Tuesday, February 26, 2013

DD multiple patchy lesions




Introduction

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Multiple white matter lesions. MS or vascular?
One of the most common questions in daily radiology practise, when we see an image like the one on the left is:
'Do we have to think of Multiple Sclerosis or are these white matter lesions the result of small vessel disease, for instance in a hypertensive patient or should we think of more uncommon diseases?

In order to be able to answer that question, we have to realise that when we study white matter lesions (WMLs):
  1. Many neurological diseases can mimic MS both clinically and radiologically.
  2. Most incidentally found WMLs will have a vascular origin.
  3. The list of possible diagnoses of WMLs is long.

Multiple sclerosis

Multiple sclerosis (MS) is the most common inflammatory demyelinating disease of the central nervous system in young and middle-age adults, but also affects older people.
According to the McDonald criteria for MS, the diagnosis requires objective evidence of lesions disseminated in time and space.
As a consequence there is an important role for MRI in the diagnosis of MS, since MRI can show multiple lesions (dissemination in space), some of which can be clinically occult and MRI can show new lesions on follow up scans (dissemination in time).

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Typical MRI findings in MS

MS has a typical distribution of WMLs.
This can be very helpfull in the differentiation from vascular lesions (see Table).
Typical for MS is involvement of corpus callosum, U fibers, temporal lobes, brainstem, cerebellum and spinal cord.
This pattern of involvement is uncommon in other diseases.
In small vessel disease there sometimes is involvement of the brainstem, but it is usually symmetrical and central, while in MS it is peripheral.


On the down a coronal PD image of a brain specimen with MS involvement.
First look at the image and look for lesions that are specific for MS.
Than continue.

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Coronal PD image of a brain specimen with MS involvement
The lesions in the deep white matter (yellow arrow) are non specific and can be seen in many diseases.


Typical for MS in this case is:

  • Involvement of the temporal lobe (red arrow)
  • Juxtacortical lesions (green arrow) - touching the cortex
  • Involvement of the corpus callosum (blue arrow)
  • Periventricular lesions - touching the ventricles

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Left: involvement of U-fibers in MS. RIGHT: U-fibers are not involved in patient with hypertension.
Juxtacortical lesions are specific for MS.
These are adjacent to the cortex. They must touch the cortex.
Do not use the word subcortical to describe this location, because that is a less specific term, indicating a larger area almost reaching the ventricles.
In small vessel disease these juxtacortical U-fibers are not involved and there will be a dark band between the WML and the (also bright) cortex (yellow arrow).

Temporal lobe involvement is also specific for MS.
In hypertensive encephalopathy, the WMLs are located in the frontal and parietal lobes, uncommonly in the occipital lobes and not in the temporal lobes.
Only in CADASIL there is early involvement of the temporal lobes.

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Multiple WMLs with typical distribution of MS.
First look at the images on the left.
Describe the lesions and decide which findings are typical for MS.


Typical findings for MS as seen in this case are:
  • Multiple lesions adjacent to the ventricles (red arrow).
  • Ovoid lesions perpendicular to the ventricles (yellow arrow).
  • Multiple lesions in brainstem and cerebellum.

These ovoid lesions are also called Dawson fingers.
They represent areas of demyelination along the small cerebral veins that run perpendicular to the ventricles.

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SE PDW-image of the spinal cord in a patient with MS
First look at the spinal cord images on the left
Describe the lesions and decide which findings are typical for MS.

There are multipel lesions in the spinal cord. This is another typical feature of MS .
By the way did you notice the lesion in the brainstem?
A spinal cord lesion together with a lesion in the cerebellum or brainstem is very suggestive of MS.
Spinal cord lesions are uncommon in most other CNS diseases, with exception of ADEM, Sarcoid, Lyme and SLE.

Notice that this image is a conventional (not fast/turbo) proton density weighted image (PDWI).
Although these CSE PDW-images need more acquisition time to obtain the same resolution compared toFSE/TSE images, they are crucial for studying the myelum.
First on SE PDW-images the MS plaques show a better contrast than on FSE images.
Secondly on SE PDW-images the CSF has a uniformly low signal intensity (like CSF), which gives the MS lesions a good contrast against the surrounding CSF and normal cord tissue.
Use a 512 matrix and cardiac gating for optimal results.

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LEFT: Typical Dawson finger with enhancement on T1WI. RIGHT: Multiple lesions and edema around enhancing lesion on T2WI.

Dawson fingers

First look at the images on the left
Describe the lesions and decide which findings are typical for MS.

