3. Imaging the Nervous System Flashcards
is the grey matter external to the brain, or internal?
external: grey matter is the ribbon at the outside of the brain. white matter is the interior stuff
on CT, is grey matter darker or lighter than white matter?
lighter. think about the fat in myelin (more in white matter) attenuating the signal and making the white matter darker.
how will a young child’s brain image differ from a 21 year olds?
the ventricles may be bigger - this is normal
how does the brain change as people age?
the volume of brain tissue decreases yearly. an older brain will have bigger ventricles and deeper sulci
what do intra-axial and extra-axial mean?
inside the brain parenchyma, or outside. referring to the source of a lesion, for example.
what are characteristics of an intra-axial mass?
expands the brain/gyrus, vasogenic edema, subarachnoid veins displaced laterally, smaller ventricles, CSF space is smaller
what are characteristics of an extra-axial mass?
widened CSF space, displaced veins, buckling of grey matter but no edema of brain itself.
what will we see if the lesion is taking up space (as opposed to being atrophy)?
crowded sulci, shifted midline, smaller ventricles
what will we see if the lesion is atrophy (as opposed to taking up space)?
no midline shift, sulci are wider, ventricles are larger
what will cause cytotoxic edema?
STROKE!!!
what will cause vasogenic edema?
leaky capillaries in the brain: tumor, inflammatory disease, HTN
what does cytotoxic edema look like?
cortex becomes less dense due to cell death.
lose the grey-white differentiation.
what does vasogenic edema look like?
Leaky capillaries
Edema spreads in WM
Accentuates gray-white differentiation
why does vasogenic edema accentuate the gray-white difference?
a failure of tight endothelial junctions at the capillary level results in plasma leakage into the white matter. The fluid tracks easily between white matter, but gray matter is a relative barrier to this fluid, so it retains its normal signal (MR) or density (if CT)
what imaging is indicated in stroke?
really only need a head CT to role out other causes.
when you get a head CT in a suspected stroke, what are you hoping to find?
a relatively normal CT, so that you can give TPA. if evidence of hemorrhage or old infarct, then can’t give TPA.
stroke will yield what type of edema? what happens to the grey/white matter differentiation?
cytotoxic edema! differentiation will be lost.
how does the CT look in the first 24 or so hrs after a stroke?
normal
what are the 4 CT signs of a stroke?
dense middle cerebral artery
loss of grey-white differentiation
loss of insular ribbon
effacement of sulci
why will you see a dense middle cerebral artery in stroke?
clotted blood in the vessel
why do you have loss of the insular ribbon with stroke?
insula = grey matter, commonly affected in MCA infarcts bc supplied by the MCA. appears darker/blends into background with a stroke
what does a new stroke look like?
cytoxic edema, sulcal effacement, swelling.
what does an old stroke look like?
loss of volume. signs of stroke on CT generally indicates tissue that is irreparable.
what is the ischemic penumbra?
the theoretic basis for acute stroke treatment
what is the theory behind the ischemic penumbra?
an underperfused area may not function, but may not be actually dead for hours to days. can still treat neurons that are alive. however, if dead, worse to treat because may cause hemorrhage.
what is TPA?
Tissue plasminogen activator. protein involved in the breakdown of blood clots.
Catalyzes the conversion of plasminogen to plasmin, the major enzyme responsible for clot breakdown. Used in clinical medicine to treat embolic or thrombotic stroke. Use is contraindicated in hemorrhagic stroke and head trauma.
what patients should be offered TPA?
pts with acute stroke, with no contraindications on CT, within 4.5 hours, if ischemic change is less than 1/3 of total area.
what is diffusion imaging?
gold standard for stroke/identyfying dead brain. shows cells that are irreversibly injured. stays + for 10-14 days post stroke.
how many days post-stroke will diffustion imaging remain positive?
10-14 d
what is the initial imaging test of choice for suspected stroke patients?
non-contrast CT
what is the hallmark imaging sign of stroke?
cytotoxic edema
what is an MRI technique that will demonstrate acute strokes (stays bright for up to 2 weeks)
diffusion imaging
where is the epidural space? do epidural hematomas cross suture lines?
space is between dura/periosteum and naked bone. epidural hematomas don’t cross suture lines
where is the arachnoid in relation to the dura? what is special about it?
opposed to the dura. bound at venous sinuses due to arachnoid granulations. cobweb like projections connect it to the pia (on the brain)
what is the potential space between the arachnoid and the dura?
subdural space
what is the order of layers from the brain to the skull?
brain tissue, pia, subarachnoid space, arachnoid, subdural space, dura, venous sinus, dura, epidural space, skull
which layer is closely opposed to the brain surface?
pia
what is the space between arachnoid and pia?
subarachnoid space
what space contains CSF?
subarachnoid.
in an epidural hematoma, the blood is between what structures?
the bone and the external layer of dura.
what kind of injury can result in an epidural hematoma?
coup/trauma.
shape of epidural hematoma? will it cross sutures?
biconvex (like a clam). will not cross suture lines.
subdural hematoma: arterial or venous bleed?
venous due to tearing of bridging veins.
subdural v epidural hematoma: which has worse prognosis?
subdural.
subdural hematoma - shape? cross suture lines?
crescent. will cross suture lines.
midline shift: at what point is it assessed? how much shift indicates surgery?
at foramen of monro. 5mm is tipping point.
where are contusions most common?
anterior/inferior frontal lobes, anterior temporal lobe as brain hits/slides over rough surfaces.
are contusions hemorrhagic or non-hemorrhagic?
can be either
what is a diffuse axonal injury?
shear injury to axons.
what does a diffuse axonal injury appear like on imaging?
whiter spots in the brain parenchyma
CT vs MRI in trauma situation: what to get?
CT first. accurately identifies all surgically impt lesions. MRI is more sensitive to a number of lesions: reserved for those with unexplained continuing deficits.
what does a sub-arachnoid hemorrhage look like on imaging?
follows the line of sulci. treatment is to just watch it. looks internal to the parenchyma and is tracing the sulci
