ICL 12.1: Head Trauma MRI & CT Patterns Flashcards
trauma to the head, 49 years old got hit in the head with a baseball bat. what imaging modality would you use?
non-contrast CT
you’re trying to look for skull fracture and hemorrhages, big bad things so a CT is faster than an MRI and you don’t want to wait when someone is bleeding out
35 year old male with new onset of seizures, not referred to neurologist. head trauma 3 months ago from MVA. what imaging modality should be used?
MRI
it’s not an immediate issue and it’s more sensitive!
how can you differentiate an epidural vs. subdural vs. subarachnoid hemorrhage?
if it crosses the suture, it’s probably subdural because the dura is bound to the sutures so the blood will stop there with an epidural bleed = lens shaped vs. crescent shaped for epidural vs. subdural bleeds
with a subarachnoid hemorrhage, the blood will flow in-between the sulci and anywhere there is CSF!! if there’s blood in the basal cisterns, the ventricles or sulci it’s most likely a subarachnoid bleed
what should you look for if there’s a temporal epidural hematoma?
MMA artery injury from a skull fracture!
so there will be a hematoma between the coronal and lambdoidal sutures!
if there wasn’t trauma, what could cause a subarachnoid bleed?
- aneurysm
- AVM
- vasculopathy
- coagulopathy
but the #1 cause of a subarachnoid hemorrhage is trauma!!!!
where can subdural hematomas spread to?
they are crescent shaped because they’re not constricted by the sutures so they spread
they can spread along the falx cerebri and tentorium!!
which type of hematoma is most likely to cause a brain herniation?
epidural hematoma
this is because it’s usually a high pressure arterial bleed that causes the brain to squeeze out of the way to decrease the pressure = herniation across the midline
what kinds of herniations can happen with an epidural hematoma of the temporal bone?
- ulcal herniation of the temporal lobe across the tentorium onto the brainstem
the brainstem then gets pushed against the contralateral tentorium which causes midbrain necrosis
- transtentorial herniation downward which causes the medial part of the brain to herniate downwards onto the midbrain
- subfalcine herniation of the frontal lobe across the falx cerebri
- extracranial herniation (usually with a gunshot or crazy trauma where the brain will swell outside the skull)
- transtentorial herniation upwards
slide 24
what is the effect of a subfalcine herniation?
subfalcine herniation of the frontal lobe across the falx cerebri
this is bad because the anterior cerebral artery branches sit on either side of the falx cerebri
so as the frontal lobe moves across, it takes the ACA and smashes it up against the falx and as the ICP goes up, it will outcompete the profusion pressure in the artery which will cause a stroke in the ACA territory which will cause more edema from ischemia and even higher ICP!
this is why it’s so important to decompress
what is subfalcine herniation?
Subfalcine herniation is when the brain is shifted underneath the falx – it is the same thing as midline shift
if you get mass effect, it will push the frontal lobe underneath the falx cerebri to the other side which has a bad effect on the anterior cerebral artery
what is an uncal herniation?
Uncal herniation is when the medial portion of the anterior temporal lobe is shifted into the suprasellar cistern
it is a subset of descending transtenorial herniation, which is when the cerebral hemisphere crosses the tentorium at the level of the incisura/notch
this puts pressure on the midbrain and you pin it against the opposite tentorium
what is the color of blood on a CT?
if it’s acute, a CT will show bright white blood
but after a while, the blood becomes less dense and you won’t be able to see the blood on an CT because it’ll turn black and at that point you need an MRI which is reallyyy sensitive to iron and you’ll be able to see where a bleed was for years
what is a brain contusion? where do they typically occur?
brain contusions are a bruise on the brain
your hard skull base is basically a cheese grater to the base of your soft brain when there’s trauma….
these injuries will happen at the bony ridges like at the petrous apex (temporal bone damage) or other places right at the base of the skull from the frontal and temporal lobes getting shredded
what is a contra-coup injury?
an injury opposite the site of trauma
if you have a patient with frontal scalp hematoma you need to look at the frontal lobe AND the occipital lobe for when the brain slide forward and hit and THEN slid back and hit the occipital lobe
what is the pattern of traumatic brain injury?
damage to the base of the frontal and temporal lobes!
from the skull shredding the brain at the crista galli and the petrous temporal bone
what happened if a child has a subdural hematoma?
it’s probably child abuse…..
if someone comes in and says their kid fell of the bed and the CT shows a subdural hematoma, the kid probably didn’t just roll of the bed because kids fall allllll the time and they don’t fracture their fricking skull…..
so pay attention to this!!!!
what if someone has a subarachnoid bleed without a scalp hematoma?
ruptured aneurism!!
the subarachnoid blood will be super diffuse, like literally everywhere all over
with traumatic subarachnoid bleeds, there’s a scalp hematoma and usually the bleed is focal
what does it mean if the whole brain is just gray and you don’t see any sulci or anything?
there’s no grey or white matter difference = diffuse hypoxic injury from a total cerebral edema
the lateral ventricles will look so little and no sulci filled with CSF because the brain is SO swollen it’s pushing all the CSF out of the head
what happens now is you’ll see psuedosubarachnoid hemorrhage which is actually just normal venous blood in the vessels of the cortex and they look bright like a subarachnoid bleed because the rest of the brain is so edematous that it looks dark
you see this a lot in MI patients or people who almost drowned because you brain has been without oxygen for 4-5 minutes
when would you get an MRI?
when it’s NOT acute!!
also if:
- the patient isn’t waking up after sedation
- patients is having seizures
- patient has lasting deficits that are not explained by CT
what can you see really well on an MRI vs a CT?
MRI susceptibility weighted or gradient imaging is significantly more sensitive than CT for subtle areas of bleeding
what is diffuse axonal injury?
shearing acceleration or deceleration forces may not be serious enough to cause large obvious contusions
they may cause microscopic structural damage to the axons themselves!
you only see a few of them if they bleed but not all of them bleed! but seeing a few of them tells you it’s diffuse and happened everywhere
how do you grade diffuse axonal injury?
they’re graded according to the structures involved
- parasagittal frontal lobes
- corpus callosum
- brainstem
the brainstem is more compact than the frontal lobe so a small DAI in the brainstem will disrupt a lot more white matter fibers than in a diffuse frontal lobe cortex
what is a concussion?
you do CT and MRI and you don’t see anything even though there’s definitely something wrong with the person
it’s an neuron metabolic crisis
what is diffuse tensor imaging?
you watch a proton move along a white matter tract and this helps you find the different white matter tracts in the brain
this is used to try and see which white matter tract were disrupted following a trauma
beautiful rainbow looking mohawk brain