Typical findings for MS as seen in this case are:
  • Ovoid lesions perpendicular to the ventricles (Dawson finger).
  • Enhancing lesion.
  • Multiple lesions adjacent to the ventricles.

Dawson fingers are typical for MS and are the result of inflammation around penetrating venules.
These veins are perpendicular to the ventricular surface.

Enhancement is another typical finding in MS .
This enhancement will be present for about one month after the occurence of a lesion.
The simultaneous demonstration of enhancing and non-enhancing lesions in MS is the radiological counterpart of the clinical dissemination in time and space.
The edema will regress and finaly only the center will remain as a hyperintense lesion on T2WI.

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Lymphocytic infiltration is seen surrounding a small vein. These lymphocytes attack the myeline.
On the left a specimen showing the perivenous inflammation in MS.
MS starts as inflammation around these veins.
In the first four weeks of the inflammation there is enhancement with gadolinium due to loss of blood brain barrier.
First there is homogeneous enhancement but this can change to ring enhancement.

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Juxtacortical MS lesion located in the U-fiber.
Juxtacortical lesions located in the U-fibers are also very specific for MS.
You really have to look hard to notice them, because they are difficult to differentiate from the hyperintense cortex.
The patient on the left not only has multiple periventricular lesions of which some have the typical Dawson finger aspect (blue arrow), but there also is a juxtacortical lesion.
The involvement of the U-fibers is best seen on the magnification view.

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T1WI: multiple enhancing lesions
On the left a patient who was re-examined 3 months after the first clinical attack.
Describe the lesions and decide which findings are typical for MS.

Typical findings for MS as seen in this case are:
  • Multiple enhancing lesions
  • Many of these lesions 'touch the cortex' and must be located in the U-fibers.
  • These enhancing lesions all are new lesions, since Gadolinium enhancement is only visible for about 1 month.
    So this finding is proof of dissemination in time.

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LEFT: Single lesion on T2WI.RIGHT: Two new lesions at 3 month follow up.
New lesions on T2W images also indicate dissemination in time.
The patient on the left had a follow up examination 3 months after the first clinical event.

Notice how similar the positioning is.
This allows good comparison of the images.
Optimal positioning is discussed in the MRI protocol (see later).

Mc Donald criteria for MS

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The McDonald criteria for MS were recommended in 2001 by an international panel and revised in 2005.
The diagnosis is either:
  • MS : all criteria fullfilled
  • possible MS : not all criteria fullfilled
  • not MS : no criteria fullfilled

The McDonald criteria make use of the clinical presentation and the advances of MR imaging.
When a patient presents with 2 or more attacks with clinical evidence of 2 or more neurological deficits, there is no need for additional requirements to make the diagnosis of MS, because there is dissemination in place and time.
In all other cases (less than 2 attacks or less than 2 clinical lesions) there is a role for MRI to fullfill the diagnostic criteria by demonstrating dissemination in space, in time or both.

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In the Mc Donald criteria the modified Barkhof criteria for dissemination in place are used (Table on the left).
These criteria are very specific, because if you want to use MRI for the diagnosis of MS, you have to make sure that the patient really has MS.
You do not want a patient to inject interferon daily if there is doubt about the diagnosis.

At least 3 out of 4 of the Barkhof criteria need to be present to fullfill the MRI criteria for MS.
These criteria were independently choosen and proved to be more specific and accurate than criteria proposed by others for the prediction of conversion of possible MS to definite MS (3).

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When patients present with only one symptom that could be a first presentation of MS (possible MS), sometimes a follow up MR is needed to prove that there is also dissemination in time in order to fullfill the McDonald criteria.
The table on the left summarises the MR criteria for dissemination in time.
Another way to prove dissemination in time is to await a second clinical attack.

MRI protocol

Indications for MRI of the brain are:
  • Clinically isolated syndrome suggestive of MS to prove dissemination in time or space in order to fullfill the McDonald criteria
  • Patients with MS to determine the prognosis or reaction to therapy
  • To specify an atypical lesion in the spinal cord

Indications for MRI of the spinal cord are:
  • Cord symptoms
  • To gain specificity in case of non-specific brain lesions

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MS Brain Protocol

At the start of the examination gadolinium is given, because the longer you wait the more enhancement you will see on the T1W images (MS lesions are not spontaneously bright on T1-weighted images without contrast administration).
A scout with additional midsagittal T1WI is made for optimal and constant positioning.
The sagittal FLAIR is ideal for detection of lesions in the corpus callosum.
The PD/T2W scan is preferably conventional-SE and not TSE/FSE, because on PD SE the CSF will be dark, enabling the visualisation of juxta-ventricular and juxta-cortical lesions.
Finally the axial T1W-images are made after about 15 minutes to provide optimal contrast enhancement.

