practical 3: facial XRs + CT/MRI Flashcards
What are some external signs of facial fracture?
Facial asymmetry subconjunctival heamorrhage dish-face deformity deviation of the nose pupils not level CSF rhinorrhoea / ear leakage
What are the standard facial XR views?
Standard: Occipitomental view and OM 30 degree view
What are the additional facial XR views?
Additional: PA facial view and PA mandibular view
What looks like an elephant head on a OM view?
Zygoma and sup/inf zygomatic arches
What is an OM 30 degree view good for?
More accurate view of MAXILLARY ARCHES
What 3 lines should you trace along on an OM view?
- Over the upper orbits
- Over the upper zygomatic arch, inferior orbit + nose
- over lower zyg. arch + alveolar process
What is the teardrop sign?
Opacity in the maxillary sinus indicating prolapse of orbital contents into maxillary sinus
What are the signs of a orbital blowout fracture?
- fluid level in maxillary sinus
- teardrop sign (opacity in maxillary sinus)
- break in the cortex of infraorbital rim
- Black eyebrow sign (seen better on CT)
What is the mechanism of a blowout fracture?
Blow to orbit –> ^ intraorbital pressure –> fracture in orbital floor
if a patient w/ an orbital floor fracture complains of ^ pain and O/E can’t detect light / no movement –> what would you do?
CT
Because this suggests compression of the optic nerve by bleeding /haematoma behind the globe
What is the measure of density in CT scans?
Hounsfield unit (air = hypodense/dark [-1000] –> bone = hyperdense/white [+1000])
How do you describe the appearance of tissues in terms of density on CT?
hyper and hypodense
What is CT used for in the acute setting?
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)
What is the advantage of using CT to diagnose/rule out renal calculi?
Can simultaneously assess for other causes of symptoms
What contrast is used in CTPA?
Iodine based
What does CTPA show if there is PE?
A GREY filling defect in the pulmonary vasculature (clot appears as dark as iodine not able to get passed)
What 4 things can you use to image the renal tract?
IV pyelogram/uretogram
NCCT-KUB
USS
AXR
What are the indications of the CT c spine?
- XR equivocal or looks normal but you are suspicious
- C spine XR shows fracture
- Hx of C spine injury + neurological sx’s/signs
- Part of major trauma series
Why is NCCT 1st line for Ix of intracranial/brain pathology?
If bleed, contrast would show up all vasculature making it difficult to assess if bleed or not
How does an acute and chronic brain bleed show up on CT?
Acute –> hyperdense
Chronic –> hypodense
How does ischaemia/infarction show up on a brain CT?
Hypodense (gets darker w/ time) –> difficult to see initially
What are the acute indications for MRI?
Suspected cauda equina syndrome and spinal cord compression
What is MRI good at visualising?
Soft tissues –> vasculature, ligaments, cartilage, tendons, spinal cord
How are things described when viewing an MRI?
High or low signal
What is phase of MRI?
When the RF pulse is applied, the H nuclei forced into SYNCHRONISED spinning
What is precession in MRI?
The frequency the H nuclei spin at when the external Magnetic field applied
How does inflammation appear on T1/T2 wieghted MRI? Which is used in MS?
T1: darker
T2: brighter/high signal (therefore better for viewing MS plaques)
How does white matter appear on T1 + T2?
T1: light/high signal (as surrounding by fatty myelin [oligodendrocutes and schwann cells])
T2: dark/low signal
How does grey matter appear on T1 + T2?
T1: low signal/dark
T2: high signal/light (therefore if you see brain w/ light outside = T2)
other than T1 + T2, what other types of MRI are there?
- FLAIR
- Diffusion weighted MRI
- Fat saturation/suppression
- Short-tau inversion recovery
- Proton density
What is FLAIR MRI used for?
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
What is diffusion weighted MRI used for?
Acute (and old) infarction –> shows up high signal
What 2 methods can you suppress fat with on T1-MRI? Why would you do this?
Fat suppresion or short-tau inversion recovery
view fluid better
What is proton density good for?
Excellent detail for normal anatomy + pathology
What is athe typical history of dissected aortic aneurysm?
Male older –> sudden onset severe chest pain radiating to the back
what is a saddle PE?
A PE that lies at the bifurcation of the pulmonary trunk extending into both L/R pulmonary arteries
How would you diagnose a jefferson fracture?
CT!!!!! (Peg XR shows widening of lateral masses from Peg but not diagnostic)
On T2 MRI of the spine, what might indicate degenerative disc disease?
low signal compared to other discs as loss of water content in the disc
