diagnostic imaging of congenital central nervous system diseases

C.N.S.Congenital Diseases

Mohamed Zaitoun

Assistant Lecturer-Diagnostic Radiology Department , Zagazig University Hospitals

EgyptFINR (Fellowship of Interventional

Neuroradiology)-Switzerlandzaitoun82@gmail.com

Knowing as much as possible about your enemy precedes successful battle

and learning about the disease process precedes successful management

Congenital Diseasesa) Neural Tube Closure Defectsb) Disorders of Diverticulation and Cleavagec) Neuronal Migration and Sulcation

Abnormalitiesd) Posterior Fossa Malformationse) Neurocutaneous syndromes (Phakomatoses)

a) Neural Tube Closure Defects :1-Anencephaly (most common anomaly)2-Chiari Malformations3-Cephalocele

1-Anencephaly (Most common anomaly) :a) Definitionb) Incidencec) Radiographic Features

a) Definition :-Absence of cortical tissue (although brainstem

and cerebellum may be variably present) as well as absence of the cranial vault

b) Incidence :-1:1000 , more in females , F:M = 4:1

c) Radiographic Features :-By Antenatal Ultrasound & Fetal MRI-No tissue above the orbits and absent calvarium-Less than expected value for crown rump length

(CRL)-Frog eye or Mickey mouse appearance may be seen

when seen in the coronal plane due to absent cranial bone / brain and bulging orbits

-May show evidence of polyhydramnios from impaired swallowing

Fetal MR images demonstrating absent cranial bone / brain and bulging orbits , in addition , polyhydramnios is seen

2-Chiari Malformations :a) Overview of Chiari Malformationsb) Chiari I Malformationc) Chiari II Malformation

a) Overview of Chiari Malformations :1-Chiari I Malformation :-Most common-Peg like cerebellar tonsils displaced into the

upper cervical canal through the foramen magnum

2-Chiari II Malformation :-Displacement of the medulla, fourth ventricle

and cerebellum through the foramen magnum-Usually with associated with a lumbosacral

spinal myelomeningocele3-Chiari III Malformation :-Features similar to Chiari II but with an

occipital and / or high cervical encephalocele

4-Chiari IV malformation :-Severe cerebellar hypoplasia without

displacement of the cerebellum through the foramen magnum

-Probably a variation of cerebellar hypoplasia

b) Chiari I Malformation :1-Definition2-Incidence3-Associations4-Radiographic features

1-Definition :-Downward displacement of cerebellar tonsils

below foramen magnum > 5 mm

2-Incidence :-Adult disease : 20 years-More in females-Most common type of Chiari-Chiari I malformations often remain

asymptomatic until adulthood, manifests with headache

3-Associations :a) Cervical cord syrinx is present in 20-56%b) Hydrocephalus in up to 30 %c) Basilar invagination (craniocervical

junction abnormality where the tip of the odontoid process projects above the foramen magnum ) , 30%

d) Klippel-Feil anomaly : fusion of 2 or more cervical vertebrae , 10%

e) Atlantooccipital fusion , 5%f) Sprengel deformity

4-Radiographic features :a) Peg-like Tonsillar herniation (the tonsils are pointed ,

rather than rounded and referred to as peg-like) , ectopia is 3 to 5 mm, herniation is >5 mm, is age dependent

b) Syringohydromyelia , more commonc) No brain anomaliesd) Hydrocephalus , less common**N.B. :If the only finding is isolated inferior displacement of

the tonsils, the term (borderline tonsillar ectopia) is generally preferred

(a) Borderline tonsillar ectopia , sagittal T1 shows cerebellar tonsils extending inferiorly below the foramen magnum (yellow arrow) , there is no hydrocephalus or cervical spine syringomyelia , (b) Chiari I in a different patient , Sagittal T2 shows inferior extension of the cerebellar tonsils (yellow arrows) , the presence of syringomyelia (red arrow) allows more confident diagnosis of Chiari I

Cerebellar tonsils (arrow) herniating through the foramen magnum (yellow line)

With syrinx

c) Chiari II Malformation :1-Definition2-Incidence3-Associations4-Radiographic features

1-Definition :-Herniation of the medulla, fourth ventricle and

cerebellum through the foramen magnum with resultant beaking of the tectum

-Myelomeningocele is universally present, typically lumbar

-Hydrocephalus is present in 80-90 % of patients2-Incidence :-Most common in newborns

3-Associations :a) Myelomeningocele, 90%b) Obstructive hydrocephalus, 90%c) Dysgenesis of corpus callosumd) Syringohydromyelia, 50%e) Abnormal cortical gyrationf) Chiari II is not associated with Klippel-Feil

anomaly or Chiari I

4-Radiographic features :a) Antenatal Ultrasound :-Lemon Sign, indentation of the frontal bone giving

the head a shape similar to that of a lemon-Banana Sign, It describes the way the cerebellum

is wrapped tightly around the brain stem as a result of downward migration of posterior fossa content, the cisterns magna gets obliterated

Lemon Sign

Banana Sign

b) MRI :(i) Posterior Fossa(ii) Supratentorial(iii) Osseous Abnormalities(iv) Spinal Cord

(i) Posterior Fossa :1-Small posterior fossa2-Elongated brainstem that extends into the cervical

spinal canal3-Downward herniation of the cerebellar tonsils into

cervical spinal canal4-Small fourth ventricle, elongated & inferiorly displaced5-Aqueductal stenosios6-Tectal beaking7-Large massa intermedia8-Thin corpus callosum

9-Cerebellum wraps around pons (heart shape)

a - Elongated brainstem that extends into the cervical spinal canalb - Downward herniation of the cerebellar tonsils into cervical spinal canalc - Small fourth ventricled - Aqueductal stenosiose - Tectal beakingf - Large massa intermediag - Thin corpus callosum

Tectal beaking

Heart shaped cerebellum

(ii) Supratentorial :1-Hypoplastic or fenestrated falx causes

interdigitation of gyri (gyral interlocking)2-Small crowded gyri (stenogyria), 50%3-Hydrocephalus almost always present before

shunting4-Batwing configuration of frontal horns (caused

by impressions by caudate nucleus)5-Small biconcave 3rd ventricle (hourglass shape

due to large massa intermedia)

Fenestrated Falx with interdigitated gyri

Stenogyria

The caudate heads and thalami are enlarged producing impressions on the frontal horns and on the third ventricle

(iii) Osseous Abnormalities :1-Scalloped clivus and petrous ridge (pressure

effect)2-Enlarged foramen magnum

The foramen magnum is enlarged and filled with cerebellar tissue

(iv) Spinal Cord :1-Myelomeningocele, 90%2-Cervicomedullary kink at foramen magnum

(pressure effect)3-Syringohydromyelia and diastematomyelia

3-Cephalocele :a) Definitionb) Incidencec) Associationsd) Locatione) Types

a) Definition :-Outward herniation of CNS content through a

defect in the cranium, the vast majority are midline

b) Incidence :-More in females

c) Associations :-Associated with other malformation (Chiari,

callosal agenesis)

d) Location :-Occipital, 80%-Fronto-ethmoidal-Parietal, 10%

e) Types :1-Encephalocoele : herniation of meninges + CSF

+ brain tissue2-Craial Meningocoele : herniation of meninges

+ CSF only

1-Encephalocele :-Intracranial tissue that herniates through a defect in

the cranium results in an encephalocele-Types :a) Occipital Encephaloceleb) Fronto-Ethmoidal Encephalocele-There are often significant associated intracranial

anomalies, occipital encephaloceles may be associated with Chiari or Dandy-Walker malformations and callosal or migrational anomalies, Frontoethmoidal lesions are not typically associated with these types of anomalies

Occipital encepahlocele

-Fronto-ethmoidal encephaloceles are subdivided into naso-frontal, naso-ethmoidal and naso-orbital types :

