Lecture 5 - CT

Question 1

What is CT?

Answer 1

A radiological technique based on x-ray, which measures the density of tissue. It shoots an array of beams at many angles of the brain.

It cannot generate a 3D image.

Question 2

Problems with CT?

Answer 2

• exposure to radiation

- not good at distinguishing between white and grey matter.

Question 3

Describe the colours seen in CT.

Answer 3

bone/hard substances = white

black = air

Question 4

What is the stripy look in CT?

Answer 4

movement artefact

Question 5

Advantages of CT?

Answer 5

” Quick - 5 to 10 minutes
“ Cost effective
“ Superior for visualising fresh haemorrhage.
“ Preferred technique for patients with head trauma or suspecter intracranial haemorrhage
“ Used in emergency settings

Question 6

How much csf is in the body?

Answer 6

120 ml

Question 7

What are the 5 ways mass effect can be seen, and can show up on a CT?

Answer 7

Blood can be very bad.

Blood
Cisterns
Brain 
Ventricles
Bone

Question 8

What brain structure is inside a pocket in the skull?

Answer 8

Pituitary gland.

it rips out if you take the brain out

anterior

Question 9

What are cisterms

Answer 9

” Cisterns are areas in the subarachnoid space which widen to form larger CSF collections.

Question 10

What are the 4 cisterns from sagittal view

Answer 10

• Suprasellar Cistern
• Quadrigeminal Cistern
• Peripontine Cistern
• Infrapontine Cistern

Question 11

What are the cisterns when viewed at high midbrain level

Answer 11

• sylvian cystern
• quadrigeminal cistern
• interhemispheric cistern

Question 12

Describe the flow of CSF in production

Answer 12

lateral ventricle choroid plexus –> intraventricular foramen (foramen monro) –> 3rd ventricle –> cerebral aqueduct –> 4th ventricle –> median and lateral aperature –> down into subdural space to lumbar system –> back up to 4th ventricle –> draining by the superior sagittal sinuses (arachnoid villi)

Question 13

How does blood appear on CT?

Answer 13

dense = acute, once it clots. = white.
isodense at 1 week
hypodense (less dense, darker) at 2 weeks

Question 14

What is an epidural haematoma

Answer 14

• due to haemorrhage between dura and skull.
• lens shaped due to sutures
• tear to meningeal artery

Question 15

Describe a subdural haematoma

Answer 15

• sickle-shaped
• crosses sutures, but not the midline.
• acute subdural haematoma marker for severe head injury
• ## chronically, it is slow venous bleed and well tolerated

Question 16

Describe a subaranoid haemorrhage

Answer 16

• usually due to the bursting of an aneurysm - an outpouching of of the vessel wall
• usually occurs in the circle of willis
  “worst headache ever”
• blood in cisterns and cortical gyral surface

Question 17

Describe CT for subarachnoid haemorrhage

Answer 17

clearest the sooner it is to the event

best 0-12 hrs.

90-95% - 24 hours
80% - 3 days
50% - 1 week
30% - 2 weeks

Question 18

What is an intraventricular/intraparenchymal haemorrhage

Answer 18

bleeding within the brain parenchyma

Question 19

What are the four main cisterns

Answer 19

• circummesencephalic
• suprasellar
• quadrigeminal
• sylvian

Question 20

What are the two key questions when looking at cisterns?

Answer 20

• is there blood

- are they open?

Question 21

Why is intracranial air bad?

Answer 21

it is effectively a lesion, because it can’t get out.

Question 22

What is the ex-vacuo phenmenon?

Answer 22

also known as compensatory enlargement of the CSF spaces, is a term used to describe the increase in the volume of CSF, characterised on images as an enlargement of cerebral ventricles and subarachnoid spaces, caused by encephalic volume loss.