3. Imaging the Nervous System

Question 1

is the grey matter external to the brain, or internal?

Answer 1

external: grey matter is the ribbon at the outside of the brain. white matter is the interior stuff

Question 2

on CT, is grey matter darker or lighter than white matter?

Answer 2

lighter. think about the fat in myelin (more in white matter) attenuating the signal and making the white matter darker.

Question 3

how will a young child’s brain image differ from a 21 year olds?

Answer 3

the ventricles may be bigger - this is normal

Question 4

how does the brain change as people age?

Answer 4

the volume of brain tissue decreases yearly. an older brain will have bigger ventricles and deeper sulci

Question 5

what do intra-axial and extra-axial mean?

Answer 5

inside the brain parenchyma, or outside. referring to the source of a lesion, for example.

Question 6

what are characteristics of an intra-axial mass?

Answer 6

expands the brain/gyrus, vasogenic edema, subarachnoid veins displaced laterally, smaller ventricles, CSF space is smaller

Question 7

what are characteristics of an extra-axial mass?

Answer 7

widened CSF space, displaced veins, buckling of grey matter but no edema of brain itself.

Question 8

what will we see if the lesion is taking up space (as opposed to being atrophy)?

Answer 8

crowded sulci, shifted midline, smaller ventricles

Question 9

what will we see if the lesion is atrophy (as opposed to taking up space)?

Answer 9

no midline shift, sulci are wider, ventricles are larger

Question 10

what will cause cytotoxic edema?

Answer 10

STROKE!!!

Question 11

what will cause vasogenic edema?

Answer 11

leaky capillaries in the brain: tumor, inflammatory disease, HTN

Question 12

what does cytotoxic edema look like?

Answer 12

cortex becomes less dense due to cell death.

lose the grey-white differentiation.

Question 13

what does vasogenic edema look like?

Answer 13

Leaky capillaries
Edema spreads in WM
Accentuates gray-white differentiation

Question 14

why does vasogenic edema accentuate the gray-white difference?

Answer 14

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)

Question 15

what imaging is indicated in stroke?

Answer 15

really only need a head CT to role out other causes.

Question 16

when you get a head CT in a suspected stroke, what are you hoping to find?

Answer 16

a relatively normal CT, so that you can give TPA. if evidence of hemorrhage or old infarct, then can’t give TPA.

Question 17

stroke will yield what type of edema? what happens to the grey/white matter differentiation?

Answer 17

cytotoxic edema! differentiation will be lost.

Question 18

how does the CT look in the first 24 or so hrs after a stroke?

Answer 18

normal

Question 19

what are the 4 CT signs of a stroke?

Answer 19

dense middle cerebral artery
loss of grey-white differentiation
loss of insular ribbon
effacement of sulci

Question 20

why will you see a dense middle cerebral artery in stroke?

Answer 20

clotted blood in the vessel

Question 21

why do you have loss of the insular ribbon with stroke?

Answer 21

insula = grey matter, commonly affected in MCA infarcts bc supplied by the MCA. appears darker/blends into background with a stroke

Question 22

what does a new stroke look like?

Answer 22

cytoxic edema, sulcal effacement, swelling.

Question 23

what does an old stroke look like?

Answer 23

loss of volume. signs of stroke on CT generally indicates tissue that is irreparable.

Question 24

what is the ischemic penumbra?

Answer 24

the theoretic basis for acute stroke treatment

Question 25

what is the theory behind the ischemic penumbra?

Answer 25

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.

Question 26

what is TPA?

Answer 26

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.

Question 27

what patients should be offered TPA?

Answer 27

pts with acute stroke, with no contraindications on CT, within 4.5 hours, if ischemic change is less than 1/3 of total area.

Question 28

what is diffusion imaging?

Answer 28

gold standard for stroke/identyfying dead brain. shows cells that are irreversibly injured. stays + for 10-14 days post stroke.

Question 29

how many days post-stroke will diffustion imaging remain positive?

Answer 29

10-14 d

Question 30

what is the initial imaging test of choice for suspected stroke patients?

Answer 30

non-contrast CT

Question 31

what is the hallmark imaging sign of stroke?

Answer 31

cytotoxic edema

Question 32

what is an MRI technique that will demonstrate acute strokes (stays bright for up to 2 weeks)

Answer 32

diffusion imaging

Question 33

where is the epidural space? do epidural hematomas cross suture lines?

Answer 33

space is between dura/periosteum and naked bone. epidural hematomas don’t cross suture lines

Question 34

where is the arachnoid in relation to the dura? what is special about it?

Answer 34

opposed to the dura. bound at venous sinuses due to arachnoid granulations. cobweb like projections connect it to the pia (on the brain)

Question 35

what is the potential space between the arachnoid and the dura?

Answer 35

subdural space

Question 36

what is the order of layers from the brain to the skull?

Answer 36

brain tissue, pia, subarachnoid space, arachnoid, subdural space, dura, venous sinus, dura, epidural space, skull

Question 37

which layer is closely opposed to the brain surface?

Answer 37

pia

Question 38

what is the space between arachnoid and pia?

Answer 38

subarachnoid space

Question 39

what space contains CSF?

Answer 39

subarachnoid.

Question 40

in an epidural hematoma, the blood is between what structures?

Answer 40

the bone and the external layer of dura.

Question 41

what kind of injury can result in an epidural hematoma?

Answer 41

coup/trauma.

Question 42

shape of epidural hematoma? will it cross sutures?

Answer 42

biconvex (like a clam). will not cross suture lines.

Question 43

subdural hematoma: arterial or venous bleed?

Answer 43

venous due to tearing of bridging veins.

Question 44

subdural v epidural hematoma: which has worse prognosis?

Answer 44

subdural.

Question 45

subdural hematoma - shape? cross suture lines?

Answer 45

crescent. will cross suture lines.

Question 46

midline shift: at what point is it assessed? how much shift indicates surgery?

Answer 46

at foramen of monro. 5mm is tipping point.

Question 47

where are contusions most common?

Answer 47

anterior/inferior frontal lobes, anterior temporal lobe as brain hits/slides over rough surfaces.

Question 48

are contusions hemorrhagic or non-hemorrhagic?

Answer 48

can be either

Question 49

what is a diffuse axonal injury?

Answer 49

shear injury to axons.

Question 50

what does a diffuse axonal injury appear like on imaging?

Answer 50

whiter spots in the brain parenchyma

Question 51

CT vs MRI in trauma situation: what to get?

Answer 51

CT first. accurately identifies all surgically impt lesions. MRI is more sensitive to a number of lesions: reserved for those with unexplained continuing deficits.

Question 52

what does a sub-arachnoid hemorrhage look like on imaging?

Answer 52

follows the line of sulci. treatment is to just watch it. looks internal to the parenchyma and is tracing the sulci