1-Nasofrontal (40%) which exits the cranium between the nasal and frontal bones

2-Nasoethmoidal (40%) which exits between the nasal bones and nasal cartilages

3-Nasoorbital (20%) which exits through a defect in the maxilla frontal process

2 year old male with bilateral naso-orbital encephaloceles and fronto-nasal encephalocele , axial T1 of the brain at the level of the orbits depicts the bilateral naso-orbital encephaloceles (solid arrows) as well as the midline fronto-nasal encephalocele (dashed arrow)

Naso-ethmoidal Encephalocele

2-Cranial Meningocoele :Contain only meninges with CSF

b) Disorders of Diverticulation & Cleavage : (D&C)

1-Dysgenesis of the Corpus Callosum2-Holoprosencephaly3-Septooptic Dysplasia4-Cerebral Hemiatrophy5-Interhemispheric Lipoma

1-Dysgenesis of the Corpus Callosum :a) Typesb) Incidencec) Associationd) Clinical Picturee) Radiographic Features

a) Types :-May be complete (agenesis) or partial (the

splenium and rostrum are absent, SR)

b) Incidence :-Relatively common congenital abnormality-More in males

Rostrum (r) , genu (g) , body (b) and splenium (s) , Anterior commissure is denoted by arrow and hippocampal commissure is denoted by arrowhead

Complete Agenesis Partial Agenesis

Partial agenesis , genu and anterior body present but posterior body , splenium and rostrum absent

c) Association :-Associated CNS anomalies occur in 60%1-DW malformation2-Lipoma (calcified in 10%)3-Chiari II4-Encephalocele5-Migration anomalies

d) Clinical Picture :-The most common clinical manifestations of agenesis of the corpus

callosum are refractile seizures &/or developmental delay

Lipoma

Quadrigeminal plate lipoma , (a) Axial T1 shows a hyperintense lipoma at the LT quadrigeminal plate (arrow) , (b) Sagittal T1 shows marked thinning of the posterior body (red arrow) & splenium of the CC , the 3rd ventricle is enlarged & high riding , the lipoma (yellow arrow) is reidentified

e) Radiographic Features :1-Ventricles :-Ventricles run parallel and widely separated

(with intervening Probst bundles) giving a racing car appearance on axial imaging

-Colpocephaly (dilatation of the trigones and occipital horns) gives a characteristic longhorn / moose head / viking helmet appearance on coronal imaging (may result from decreased white matter volume posteriorly)

-Dilated high riding 3rd ventricle communicating with the interhemispheric cistern or projecting superiorly as a dorsal cyst

2-Cortex :-Absence of corpus callosum-Abnormal callosal bundles (bundles of Probst)

causing medial impressions on the lateral ventricles which are axons that normally constitute the corpus callosum but instead pursue an aberrant course parallel to the interhemispheric fissure

Parallel Lateral Ventricles

Coronal T1 shows absence of the normal corpus callosum , the lateral ventricles form a bull's-horn appearance and are indented medially by the Probst bundle (arrows)

Probst bundles , T1 shows lateral callosal bundles of Probst (arrows) indenting superomedial margins of lateral ventricles

Callosal agenesis and Probst bundle fibres callosal agenesis and Probst bundle fibers

Colpocephaly

Dorsal Cyst

FLAIR shows high riding 3rd ventricle communicating with the interhemispheric fissure (thin arrow) and crescent shaped frontal horns indented medially by white matter tracts of Probst's bundles (thick arrow)

2-Holoprosencephaly :a) Definitionb) Associationc) Typesd) Clinical Picturee) Radiographic Findingsf) Differential Diagnosis

a) Definition :-Failure of primitive brain to cleave into left and right

cerebral hemispheres

b) Association :-50% of patients with holoprosencephaly have

trisomy 13-Associated with azygos configuration of ACA (single

ACA)

c) Types :From most severe to least severe1-Alobar2-Semilibar3-Lobar

Alobar Semilobar Lobar

1-Falx Absent Presented posteriorly

Present with most anteroinferior aspect absent

2-Lateral Ventricle U-shaped monoventricle

Partially fused anteriorly

Near normal

3-Third V Absent Rudimentary Near normal

4-Cerebral Hemispheres

One brain Partial formation Near normal

5-Thalamus Fused Variable fusion Near normal

6-Facial Anomalies Severe Less severe None or mild

7-Septum Pellucidum

Absent Absent Absent

d) Clinical Picture :-Facial abnormalities usually correlate with

severity of brain abnormalities but not vice versa

-Hypotelorism (eyes too close together)-Cleft lip &/or palate-Cyclopia (single eye)

e) Radiographic Findings :-Presence of a septum pellucidum excludes the

diagnosis of holoprosencephaly

Septum pellucidum Absent septum pellucidum

1-Alobar Form :-No cleavage into two hemispheres : cup-shaped brain-Single U-shaped monoventricle almost always

communicates with a large dorsal cyst-Absent third ventricle-Thalamic fusion-Absent falx , corpus callosum , fornix , optic tracts and

olfactory bulbs-Midbrain , brainstem and cerebellum are structurally

normal

(a) T1 , (b) T2 show severe alobar holoprosencephaly , there is continual frontal lobe across the midline , a midline monoventricle communicates with a dominant dorsal cyst

Fused thalami (Arrows) , monoventricle with absence of septum pellucidum and absence of interhemispheric fissure and falx

2-Semilobar Form :-Partial cleavage into hemispheres (posterior

cerebral hemispheres) , partially fused anteriorly

-Partial occipital and temporal horns

(a) , (b) T2 , (c) T1 show semilobar holoprosencephaly , there is partial separation of the posterior cerebral cortex with complete fusion of the frontal lobes , there is large midline posterior interhemispheric cyst

Single large ventricle , absence of septum pellucidum and rudimentary interhemispheric fissure (Arrow)

3-Lobar Form :-Complete cleavage into two hemispheres

except for fusion in the most rostral aspect of the frontal neocortex

-Lateral ventricles are normal or slightly dilated , frontal horns may be squared

-Absent septum pellucidum

f) Differential Diagnosis :*Alobar Type :a) Semilobar Holoprosencephaly :-Partial separation into hemispheres-Rudimentary occipital and temporal hornsb) Hydranencephaly :-Thalami are often visible and are not fused-Not associated with midline facial abnormalities-No cortex present or sometimes small islands of

tissue

c) Severe Hydrocephalus :-Falx usually present but may be absent due to

severe long standing hydrocephalus-Bilateral choroid plexus -Thalami not fused-Not associated with midline facial abnormalities*Semilobar Holoprosencephaly :-From alobar & lobar types

*Lobar Holoprosencephaly :a) Semilobar Holoprosencephaly :-Fusion of the anterior aspects of the

hemispheres-Falx and interhemispheric fissure incomplete-Partial fusion of the thalami

b) Septooptic dysplasia :-Can appear very similar-Fusion of the frontal lobes and of the fornicies

is not a feature-Optic nerve hypoplasia & hypothalamic /

pituitary dysfunction

3-Septooptic dysplasia :a) Definitionb) Radiographic features

a) Definition :-Absence of septum pellucidum and optic nerve

hypoplasia (mild form of lobar holoprosencephaly)

-70% have hypothalamic / pituitary dysfunction-Associated with schizencephaly (50 % of cases)

b) Radiographic features :-Absence of septum pellucidum-Squared frontal horns of lateral ventricles-Hypoplasia of optic nerve and chiasm-Hypoplastic pituitary stalk

