CT Head

Question 0

Reasons for contrast CT head

Answer 0

Acute bleed

Question 1

What do Hounsfield Units give a measure of?

Answer 1

…the attenuation (absorption and resultant brightness) of each pixel. HU.
Reps the relative density of the scanned substance.
-1000 (air) to 1000 (bone)
W -50 (fat); 0 (water); +40 (soft tissue); +40-80 (blood); +100-400 (stones)

Question 2

Reasons for contrast CT head

Answer 2

Vascular structures
Infection
Tumor

Question 3

Relative CIs to contrast

Answer 3

Allergy

Renal failure

Question 4

Why must we window?

Answer 4

CT density values range from -1024 to +3071 but the eye can only distinguish 30 to 40 gray scales at best… Therefore I just window settings in accordance with structures to be visualized. There are presets

Question 5

How to set the level L?

Answer 5

At a point which is roughly at the same value as the average HU number of the tissue of interest.

• the HU at the centre of the window width.
• controls the brightness of the image.
• brightness is proportional to window Level.

Question 6

Windowing entails which two components?

Answer 6

The window width W: density range represented within the gray scale.
Window Centre C: the centre of the density range.

Question 7

What 3 windows are commonly used in CT head?

Answer 7

Brain window: W 80, L 40
Bone window: W: 2500, L 480
Subdural window: W 350, L 90

Question 8

What are major veins seen on a sagittal cut of the brain w contrast?

Answer 8

Internal cerebral veins course posteriorly under the roof of the third ventricle.

They unite w the basal veins of Rosenthal to form the Great cerebral vein of Galen, just below the splenium of the corpus callosum.

Confluence of the great cerebral vein and inf sagittal sinus form the straight sinus.

Question 9

Describe the paired cerebral sinus system.

Answer 9

Sphenoparietal sinuses anterolateral skull to the cavernous sinus.

Cavernous sinus connects one way to the central basilar venous plexus and more laterally along the petrous bone to inferior then superior petrosal sinuses.

These then reattach with the jugular bulb (from central basilar venous plexus) into sigmoid sinuses laterally, which also recieve input from the transverse sinuses wrapping around from posterior aspect of brain.

Question 10

Describe the unpaired Dural sinus system.

Why Are the paired internal cerebral veins important clinically?

Answer 10

Internal cerebral veins run posteriorly in roof of third ventricle and unite beneath splenium of corpus callosum to form Great cerebral vein of Galen.

The internal cerebral veins are important clinically because the both lie w/in 2 mm of the midline and so can be used to Dx midline shifts.

The short (1-2 cm) great cerebral vein of Galen passes postero superiorly behind splenium of corpus callosum into the quadrigeminal cistern, where it receives basal veins and posterior fossa veins.

QuadrigeminL cistern drains to the anterior end of the straIght sinus, which also recieves from inf sagittal sinus.

Straight sinus then unites w superior sagittal sinus (Falx cerebri runs between sup and inf sag sinuses)

Straight sinus leads to the confluence of the sinuses, where midline occipital sinus also connects. Then splits into w the transverse sinuses which fuse w sigmoid sinuses and into internal jugular vein which runs thru the jugular foramen.

Question 11

Approach #1

Answer 11

Easy stuff:
Pt ID, age, date of exam

ALWAYS CHECK FOR PREV SCANS TO COMPARE
- also look at old chest and abdo films… Think mets down the road

Question 12

Approach #2

Answer 12

Study parameters

Study technique:

Anatomic region:

• head
• neck
• spine

Slice thickness

Window level and width

Plane:

• transaxial
• coronal
• sagittal

Contrast vs Non contrast
- look for Circle of Willis, which will be enhanced on those w contrast

Question 13

Approach #3

Answer 13

Midline structures midline? Both sides look the same?

• find a slice where the two lateral ventricles are prominent
• draw vertical line down middle joining the falx cerebri anteriorly and posteriorly.

Question 14

Approach #4

Answer 14

Ventricles

• lat x 2
• third
• can be seen on sag view under the corpus callosum and between the two lobes of the thalamus.
• fourth

Look for changes in
- symmetry, size, shape, density.

Pathologies:
V: intra-vent hemorrhage (similar pres to SAH)...appears as hyperdense material, tends to pool dependently in the occipital horns
Degen: atrophy ie ex vacuo (n ICP)
Anatomic: Mass effect
Hydrocephalus

Question 15

What is a displaced ventricle often the product of?

Answer 15

Mass effect or atrophy