ICL 12.1: Neuroimaging of Neoplasms Flashcards
what is MR spectroscopy?
a special type of MR sequence that shows you the amount of a particular metabolic in the tissue
what metabolites are you looking for in an MR spectroscopy?
- N-acetyl aspartate
- creatine
- choline
- lipid/lactate
what is the significance of finding N-amino aspartate in a tissue?
amino acid found in high concentration within healthy neurons (axons)
so if something is destroying neurons, NAA will be low
what is the significance of finding creatine in a tissue?
metabolic product found in a near constant concentration in many tissues through the body
what is the significance of finding choline in a tissue?
acetylcholine precursor present in high concentrations in actively proliferating tissues
so if you’re making new cell membranes and turning over cells really fast like in tumors or healing, you’ll have high choline levels
what is the significance of finding lipid/lactate in a tissue?
markers for anearobic metabolism (necrosis) and phospholipid membrane breakdown
lipids is in reference to the phospholipids in the cell membranes so if you’re breaking down cell membranes you’r going to get increased lipid levels
lactate is in reference to lactic acid from anaerobic metabolism so you’ll get high lactate levels in strokes because there’s anaerobic activity or with tumors that overgrow their blood supply because you’ll get necrosis from ischemia in the cell which will also give you a high lactate
what will happen to the choline, NAA, lipid/kactate and creatine levels when there is neuron destruction?
- choline increase
- NAA decrease
- creatine will remain relatively constant
- lipid/lactate may increase or stay the same depending on the aggressiveness of tumor growth/stroke
slow growing will show little change
fast growing will show significant increase
what does an MR spectroscopy look like in a normal vs. tumor tissue?
normal tissue has upward slope to the right because there’s a lot of neural tissue with a lot of NAA
tumor tissue like a high grade astrocytoma will have a downward slop to the right because the choline goes way up and you start to get a lipid and lactate peak; creatine will stay relatively constant
slide 6
what is an MR perfusion?
contrast enhanced imaging demonstrating dynamic enhancement and washout of vascular contrast
can help demonstrate the presence of a hyper-vascular tumor
if you have a stroke, you won’t see a lot of perfusion on an MR perfusion but with an aggressive tumor that’s growing a lot of new blood vessels you’ll see a lot of perfusion with high blood volume and blood flow
what are the 2 parameters you use to differentiate intra-axial neoplasms?**
- age
age of the patient may be the single most important factor!!
- location
probably almost as important as age
- comorbidites are helpful to know – some tumors occur with higher frequencies or patients with conditions like von Hipple-Lindau or neurofibromatosis which are conditions that predispose them to a certain tumor it will drive your differential
ex. von hippie lindow will almost always have a hemangioblastoma
what is a low grade astrocytoma?
diffuse low grade gliomas of the cerebral hemispheres that are typically diagnosed in young adults between 20-45 years old (mean 35 years of age)
they can grow slowly for a really long time without symptoms
WHO grade I
there is a slight malepredilection (M:F ~1.5)
what is often the presenting feature of a low grade astrocytoma?
seizure
~40% of cases the presenting feature isseizure – this is particularly the case in adults
how do you image low grade astrocytomas? what part of the brain do they usually effect?
frontal and temporal lobes
T2/Flair MRI is the modality of choice for characterizing these lesions, and in the case of smaller tumors, they may be subtle and difficult to see on CT, especially as they tend not to enhance
typically low grade infiltrating astrocytomas appear as isodense or hypodense regions of positive mass effect, often without any enhancement
do glial tumors infiltrate the brain?
yes they are glial cell tumors which love the brain!
they like the white matter tracts so they will use things like the corpus callosum to cross to the other hemisphere
this goes for low grade astrocytomas, anaplastic astrocytoma or glioblastoma
what does a T2/Flair and post-contrast for a low grade astrocytoma look like?
T2/Flair will show a mass-likehyperintense signal that always follow the white matter distribution and causes expansion of the surrounding cortex
there will be NO enhancement with contrast
so a supratentorial lesion that’s T2 bright in a 20 year old with no necrosis, no enhancement it’s going to be a low grade astrocytoma
what will you see in an MR spectroscopy of a low grade astrocytoma?