A: Absence of septum pellucidumB : Non-visualization of bilateral optic nerves

4-Cerebral Hemiatrophy (Dyke-Davidoff) :a) Etiologyb) Radiographic features

a) Etiology :-Intrauterine and perinatal ICA infarction leads

to hemiatrophy of a cerebral hemisphere

b) Radiographic features :-Atrophy of a hemisphere causes midline shift-Compensatory ipsilateral skull thickening (key

finding)-Ipsilateral paranasal and mastoid sinus

enlargement

Atrophy of the right hemisphere , the right frontal sinus is larger than the left , diploic spaces on the right seem to be widened

Ipsilateral diploic calvarial expansion

5-Interhemispheric Lipoma :a) Siteb) Associationc) Radiographic Featuresd) Differential Diagnosis

a) Site :-Collection of primitive fat within or adjacent to

corpus callosum

b) Association :1-Absence of corpus callosum, 50%2-Midline dysraphism3-Agenesis of cerebellar vermis4-Encephalocele, myelomeningocele & spina

bifida

c) Radiographic Features :-CT : pure fat (-50 to -100 HU, no associated

hair/debris) is pathognomonic-T1 hyperintense-Most common location is splenium and genu-Curvilinear calcifications are common

There is concurrent partial posterior commissural agenesis (empty arrow , a) as well as a small interhemispheric cyst (arrow , a)

d) Differential Diagnosis :1-Intracranial dermoid cyst2-Intracranial teratoma3-Fatty falx cerebri

c) Neuronal Migration and Sulcation Abnormalities :

1-Lissencephaly-Pachygyria2-Schizencephaly3-Polymicrogyria4-Cortical Heterotopia5-Focal Cortical Dysplasia6-Hemimegalencephaly

1-Lissencephaly-Pachygyria :a) Type I (classic) lissencephalyb) Type II (cobblestone complex) lissencephaly

a) Type I (classic) Lissencephaly :1-Definition2-Etiology3-Clinical Picture4-Radiographic features5-Band Heterotopia

1-Definition :-Characterized by absence or decreased cortical

convolutions causing a smooth thickened cortical surface

-Patients with classic lissencephaly may have a smooth brain surface in the complete form or more commonly they have a smooth surface with some few broad gyri with shallow sulci (pachygyria) along the inferior frontal and temporal lobes in the incomplete form (agyria/pachygyria complex)

-Named 4-Layer Lissencephaly as there is a four layered cortex histologically

(a) Complete form , arrows indicate underdeveloped perisylvian region that creates characteristic figure eight appearance , (b) Incomplete form , T2 shows a smooth brain surface with no sulci on the anterior region (agyria) & few shallow sulci posteriorly with thick & broad gyri (pachygyria)

2-Etiology :-This anomaly results from arrest of the migration

process-May be caused by CMV, in which case calcifications

are often present

3-Clinical Picture :-Patients present with seizures and developmental

delay in the complete form or complex seizures, hypotonia, microcephaly (50%) and facial dysmorphism (30%) in the incomplete form

4-Radiographic features :-Cerebral configuration is oval or hourglass (figure of 8) with

shallow Sylvian fissures-Complete agyria in the complete form or parieto-occipital

agyria with frontotemporal pachygyria (broad gyri) in the incomplete form

-The cortex is markedly thickened measuring 12-20mm (rather than the normal 3-4mm), the subcortical white matter is thin with a lack of the normal gray-white matter interdigitation

-There is a circumferential band of high signal intensity on T2 most prominent in the parieto-occipital cortex corresponding to a sparse cell zone with increased water content (separates the outer cortical layer from the inner thicker cortical layer)

(a) T1 , (b) T2 shows classical type I lissencephaly with a complete smooth cortex and hour glass or figure of 8 configuration to the cerebral hemispheres

Complete lissencephaly , axial T2 shows complete absence of sulci with a thick cortex , a shallow Sylvian fissure and a circumferential band of high signal intensity in the parietooccipital cortex

Prominent cell sparse zones are seen in areas of agyria (arrows)

5-Band Heterotopia :a) Definitionb) Incidencec) Clinical Pictured) Radiographic Features

a) Definition :-Bilateral thick layers of arrested neurons

located approximately half-way between the ventricles and the cortical plate resembling a doubling of the cortex, more severe in the frontal lobes

b) Incidence :-The majority of patients with double cortex

syndrome are female on account of the genetic abnormality often being located on the X chromosome

c) Clinical Picture :-Seizures and delayed development are the

most common presentations, usually evident in the first decade

d) Radiographic Features :-On MR imaging, it shows the characteristic 3-

layer cake (continuous double cortex) with the cortex and bilateral symmetric circumferential subcortical layer of band heterotopia separated from each other by a thin white matter band

-The cortex may be relatively normal or pachygyric

(a) Axial T1 & (b) axial T2 show a large band of isointense tissue (dots, a,b) is interposed between the ventricles and the cortex , between the band heterotopia and the cortex is a thin layer of myelinated white matter (arrows, a,b) , there is poor, irregular sulcation of the cerebral cortex

b) Type II (Cobblestone Complex) lissencephaly:

1-Definition2-Etiology3-Clinical Picture4-Radiographic features

1-Definition :-Cobblestone lissencephaly is characterized by a

reduction in normal sulcation and nodular brain surface

2-Etiology :-Unlike type I lissencephaly which is the result of

neuronal undermigration, type II is due to over migration

3-Clinical Picture :-Ocular anomalies and congenital muscular

disorders-It includes a spectrum of anomalies with

Walker-Warburg syndrome (WWS) being the most severe form , Fukuyama congenital muscular dystrophy (FCMD) the mildest form and muscle-eye-brain (MEB) disease the intermediate form

4-Radiographic features :-Multi-nodular surface of the cortex

(cobblestone) most pronounced anteriorly-Lack of normal sulcation-Small sylvian fissure-Hour glass or figure-8 appearance of the brain

on axial imaging

(a) T1 , (b) T2 shows cobblestone (type II) lissencephaly with a gently lobulated external cortex & a finely undulating or serrated interface at the grey-white junction

Cobblestone lissencephaly , (a) & (b) , axial and coronal T2 show an irregular nodular cortex with hypomyelination of the white matter

(a) lissencephaly in a boy , (b) pachygyria in a boy and (c) double cortex in a girl

2-Schizencephaly :a) Definitionb) Associationsc) Types & Radiographic Featuresd) Differential Diagnosis

a) Definition :-Cleft extending through the whole hemisphere

from the ependymal lining of the lateral ventricle to the pia covering the brain forming an abnormal communication between the ventricles & the extra-axial subarachnoid space

-The cleft may be unilateral or bilateral and is constantly lined by polymicrogyric cortex

b) Associations :-Frequent association with cortical

malformations (grey matter heterotopia) with up to 30 % of patients with schizencephaly also having cortical malformations

-Associated with septo-optic dysplasia (agenesis of the septum pellucidum & optic nerve hypoplasia)

Schizencephaly (closed-lip) with PMG , T1 shows indentation in the ependymal surface , called “nipple” (red arrow) lined by polymicrogyria (green arrow)

Schizencephaly with septo-optic dysplasia , (a) T1 shows complete absence of the septum pellucidum & open lip schizencephaly with dysplastic gray matter along the cortical surface , (b) T1 shows optic nerve & chiasma atrophy

c) Types & Radiographic Features :-Frontal involvement is the most common1-Open Lip :-The walls of the cleft may be widely separated , in this

case , the cleft is occupied by CSF2-Closed Lip :-When the walls abut one another (fused lips)-The cleft may not be easily visible, however, a dimple

may be seen in the wall of the lateral ventricle where the cleft communicates

Open lips schizencephaly , the cleft is bilateral and involves the full thickness of the brain , the margins of the cleft are composed of polymicrogyric cortex , here is no septum pellucidum

Open lip schizencephaly , T2 shows a cleft in the LT temporoparietal cortex (arrows) extending from the cortical surface to the LT lateral ventricle , the cleft is lined by dysplastic appearing gray matter

