White Matter And Neurodegenerative Diseases

Front 1

what is grey matter comprised of

Back 1

neuronal cell bodies

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what is white matter comprised of

Back 2

long processes of these neurons, wrapped by myelin sheaths

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2 types of cerebral white matter dz

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demyelination - acquired d/o that affects normal myelin
dysmyelination - affects formation of myelin (seen in peds), rare

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potential categories that demonstrate etiologies of demyelinating dz

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primary
ischemia
infectious
toxic/metabolic

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pathophys of MS

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abn AB and T cell production against myelin

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what is seen histopathologically in MS

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selective destruction of myelin sheaths and periventricular inflammation
underlying axons are spared

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how to differentiate (histopathologically) MS from other WM conditions

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MS is the only WM dz to have associated inflammation on histopath

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dawson's fingers

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associated with MS
ovoid lesions perpendicular to the long axis of the ventricles

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common locations of MS plaques

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periventricular
subcortical WM

the following are not commonly associated with ischemic disease and have a higher assoc with MS:
cbl and cerebral peduncles
CC
medulla
spinal cord

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how does scarring occur in MS lesions

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focal proliferation of astroglia at site of injury ("gliosis")

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appearance of subacute or chronic MS plaques

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gliosis occurs
there can be actual loss of neuronal tissue and WM can have dark signal on T1 (poor prognosis)

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what is the callosal-septal interface

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region where septum pellucidum contacts the undersurface of the corpus callosum

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why is the callosal-septal interface impt in MS

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a characteristic feature of MS is for lesions to form at this interface

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appearance of tumefactive MS

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lrg conglomerate deep white matter mass that looks like a neoplasm
often there is a ring of peripher al enhancement

Front 15

what are the most commonly enctountered WM lesions

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ischemic WM changes

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pathophys of age related WM demyelination

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the deep white matter is susceptible to ischemic injury (moreso than GM) b/c the BV are small caliber and are end arteries without collaterals (GM has collaterals).

ATH dz of the peneterating cerebral arteries

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which parts of the brain are usually spared from age related demyelination

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cortex
subcortical U fibers
central CC
midbrain
cbl peduncles

(these all have dual blood supply)

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histologically, what does age related demyelination look like

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axonal atrophy
diminshed myelin

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how does age related demyelination differ from lacunar infarcts in terms of location

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lacunes occur in GB, upper 2/3 of putamen
lacunes are discrete 5-10mm hypodensities

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ddx for young adult p/w small white matter lesions

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hypercoag conditions
cardiogenic emboli
PFO
valvuluar vegetation

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MR appearance of ependymitis granularis

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area of hihg T2 along tips of frontal horns

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histologically, what is ependymitis granularis

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loose network of axons with low myelin count

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location of VR spaces

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centrum semiovale
lower BG at level of anterior commissure

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what is a VR space composed of

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CSF

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how does location btwn ischemic lesion and VR space differ

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lacunes are msot often in upper 2/3 of corpus striatum (end-arteriole infarcts) in distal vascular distribution

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pathophys of PML

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reactivation of the JC virus
JC virus infects the oligodendrocytes that make myelin. When they are infected --> widespread demyelination

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what parts of the brain does PML usually affect

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deep cerebral white matter
subcortical U fibers
GM and cortex are spared

parieto-occipital region typically affected

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appearance of PML

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discrete lesions without mass effect, hemorrhage, or contrast enhancement

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course of PML

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rapidly progressive, with death often svl months from time of dx

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clinical presentation of HIV encephalopathy

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progressive dementia without focal neurologic signs

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pathophys of HIV encephalopathy

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acitve HIV infx develops in microglia (brain macrophages)
cytokines and excitatory compounds are produced --> toxic effect on adjacent neurons

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appearance of HIV encephalopathy

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subtle diffuse T2 hyperintensity that is often b/l adn symmetric
ill-defined, involves large area
no contrast enh

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difference btwn HIV encephalopathy and PML on MR

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PML tends to have more dense lesions

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pathophys of ADEM

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theory is that body's antiviral immune rxn cross-reacts with myelin sheaths --> acute agressive form of demyelination

this is likely b/c there is shared molecular homology btwn viral proteins and CNS proteins

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time frame of ADEM to present

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usually 2 wks after viral infx with abrupt clinical onset of neurologic sx

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where does ADEM usually occur (white or gray matter)

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white matter mostly, occassionaly GM

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subacute sclerosing pancencephalitis

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reactivated, slowly progressive infx caused by measles

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who gets subacute sclerosing panencephalitis

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children btwn 5-12 yrs who had measles before 3 yo

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appearance of subacute sclerosing panencephalitis

