experience lingering symptoms after treatment, including anxiety, difficulty concentrating, dizziness, headaches, and memory problems. These post-treatment effects can persist for months and are more common in older patients or those who had larger hematomas at the time of diagnosis.