🧠 CT Scan Criteria After Head Injury: A PLAB 2 Essential Guide

Ann Augustin
Aug 1, 2025
4 min read

Updated: May 2

Head injuries are commonly tested in PLAB 2 stations, especially in paediatric and emergency care scenarios. Knowing when to request a CT scan is crucial—not only to identify serious injury but also to avoid unnecessary radiation exposure, especially in children.

This guide simplifies the NICE (NG232) recommendations and highlights key differences between adults and children, with an easy-to-remember system to help you shine in your exam.

✅ Why CT and Not X-Ray or MRI?

CT is the first-line imaging tool for head injury—it’s fast, effective, and shows bleeding or fractures.
MRI is not used initially—it’s slower, less available, and harder to use in emergencies.
Skull X-rays are NOT used unless discussed with neurosurgery, or for non-accidental injuries in children (as part of skeletal survey).

👨‍🦳 CT Scan Criteria for Adults (Age 16 and Above)

📍 CT Head within 1 hour if any of the following are present:

GCS ≤ 12 on arrival
GCS < 15 at 2 hours post-injury
Open or depressed skull fracture
Signs of basal skull fracture:
- Battle's sign (bruising behind the ears)
- 'Panda' eyes (periorbital bruising)
- CSF leak from nose or ears
Post-traumatic seizure
Focal neurological deficit
More than 1 episode of vomiting

⏳ CT Head within 8 hours (or immediately if delay >8h) if:

Any loss of consciousness or amnesia + ≥1 of the following :
- Age ≥ 65 years
- Bleeding/clotting disorder
- Dangerous mechanism (e.g. pedestrian hit, fall >1m or >5 stairs)
- Retrograde amnesia > 30 minutes

🧒 CT Scan Criteria for Children (Under 16)

📍 CT Head within 1 hour if:

Suspected non-accidental injury
Post-traumatic seizure
GCS < 14 (or <15 in under 1 year)
GCS <15 at 2 hours post-injury
Open/depressed skull fracture or tense fontanelle
Signs of basal skull fracture
Focal neurological deficit
In babies <1 year: bruise/swelling or laceration >5 cm

⏳ CT Head within 1 hour if 2 or more of these are present:

Loss of consciousness > 5 minutes
Abnormal drowsiness
3 or more episodes of vomiting (✅ Not just 1 or 2)
Dangerous mechanism (e.g. fall >3m, hit by high-speed object)
Amnesia >5 minutes
Bleeding/clotting disorder

👀 If only 1 of the above → Observe for 4 hours

CT scan is done only if:

GCS drops <15
Further vomiting
New drowsiness

💊 Special Case: Patients on Blood Thinners (Anticoagulants or Antiplatelets)

Even without other signs, consider a CT head within 8 hours (or immediately if they present late), especially if:

They're on warfarin, DOACs, or other anticoagulants
Or antiplatelets (except aspirin alone)

🎓 Easy Way to Remember (Adults ≥16)

Use the “G-F-V-S” Rule to group the key red flags:

🧠 G – Glasgow Coma Scale (GCS)

GCS ≤12 at arrival
GCS <15 at 2 hours after injury

💀 F – Fractures and Focal signs

Suspected open or depressed skull fracture
Signs of basal skull fracture (Battle’s sign, CSF leak, panda eyes)
Focal neurological deficit

🚑 V – Vomiting and Vulnerability

More than 1 episode of vomiting
Very old (age ≥65)
Very risky mechanism (e.g., high-speed accident, fall >1m, ejected from vehicle)

⚡ S – Seizure

Any post-traumatic seizure

Children and Adolescents <16

“SCAN IF 1 RED or 2 YELLOWS”

1 red flag → CT now
2 yellow flags → CT now
1 yellow flag → observe 4 hours

🏠 Discharge Advice After a Normal CT / Minor Head Injury

The patient should be advised to:

Have a responsible adult stay with them for at least the first 24 hours
Rest and avoid stress initially
Take simple pain relief such as paracetamol if needed
Avoid alcohol or recreational drugs
Avoid driving, cycling, operating machinery, work/school, or sports until recovered
Return urgently if symptoms worsen

The NHS advises that after a head injury, an adult should stay with the patient or child for at least the first 24 hours. It also advises avoiding work/school, driving, alcohol, drugs, and contact sports until recovered.

🏥 Does the Patient Need to Stay in Hospital for 4 Hours After a Normal CT?

Not always.

The 4-hour observation rule mainly applies to children under 16 who have only one intermediate/yellow risk factor and do not immediately need a CT scan.

If the CT scan is normal, the decision to discharge depends on whether the patient is clinically safe to go home.

✅ The Patient Can Usually Be Discharged If:

CT head is normal
GCS is 15 / back to normal conscious level
Observations are stable
Neurological examination is normal
Symptoms are improving or resolved
There are no safeguarding concerns
There are no other injuries or medical reasons for admission
A responsible adult can stay with them for the first 24 hours
They receive clear verbal and written head injury advice

NICE says people admitted after a head injury may be discharged once all significant symptoms and signs have resolved, provided they have suitable supervision arrangements at home or in continued care. NICE also states that people should only be transferred home if there is somebody suitable at home to supervise them.

⚠️ When Might the Patient Still Be Observed or Admitted Despite a Normal CT?

They may still need hospital observation/admission if there is:

Persistent drowsiness or confusion
GCS not back to 15
Ongoing severe headache or repeated vomiting
Abnormal neurological signs
Post-traumatic seizure needing further assessment
Significant intoxication
Safeguarding concern or suspected non-accidental injury
No responsible adult available at home
Other injuries or medical/social concerns
High bleeding risk, depending on clinical judgement/local policy

NICE also says that if a person has had a normal CT scan but does not have a GCS of 15 after 24 hours of observation, clinicians should consider further CT or MRI and discuss with radiology.

💡 PLAB 2 Tip

In a station, if a child is well, alert, and had only one vomit or minor fall—CT is not needed. Explain gently to the parent why observation is safer than exposing their child to radiation.

📌 Final Takeaway

CT scans are vital in picking up serious brain injuries—but knowing when not to scan is equally important in UK practice. Use NICE criteria wisely, apply structured reasoning in OSCEs, and always consider the risk vs benefit, especially in children.