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patchy areas of periventricular demyelination + lesions in BG

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histopath of herpes enchephalitis

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necrotizing meningoencephalitis associated with edema, necrosis, hemorrhage, encephalomalacia

often there is hemorrhage in affected areas

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clinical course of central pontine myelinolysis

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biphasic:
1. generalized encephalopathy from hyponatremia, whihc transiently improves.
2. 2-3d after electrolyte correction --> rapidly evolving corticospinal syndrome with quadriplegia, acute changes in mental status, and locked-in state

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pathophys of central pontine myelinolysis

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oligodendroglial cells are most susceptible to osmotic stresses so demyelination occurs in affected areas

there is vaculoization adn rupture of myelin sheaths (prob from osmosis)

neurons and axons are preserved

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other than pons, which parts of the brain are affected in central pontine myelinolysis

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thalamus
GB
putamen
lateral geniculate body
cbl

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appearance of central pontine myelinolysis

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abn high signal on T2, which corresponds to demyelination

in the pons, there are often 2 rounded areas of spared central pontine tracts (central corticospinal tracts are often preserved)

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ddx for central pontine myelinolysis

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should be differentiated from ischemic demyelination (need hx!)

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what does PRES stand for

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posterior reversible encephalopathy syndrome

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appearance of PRES

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signal changes within subcoritcal and cortical regions, esp w/i posterior vascular distribution

there is vasogenic edema w/i parietoccipital lobes

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presentation of PRES

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ha
sz
visual changes
AMS

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presumed pathophys of PRES

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temporary failure of autoregulatory capabilites of cerebral BV --> hyperperfusion, breakdown of BBB, and vasogenic edema.

no acute ischemic changes!

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why is the posterior brain most affected in PRES

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relatively poor sympathetic innervation of posterior circuliation

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etiologies of PRES

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medications
HUS
ARF
eclampsia

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common factor of etiologies of PRES

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likely common final pathway that includes high BP and/or endothelial injury

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complication of PRES

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hemorrhagic infarction

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who clasically gest marchiafava-bignami disease

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alcoholics

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pathophys of marchiafava-bignami disease

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demyelination of central fibers of corpus callosum, ant/post comissure, cso, middle cerebral peduncles

thought to be secondary to osmotic demyelination

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presentation of marchiafava-bignami disease

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non-sp dementia

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etiology of wernicke encephatlopathy

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B1 deficiency

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appearance of wernicke-korsakoff syndrome

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acute: T2 hyperintensity or contrast enhancement of mamillary bodies, basal ganglia, thalamus, and brainstem

chronic: atrophy of mamillary bodies, midbrain tegmentum, and 3rd vent dilatation

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DDx wernicke-korsakoff syndrome

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Leigh syndrome (does not affect mamillary bodies, remainder of findings are the same)

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pathophys of radiation leukoencephalitis

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damage to white matter 2/2 radiation induced vasculopathy

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complicatios of radiation to brain

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radiation leukoencephalitis
radiation necrosis
radiation arteritis

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when does radiation leukoencephalitis occur

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6-9 months after radiation

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appearance of radiation leukoencephalitis

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high signal on T2 in confluent areas of white matter extending to subcortical U fiberse in distribution of irradiated brain

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another name for dysmyelinating conditions

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leukodystropihies

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pathophys of dysmyelinating conditions

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myelin is abnormally formed or cannot be maintained b/c of an enzymatic or metabolic d/o that leads to accumulation of catabolites that break down myelin

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how do pts present with dysmyelinating d/o

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progerssive mental and motor deterioration

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which dysmyelinating dz is most common

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metachromatic leukodystrophy

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pattern of inheritance of metachromatic leukodystrophy

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autosomal recessive

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pathophys of metachromatic leukodystrophy

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deficiency of arylsulfatase A

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types of metachromatic leukodystrophy

* MC?

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infantile form (1-2 yo)**
juvenile form (5-7 yo)

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appearance of metachromatic leukodystrophy on MR

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progressive, symmetric areas of ns white matter involvement;
cortical U fibers are spared
finidngs are non-specific

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pattern of inheritance of adrenal leukodystrophy

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sex linked

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pathophys of adrenal leukodystrophy

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peroxisomal enzyme deficiency

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age of onset in adrenal leukodystrophy

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5-10 yo boys

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clinical findings assoc with adrenal leukodystrophy

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adrenal insufficiency
abn skin pigmentation
visual and auditory sx (predilection for involvement of medial and lateral geniculate nuclei)

Front 76

what do the medial and lateral geniculate nuclei do

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medial: relays for auditory pathway
lateral: relays for the visual pathway

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areas of brain assoc with adrenal leukodystrophy

