Neuroradiology

Question 1

When should you perform a head scan?

Answer 1

GCS < 13 at initial assessment or < 15 at 2 hours after injury on A&E assessment
Suspected open or depressed skull fracture
Post-traumatic seizure
Focal neurological deficits
Any sign of basal skull fracture
More than one episode of vomiting since head injury
Risk factors

Question 2

What risk factors might make you want to perform a head scan?

Answer 2

Age > 65
Hx of bleeding or clotting disorder
Dangerous mechanism of injury - pedestrian or cyclist struck by motor vehicle, occupant ejected from motor vehicle or fall from height > 1m or 5 stairs
More than 30 mins retrograde amnesia of events immediately before head injury

Question 3

What are the primary traumatic brain injuries?

Answer 3

Injury to scalp, skull fracture
Surface contusion/laceration
Intracranial haematoma
Diffuse axonal/vascular injury

Question 4

What are the secondary traumatic brain injuries?

Answer 4

Hypoxia-ischaemia
Swelling/oedema
Raised ICP
Meningitis/abscess

Question 5

What is the monro-Kellie doctrine?

Answer 5

Brain is box filled with blood, brain, CSF
Brain takes up most of space
In adults intracranial compartment protected by skull with fixed internal volume
Increase in one component must reduce volume of another

Question 6

What should you look at when looking at a CT brain?

Answer 6

Look at scout film - fracture of upper cervical spine or skull
Look for brain asymmetry
Look at sulci, sylvian fissure and cisterns to exclude subarachnoid haemorrhage
Change windows to look for subdural collection
Look at bone windows to see fractures
Determine if mass intra-axial (in brain) or extra-axial (outside)

Question 7

What does blood look like on a CT?

Answer 7

Acute blood is bright - HYPERdense once it clots
Becomes ISOdense at approx 1 week
HYPOdense at approx 2+ weeks

Question 8

What does an epidural haematoma look like?

Answer 8

Biconvex

Look for associated fractures

Question 9

What does a subdural haematoma look like?

Answer 9

Can cross suture but not dural reflections

Crescent shaped

Question 10

What does a subarachnoid haematoma look like?

Answer 10

Streaky blood in sulci of brain

Question 11

What are the rules of thumb for CNS imaging?

Answer 11

1. Always check radiology report
2. Always note name and DOB to confirm correct scan
3. Always determine whether any previous imaging with which to compare
4. Acute head presentation - start with CT
5. Worried about blood - CT
6. Worried about MS, sinus thrombosis, arterial dissection - MRI
7. Excluding or better visualising pathology in posterior fossa - MRI
8. Non-acute head - MRI
9. Spine - MRI
10. Possibility for infection/tumour - always include post-contrast whether CT/MRI

Question 12

What are the golden rules for scans?

Answer 12

Always ensure stable before sending for scan - airway secure, vital signs normal, scalp laceration sutured
Before LP ensure prior imaging

Question 13

What is the simple matrix CT head concept?

Answer 13

Each CT slice is matrix of small squares determining resolution of image and contain value representing amount of X-ray radiation by square of tissue

Question 14

What is the Hounsfield units concept of CT head?

Answer 14

CT scan raw data pixel values given in Hounsfiled units, bone + 1000, water 0, air -1000

• Blood +60-70
• Grey matter + 40
• White matter +30
• CSF +7
• Fat -100

Question 15

What is the grey scale concept of CT head?

Answer 15

Higher attenuation means more positive Hu (whiter), lower attenuation means more negative Hu (darker), can change grey scale to help identify different structures easier

Question 16

What questions should you ask yourself about the soft tissue window of a CT?

Answer 16

Is there an intracranial mass?
- Give dimensions in 3 planes
- Comment on surrounding oedema
- Comment on presence/absence of features of mass effect - loss of sulci/gyri, loss of basal cisterns, ventricular effacement, midline shift
Is there hydrocephalus? Ie is third ventricle enlarged?
Is there intracranial blood?
- Looks white of soft tissue window
- Comment on pattern of haemorrhage

Question 17

What question should you ask yourself about the bone window CT?

Answer 17

What about skull and extracranial soft tissues?

Question 18

What should you do before sending someone for MRI?

Answer 18

Ask…

• Do they have metal or implants that may preclude and MRI or significantly impair image quality?
• Could they be claustrophobic?

Question 19

What do MRI’s look like?

Answer 19

Main sequences
- T2 (CSF = white) - main sequence to look at for spinal imaging
- T1 (CSF = black) - main sequence for pathologies in which contrast (gadolinium) is given
Often in 3 planes - axial, coronal, sagittal

Question 20

What incidental findings could you find on imaging?

Answer 20

Increase with age
Arachnoid cyst 1%
Intracranial berry aneurysm-associated 1%
Meningioma 1%
Chiari malformation 1%
Demyelination 1%