congenital brain anomalies
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CONGENITAL BRAIN ANOMALIES
DR. DEV LAKHERA
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• Embryology
• Hindbrain Herniations /Malformations
• Disorders of Commissural development
• Disorders of Cortical development
• Disorders of Diverticulation/Cleavage
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DEVELOPMENT OF THE CENTRAL NERVOUS SYSTEM
• EARLY (>3rd wk): NEURULATION NEURAL TUBE CLOSURE
NEURONAL PROLIFERATION MIGRATION
• LATER (>11th wk): OPERCULIZATION, GYRAL AND SULCAL DEVELOPMENT
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CNS DEVELOPMENT
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NEURONAL PROLIFERATIONANDMIGRATION
Peak migration 11-15 wks
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Posterior fossa herniation/malformations
• CHIARI MALFORMATION
• DANDY WALKER MALFORMATION
• MEGA CISTERNA MAGNA
• RHOMBOENCEPHALOSYNAPSIS
• JOUBERT’S SYNDROME
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CHIARI MALFORMATION- I
• Herniation of cerebellar tonsils into cervical canal
• Incidental (50 % asymptomatic)
• Valsalva-induced suboccipital headache, neck pain
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• Elongated, peg-shaped cerebellar tonsils
• Tonsillar descent below basion-opisthion line
• Diminished/absent CSF flow at posterior FM
• Crowded foramen magnum
IMAGING FEATURES
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Associated conditions
Hydrocephalus in up to 30% of cases-
In ~35% -associated skeletal anomalies :
platybasia/basilar invagination/reduced clival
length
atlanto-occipital assimilation
syndromic associations
Klippel-Feil syndrome, Achondroplasia,
Marfans
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CHIARI II
• Complex hindbrain malformation with myelomeningocele
Etiology
• Posterior neuropore closure disorder
• Paraxial mesodermal abnormalities
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IMAGING
• Small posterior fossa
• Inferiorly displaced medulla, vermis
• “Straw shaped” fourth ventricle
• Prominent massa intermedia
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o Lacunar skullo Abnormal dura (gaping FM, fenestrated falx)o o “Towering” and “creeping” cerebellum
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Chiari malformation type III
o Small posterior fossao Caudally displaced brainstemo Low occipital or upper cervical bony defecto Cephalocele with herniation of meninges, dysplastic brain, ventricles
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Hindbrain MalformationsDandy-Walker Spectrum
•Dandy-Walker malformation (“classic”)
•Dandy-Walker variant
• isolated inferior vermian hypoplasia
•Persistent Blake pouch cyst (BPC)
•Mega cisterna magna (MCM)
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Large posterior fossa (PF)
Cyst extending posteriorly from fourth
ventricle
Variable vermian, cerebellar hypoplasia
High-inserting venous confluence
CLASSIC DANDY WALKER ON MRI
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BLAKE POUCH CYST MEGA CISTERNA MAGNA
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Differential Retro-cerebellar arachnoid cyst
No communication with 4th ventricle
Hypoplastic Rotated Vermis PF normal size “Keyhole” opening of fourth ventricle
Dandy-Walker variant
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DWM DWV Persistent Blake’s pouch
Mega cisterna magna
protrusion of thefourth ventricle through the foramen ofMagendie
Retro-cerebellar cystVermis Hypo-plastic
Rotated upwardsHypo-plastic No or mild
hypoplasiaNo or mild hypoplasia
4th ventricle Markedly dilated Dilated Dilated Normal
Posterior fossa Expanded Normal size Normal size Normal size
hydrocephalus 75 % of cases 25% of cases Present No
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Rhombencephalosynapsis
• Midline brain malformation• Absent cerebellar vermis • Apparent fusion of the cerebellar
hemispheres
• VACTERL association
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Joubert’s Syndrome (Congenital Vermian Hypoplasia)
• AR syndrome
• Associated ocular, renal , digital anomalies may be seen
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IMAGING
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Commissural maldevelopment
Major Commissures
Corpus callosum (13th wk)
Anterior (8th wk)
Posterior (11th wk)
Incidental, Seizure disorder,
Developmental disorder
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Corpus Callosum agenesis
Corpus callosum agenesis
Complete corpus callosum agensis
Partial corpus callosum agenesis
Splenium & rostrum absent
Genu & body present
Common congenital brain disorder
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COMPLETE AGENESIS
Complete absence of corpus callosum (CC) = agenesiso Hippocampal commissure (HC) absento Anterior commissure (AC) often present
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Coronal
o “Viking helmet” or “moose
head” appearance
o “High-riding” third ventricle
o Probst bundles
IMAGING
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Axial