Bilateral Open & Closed Lips

Fused lips schizencephaly , both CT and MR adequately depict the presence of cortex bordering the cleft , a dimple along the lateral wall of the right lateral ventricle is visible in the coronal section (arrow, b) and corresponds to the opening of the schizencephalic cleft , the opening on the brain surface is best seen in the CT image in this particular case (a)

Closed lip schizencephaly , the gray matter-lined cleft in the right posterior frontal lobe communicating with the right lateral ventricle (arrow) , in addition , there is agenesis of the septum pellucidum

d) Differential Diagnosis :1-Focal Cortical Dysplasia :-Sometimes may have a cleft on the cortical

surface that does not extend completely to the ventricular surface

2-Heterotopic grey matter :-Closed lip schizencephaly can mimic a band of

grey matter heterotopia

-Assessing the ventricular outline will often demonstrate a slight cleft whereas periventricular grey matter will usually bulge into the ventricle

3-Porencephaly :-A zone of encephalomalacia that extends from

the cortical surface to the ventricular surface but is lined by gliotic white matter not grey matter

(a) Prosencephalic cyst , note the absence of grey matter lining the defect , (b) Open lip schizencephaly , note the grey matter lining

**N.B. :-There are several entities that can cause an

interruption or cleft in the cortex, but only schizencephalic cleft is lined by gray matter, other cortical clefts include :

1-Porencephaly (where there is replacement of cortex by a cystic structure)

2-Encephalomalacia3-Surgical resection cavity

3-Polymicrogyria (PMG) :a) Definitionb) Clinical Picturec) Radiographic Features

a) Definition :-A developmental malformation characterized by an

excessive number of small convolutions (gyri) on the surface of the brain with increased cortical thickness

-Either the whole surface (generalized) or parts of the surface (focal) can be affected

-The insult occurs after the end of neuronal migration that is in the phase of cortical organization

-May be caused by in-utero infection (especially CMV), in-utero ischemia or genetic causes

b) Clinical Picture :-The most frequent cause of partial epilepsy in

the pediatric age-Developmental delay & quadriparesis

b) Radiographic Features :-Appears as an area of increased cortical thickness

composed of multiple small gyri-The gray white matter junction is generally

irregular-The abnormal cortex itself is isointense to normal

gray matter whereas the underlying white matter may show T2 prolongation

-Bilateral perisylvian polymicrogyria is the most common distribution

T2 shows bilateral perisylvian & bifrontal polymicrogyria (arrows point to the perisylvian PMG) , the affected regions have an irregular junction of the abnormal cortex & the white matter

Bilateral Perisylvian Polymicrogyria

Polymicrogyria , 8-month-old infant with CMV infection , (a) Axial T1 (b) axial T2 (c) coronal T2 show shallow Sylvian fissure is visible in T1 (empty arrow, a) , T2 is better suited to depict the cortical anomaly by detecting bilateral thickening of the brain cortex (arrows, b,c) , a few broad shallow sulci are visible in the anomalous area

T2 shows PMG with normal cortical thickness that is associated with the high signal intensity of the white matter

4-Cortical Heterotopia :a) Definitionb) Associationc) Clinical Pictured) Types

a) Definition :-Interruption of normal neuronal migration from

near the ventricle to the cortex thus resulting in (normal neurons in abnormal locations)

b) Association :1-Agenesis of the corpus callosum2-Pachygyria3-Schizencephaly4-Polymicrogyria5-Chiari II malformation6-Cephalocoeles

c) Clinical Picture :-Epilepsy and possible delayed milestones

and/or mental retardation

d) Types :1-Subependymal Heterotopia : most common2-Subcortical Heterotopia

1-Subependymal Heterotopia :a) Incidenceb) Locationc) Typesd) Radiographic Features

a) Incidence :-More Common than subcortical Heterotopia

b) Location :-Subependymal (periventricular) heterotopias

(PVH) are located in close proximity to the ventricular wall , commonly seen in the region of the trigone and occipital horns of the lateral ventricles

-PVH are usually bilateral with predilection for the right cerebral hemisphere due to later migration of the right-sided neuroblasts

c) Types :-Can be subdivided into :1-Unilateral focal2-Bilateral focal3-Bilateral diffuse

d) Radiographic Features :-They appear as round or oval nodules-Isointense to the normal gray matter on all

pulse sequences and do not enhance after contrast injection

-They may lie in the wall of the ventricle and project into the ventricular lumen or lie within the periventricular white matter

-Mild ventricular dilation might be seen

28 month old child with Chiari II malformation , (a) T1 , (b) T2 , there is a subependymal heterotopic nodule in the lateral wall of right frontal horn (white arrow, a,b) , the nodule is isointense with gray matter both in T1 and T2 , notice abnormal configuration of the lateral ventricles in this Chiari II patient and the presence of a shunt catheter (black arrow, b)

2-Subcortical Heterotopia :a) Locationb) Typesc) Differential Diagnosis

a) Location :-Located within the subcortical or deep white

matter and are always seen contiguous to the overlying cortex or the underlying ventricular system

-The affected hemisphere may decrease in size as a result of the decreased volume of the neurons

-The overlying cortex appears thin with shallow sulci

b) Types :1-Nodular form : extend from the ventricle into

the white matter2-Curvilinear form : extend from the cortex into

the underlying white matter3-Mixed form

1-Nodular SCH :-Appear as nodules that extend from the

ventricular surface outward into the white matter without continuity with the cerebral cortex

Axial T2 (a) & Coronal T1 (b) in a 1-month-old patient shows multiple nodular heterotopia (arrows) lining the frontal horn of the right lateral ventricle and extending into the center of the frontal white matter , the right hemisphere is reduced in size , the overlying cortex is thin and has a reduced number of sulci , the sulci present are abnormally shallow , the corpus callosum is agenetic

T1 shows multiple nodules isointense to gray matter in subcortical location in the LT cerebral hemisphere

2-Curvilinear SCH :-Consist of swirling heterogeneous curvilinear

masses of gray matter that have an appearance that closely resembles convolutions of the cortex extending from the cortical surface into the white matter

Curvilinear SCH , axial T2 shows curvilinear heterotopias in the right cerebral hemisphere that are associated with its decrease in size

3-Mixed :-Nodules are seen in the deep part of the brain

adjacent to the lateral ventricle and the curvilinear convolutions are seen in the superficial part

(a) T2 shows nodular heterotopia (white arrows) in the periventricular white matter bilaterally , no cortical connection is seen at this level , (b) T2 shows that the heterotopia (white arrows) are contiguous with the cortex bilaterally

c) Differential Diagnosis :-MR spectroscopy can differentiate heterotopia

from low-grade glioma-The metabolites appear to be similar to those

of normal brain in heterotopia whereas loss of N-acetylaspartate and increase of choline were observed in low-grade gliomas

5-Focal Cortical Dysplasia :a) Definitionb) Clinical Picturec) Typesd) Radiological Findingse) Differential Diagnosis

a) Definition :-Is a heterogeneous group of lesions

characterized by the presence of abnormal neurons and glial cells within a localized region of the cerebral cortex

b) Clinical Picture :-Patients usually present with intractable

seizures

c) Types :1-FCD type I (non-Taylor dysplasia) : Ia & Ib2-FCD type II (Taylor dysplasia) : IIa : No ballon cellsIIb : Ballon cells present

d) Radiological Findings :-Localized area of cortical thickening with an

indistinct gray-white matter junction-A subcortical focus of abnormal signal intensity

extending from the gray-white matter junction to the superolateral margin of the lateral ventricle , these foci show low signal intensity on T1 and high signal intensity on T2 (Transmantle sign)

(a) There is cortical thickening and blurring of the grey/white matter junction on T1WI , (b) FLAIR shows the subcortical hyperintensity