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Coronal and midsagittal scout views are needed for reproducible positioning of the slices, so you are able to compare follow up studies.
Use the coronal scout to plan the true midsagittal image parallel to the falx and other midline structures.
On a true midsagittal image a line is drawn through the hypophysis and the roof of the fourth ventricle (fastigium).
This is called the HYFA: hypophysis-fastigium line.
Subsequently the slices are positioned with the middle slice at the lower border of the splenium of the corpus callosum.

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MS Spinal cord Protocol

Gadolinium is not necessary when only the spinal cord is examined.
Contrary to the brain there will only rarely be enhancement in the cord.
Only when other diagnoses are considered (e.g. sarcoid) Gd is necessary.
The most diagnostic sequence is the conventional SE PDW, because this is the most sensitive technique.
FLAIR should NOT be used in the spinal cord and will only demonstrate 10% of the lesions.

Prevalence and a priori chance

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When we look at the prevalence of the white matter diseases, you will notice that there are enormous differences.
Heriditary diseases are extremely uncommon as individual diseases, but as a group they are not that uncommon, but still far more uncommon than MS.
If we look at the prevalence of Lyme's disease, which is a rather popular disease at the moment, than we will notice that it still is a very uncommon disease despite of all the serological tests that are being performed nowadays.

When incidental WMLs are found, these are usually the result of small vessel disease, since up to 50% of patients that get an MR examination for whatever reason, will have WMLs of vascular origin.
They are more common in older people and in patients with vascular risk factors like atherosclerosis, high blood pressure, high cholesterol, diabetes, amyloid angiopathy, hyperhomocysteinemia, atrial fibrillation etc.

Reporting

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If a patient is clinically suspected of having MS and the MR-images support that diagnosis, than you should not consider the possibility of Lyme's disease and neuro-SLE in the differential diagnosis, because they have such a low prevalence.
There must be other ways to impress your collegues.
These diagnoses are only worth mentioning if there are clinical findings that support these diagnoses.

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Consequently, it is not wise to put MS in the differential diagnosis, if the clinician does not suspect the patient of having MS and on the MR incidental WMLs are found.
The odds are against the diagnosis of MS, because vascular WMLs are 50-500 times more likely than MS plaques.
On the other hand if a patient is clinically suspected of having MS and multiple WMLs are found, our major concern is the differential diagnosis MS versus vascular disease and we have to follow the McDonald criteria.

Differential diagnosis of WMLs

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The differential diagnosis of white matter lesions is extremely long.
In normal aging WMLs are seen, but most WMLs are acquired and of hypoxic-ischemic origin.
The most common inflammatory disease is Multiple Sclerosis.
The most comon viral infections are PML and HIV.
Inherited diseases usually will have symmetrical abnormalities, so they have to be differentiated from intoxication.

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DD multiple patchy lesions

On the left a collection of images with multiple punctate and patchy lesions in the WM.
Some will be discussed in more detail.
There is no complete overlap between the images on the left and the text on the right.

Borderzone infarction
Key finding: typically these lesions are located in only one hemisphere, either in deep watershed area or peripheral watershed area. Case on the left is infarction in deep watershed area.

ADEM
Key findings: Multifocal lesions in WM and basal ganglia 10-14 days following infection or vaccination.
As in MS, ADEM can involve the spinal cord, U-fibers and corpus callosum and sometimes show enhancement.
Different from MS is that the lesions are often large and in a younger age group. The disease is monophasic.

Lyme
2-3mm lesions simulating MS in a patient with skin rash and influenza-like illness. Other findings are high signal in spinal cord and enhancement of CN7 (root entry zone).

Sarcoid
Sarcoid is the great mimicker. The distribution of lesions is quite similar to MS.

PML
Progressive Multifocal Leukencephalopathy (PML) is a demyelinating disease caused by JC virus in immunosuppressed patients.
Key finding: space-occupying, non enhancing WMLs in the U-fibers (unlike HIV or CMV).
PML may be unilateral, but more often asymmetrical bilateral.

Virchow Robin spaces
Key finding: Bright on T2WI and dark on FLAIR.

Small vessel diease
WMLs in the deep white matter. Not located in corpus callosum, juxtaventricular or juxtacortical.

