practical 3: facial XRs + CT/MRI

Question 1

What are some external signs of facial fracture?

Answer 1

Facial asymmetry
subconjunctival heamorrhage
dish-face deformity
deviation of the nose
pupils not level
CSF rhinorrhoea / ear leakage

Question 2

What are the standard facial XR views?

Answer 2

Standard: Occipitomental view and OM 30 degree view

Question 3

What are the additional facial XR views?

Answer 3

Additional: PA facial view and PA mandibular view

Question 4

What looks like an elephant head on a OM view?

Answer 4

Zygoma and sup/inf zygomatic arches

Question 5

What is an OM 30 degree view good for?

Answer 5

More accurate view of MAXILLARY ARCHES

Question 6

What 3 lines should you trace along on an OM view?

Answer 6

1. Over the upper orbits
2. Over the upper zygomatic arch, inferior orbit + nose
3. over lower zyg. arch + alveolar process

Question 7

What is the teardrop sign?

Answer 7

Opacity in the maxillary sinus indicating prolapse of orbital contents into maxillary sinus

Question 8

What are the signs of a orbital blowout fracture?

Answer 8

1. fluid level in maxillary sinus
2. teardrop sign (opacity in maxillary sinus)
3. break in the cortex of infraorbital rim
4. Black eyebrow sign (seen better on CT)

Question 9

What is the mechanism of a blowout fracture?

Answer 9

Blow to orbit –> ^ intraorbital pressure –> fracture in orbital floor

Question 10

if a patient w/ an orbital floor fracture complains of ^ pain and O/E can’t detect light / no movement –> what would you do?

Answer 10

CT

Because this suggests compression of the optic nerve by bleeding /haematoma behind the globe

Question 11

What is the measure of density in CT scans?

Answer 11

Hounsfield unit (air = hypodense/dark [-1000] –> bone = hyperdense/white [+1000])

Question 12

How do you describe the appearance of tissues in terms of density on CT?

Answer 12

hyper and hypodense

Question 13

What is CT used for in the acute setting?

Answer 13

Chest –> CTPA (PE), suspected thoracic aneurysm rupture, chest trauma
Abdomen –> serious intr-abdo path. (AAA, perforation viscus, acute pancreatitis)
Renal calculi –> NCCT-KUB
C-spine –> fractures
Brain –> acute/serious intracranial pathology (e.g. bleeds)

Question 14

What is the advantage of using CT to diagnose/rule out renal calculi?

Answer 14

Can simultaneously assess for other causes of symptoms

Question 15

What contrast is used in CTPA?

Answer 15

Iodine based

Question 16

What does CTPA show if there is PE?

Answer 16

A GREY filling defect in the pulmonary vasculature (clot appears as dark as iodine not able to get passed)

Question 17

What 4 things can you use to image the renal tract?

Answer 17

IV pyelogram/uretogram
NCCT-KUB
USS
AXR

Question 18

What are the indications of the CT c spine?

Answer 18

1. XR equivocal or looks normal but you are suspicious
2. C spine XR shows fracture
3. Hx of C spine injury + neurological sx’s/signs
4. Part of major trauma series

Question 19

Why is NCCT 1st line for Ix of intracranial/brain pathology?

Answer 19

If bleed, contrast would show up all vasculature making it difficult to assess if bleed or not

Question 20

How does an acute and chronic brain bleed show up on CT?

Answer 20

Acute –> hyperdense

Chronic –> hypodense

Question 21

How does ischaemia/infarction show up on a brain CT?

Answer 21

Hypodense (gets darker w/ time) –> difficult to see initially

Question 22

What are the acute indications for MRI?

Answer 22

Suspected cauda equina syndrome and spinal cord compression

Question 23

What is MRI good at visualising?

Answer 23

Soft tissues –> vasculature, ligaments, cartilage, tendons, spinal cord

Question 24

How are things described when viewing an MRI?

Answer 24

High or low signal

Question 25

What is phase of MRI?

Answer 25

When the RF pulse is applied, the H nuclei forced into SYNCHRONISED spinning

Question 26

What is precession in MRI?

Answer 26

The frequency the H nuclei spin at when the external Magnetic field applied

Question 27

How does inflammation appear on T1/T2 wieghted MRI? Which is used in MS?

Answer 27

T1: darker
T2: brighter/high signal (therefore better for viewing MS plaques)

Question 28

How does white matter appear on T1 + T2?

Answer 28

T1: light/high signal (as surrounding by fatty myelin [oligodendrocutes and schwann cells])
T2: dark/low signal

Question 29

How does grey matter appear on T1 + T2?

Answer 29

T1: low signal/dark
T2: high signal/light (therefore if you see brain w/ light outside = T2)

Question 30

other than T1 + T2, what other types of MRI are there?

Answer 30

1. FLAIR
2. Diffusion weighted MRI
3. Fat saturation/suppression
4. Short-tau inversion recovery
5. Proton density

Question 31

What is FLAIR MRI used for?

Answer 31

FLAIR MRI is like T2 but suppresses signal from tissues w/ high water content (i.e. CSF) –> useful for identifying high signal lesions that lie close to CSF spaces

Question 32

What is diffusion weighted MRI used for?

Answer 32

Acute (and old) infarction –> shows up high signal

Question 33

What 2 methods can you suppress fat with on T1-MRI? Why would you do this?

Answer 33

Fat suppresion or short-tau inversion recovery

view fluid better

Question 34

What is proton density good for?

Answer 34

Excellent detail for normal anatomy + pathology

Question 35

What is athe typical history of dissected aortic aneurysm?

Answer 35

Male older –> sudden onset severe chest pain radiating to the back

Question 36

what is a saddle PE?

Answer 36

A PE that lies at the bifurcation of the pulmonary trunk extending into both L/R pulmonary arteries

Question 37

How would you diagnose a jefferson fracture?

Answer 37

CT!!!!! (Peg XR shows widening of lateral masses from Peg but not diagnostic)

Question 38

On T2 MRI of the spine, what might indicate degenerative disc disease?

Answer 38

low signal compared to other discs as loss of water content in the disc