Axial T1 , T2 & FLAIR of a 15 year old boy with epilepsy, notice thickening and hyperintensity of the cortex of the left superior frontal gyrus , the FLAIR also show high signal in the subcortical white matter

(a) T1 shows an area of mild cortical thickening with blurring of the white-gray matter interface in the LT frontal lobe , (b) FLAIR shows hyperintense signal in the underlying white matter (arrow)

FCD , Transmantle sign

Coronal FLAIR and axial T2 show T2-hyperintense cortical thickening and high signal in cortex and subcortical region , notice subcortical hyperintensity extending to the right ventricle indicating transmantle sign (blue arrow)

e) Differential Diagnosis :-FCD should be differentiated from gliomas-A frontal location is in favor of FCD whereas a temporal

location is suggestive of neoplasm-High signal intensity on T2 is less distinct in FCD than in

tumors because the main portion of cortical dysplasia lesions is located within the gray matter and is infrequently associated with edema or gliosis

-Gliomas are associated with some degree of mass effect and might show a degree of enhancement after contrast injection

6-Hemimegalencephaly :a) Definitionb) Clinical Picturec) Radiological Findings

a) Definition :-Is a rare congenital disorder of cortical

formation with hamartomatous overgrowth all or a part of a cerebral hemisphere

-This results from either increased proliferation or decreased apoptosis (or both) of developing neuron

b) Clinical Picture :-Affected newborns suffer from untreatable

epilepsy

c) Radiological Findings :-Enlargement of a whole hemisphere-The cortex is affected by diffuse migration

anomalies, while the white matter is gliotic and dysmyelinated

-The ipsilateral ventricle is frequently dilated and the frontal horn is stretched

-The homolateral cerebellar hemisphere is usually enlarged as well

Coronal T2 show an enlarged left cerebral hemisphere , a dilated left lateral ventricle and a thickened cerebral cortex

d) Posterior Fossa Malformations :1-DW Malformation2-DW Variant3-Mega Cisterna Magna4-Persisting Blake’s Pouch5-Chiari I6-Syndromes Associated With Vermian-

Cerebllar Hypoplasia

1-Dandy Walker Malformation :a) Definitionb) Incidencec) Radiographic findingsd) Differential Diagnosis

a) Definition :-The definition of DWM classically includes

partial or complete vermian agenesis associated with hypoplastic cerebellar hemispheres, cystic dilatation of the fourth ventricle and expansion of the posterior fossa associated with high insertion of the tentorium, torcular Herophili and transverse sinuses

b) Association :1-Agenesis of corpus callosum , 25%2-Lipoma of corpus callosum3-Malformation of cerebral gyri4-Holoprosencephaly , 25%5-Cerebellar heterotopia , 25%6-GM heterotopia7-Occipital cephalocele8-Tuber cinereum hamartoma9-Syringomyelia10-Cleft palate11-Polydactyly12-Cardiac abnormalities

c) Clinical Picture :-Patients usually manifest in the first year of life

with symptoms of hydrocephalus and associated neurological symptoms

-In 80% of cases, the diagnosis is made by the first year of life

d) Radiographic findings :-Absent or abnormal inferior cerebellar vermis (key

finding) and cephalad rotation of the vermian remnant

-Cystic dilatation of the fourth ventricle extending posteriorly (which communicates with a retrocerebellar cyst)

-Enlarged posterior fossa with torcular-lambdoid inversion, i.e. torcular herophili lying above the level of the lambdoid suture due to abnormally high tentorium, (the torcular herophili is the confluence of the transverse sinus & the straight sinus)

-Hydrocephalus

T1 shows a large posterior fossa cyst elevating the torcular herophili and sinus rectus (short arrow) , the hypoplastic vermis is everted over the posterior fossa cyst (long arrow) , the cerebellar hemispheres and brainstem (b) are hypoplastic, thinned occipital squama is seen (arrowheads)

T2 shows enlarged posterior fossa and communication of the anterior fourth ventricle with its large retrocerebellar portion , bilateral temporal horns are dilated due to obstructive hydrocephalus

T1 shows the posterior fossa is larger than normal due to the presence of a cyst-like fourth ventricle (4V) (a,b) , whose inferior tip protrudes into the foramen magnum (white arrow, a) , the vermis (v) is hypoplastic and rotated in a counterclockwise fashion (a) , the tentorium is elevated (empty arrow, a) so that the torcular comes to lie cranial to the lambda (so-called torcular-lambdoid inversion) , notice the scalloped profile of the occipital squama in the sagittal section (a) , in the axial plane , the hypoplastic cerebellar hemispheres (h) are winged outward (b) , the pons is hypoplastic (a) , the third ventricle appears to communicate with a dilated interhemispheric fissure (c) , associated malformations in this particular case include agenesis of the corpus callosum with the classical spokewheel-like arrangement of the mesial cortical sulci (a) and a right parietal cephalocele (arrowhead, c)

(a) Normal Torcula , (b) Torcular-lambdoid inversion , large posterior fossa cyst elevating the torcular herophili and sinus rectus (short arrow)

(a) T1 shows agenesis of the corpus callosum , a hypoplastic brainstem (b), elevation of the torcular herophili (lambdoid-torcular inversion, large arrow), a large fourth ventricle, and a markedly hypoplastic vermis that is rotated superiorly (small arrow) , (b) T1 shows an elevated , anteriorly displaced torcular herophili (arrow) and a superiorly displaced posterior fossa cyst

Axial CT scan showing the sinus confluence (large arrow) and sinus transversus (small arrows) displaced superiorly in Dandy-Walker malformation (lambdoid-torcular inversion)

d) Differential Diagnosis :1-Mega cisterna magna2-Epidermoid cyst3-Arachnoid cyst (see brain tumors , cystic

lesions)4-Blake’s pouch cyst5-Vermian hypoplasia (Joubert anomaly)

2-Dandy Walker Variant (DWV) :a) Definitionb) Incidencec) Radiographic Features

a) Definition :-The definition of DWV classically includes key

features of DWM such as a rotated hypoplastic vermis and a cystic dilatation of the fourth ventricle (the 4th ventricle is not as dilated as in the DW malformation) with an essentially normal posterior fossa

-The main difference between DWM & DWV being in the degree of dilatation of the fourth ventricle and therefore of the posterior fossa

b) Incidence :-The incidence of DWV is actually higher than

that of the full-blown DWM representing at least one-third of all cerebellar malformations

c) Radiographic Features :-4th ventricle communicates dorsally with

enlarged cisterna magna (keyhole deformity)-Hydrocephalus not common

DWM DWV

3-Mega Cisterna Magna :a) Definitionb) Incidencec) Radiographic Features

a) Definition :-Refers to adult patients with significantly

enlarged CSF retrocerebellar cisterns in the posterior fossa with normal cerebellar morphology

b) Incidence :-MCM is a fairly common condition, accounting

for approximately 54% of cystlike posterior fossa malformation

c) Radiographic Features :- Expansion of the cisterna magna typically seen

as prominent retrocerebellar CSF appearing space which freely communicates with the ventricular system and with the perimedullary subarachnoid spaces with a normal vermis and normal cerebellar hemispheres

-The fourth ventricle has normal shape and size

4-Persisting Blake’s Pouch :a) Definitionb) Radiological Findings

a) Definition :-The persistent Blake’s Pouch Cyst is a cystic

malformation of the posterior fossa thought to derive from persistence and expansion of the normally transient Blake pouch that arises from the area membranacea inferior (AMI) and that normally regresses during the fifth to eighth gestational weeks

b) Radiological Findings :-Retrocerebellar cyst formation with CSF signal

intensity , hypointense on T1 and hyperintense on T2 without abnormal enhancement