- elevated choline peak
- low/normal NAA peak
- elevated choline:creatine ratio
- there is lack of the lactate peak because you’re not destroying a lot of brain because it’s so low growing
slide 14
what will you see with an MR profusion of a low grade astrocytoma?
normal blood volume because they’re not really vascular since they’re not growing very fast and therefore they don’t have alot of requirements
what will you see with a PET scan of a low grade astrocytoma?
a little tiny bit of increased FDG uptake but it’s basically the same glucose uptake as normal white matter
PET scans are where you tag glucose
what is an anaplastic astrocytoma?
WHO grade II glial tumor
it has an intermediate prognosis between a low grade astrocytoma and glioblastoma
effects 40-50 year olds mostly
patients typicallypresent in one of three ways:seizures,focal neurological deficit or symptomsof increased intracranial pressure –> white matter tracts are now being destroyed and the tumor is growing a little faster
what’s the difference on MRI between a low grade astrocytoma and an anaplastic astrocytoma?
on imaging, anaplastic astrocytoma tumors share common features with diffuse low grade astrocytomas, however they tend to present with contrast enhancement
what is the key feature of an anaplastic astrocytoma?
the key features present in anaplastic astrocytomas that areabsent in low grade tumors aremitotic activity and cellular pleomorphism.
unlike glioblastomas, however, theydo not demonstrate necrosis or vascular genesis
slide 19
what do you see on an MR spectroscopy of an anaplastic astrocytoma?
- increased choline-to-creatine ratio (choline levels increased)
- NAA preserved or mildly depressed because white matter tracts are being killed
- no significant lactate
- intermediate levels of myo-inositol(lower than low grade, buthigher than GBM)
slide 22
what do you see on an MR perfusion of an anaplastic astrocytoma?
elevated cerebral blood volume because there’s angiogenesis
what is a glioblastoma?
WHO grade IV glial tumor
it has a terrible prognosis; it’s a death sentence the life span is 6 months to a year
usually effects 65-75 years old but can effect people starting at 40
slight male predominance with 3:2 ratio
what does a glioblastoma look like on a gross brain sample?
glioblastomasare typically poorly-marginated, diffusely infiltrating necrotic masses localized to the cerebral hemispheres –> so there’s no way for you to go in and cut these things out ): you can try to treat with VEGF inhibitors but then you stop angiogenesis everywhere in the body and that’s not very well tolerated
necrosis and microvascular proliferation are hallmarks of glioblastomas
peripheral enhancement and central necrosis on imaging
they give rise to the so calledbutterfly glioma,to involve the contralateral hemisphere
what part of the brain do glioblastomas most often effect?
supratentorial white matter isthe most common location
they have a preferential spreading along the condensed white matter tracts such as corticospinal tracts and corpus callosum (MS and Lymphoma also do this)
what does an MR perfusion of a glioblastoma look like?
blood volume is elevated compared to lower grade tumors and normal brain
blood volume won’t be elevated in the necrotic part of the glioblastoma, it’ll be elevated in the periphery where the tumor is growing and infiltrating
what does an MR spectroscopy of a glioblastoma look like?
- choline: increased a ton because lots of cell turnover and cell growth
- lactate: increased because of all the necrosis
- lipids: increased because of all the cell membrane breakdown
- NAA: decreased because all of the neural tissue is dying
- myo-inositol: decreased
slide 31
what does a PET scan of a glioblastoma look like?
PET demonstrates accumulation of FDG (representing increased glucose metabolism) which typically is greater than or similar to metabolism in gray matter (peripheral)
what is a central neurocytoma?
WHO grade II neuroepithelialintraventricular tumors
on imaging they appear as heterogeneous masses of variable size and enhancement within the lateral ventricle – usually arises from septum pellucidum!!
imaging will usually show calcifications and cysts
typically seen in 20-40 year olds
only accounts for 15 of intracranial tumors
what are the 3 types of choroid plexus tumors?