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periatrial WM (which spreads to medial and lateral geniculate nuclei)
splenium of CC

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another name for Leigh dz

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subacute necrotizing encephalomyelopathy

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pathophys of Leigh dz

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mitochondrial enzyme defect that likely affects metabolism of thiamine

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age of presentation for Leigh dz

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<5 yo

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MR findings of Leigh dz

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white matter: frontal areas of subcortical white matter
gray matter: basal ganglia and periaquiductal gray matter

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which leukodystrophies are associated with macrocephaly

at what age do they present

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alexander and canavan disease

first few wks of life

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which portions of the brain are affected in alexander dz

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begin in frontal white matter and progress posteriorly
no gray matter involvement

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what is deficient in canavan dz

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aspartoacylase --> NAA buildup in brain and myelin destruction

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areas of brain affected in canavan dz

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diffuse white matter
vacuolization of cortical gray

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which dysmyelinating dzs have BG involvement

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Leigh dz
Canavan dz

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how to differentiate canavan dz from other advanced leukodystrophies

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if MR spect is performed, there would be a markedly elevated peak at NAA, which is diagnostic for deficeicny of aspartoacylase

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involvement of periaquiductal gray matter is characteristic for what

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Wernicke-Korsakoff
Leigh dz

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finding assoc with acute hydrocephalus

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transependymal flow of CSF

Front 90

describe path of CSF

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CSF produced by choroid plexus
CSF flows from lat vents -> 3rd vent -> 4th vent
CSF leaves vents vial foramina of luschka an dMagedie
CSF travels through basilar cisterns and over surfaces of cerebral hemispheres and gets absorbed in venous circulation through arachnoid villi that project mostly into superior sag sinus

Front 91

alternative pathway of reabsorption of CSF

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can be reabsorbed via ependymal lining of ventricles (transependymal flow)

Front 92

types of hydrocephalus
describe pathophys of each

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communicating: obstruction beyond ventricular system (obx is in subarachnoid space)
non-communicating: obx occuring within ventricular system that prevents CSF from exiting ventricles

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t or f: dilatation of the 4th ventricle is diagnostic of communicating hydrocephalus

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false; in non-communicating hydrocephalus, there could be an obx at foramen of magendie or luschka which could mimic the same appearance

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where is the 1st place to look to dx hydrocephalus

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temporal horms of lateral ventricles, as well as 3rd vent
also, bowing and stretching of the corpus callosum on sag images may help

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etiology of ex vacuo vetriculomegaly

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enlarged ventricular system from atrophy

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appearance of ex vacuo vetriculomegaly vs hydrocephalus

best place to look to make distinction

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in ex vacuo vetriculomegaly, vents and sulci are equally prominent
in hydrocephalus, the vents are dilated out of proportion to the sulci

look at temporal horns and 3rd vent - tissue surrounding these structures doesn't typically atrophy

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most common causes of acute hydrocephalus

whihc type of hydrocephalus results

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SAH
meningitis

both; obx is caused by adhesions and inflammation

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congenital cause of aqueductal stenosis

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benign congenital web can form across cerebral aqueduct

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why does hydrocephalus occur in dandy walker malf and chiari malf

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thought to be assoc with adhesions occuring during CNS development

Front 100

which tumors block the aqueduct

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tectal glioma
pineal tumors

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which tumor blocks the 3rd ventricle

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colloid cyst

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most common cause of NPH

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previous SAH or meningeal infx

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histopathology of alzheimers

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neuritic plaques (made of tortuous neuritic processes surrounding a central amyloid core )
neurofibrillary tangles (contain abn tau proteins)

both interfere with nml neuronal fxn

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imaging of alzheimers

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diffuse atrophy, esp in hippocampus, temporal lobes, and parietotemporal cortices

look for enlargement of temproal horns, suprasellar cisterns adn sylvian fissures

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what % of parkinson's pts develop dementia

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25%

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pathophys of parkinsons

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deficiency of dopamine caused by a dysfxn of hte pars compacta of the substantia nigra
after 80% of these cells die, pts become symptomatic

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MR findings of parkinsons

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relatively non-specific findings
can show thinning of pars compacta occcasionally

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where is pars compatca

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posterior portion of hte substantia nigra btwn pars reticularis anteriorly and red nuclei posteriorly

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what type of imaging study is most specific for parkinsons dx

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F labelled PET ligands which are specific for dopaine receptors

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findings in huntington disease

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diffuse cortical atrophy, esp in caudate and putamen
--> enlargement of the frontal horns which look heart-shaped

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pathophys of wilson dz

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error of copper metabolism

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findings assoc with CO poisoning

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signal abn of globus pallidus

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findings assoc with methanol poisoning

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sign abn within putamen