• o Parallel lateral ventricles
• nonconverging, widely separated
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Malformations of Cortical Development Abn Glial proliferation/apoptosis
• Microcephaly
• Megalencephaly
• Cortical dysgenesis
Abn Neuronal migration
• Heterotropia
• Lissencephaly spectrum
Abn Postmigration development
• Polymicrogyria
• Schizencephaly
• Focal cortical dysplasia
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Malformations Secondary to Glial/Neuronal Proliferation or Apoptosis
MicrocephalyPrimary- geneticSecondary –Infection. Ischemia, Maternal DM, Trauma
Imaging
Small cranial vaultClosely opposed suturesCortex may be normal or show simplified gyration
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Enlarged righthemisphere, hemicranium
Enlarged WM in the corona radiata
Hyperintense WM
Hemimegaloencephaly
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Abnormal Neuronal migration
Heterotopias:
- Characterized by the presence of normal neurons at abnormal sites
Nodular type(common) Diffuse(uncommon)
Subependymal/ Periventricular Lissencephaly
Subcortical Band type
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-Nodular type:
Focal subependymal nodules - indent the ventricular wall
Diffuse subependymal nodules - border the walls of the lateral ventricle.
Do not enhance on administration of intravenous contrast.
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Subcortical heterotropia
focal subcortical mass of heterotopic gray matter
Thin overlying cortex
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Band Heterotopia
Double cortex syndromeAffects Females
ImagingBand of GM deep to cortex
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Lissencephaly pachygyria spectrum
Refers to “smooth brain” with absent or poor sulcation.
Due to neuronal under migration
type I (classic) lissencephaly type II (cobblestone complex) lissencephaly
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Classic Lissencephaly
CT APPEARANCE
• smooth, nearly agyric surface
• shallow sylvian fissures (Axial)
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Classic Lissencephaly
MRI APPEARANCE
• Thin cortical ribbon
• Hyperintense cell-sparse zone
• Thickened cortex
• Agyria
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Type 2 Lissencephaly
Cobblestone appearance Associated with muscular dystrophy syndromes
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Abnormalities of Postmigrational Development
Polymicrogyria• Irregular cortex with multiple small
convolutions • Shallow sulci• Irregular GWM interface• Similar to Lissencephaly type II
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Schizencephaly
• Cleft extending from ventricle to the pial surface lined by gray matter
• Types
Close lipped
Open lipped
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Open lipped Schizencephaly
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ANOMALIES OF VENTRAL PROSENCEPHALON DEVELOPMENT
• Holoprosencephaly and variants
• Septo-optic dysplasia
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HOLOPROSENCEPHALY Incomplete separation of the two hemispheres
‘Holo’ –Single
alobar holoprosencephalysemilobar holoprosencephaly lobar Holoprosencephaly
Can effect diencephalic structures
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Alobar Holoprosencephaly
• single midline monoventricle
absent midline structures
• absent septum pellucidum
• agenesis or hypoplasia of the corpus callosum
• absent interhemispheric fissure and falx cerebri
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• More cephalad
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• occurs in-utero
• Causes
Infarction, Infection, hypoxic ischemic encephalopathy
• The falx is usually present
Differential - Hydranencephaly
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Semilobar holoprosencephaly
• absence of septum pellucidum
• monoventricle with partially developed
occipital and temporal horns
• rudimentary falx cerebri: absent anteriorly
• incompletely formed interhemispheric
fissure
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Lobar Holoprosencephaly
• fusion of the frontal horns of the lateral ventricles
• wide communication of this fused segment with the third ventricle
• absence of septum pellucidum
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Syntelencephaly• middle interhemispheric variant
(MIHV), is a mild subtype of holoprosencephaly
Mids frontal and parietal lobes are fused across the midline
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Septooptic dysplasia
• Optic nerve hypoplasia
• Absence of septum pellucidum
• Two-thirds of patients hypothalamic-pituitary dysfunction.
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THANK YOU
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Normal brain development
Neurulation(neural tube formation & dysjunction)
Regionalization (vesicle formation &
cleavage)
Cortico-genesis(histogenesis &
migration)
Proliferation
Migration
Organization
Myelination
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