Neurohistology: Lin Flashcards
What are the different type of imaging techniques?
- Computed Tomography (CT)–Magnetic resonance imaging (MRI)
- Intravenous contrast
Role intravenous contrast ???
to help differentiate btw different diseases
Hemorrhagic transformation
when an ischemic stroke turns in to a hemorhagic stroke
Hydrocephalus
this is on the USMLE
-can be communicating or non-communicating
CT
computed tomography
- uses ionization radiation (xray)
- you have an xray detector and xray source; it spins around and basically takes xray of all the different parts of your body from all the different directions
- the different tissues in body will attenuate the xray in different amounts (measures attenuation of radiation by tissues)
- develops initally at EMI (a music company)
RISKS
- cancer induction (1/10,000)
- contrast neuropathy (injuring kidneys)
Reading head CT
talk about 4 different Head CT densities
- CSF (dark)
- grey matter (light grey)
- white matter (dark grey)
- Bone (bright
blood on CT
looks different depending on how old it is (epidermal hematoma)
- acute (bright)
- chronic (dark)
CT with IV contrast
-intravenous contrast: iodinated; high attenuation of x-rays; appears bright
-molecule that contain take iodine which attenuate xrays a lot
by doing that you can make the blood vessel look more dense and thus appear brighter
When to use CT WITH IV contrast?
since IV and blood are both appear bright you don’t want to use it at any time
DON’T USE for head trauma
-if someone comes in with hematoma (don’t use)
-acute hemorrhage and contrast both appear bright
USE: helpful for intracranial infection or tumor
-it to look for infection or a tumor (enhancement on the CT scan with IV contrast) ie. glioblastoma multiforme
-inflammation from infection and tumor disrupts the blood-brain barrier
-contrast enters into diseased areas of brain and causes them to become brighter and easier to detect
MRI
magnetic resonance imaging
- it uses a huge magnetic field (2,000 times more than the magnetic field of the earth)
- complex physics; measures radiofrequency signal
- it aligns the protons in your body in a certain direction, shoot them with the a radio frequency signal and protons start to rotate giving off their own radio frequency field
- super conductor and chilled in liquid nitrogen
- it never turns off but you can push a button to quench it
- MRI uses a strong magnetic field that can turn metal objects into dangerous projectiles (can turn ordinary objects into bullet)
NO XR used so NO CANCER (no known increased cancer risk)
Different sequences in MRI
depending on what you’re measuring you can have multiple sequences, here are the four basic:
- T1 weighted: fat is bright, water is dark (fat has lots of H1s)
- T2 weighted: water is bright (WW2) water is white
- diffusion weighted imaging (DWI): measures how fast the water moves in the body in the anatomy; good at looking for acute stroke (decreased density of water molecules)
- blood is very dark (blood disrupts the magnetic field so you can’t get signals from it
MRI imaging sequencing strengths
T1 weighted: good for anatomy and BONE marrow pathology (such as tumor)
T2 good for pathology such as edema (which is all increase water content), infection, tumor, inflammation
Bone is what color in T1?
- bright (white)
- bright fatty bone marrow in skull
susceptibility weighted sequence (SWI)
blood on MRI
what disrupts the magnetic field and you cannot get the signal back
-blood on MRI appearance depends on age and composition of blood products
more sensitive than blood in CT???
IV contrast in MRI
use gadolinium, large radiofrequency signals
- disrupts T1 magnetic moment and causes things to appear very bright on the T1 weighted sequences
- use when interested in infection, inflammation, and tumor because they allow more blood to go into these places
T1 abscess
fluid is dark
fat is bright
contrast causes enhancement of the abscess on T1 (remember fluid is dark)
Glioblastoma Multiforme CT vs MRI
CT: bone bright, scalp fat dark
MRI (T1 weighted): bone is bright (cortical) AND dark (scalp) (why???), scalp fat is bright)
Stroke types
hemorrhagic stroke: bleeding to brain usually due to HTN or from an ischemic stroke because of tissues dying
ischemic stroke: lack of blodo to brain usually due to clot
Acute Ischemic Stroke Timing and pathology
- timing: less than 2 weeks old (including acute and subacute stages)
- physiology: cytotoxic edema b/c cells are dying; INCREASE amount in INtracellular fluid; DECREASE in EXtracellular fluid
Acute Ischemic Stroke CT
- don’t use CT if you think pt has an acute stroke (it takes 6 hours to see a CT abnormality)
- YOU NEED TO GET AN MRI
- increased water in brain tissues
- affected tissue becomes darker with time
- very early stroke is difficult to detect
-At 24 hours, all patient will have CT abnormality.