-The cysts are well marginated , have a smooth wall and are nearly always unilocular and located in midline

-The persistent Blake`s pouch cyst is in communication with the fourth ventricle and separated from the subarachnoid space

-Size of The posterior fossa is normal in size-Because the foramen of Magendie never

opens , CSF obstruction with tetraventricular hydrocephalus results

-Persisting Blake’s pouch , 5-month-old infant-The Blake’s pouch (asterisk) widely communicates with a dilated fourth ventricle-There is marked tetraventricular hydrocephalus

5-Chiari I :-See Before

6-Syndromes Associated With Vermian-Cerebllar Hypoplasia :

1-Joubert Syndrome2-Walker-Warburg Syndrome3-Muscle-Eye-Brain Syndrome4-Rhombencephalosynapsis5-Tectocerebellar dysraphism

1-Joubert Syndrome :a) Definition b) Clinical Picture

a) Definition :-Vermian aplasia or molar tooth midbrain-

hindbrain malformation-Presents clinically in the neonatal age-Vermian dysgenesis is the key feature

b) Clinical Picture :-Respiratory disturbances-Abnormal eye movement-Facial Asymmetry-Ataxia-Psychomotor retardation

c) Radiographic Features :-Small dysplastic or aplastic cerebellar vermis, unlike

Dandy Walker complex, hydrocephalus & a large posterior fossa cyst are uncommon

-The posterior fossa typically shows a bat wing 4th ventricle

-The mid brain has a characteristic molar tooth configuration

-Cleft between the two adjoining cerebellar hemispheres

Cleft between the two adjoining cerebellar hemispheres ( arrow )

Coronal T2 shows complete absence of the cerebellar vermis and the presence of a narrow interhemispheric cleft (arrow heads) that connects the 4th ventricle with the cisterna magna

2-Walker-Warburg Syndrome (WWS) :-Sometimes known as HARDE syndrome-Is an extremely rare lethal form of congenital

muscular dystrophy-It is primarily characterized by :1-Hydrocephalus 2-Agyria (Cobble-stone lissencephaly)

3-Retinal Dysplasia4-DW Continuum (enlargement of the 4th

ventricle , a retrocerebellar cyst and no enlargement of the posterior fossa )

5-Encephalocele

(a) Sagittal T1 shows hypoplasia of the cerebellar vermis (arrow) and a posterior fossa cyst communicating with the 4th ventricle , also note the associated parietal encephalocele , (b) Axial PD shows the abnormal right globe (arrow) , the patient had persistent hyperplastic primary vitreous , (c) Axial PD shows the smooth contour of the cerebral cortex (lissencephaly) and the enlarged ventricular system

Coronal T1 shows marked ventriculomegaly and cobblestone cortex

3-Muscle-Eye-Brain Syndrome (MEB) :-Finland remains the country with the largest

group of MEB patients-Floppy infants with visual problems and severe

mental retardation

4-Rhombencephalosynapsis :a) Definitionb) Radiographic Features

a) Definition :-All patients with rhombencephalosynapsis had

absence of the cerebellar vermis with midline fusion of the two cerebellar hemispheres

b) Radiographic Features :1-Vermian abnormalities :-Absent anterior (rostral) vermis-Deficient posterior (caudal) vermis2-Fusion of the cerebellar hemispheres3-This usually results in an abnormally small

posterior fossa and an abnormally shaped fourth ventricle which takes on a (diamond shaped or key hole)

Axial T2 MRI at the level of the posterior fossa showing AP elongation of the fourth ventricle giving it a "diamond shaped" appearance

(a) Axial IR (b) Axial T1 (c) Sagittal T1 (d) Coronal T1 , the posterior fossa is small , cerebellar convolutions are orientated transversely and the white matter is continuous across the mid-line (a,b) , the tonsils and the vallecula are not visible (b,d) On a mid-sagittal section (c) , the vermis is actually a mid-line cut through the monolobated cerebellum whose fissures are clearly visible (c)

5-Tectocerebellar dysraphism :a) Definitionb) Radiographic Features

a) Definition :-This rare abnormality is characterized by

vermian hypo-aplasia , occipital cephalocele and marked deformation of the quadrigeminal plate and brain stem , the colliculi are fused to form a beak pointing towards the site of the cephalocele

b) Radiographic Features :-Vermian hypo-aplasia is well depicted and the

tectal beak is visible both in the sagittal and axial planes

-The cerebellar hemispheres usually tend to engulf the brain stem

-Associated supratentorial anomalies and hydrocephalus are common findings

(a,b) Sagittal T1 , (c) Axial T1 (d) Coronal T1 , the brain stem is markedly distorted and stretched towards the cephalocele site (thick arrow, a) , the corpus callosum is thin and the mammillary bodies are hypoplastic (arrow, b) , the mesial cortex is diffusely arranged into multiple small gyri (stenogyria) (a) , there is extreme beaking of the quadrigeminal plate (thin arrows, a,c) , the vermis is agenetic and the two cerebellar hemispheres face one another at the mid-line (arrowheads, d) , the falx cerebri is fenestrated resulting in interdigitation of gyri across the interhemispheric fissure (arrows, d)

e) Neurocutaneous syndromes (Phakomatoses):

1-Tuberous Sclerosis2-Neurofibromatosis3-Sturge-Weber Syndrome4-Von Hippel-Lindau (VHL) disease5-Osler-Weber-Rendu

1-Tuberous Sclerosis : (Bourneville disease)a) Clinical Pictureb) Radiographic Features

a) Clinical Picture :-Tuberous sclerosis is a hamartomatous disorder

affecting several organ systems with multiple skin manifestations

-Presenting in childhood with a triad of :1-Seizures :- Present in about 3/4 of patients2-Mental retardation :-Up to half have normal intelligence3-Adenoma sebaceum :-Nodular rash originating in the nasolabial folds-Present in about 3/4 of patients

b) Radiographic Features :1-CNS Lesions2-Kidney3-Bone4-Chest

1-CNS Lesions : Four major CNS lesionsa) Subependymal Hamartomab) Cortical / Subcortical Tubersc) Subependymal Giant Cell Astrocytomad) White Matter Abnormalities

a) Subependymal Hamartoma :-88% are associated with calcification, although

calcification absent in early childhood-Visible within the first 6 months of age-Variable signal, frequently high T1 and iso to

high T2-Enhancement is variable

(a) NECT reveals subependymal calcifications , a hypointense right frontal lesion represents a white matter lesion or tuber , it extends from the lateral ventricle through the cerebral cortex , (b) CT+C shows no enhancement in the white matter lesion in the right frontal lobe

T1 T2 T1+C

FLAIR T1+C GE

b) Cortical / Subcortical Tubers :-50 % are in the frontal lobe-Low T1 and high T2 with only 10 % of tubers

showing enhancement

CT+C reveals a low-attenuating cortical tuber (arrow) in a 10-year-old patient with tuberous sclerosis

T2 shows numerous bilateral T2 hyperintense cortical tubers (yellow arrows) , subcortical tubers (blue arrows) & subependymal tubers (blue arrows) & subependymal nodules (red arrows)

Sagittal T1 shows multiple hyperintense cortical and subependymal nodules

FLAIR

c) Subependymal Giant Cell Astrocytoma :1-Incidence2-Location3-Radiographic Features4-Differential Diagnosis

1-Incidence :-Are benign tumors seen almost exclusively in

tuberous sclerosis (TS)-Peak occurrence 8-18 years-The tumor arises when a subependymal

nodule transforms into SGCA over a period of time

2-Location :-Located at foramen of Monro

3-Radiographic Features :a) CTb) MRI

a) CT :-Typically appears as an intraventricular mass near the

foramen of Monro -They are usually larger than 1 cm-Lesions are iso or slightly hypo-attenuating to grey matter-Calcification is common and hemorrhage is possible-Hydrocephalus may be present-Marked contrast enhancement (differentiating feature from

a subependymal nodule)