- choroid plexus papiloma
- choroid plexus carcinoma
- choroid plexus metastasis
what is a choroid plexus papilloma?
uncommon, benignneuroepithelial intraventricular tumor –> but fives times more common than CP carcinomas
occur in both the paediatric (more common) and adult population –> 85% occur in kids under 5 years old!!!
what do choroid plexus papillomas look like on imaging in general?
tumors are usually identified in the fourth ventricle in adults and in the lateral ventricles inthe pediatric population
commonly present as a solid vascular tumor with vividfrond-like patternenhancement –> they look like cauliflower!
quarter of casesspeckled calcifications are present
how can you differentiate a choroid plexus papilloma from a central neurocytoma?
central neurocytoma usually arises from the septum pallucidum so it’s more centrally located
the choroid plexus papilloma arises from the choroid plexus so it’ll usually be more laterally located in the 4th or lateral ventricle s
why are choroid plexus papillomas so devastating if they’re benign?
WHO grade I so it’s benign but they’re devastating in that they cause hydrocephalus because the tumor causes overproduction of CSF since it’s a tumor of the choroid plexus
what is a choroid plexus carcinoma?
WHO Grade III
considerable overlap in imaging characteristics it carries significantly poorer prognosis thanchoroid plexus papilloma
choroid plexus carcinomas occurs predominantly in children, typically in the first 5 years of life
what makes a choroid plexus carcinoma lethal?
can cause hydrocephalus
not from over production of CSF like with a choroid plexus papilloma but from mass effect –> it grows and occludes the foramen of Monroe
if it gets big enough it can occlude both aqueducts and lateral ventricles get huge
it can also cause brain herniation because the laterals are getting pushed over across the midline
what part of the brain is related to seizures?
temporal lobe
specifically the hippocampus!
how can you differentiate between a pleomorphic xanthoastrocytoma and a ganglioglioma?
they’re going to have identical imaging and locations in the temporal lobes and identical age rages –> so you can’t differentiate with imaging! you can only do it pathologically after you take the lesion out
both WHO grade I or II so if you take them out usually seizures go away
what are pleomorphic xanthoastrocytomas?
rare, low grade astrocytoma WHO grade II
found in young patients who usually present with temporal lobe epilepsy
they’re cortical tumors with a cystic component and vivid contrast enhancement
typically these tumors are found in young patients (children or young adults), have a predilection for the temporal lobe, and patients frequently present with seizures (~75% of cases)
what do you see on MRI imaging for a pleomorphic xanthoastrocytoma?
very very enhancing!!!
most have a cyst and the inside the cyst will be a super enhancing lesion
so black cystic portion and white tumor tissue portion inside
what is a ganglioglioma?
uncommon low grade (WHO Grade I or II) CNS tumors
most frequent of the neuronal-glial CNS neoplasms
epilepsy is a common clinical presentation
typical occurrence is in the temporal lobes and cystic
kids and young adults effected; more young adults
what is a dysembrioplastic neuroepithelial tumor?
benign (WHO Grade I) slow growing tumours arising from either cortical or deep grey matter
frequently associated with cortical dysplasia(up to 80% of cases)
characteristically cause intractable partial seizures
typically these tumors are diagnosed in children or young adults
which parts of the brain are most often effected by a dysembrioplastic neuroepithelial tumor?
- temporal lobe: over 60% of cases
- frontal lobe: 30% of cases
- caudate nucleus
- cerebellum: presentation is then more commonly with ataxia rather than seizures
- pons
what does a dysembrioplastic neuroepithelial tumor look like on MRI?
soap bubble on T2 that involves the cortex and subcortical grey matter
really bright and bubbly looking
its imaging is super characteristic; it’s one of the ones that you don’t even really need to ask the location or age of the patient
slide 63
what is an oligodendroglioma?
glial tumor of oligodendrocytes
accountfor 5-25% of all gliomas and 5-10% of all primary intracranial neoplasms
occur most commonly in the 4thand 5thdecades of life
third most common glioma accounting for 2%–5% of primary brain tumors and 5%–18% of all glial neoplasms
if you see calcifications in a tumor, which type of tumor should 100% be in your differential?
oligodendroglioma!!
most brain tumors have the ability to form calcifications and they’re usually tiny ones but with oligodendroglioma it always forms calcifications and giant ones too most of the time!!
so no matter what the age of the patient is or the location, if you see dense calcification you should at least consider an oligodendroglioma
which posterior fossa tumors are common in adults?