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DD multiple enhancing lesions

On the left a collection of images with multiple enhancing lesions in the WM.
Some will be discussed in more detail.
There is no complete overlap between the images on the left and the text on the right.

Vasculitis
Most diseases with vasculits are characterised by punctiform enhancement.
Vasculitis in the brain is seen in SLE, PAN, Behcet, syphilis, Wegener, Sjogren and Primary angiitis of CNS

Behcet
Behcet is more commony seen in Turkish patients.
Typicall findings are brainstem lesions with nodular enhancement in the acute phase

Metastases
Metastases are mostly surrounded by a lot of edema.

Borderzone infarction
A peripheral border zone infarction may enhance in the early phase.

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T2WI and FLAIR

Virchow Robin spaces

First look at the images on the left and describe the lesions.
Then continue.

On the T2W image there are multiple high intensity lesions in the basal ganglia.
On the FLAIR image these lesions are dark, so they follow the intensity of CSF on all sequences (they were hypointense ion the T1WI).
This signal intensity in combination with the location is typical for VR spaces.

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FLAIR image
Virchow Robin spaces are CSF spaces around penetrating leptomeningeal vessels.
They are typically located in basal ganglia, around atria, near the anterior commissure and in the middle of the brainstem.
On MR they follow the signal intensity of CSF on all sequences.
They are dark on FLAIR and PD unlike other WMLs.
Usually they are small except around the anterior commissure, where perivascular spaces can be larger.

On the image on the left we see both very wide VR spaces aswell as confluent hyperintense lesions in the WM.
This case nicely illustrates the difference between VR spaces and WMLs.
This is an extreme case and this condition is known as ?tat cribl?.
VR spaces enlarge with age and hypertension as a result of atrophy of surrounding structures.

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Normal aging: Widening of sulci, periventricular caps (arrow) and bands and some punctate WMLs in the deep white matter.

Normal Aging

In normal aging we can see:
  • Periventricular caps and bands
  • Mild atrophy with widening of sulci and ventricles
  • Punctate and sometimes even confluent lesions in the deep white matter (Fazekas I and II).

Periventricular caps are hyperintense regions around the anterior and posterior pole of the lateral ventricles and are associated with myelin pallor and dilated perivascular spaces.
Periventricular bands or 'rims' are thin linear lesions along the body of the lateral ventricles and are associated with subependymal gliosis.

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White matter changes in Fazekas I, II and III.
Normal Aging (2)
The clinical significance of white matter changes in aging has not been fully elucidated.
There is a relationship between several cerebrovascular risk factors and the presence of white matter changes.
One of the strongest risk factors however, apart from hypertension, is that of age.

What is still considered normal depends on the age of the patient.
These white matter changes are classified according to Fazekas (see Fazekas classification in Addendum).
Mild (punctate WMLs: Fazekas I) and sometimes even moderate changes (confluent WMLs: Fazekas II) in the deep white matter can be considered normal in aging.
The severe form of white matter lesions (extensive confluent WMLs: Fazekas III) however is never considered normal.

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SE T2WI: multiple WMLs in a hypertensive patient.

Vascular disease

First look at the images on the left and describe the lesions.
Then continue.

The location of these white matter lesions is in the deep white matter and it is important to notice that these lesions are not juxtaventricular, not juxtacortical and not located in the corpus callosum.
Unlike in MS, they do not touch the ventricles or the cortex.
Given the a priori greater chance of hypoxic-ischemic WM lesions, we must conclude that these WMLs probably have a vascular origin.
Only if the clinical findings strongly direct us towards inflammatory, infectious, toxic or other diseases, we should consider these diagnoses.
Suggesting the diagnosis of MS in a patient with these MR findings and with no clinical suspicion for MS would be unwise.

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The spinal cord in this patient was normal.
In a patient with vasculitis or ischemia the spinal cord is usually normal, while in a MS patient in more than 90% of the cases it will be abnormal (2).
If the differentiation between a vascular origine of WMLs and MS is difficult for instance in an older patient who is suspected of MS, than a MR of the spinal cord can be helpfull (2).

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Vascular disease (2)
When we go back to the first case that was shown, it is now very obvious that this is vascular disease.
There is widespread disease in the deep white matter, but the U-fibers and corpus callosum are not involved.

Ischemic WMLs present as lacunar infarcts, watershed infarcts or diffuse hyperintens lesions within the deep white matter.
Lacunar infarcts are due to arteriolar sclerosis of small penetrating medullary arteries.
Watershed infarctions are the result of atherosclerosis of larger vessels, for instance carotid obstruction or the result of hypoperfusion.
Atherosclerotic brain changes are seen in 50% of patients older than 50 years.
They are found in normotensive patients, but more common in hypertensives.

