concussion
Meaning of concussion: A problem of brain function rather than brain structure, which is why the scan comes back normal and the person does not.
Definition of concussion
A concussion is a brief disturbance of brain function caused by a blow to the head or by force transmitted to it, without damage visible on a routine scan. Symptoms start at once or build over hours and include headache, confusion, dizziness, slowed thinking, sensitivity to light and disturbed sleep. Loss of consciousness occurs in only a minority of cases.
Why does the scan look normal?
The brain floats in fluid inside a rigid skull. A blow, or a sudden change in speed with no blow at all, makes it move and rotate against that casing, stretching the long fibers carrying signals between regions. The injury is one of function rather than structure: channels in the cell membranes open, ions and chemical messengers pour across, and cells burn through energy restoring order. Standard imaging maps tissue and blood, so it finds a bruise or a bleed and cannot see a temporary electrical and chemical disturbance. A normal scan therefore says nothing about whether a concussion happened. It answers a different question, which is whether something is bleeding inside the skull.
What are the symptoms?
They fall into four groups and rarely arrive alone. Some appear at the moment of injury and others creep in over hours, so a headache that begins the next morning is a familiar pattern rather than a surprising one. Most people recover within weeks. A minority carry symptoms much longer, and a further head impact while symptoms are still present is associated with a slower recovery.
| Group | Common features |
|---|---|
| Physical | Headache, dizziness, nausea, blurred vision, ringing in the ears, sensitivity to light |
| Thinking | Feeling slowed or foggy, poor concentration, no memory of the moments around the impact |
| Emotional | Irritability, low mood, tearfulness, reacting more strongly than usual |
| Sleep | Sleeping much more or much less, trouble falling asleep, daytime drowsiness |
How does it differ from a more serious head injury?
By definition a concussion involves no bleeding or bruising inside the skull. A bleed can start at the moment of impact and take hours to declare itself, so an injury that looked straightforward at first can be something else by evening. The features marking that change are a headache that keeps worsening, repeated vomiting, growing drowsiness or confusion, weakness or numbness down one side, unequal pupils, a seizure, or clear fluid draining from the nose or ear. Bleeding inside the skull is a time-critical emergency, because the space around the brain cannot expand to accommodate it. Where symptoms persist, formal neuropsychology testing measures memory and concentration, and physical therapy addresses balance and neck pain.
Also known as
Used in a sentence
Concussion was diagnosed after the fall, with a normal CT scan and a persistent headache.
Good to know
Imaging is normal in concussion by definition, so a normal scan does not mean no injury occurred; a worsening headache, repeated vomiting, growing drowsiness, one-sided weakness or a seizure after a head impact points instead to bleeding inside the skull, which can develop hours later.
Word origin
Where “concussion” comes from
Concussion comes from the Latin concutere, meaning to shake violently, through the noun concussio, a shaking.