- metastasis*** (tumors love to go to the cerebellum so this is the most common cause of PFT in adults)
- hemangioblastoma
- lehrmitte-Duclos
which posterior fossa tumors are common in kids?
- medulloblastoma*** (usually in 4th ventricle but as it grows it can push out into the cerebellum)
- ependymoma
- pilocytic astrocytoma
can you differentiate posterior fossa tumors based on age?
nope
a PFT in a kid and 70 year old will look the same so you need to know how old they are and if they have any other diseases
what is a hemangioblastoma?
the most common posterior fossa tumor in young adults!!
WHO grade I
super closely associated to von hippie landau –> will get hemangioblastomas in the cerebellum or spine most often
in what population are hemangioblastomas most common?
more common in males
30-60 years old so it’s an adult tumor!
very common in Von Hippel-Lindau disease–> 80% are sporadic but the rest are in VHL patients
what does a hemangioblastoma look like on MRI imaging?
will have a big cystic component with a tumor nodule inside
tumor will be really vascular so it’ll be really bright white
slide 73
what is a Lehrmitte-Duclos tumor?
dysplastic cerebellar gangliocytoma,is a rare tumor ofcerebellum
it’s so slow growing so we usually just watch them; you only do something if it causes a mass effect if it gets too big in the cerebellum and starts pushing on the brainstem but until then you just image and watch
probably hamartomatous, although the exact pathogenesis remains unknown
WHO Grade Itumor
typically presents in young adults
what does a Lehrmitte-Duclos tumor look like on MRI?
tiger-stripped appearance almost always in the cerebellum
not a lot of enhancement
slide 78 – it’s so distinct go look at it!!
what is an ependymoma?
a broad group of glial tumors which share common origin fromdifferentiated ependymalcells liningtheventricles (usually the 5th ventricle)
they account for ~5% of all neuroepithelial neoplasms, ~10% of all pediatric brain tumorsand up to 33% of brain tumors occurring in those less than 3 years of age
mean age at diagnosis is 6 years of age –> second peak for supratentorial tumors around the 3rddecade
WHO grade I, II or III so they’re all over with lots of subtypes too of varying severity
what is the presenting feature of ependymoma?
kid with hydrocephalus!
ependymomas usually arise for the floor of the 4th ventricle in the posterior fossa (infratentorial)
what is the one feature that can differentiate an ependymoma from a medulloblastoma?
ependymoma tend to extend through the foramina of Luschka and Magendie, hence the term plastic ependymoma because they’re really soft and look like toothpaste in the canals –> this is a characteristic feature and can be seen on both CT and MRI
medulloblastomas just look like a solid mass that’s expanding that doesn’t look like it’s trying to squeeze through any openings –> they’re blue cell tumors so the cells are packed so tightly together that they restrict diffusion and protons and water can’t move –> so diffusion restricting tumor in the 4th ventricle is a medulloblastoma almost all the time (slide 89)
what are the characteristics of an ependymoma?
- calcification is common (50%)
- cystic areas (50%)
but there’s so much variation
what is a medulloblastoma?
most common malignant brain tumor of childhood
they most commonly present as midline masses in the roof of the 4th ventricle with associated mass effect and hydrocephalus
usually effects young kids like under 6 years old
they account for 12-25 % of all pediatric CNS tumors, and 30-40% of pediatric posterior fossa tumors
what is a pilocytic astrocytoma?
aka Juvenile pilocytic astrocytomas (JPA), arelow-grade, relatively well-definedastrocytomasin the cerebellum (WHO Grade I) –> really hard to tell apart from a hemangioblastoma because it also has a cyst with a tumor nodule so that’s why age is so important!
tend to occur in young patients and have a relatively good prognosis
75% occurring in the first two decades of life, typically late in the first decade (9-10 years)
there’s a second age peak in the 50s but they’re usually supratentorial, not in the posterior fossa like in the kids