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Sarcoid

First look at the images on the left and describe the lesions.
Then continue.

The distribution of lesions is quite similar to MS.
Besides lesions in the deep WM, there are some juxtaiventricular lesions and even Dawson finger-like lesions.
The final diagnosis was sarcoid.
Sarcoid has surpassed neurosyphilis as the great mimicker.

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Sarcoid (2)
On the left we see the coronal Gd-enhanced T1W images of this patient.
First study these images, than continue.

There is punctate enhancement in the basal nuclei.
This is seen in sarcoid and can also be seen in SLE or other vasculitis.
Typical for sarcoid in this case is the leptomeningeal enhancement (yellow arrow).
This is the result of granulomatous inflammation of the leptomeninges.

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Sarcoid (3)
Another typical finding in this same case is the linear enhancement (yellow arrow).
This is due to inflammation along the Virchow Robin spaces.
This is also a form of leptomeningeal enhancement.
This explains why sarcoid has a similar distribution as MS, because the Virchow Robin spaces follow the small penetrating veins, that are involved in MS.

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Typical skin rash caused by spirochaet transmitted by a tick.

Lyme disease

Lyme disease is caused by a spirochaet (borrelia Burgdorferi) that is transmitted by a tick.
It first causes a skin rash.
A few months later the spirochaet can infect the CNS and MS-like WMLs are seen.

Clinically Lyme presents with acute CNS symptoms (e.g.cranial nerve palsy) and sometimes transverse myelitis.
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MS like lesions in Lyme's disease.
Lyme disease (2)
Key finding: 2-3mm lesions simulating MS in a patient with skin rash and influenza-like illness.
Other findings are high signal in spinal cord and enhancement of CN7 (root entry zone).

HIV

Key finding: Atrophy and symmetric periventricular or more diffuse WMLs in AIDS patient
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Cadasil

Cadasil is short for cerebral autosomal dominant arteriopathy with subcortical infarcts and leukencephalopathy.
It is an inherited small vessel disease.
Clinical clues: migraine, dementia and family history.
Key finding: subcortical lacunar infarcts with small cystic lesions and leukencephalopathy in young adults.
Localisation in anterior temporal pole and external capsule have a high specificity.

Addendum

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2005 Revised McDonald MS Diagnostic Criteria

In April, 2001, an international panel in association with the NMSS of America recommended revised diagnostic criteria for multiple sclerosis.
These new criteria have become known as the McDonald criteria after their lead author.
They make use of advances in MRI imaging techniques and are intended to replace the Poser Criteria and the Schumacher Criteria.
These criteria were revised in 2005 and listed in the table on the left.

An Attack is defined as:
  • Neurological disturbance of kind seen in MS
  • Subjective report or objective observation
  • 24 hours duration, minimum
  • Excludes pseudoattacks, single paroxysmal episodes

Time Between Attacks is defined as 30 days between onset of event 1 and onset of event 2.
MRI Evidence Of Dissemination In Space is when three out of four criteria are seen:
  • 1 Gd-enhancing or 9 T2 hyperintense lesions if no Gd-enhancing lesion
  • 1 or more infratentorial lesions
  • 1 or more juxtacortical lesions
  • 3 or more periventricular lesions (1 spinal cord lesion can replace a missing infratentorial lesion and contribute to the 9 T2-lesions)

MRI Evidence Of Dissemination In Time is defined as:
  • A Gd-enhancing lesion demonstrated in a scan done at least 3 months following onset of clinical attack at a site different from attack
  • or In absence of Gd-enhancing lesions at 3 month scan, follow-up scan after an additional 3 months showing Gd-lesion or new T2 lesion.

Positive CSF is oligoclonal IgG bands in CSF (and not serum) or elevated IgG index.
Positive visual evoced potentials (VEP) is delayed but well-preserved wave form

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Fazekas classification

The Fazekas classification is used to describe changes in the deep white matter.
Whenever you see these WMLs, try to describe them according to this Fazekas classification:

  • Fazekas I : small punctate lesions in the deep white matter.
  • Fazekas II : larger WMLs that are beginning to become confluent.
  • Fazekas III : extensive confluent WMLs.

Fazekas I is considered normal in aging.
Fazekas II is considered abnormal in patients Fazekas III is abnormal in any age group.
These WMLs are probably due to microangiopathy and seen more frequently in patients with vascular risk factors .

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