CT CT+C

b) MRI :*T1: Heterogenous and hypo to isointense to

grey matter *T2 : Heterogenous and hyperintense to grey

matter , calcific components can be hypointense

*T1+C : Marked enhancement

An intraventricular , ovoid , voluminous mass is observed which produces hydrocephalus as it occludes foramen of Monro , this mass is hyperintense on T2 (a) , isointense on T1 (b) and is significantly enhanced after the administration of contrast (c)

4-Differential Diagnosis :-In known cases of TS, the appearance is virtually

pathognomonic and the main differential is between a subependymal nodule and SGCA, serial imaging is most helpful here as growth implies SCGA

-Other general considerations include :1-Central Neurocytoma2-Choroid plexus papilloma (CPP)3-Choroid plexus carcinoma (CPC)

d) White matter abnormalities : Radial bands sign -Refers to linear bands seen on MRI radiating from

the periventricular white matter to the subcortical region , thought to be specific for tuberous sclerosis

-MRI :These radial bands appear a linear regions of signal

abnormality extending form the ventricle to the cortex , slightly fanning out as it reaches the periphery , best appreciated on a FLAIR & PD sequences

Hyperintense radial bands extending linearly at the level of right cerebral hemisphere and a cortical tuber located at left parietal lobe in FLAIR in a case with tuberous sclerosis complex

Radial band sign , (a) PD in a patient with TS shows hyperintense bands in the white matter radiating from the ventricular margin to the subcortical region (arrows) , (b) FLAIR shows irregular hyperintense areas in the subcortical white matter suggestive of subcortical tubers. A large hyperintense nodule is seen in the region of the foramen of Monroe , representing a subependymal giant cell astrocytoma (thick arrow)

2-Kidney :a) Angiomyolipoma :50 %, usually multiple and bilateralb) Multiple cysts

3-Bone :-Bone islands in multiple bones-Periosteal thickening of long bones-Bone cysts

4-Chest :a) Pulmonary Lymphangioleiomyomatosisb) Spontaneous pneumothorax , 50%c) Chylothoraxd) Cardiac rhabdomyomas, 5%e) Aortic aneurysm

LAM with spontaneous pneumothorax

2-Neurofibromatosis :a) Typesb) NF1c) NF2

a) Types :NF1 NF2

1-Name von Recklinghausen disease

Bilateral acoustic neuroma

2-Defect Chromosome 17 Chromosome 22

3-Incidence 90% 10%

4-Skin changes Prominent Minimal

5-Tumors Hamartomas, gliomas, malignant nerve sheath tumor

Meningiomas, schwannoma, ependymoma

6-Spine Neurofibroma Schwannoma

b) NF1 :1-Definition2-Diagnostic Criteria 3-Radiographic Features

1-Definition :-NF1 also known as von Rechlinghausen disease , is a

multisystemic neurocutaneous disorder with prominent skin manifestation (e.g. café au lait spots) , peripheral nerve sheath tumors (e.g. plexiform neurofibroma) , CNS malignancies (e.g. optic nerve glioma) & bony abnormalities (e.g. sphenoid wing dysplasia)

-AD in 50 % of cases & occurs sporadically in 50 % , caused by a defect in chromosome 17

2-Diagnostic Criteria : Need ≥2 criteria1-≥6 cafe au lait spots2-≥2 pigmented iris hamartomas (Lisch nodules)3-Axillary , inguinal freckling4-≥2 neurofibroma (or 1 plexiform neurofibroma)5-Optic nerve glioma6-First-degree relative with NF17-Dysplasia of greater wing of sphenoid

Café au lait spots

Lisch nodules

Café au lait spots , axillary freckling and neurofibromas

3-Radiographic Features : NF1 typically has lesions of neurons and astrocytes

a) CNSb) Spinal cord / Canalc) Skulld) Skeletale) Chestf) Vascularg) Other

a) CNS :1-FASI (Focal Area of Signal Intensity)2-Optic Nerve Glioma3-Low Grade Pilocytic Astrocytoma4-Diffuse Brain Stem Glioma5-Moyamoya Cerebral Occlusive Disease6-Aneurysms

1-FASI (Focal Areas of Signal Intensity) :-Are bright areas on T2 commonly identified in the

basal ganglia (often the globus pallidus), thalamus, brainstem (pons), cerebellum and subcortical white matter

-FASI areas are the most common neuroimaging feature in NF1 patients 1, with a significant frequency (86%) of one or more FASI areas in children with NF1

-FASI lesions are usually isointense on T , without contrast enhancement and with a bright signal on T2 and FLAIR

T2 through the cerebellum shows hyperintense (unidentified bright objects) of NF representing myelin vacuolation (arrows)

T2 T1+C

T2 shows hyperintense signals in the left globus pallidus and bilateral posterior aspects of the thalami (white arrows)

FLAIR shows hyperintense signal changes on both sides in the area of the basal ganglia , right more than left

2-Optic Nerve Glioma :-Typically present in children, and often in the

setting of NF13-Low Grade Pilocytic Astrocytoma :-Seen in up to 20% of all patients with NF1 and

typically manifest in early childhood-Approximately 1/3 of pilocytic astrocytomas

involving the optic nerves have associated NF1

Optic nerve glioma in NF1 , (a) T1 reveals circumscribed enlargement of the optic nerve with an isointense signal , (b) T2 shows hyperintense signaling of the mass that is contained within the dura of the optic nerve , (c) T1+C shows enhancement of the fusiform kinked shaped optic nerve tumor , (d) FLAIR shows the fusiform image of the optic nerve tumor is again seen , also here evident are several high signal lesions in the midbrain and cerebellum , consistent with the classic hamartomatous CNS neurofibromas of NF1

Optic nerve glioma in NF1 , (a) T1 shows an Infiltrating lesion within the right optic nerve with associated proptosis , (b) T1+C shows an enhancing infiltrating mass extending from the right optic nerve to the chiasm and into the suprasellar space

The lesion is hypointense on T1 and hyperintense on FLAIR , Optic chiasma and left optic nerve are involved. It was enhancing uniformly on T1+C (not shown) , the histopathologic diagnosis was pilocytic astrocytoma

4-Diffuse Brain Stem Glioma :-Account for 60-75% of all brainstem gliomas

and most frequently arise in the pons-Typically present in childhood (3 to 10 years of

age-Hypo in T1 , Hyper in T2 , no enhancement or

enhances minimally , no diffusion restriction5-Moyamoya Cerebral Occlusive Disease (rare)6-Aneurysms

Diffuse brain stem glioma , (a) T1 , (b) T2 , (c) T1+C

Diffuse brain stem glioma , (a) T1 , (b) T2 , (c) T1+C , (d) Diffusion

b) Spinal cord / Canal :1-Neurofibromas of exiting nerves :-Enlarged neural foramen-Intradural extramedullary tumors (classic dumbbell tumors)-Neurofibromas are WHO grade I nerve sheath tumor-The cutaneous & subcutaneous nerves are more commonly

involved than the more proximal peripheral nerves -A plexiform subtype is more aggressive and consists of network

of fusiform-shaped masses with malignant degeneration (in 5 %)

-Like schwannomas, neurofibromas are likely of Schwann cell origin

-The target sign can be seen with either neurofibromas or schwannomas and reflects central T2 hypointensity thought to be due to a fibrocollagenous core, the target sign is suggestive of benignity

-In contrast to schwannomas, neurofibromas aren’t encapsulated and involve the entire cross-sectional area of the nerve , if a neurofibroma is resected, the parent nerve must therefore be sacrificed

