Head injury: when a scan is needed

A CT scan is generally recommended for head injuries with loss of consciousness, ongoing confusion, repeated vomiting, seizures, a worsening or severe headache, or in people taking blood-thinning medication, since these features increase the risk of bleeding or significant brain injury. Certain higher-risk groups, including older adults and those with a significant mechanism of injury (such as a fall from height or road traffic accident), are also more often scanned. Established clinical guidelines help doctors decide when scanning is genuinely needed.

Scanning is used to check for bleeding within or around the brain, skull fractures, or brain swelling, all of which need to be identified and, if present, treated urgently. These serious complications are relatively uncommon after straightforward, mild head injuries but need to be actively excluded when specific risk factors or warning symptoms are present. The decision to scan balances the small risks of radiation exposure against the benefit of not missing a serious injury.

Warning signs include loss of consciousness, worsening or persistent headache, repeated vomiting, confusion or drowsiness that is not improving, seizures, weakness, or slurred speech. Blood thinning medication use and a significant mechanism of injury also lower the threshold for scanning. Any combination of these features after a head injury should prompt urgent medical assessment.

No, the vast majority of head injuries are mild and do not need scanning, since scanning every single head injury would expose many people unnecessarily to radiation without benefit. Scanning is reserved for those with specific risk factors or warning symptoms where the benefit clearly outweighs this small risk, based on well-established clinical decision rules. Doctors are trained to apply these rules consistently to decide who genuinely needs a scan.

If a scan identifies bleeding, a fracture, or significant swelling, further specialist neurosurgical or neurology assessment is arranged promptly, and treatment ranges from close monitoring to urgent surgery, depending on the specific finding and its severity. Hospital admission for observation is common in these situations even if immediate surgery is not needed. Your medical team will explain the specific finding and recommended next steps.

If scanning criteria are met, a CT scan is generally performed promptly, often within an hour or two of assessment in an emergency department, given the potential seriousness of what is being excluded. This reflects how time-sensitive some of the serious complications being ruled out, such as significant bleeding, can be. Immediate emergency assessment is the appropriate route if any relevant warning signs are present.

A straightforward mild concussion without any of the recognised warning signs, such as loss of consciousness, repeated vomiting, or worsening symptoms, generally does not need scanning and can be managed with rest and gradual return to activity. A head injury with any of these warning features crosses into needing urgent scanning to rule out a more serious injury. Clinical assessment by a doctor, applying standard decision rules, is the best way to determine which category applies to a specific injury.

Yes, there are separate, specifically validated clinical decision rules for children, since younger children in particular can show different signs of serious injury and have different radiation sensitivity considerations. A doctor experienced in paediatric assessment will apply these specific paediatric criteria when deciding whether scanning is needed. Parents should still seek prompt assessment for any concerning symptoms after a child’s head injury, regardless of these specific criteria.

Seek emergency care immediately for loss of consciousness, worsening headache, repeated vomiting, seizures, confusion, drowsiness, weakness, or if you are on blood-thinning medication and have had any significant head injury. If none of these features are present but you remain concerned, a same-day GP or urgent care assessment is a reasonable alternative to A&E. When in doubt after any head injury, err on the side of seeking prompt medical assessment.