CT: acute brainstem ischemic stroke
bright clot
not reliable finding not all the time
diffusion weighted imaging (DWI) cerebellar ischemic stroke
- VERY good for detecting early ischemic stroke (btw 10 and 60 minutes)
- measures diffusion of water
- acute ischemic stroke is bright (water is bright)
MRI: Acute ischemic stroke (DW)–> What causes the bright signal? What about on the T2 sequence?
- brain cells swell, taking in extracellular water
- restricted motion of free water outside cells causes the bright signal
T2 weighted
- increased in water in brain tissue
- bright signal
- PRESENT ABOUT 3 hours after the ischemic stroke
how can we tell timine 35mintures????
Hemorrhage Transformation
- this is where ischemic stroke becomes a hemorrhaging stroke
- cells die and you disrupt the BBB and the blood can leak into the brain parenchyma
- usually occurs 205 days after ischemic stroke onset
- related to reperfusion of infarcted brain
- most common cause is treatment with thrombolytic drugs (break clots which cause bleeding)
- occasionally spontaneous transformations
-usually give thrombolytic drugs for hemorrhaging stroke
acute blood is bright
old blood is dark
we know it is CT scan because bone is BRIGHT
Chronic ischemic stroke
timing: greater than 2 weeks old
physiology: edema resolved; dead tissue is removed
imaging appearance: dead tissue is replaced by fluid
on CT
-very dark (near water) density
on MRI
-very bright (near water) signal of T2 sequence
greater than 2 weeks old (edema is resolved and dead tissue is removed and have a hole in brain replaced by fluids): fluid is dark on CT; MRI (T2) fluid is bright remember WW2
T2 weighted MRI vs CT of old cerebral artery stroke
on CT
-bone is very bright; stroke is dark (looks just like the ventricles)
on MRI (T2 weighted) -skull is dark; more H2O so more signal (stroke is BRIGHT)
Stroke and vessels
strokes will look different based on which one of the vessel below are occluded
there are different cerebral arteries that arise in the brain (on CT scan):
- anterior cerebral artery: chronic stroke in which blood is dark
- middle cerebral artery: more acute because of all the edema
- posterior cerebral artery: chronic stroke due to the darker color
CT angiogram: arteriogram and venogram
looks at vessels; give contrast which creates a cast of the vessels (you can reconstruct them)
-to look at which vessels are affected (the ones that are missing which implies that there is a clot)
CT perfusion imaging
Howard doesn-t do it
it is at stroke centers
-can use CT to look at the perfusion (blood flow) of the brain
Basilar Artery Occlusion (CT)
coronal view
-vessels on the posterior circulation vertebral artery to the basilar artery and then you get the posterior vertebral arteries
-darker means more fluid
MRI angiogram
- axial view
- internal carotid arteries
- anterior cerebral arteries
- posterior cerebral arteries
we can look for occlusion just like we did in the CT
left middle cerebral artery occlusion
carotid artery goes to form anterior and posterior cerebellar arteries?????????
communicating hydrocephalus
- all ventricles are enlarged
- usually caused by hemorrhage or infection
noncommunicating hydrocephalus
- not all the ventricles are enlarged
- structural CSF flow obstruction
- causes include brain mass or developmental anomaly
communicating hydrocephalus: MRI sagittal T1
- skull is dark
- fat outside is bright so this is T1 weighted
- lateral, 3rd, and 4th ventricles are enlarged
communicating hydrocephalus: MRI axial T2
gigantic lateral ventricle and 3rd and 4th ventricle are enlarged
-ventricles are bright (T2: water is bright) WW2
noncommunicating hydrocephalus: large mass in posterior fossa
CT because bone is bright
