Subdural hematoma: the head knock that shows up weeks later
In an older adult, a knock that seemed insignificant can cause symptoms six weeks later.
Before you read on. This article is general information for
patients. It cannot be used to reach a diagnosis and does not replace a
consultation: similar symptoms can have very different causes, and only an
in-person assessment — your history, your examination and your imaging — can
establish what is happening and what suits you. If something here worries you,
the right step is to discuss it with a doctor, not to draw conclusions.
A traumatic brain injury (TBI) is any blow, jolt or wound to the head that disrupts normal brain function. It ranges from a mild concussion to a life-threatening injury.
Most TBIs arriving at an emergency department are mild and resolve without lasting effects. The purpose of assessment is to identify the small percentage that will deteriorate — because in that group, acting fast changes the outcome.
Go to the emergency department immediately if, after a head injury, there is:
- Loss of consciousness, however brief
- Repeated vomiting
- Severe or worsening headache
- Seizures
- Confusion, disorientation or strange behaviour
- Excessive drowsiness or difficulty waking the person
- Weakness, numbness or clumsiness in arms or legs
- Difficulty speaking or understanding
- Double vision or unequal pupils
- Blood or clear fluid from the nose or ear
- Bruising around the eyes or behind the ears
Classification by severity
| Severity | Glasgow | Features |
|---|---|---|
| Mild | 13 – 15 | The vast majority. May involve brief loss of consciousness or passing confusion. |
| Moderate | 9 – 12 | More prolonged altered consciousness. Requires admission and observation. |
| Severe | 3 – 8 | Coma. Intensive care management, frequently neurosurgery. |
Important: a TBI classified as "mild" is not always harmless. A patient with a Glasgow score of 15 can have an expanding hematoma. That is why risk factors and monitoring in the following hours matter so much.
Types of injury
Concussion
Transient disruption of brain function with no visible lesion on CT. It causes confusion, headache, dizziness, a "foggy" feeling, difficulty concentrating and sometimes amnesia for the event. The most common injury in contact sports.
Cerebral contusion
A bruise in the brain tissue itself. It can appear beneath the point of impact or on the opposite side, from the brain moving inside the skull.
Epidural hematoma
Blood between the skull and the dura, typically from a torn middle meningeal artery associated with a fracture. Its classic pattern is the lucid interval: the person is hit, loses consciousness, recovers and seems fine, then deteriorates rapidly hours later. It is a surgical emergency.
Subdural hematoma
Blood between the brain and the dura. It can be acute, after significant trauma, or chronic, appearing weeks after a minor knock, especially in older adults. Covered in depth in our article on subdural hematoma.
Diffuse axonal injury
Caused by abrupt acceleration and deceleration — high-speed road accidents — stretching and damaging axons throughout the brain. It may not show well on the initial CT and explains prolonged alterations in consciousness.
Skull fracture
May be linear, depressed — when a fragment presses inwards toward the brain — or of the skull base. Depressed and open fractures frequently require surgery.
When is a CT scan done?
- Glasgow below 15 two hours after injury
- Suspected fracture — open, depressed or skull base
- Two or more episodes of vomiting
- Age over 65
- Amnesia of more than 30 minutes before impact
- Dangerous mechanism: pedestrian struck, ejection from a vehicle, fall from height
- Use of anticoagulants or antiplatelets — a heavily weighted factor
- Post-traumatic seizure or focal neurological deficit
Monitoring at home after a mild TBI
If injury is excluded in the emergency department and discharge is approved, home observation for 24 to 48 hours with someone present is appropriate:
- Check the person wakes normally. Waking them hourly is not necessary if they sleep calmly and breathe well, but do verify they respond normally when woken.
- Relative rest, physical and cognitive: limit screens, heavy reading and demanding mental work in the first days.
- Simple analgesia; avoid anti-inflammatories in the first hours if there is bleeding risk, as medically advised.
- No alcohol.
- No driving or operating machinery while symptoms persist.
- Return to the emergency department for any of the red flags listed above.
In children, also watch for
- Inconsolable crying or persistent irritability
- Refusing food
- Bulging fontanelle in infants
- Loss of skills already acquired
- Unusual drowsiness
Post-concussion syndrome
- Persistent headache
- Dizziness and unsteadiness
- Difficulty with concentration and memory
- Mental fatigue
- Irritability, anxiety or low mood
- Sleep disturbance
- Sensitivity to light and noise
It is real and has a neurobiological basis, even when the CT is normal. Most cases resolve with relative rest and a gradual, stepwise return to activity without skipping stages. When prolonged, patients benefit from neurocognitive and vestibular rehabilitation.
Sport: never return to competition while symptoms persist. A second impact before full recovery can cause second impact syndrome — rare but very serious. Return is done in progressive, supervised stages.
When neurosurgery is involved
- Epidural, subdural or intraparenchymal hematoma with mass effect
- Depressed or open fracture
- Raised intracranial pressure not responding to medical management
- Need for intracranial pressure monitoring
- Persistent cerebrospinal fluid leak
In severe TBI, time is the factor weighing most on outcome: early evacuation of a hematoma with mass effect clearly improves prognosis. That is why, faced with a head injury showing red flags, "waiting to see if it passes" is not advisable.
What patients ask most
Should someone be woken every hour after a head injury?
Waking them hourly is not necessary if they are sleeping calmly and breathing normally. What matters is periodically confirming that they wake normally and respond coherently. If they do not wake easily, are confused on waking, or breathing is irregular, go to the emergency department immediately.
How long does a concussion last?
Most symptoms improve within days to two weeks with relative rest and a gradual return to activity. A smaller proportion of patients develop post-concussion syndrome, with symptoms persisting for weeks or months, which benefit from targeted neurocognitive and vestibular rehabilitation.
Does every head injury need a CT scan?
No. Validated decision rules help avoid unnecessary radiation. A CT is indicated for significant loss of consciousness, repeated vomiting, suspected fracture, older age, high-energy mechanism, neurological deficit, seizure, or anticoagulant use, among other criteria.
Can I take anticoagulants after a head injury?
Anticoagulants and antiplatelets significantly increase the risk of intracranial bleeding after trauma, even minor trauma. If you take them, seek medical assessment even if the knock seemed minor, and never change the dose yourself: any change must be decided by the doctor who prescribed them.
When can I return to sport?
Only once symptoms have completely resolved at rest and on exertion, and following a stepwise, supervised return-to-play protocol. Returning earlier risks second impact syndrome — rare but potentially very serious, especially in minors.
Written and reviewed by Dr. Ricardo Bermúdez, neurosurgeon. Last reviewed: 2026-09-09.
General informational content. It is not medical advice, does not create a doctor-patient relationship, and must not be used to self-diagnose or to decide on treatment. Outcomes vary from person to person. If you have symptoms, see a doctor.
