Subdural hematoma

3 things to know first

1. It can be serious and sometimes life-threatening. The degree of risk depends on the size, location, and how quickly it develops.
2. It may follow even a minor head injury, especially in older adults. A seemingly small bump can lead to a slow bleed days or weeks later.
3. Symptoms can appear gradually. A chronic subdural hematoma may cause headaches, confusion, or drowsiness that worsen over time.

What it is

A subdural hematoma is a buildup of blood in the space between the surface of the brain and the dura mater, the tough outer membrane that covers the brain. This blood puts pressure on the brain tissue beneath it.

Subdural hematomas are classified by how old the blood is:

• Acute — develops within days of an injury
• Subacute — develops over several days to weeks
• Chronic — develops slowly over weeks to months

They are more common in older adults, people taking blood-thinning medication, and those who have had a recent fall or head injury.

Why it appears on your report

On CT or MRI, a subdural hematoma usually appears as a crescent-shaped collection of blood along the inner surface of the skull. The report may describe its thickness, how much it is compressing the brain, and whether there is a shift of the brain's midline structures.

How serious is it

Severity ranges from small and asymptomatic to large and dangerous:

• Small, stable collections — may be monitored closely without immediate surgery.
• Larger collections or those causing pressure — often require surgical drainage.
• Acute large hematomas — can be life-threatening and require emergency surgery.
• Chronic hematomas — may cause subtle neurological decline and may still need intervention.

The decision depends on symptoms, size, location, age, and use of blood thinners.

When to seek care urgently

Call emergency services or go to the emergency department immediately if you or someone you care for has any of the following after a head injury:

• Severe or worsening headache
• Confusion, memory loss, or altered behavior
• Drowsiness or difficulty waking
• Weakness or numbness on one side of the body
• Slurred speech or vision changes
• Seizure
• Repeated vomiting

These symptoms can indicate increasing pressure on the brain.

What usually happens next

1. Urgent clinical assessment. A neurologist or neurosurgeon will review the imaging and examine the patient.
2. Medication review. Blood-thinning medications may be paused or reversed under medical supervision.
3. Monitoring or surgery. Small, stable hematomas may be watched in hospital. Larger or symptomatic ones are often treated with burr-hole drainage or craniotomy.
4. Rehabilitation and follow-up. After treatment, physical, occupational, or speech therapy may be needed, along with repeat imaging.

A simple analogy

Imagine placing a thin water balloon between a soft pillow and a hard box. As the balloon slowly fills, it presses on the pillow and changes its shape. A subdural hematoma works similarly: even a slow accumulation of blood can press on the brain and cause symptoms.

Further reading

• NHS — Subdural haematoma
• Mayo Clinic — Subdural hematoma