Neurofibroma , spine

T2 shows L3 nerve root neuroma , note the target sign

Coronal T2 of the lumbar spine shows the characteristic Target appearance of plexiform neurofibromas (red arrow) which are hyperintense with central hypointensity

Right orbital plexiform neurofibroma , sphenoid wing hypoplasia and likely optic nerve glioma

T2 shows subcutaneous mass over the left occipito-temporal region with multiple serpiginous lesions and targetoid appearance manifested with peripheral bright and central dark signal (arrow) suggestive of plexiform neurofibroma

T2 shows plexiform neurofibroma

2-Dural Ectasia :-Enlarged neural foramen-Posterior vertebral scalloping

3-Low-grade cord astrocytoma

Dural ectasia , T2 showing posterior vertebral scalloping by dural ectasia (asterisks)

c) Skull :1-Hypoplastic sphenoid wing :-Is a characteristic yet not a pathognomonic

feature of NF1, it can also occur in isolated case

-Sphenoid wing dysplasia is seen in 5-10% of cases of NF1 and is one of the diagnostic criteria of NF1

It can be seen isolated or associated with underlying plexiform neurofibroma

2-Macrocrania3-Lambdoid suture defect

Sphenoid wing dysplasia

Absence of the right sphenoid wing and the intracranial and orbital contents separated only by dura mater

Absence of the sphenoid wing with underlying plexiform neurofibroma

d) Skeletal :-50-80 %-Erosion of bones and foramina by slow-growing

neuromas-Bowing of tibia and fibula, pseudarthroses-Unilateral overgrowth of limbs : focal gigantism-Rib notching (Twisted ribbon ribs) : due to

erosion from neurofibromas of the intercostal nerves

-Cervical kyphoscoliosis with a characteristic acute angle

Ulnar pseudoarthrosis

Tibial pseudoarthrosis

Rib notching

The PA chest film shows a rounded lesion with the (incomplete border sign) (medial aspect outlined by air, lateral border not visible because in contact with chest wall) , in addition , there is erosion of the lower border of the rib (arrow) , this combination of signs is pathognomonic of a mass in the underside of the rib , CT confirms the presence of a soft-tissue mass and the erosion of the rib (arrows)

e) Chest :1-Progressive pulmonary fibrosis2-Intrathoracic meningocele3-Lung and mediastinal neurofibromas

NF1 , CT shows an associated large , lateral thoracic meningocele (arrows)

Known patient with NF1 , (a) CT shows multiple large prevascular and paratracheal neurofibromas , (b) CT shows paraesophageal and pleura-based neurofibromas (arrows)

f) Vascular :1-Renal artery stenosis2-Renal artery aneurysm3-Abdominal coarctation

g) Other :-Pheochromocytoma

c) NF2 :1-Definiton2-Diagnostic Criteria 3-Radiographic Features

1-Definiton :-Autosomal dominant neurocutaneous disorder

completely unrelated to NF1-Despite the name , neurofibromas are not a

component of NF2-Caused by a defect on chromosome 22 and is

approximately ten times less common than NF1-The typical clinical presentation of NF2 is hearing loss

caused by bilateral vestibular schwannomas , the presence of bilateral vestibular schwannomas is diagnostic of NF2

2-Diagnostic Criteria : need ≥1 criteriona) Bilateral acoustic neuromasb) First-degree relative with NF2 and unilateral

acoustic neuroma or meningioma , glioma , schwannoma & neurofibroma (any two)

3-Radiographic Features : NF2 typically has lesions of Schwann cells and meninges

-(MISME): Multiple Inherited Schwannomas , Meningiomas and Ependymomas

a) CNS :1-Bilateral acoustic schwannoma (diagnostic)2-Other cranial nerves schwannomas (Trigeminal

schwannoma)3-Meningioma (often multiple)

Meningiomatosis & bilateral vestibular schwannomas in NF2 , multiple axial T1+C show numerous enhancing extra-axial , dural based masses bilaterally , representing meningiomas , there are bilateral enhancing cranial nerve VIII schwannomas (arrows)

(a) Bilateral schwannomas , (b) Multiple Meningiomatosis

b) Spinal cord / Canal :1-Intradural , extramedullary meningiomas2-Schwannomas3-Intramedullary ependymoma

Intradural extramedullary meningioma

3-Sturge-Weber Syndrome :a) Definitionb) Clinical Picturec) Radiographic Findingsd) Differential Diagnosis

a) Definition :-A neurocutaneous disorder characterized by facial port-wine

stain (capillary malforamtion) , ocular abnormalities & failure of normal cortical venous development

-It is a vascular disorder , thought to be caused by failure of regression of the primitive embryologic cephalic venous plexus , this developmental anomaly results in the formation of leptomeningeal venous angiomatosis , which is a vascular malformation characterized by dilated capillaries & venules

-The underlying vascular anomaly ultimately leads to chronic ischemia , cortical atrophy & cortical calcification

b) Clinical Picture :1-Congenital facial cutaneous hemangioma (port

wine stain or facial naevus flammeus) -Almost always present and usually involves the

ophthalmic division (V1) of the trigeminal nerve2-Seizures , 90 %3-Mentral Retardation4-Ipsilateral Glaucoma5-Hemiparesis , 50 %

c) Radiographic Findings :1-CT :-Tramtrack cortical calcifications (characteristic) that follow cortical

convolutions , most common in parietal & occipital lobes-Atrophic cortex with enlarged adjacent subarachnoid space-Ipsilateral thickening of skull and orbit-Leptomeningeal venous angiomas : parietal > occipital > frontal

lobes , enhancement-Enlargement and increased contrast enhancement of ipsilateral

choroid plexus

NECT shows subcortical calcification & cerebral atrophy

2-MRI :*T1+C :-Prominent leptomeningeal enhancement in

affected area*GE / SWI / EPI :-Sensitive to calcification

T1+C shows diffuse leptomeningeal enhancement , most prominent in the RT occipital lobe and bilateral choroid plexus engorgement

T1+C showing gyriform contrast enhancement in the right cerebral hemisphere , there is brain atrophy on the right side , the cranial vault is asymmetric as secondary to brain atrophy

T1+C

d) Differential Diagnosis :-The differential is a combination of that for

multiple intracranial calcifications , cerebral hemiatrophy and leptomeningeal enhancement

4-Von Hippel-Lindau (VHL) disease :a) Definitionb) Clinical Picturec) Radiological Findings

a) Definition :-Cerebelloretinal Hemangioblasotma-Characterized by the presence of

hemangioblastomas and renal (renal cell carcinoma and cysts) , adrenal , pancreatic and scrotal abnormalities

b) Clinical Picture :1-Hemangioblastoma :-50 %-Cerebellum (most common location)-Brainstem , spinal cord-Retinal

2-Renal :-RCC , 50 % ( bilateral in 65 % , multiple in 85 % ) -Benign Renal Cysts , 60 %3-Adrenal Glands :-Pheochromocytoma , 15 % , bilateral in 40 %

4-Pancreas :-Multiple cysts , 70 %-Cystadenocarcinoma-Islet cell tumor5-Scrotum :-Epididymal cysts , 10 %6-Other :-Hepatic cysts , 20 %-Splenic cysts , 10 %

c) Radiological Findings :-Hemangioblastomas: See Brain tumors-Multiple hemangioblastomas is diagnostic of VHL

disease-MRI is the first study of choice-CT is often used to evaluate kidneys , adrenals and

pancreas-Most patients with solitary hemangioblastoma do

not have VHL disease

T1 T2

5-Osler-Weber-Rendu : ( Hereditary Hemorrhagic Telangiectasia )

a) Embolic Infarcts :-Emboli through pulmonary AV shuntsb) Cerebral Abscess :-Septic emboli through pulmonary AV shuntsc) Vascular Malformations :-Telangiectasia , cavernomas , AVM & AVF