How are Head Injuries Diagnosed?

Head injuries come in a wide range of severities. Thankfully the overwhelming majority of injuries are mild and do not cause long term damage.

When a brain is damaged several things can happen:

  • there can be a bruise to an area of the brain, much the same as if you get hit on your arm or leg,
  • damage can be caused to the ‘axons’ of the brain (the brain’s wiring system),
  • the brain can respond to injury by swelling, in just the way that an ankle might if it gets hurt.

In all these circumstances where the brain gets injured, it responds by losing consciousness. This can vary in severity from feeling groggy and ‘not quite with it’ to a deep coma. Doctors can assess the severity of a head injury by assessing the degree of loss of consciousness that occurred at the time of the injury. A lot of research has been done on this topic and we know that assessment of the degree of loss of consciousness gives a very accurate picture of the severity of the injury.

Of course, head injuries do not always lead to loss of consciousness. It is important to keep in mind that a head injury without loss of consciousness is unlikely to actually involve any brain injury.

How does a doctor assess the severity of a head injury?

Loss of consciousness≤ 30 minutes30 minutes – 24 hours> 24 hours
Glasgow Coma Scale score≥ 139 – 12<9
Post traumatic amnesia≤ 1 day2 – 7 days> 7 days

A doctor will want to know how long you were totally unconscious for, i.e. ‘flat out and completely unresponsive’.

Many people however are not ‘out cold’ but are rousable if pinched or talked to but equally are not fully conscious either. Doctors can grade how bad this is by using what is called the Glasgow Coma Scale or a similar measure.

Doctors will also try to find out how long the memory gap is after the accident. For most people they will ‘come to’ at the site of the accident often with people standing around. This usually means a memory gap of only a few minutes but for others they may not remember anything until later that day or sometimes until a few days later. This gap is called a ‘post traumatic amnesia’.

By assessing these measures doctors can estimate how severe an injury was. The World Health Organization have assessed all the research on this and have advised that an injury can be considered mild you were ‘flat out’ ie totally unconscious for less than 30 minutes, doctors measured your Glasgow Coma Scale score as 13 or above and your memory gap after the accident is less than one day.

> Does this mean I am brain damaged?

Should I have had a Brain Scan?

Most head injuries are mild and carry no risk to the patient so most people who have a head injury don’t need a brain scan. Doctors follow a set of guidance ‘rules’ for deciding who does or does not need a brain scan. These rules are very accurate and it is very unusual for anything to be missed. One commonly used set of rules are the Canadian CT scan rules. These are a bit ‘medical’ so might not seem very clear to you but we have copied them just to give you an idea of how assessments work.

High risk (for predicting neurosurgical intervention)Odds ratio
GCS score <15 at two hours after injury7.3
any sign of basal skull fracture (e.g. haemotympanum, bilateral periorbital haematoma, ‘racoon or panda eyes’, cerebrospinal fluid otorrhea/rhinorrhea, Battle’s sign)5.2
≥ 65 years of age4.1
≥ two episodes of vomiting3.8
suspected open or depressed skull fracture3.6
Medium risk (for brain injury on CT)Odds ratio
amnesia before impact of > 30 minutes (retrograde)1.6
dangerous mechanism of injury (e.g. pedestrian struck by motor vehicle, occupant ejected from motor vehicle, fall from height > three feet or five stairs)1.4

There are slight variations in guidance from country to country. These rules have been tested in many studies and have 100% sensitivity for identifying patients who need emergency treatment. What this means is that if the rules are followed every patient who needs to have an emergency operation, or other form of treatment, will be picked up. However, the rules are designed to be overinclusive so in order to make sure they pick up everyone who has any brain damage they will also lead to many people having brain scans whose brains are normal; depending exactly what rules are used as many as 9 out of 10 patients scanned have no problems.  

What this means is that if you didn’t have a scan at the time of your injury it is highly unlikely that you needed one and even if you were scanned it is quite likely that the scan was normal. You doctors will have told you if it wasn’t.

What if something happens later?

Brain injuries are at their worst at the time of the injury and then get better over time. It is unusual for them to get more severe after the event. If this does happen it is usually for one of two reasons:

One, in very severe injuries as a brain swells it can get too big to fit inside the skull or there might be severe bleeding into the brain. In these circumstances an operation might be required. When there is any risk of this it will have been detected using the methods described above.

Two, the other problem is that after a seemingly mild injury in a very small number of patients the blood vessels that go from the skull to the outside of the brain can be damaged and start to bleed. Thankfully, this is very rare. However, if you were discharged from hospital after your head injury you will have been given a head injury advice sheet describing some specific symptoms that indicate that may be happening and you should go back to hospital. Please be aware that almost everyone who has a head injury has symptoms afterwards and feels strange and unwell – it is only if you have these specific alarm symptoms that you need to come back to the Emergency Department. If this is going to happen it almost always happens in the first 24 hours and is incredibly rare after 2 weeks.

Will a brain scan help if I still have symptoms some months later?

The answer to this is almost always no. The types of symptoms commonly experienced after a mild head injury are not associated with brain damage and therefore will not show on a scan.