CONGENITAL BRAIN ANOMALIES

DR. DEV LAKHERA

• Embryology

• Hindbrain Herniations /Malformations

• Disorders of Commissural development

• Disorders of Cortical development

• Disorders of Diverticulation/Cleavage

DEVELOPMENT OF THE CENTRAL NERVOUS SYSTEM

• EARLY (>3rd wk): NEURULATION NEURAL TUBE CLOSURE

NEURONAL PROLIFERATION MIGRATION

• LATER (>11th wk): OPERCULIZATION, GYRAL AND SULCAL DEVELOPMENT

CNS DEVELOPMENT

NEURONAL PROLIFERATIONANDMIGRATION

Peak migration 11-15 wks

Posterior fossa herniation/malformations

• CHIARI MALFORMATION

• DANDY WALKER MALFORMATION

• MEGA CISTERNA MAGNA

• RHOMBOENCEPHALOSYNAPSIS

• JOUBERT’S SYNDROME

CHIARI MALFORMATION- I

• Herniation of cerebellar tonsils into cervical canal

• Incidental (50 % asymptomatic)

• Valsalva-induced suboccipital headache, neck pain

• Elongated, peg-shaped cerebellar tonsils

• Tonsillar descent below basion-opisthion line

• Diminished/absent CSF flow at posterior FM

• Crowded foramen magnum

IMAGING FEATURES

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

CHIARI II

• Complex hindbrain malformation with myelomeningocele

Etiology

• Posterior neuropore closure disorder

• Paraxial mesodermal abnormalities

IMAGING

• Small posterior fossa

• Inferiorly displaced medulla, vermis

• “Straw shaped” fourth ventricle

• Prominent massa intermedia

o Lacunar skullo Abnormal dura (gaping FM, fenestrated falx)o o “Towering” and “creeping” cerebellum

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

Hindbrain MalformationsDandy-Walker Spectrum

•Dandy-Walker malformation (“classic”)

•Dandy-Walker variant

• isolated inferior vermian hypoplasia

•Persistent Blake pouch cyst (BPC)

•Mega cisterna magna (MCM)

Large posterior fossa (PF)

Cyst extending posteriorly from fourth

ventricle

Variable vermian, cerebellar hypoplasia

High-inserting venous confluence

CLASSIC DANDY WALKER ON MRI

BLAKE POUCH CYST MEGA CISTERNA MAGNA

Differential Retro-cerebellar arachnoid cyst

No communication with 4th ventricle

Hypoplastic Rotated Vermis PF normal size “Keyhole” opening of fourth ventricle

Dandy-Walker variant

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

Rhombencephalosynapsis

• Midline brain malformation• Absent cerebellar vermis • Apparent fusion of the cerebellar

hemispheres

• VACTERL association

Joubert’s Syndrome (Congenital Vermian Hypoplasia)

• AR syndrome

• Associated ocular, renal , digital anomalies may be seen

IMAGING

Commissural maldevelopment

Major Commissures

Corpus callosum (13th wk)

Anterior (8th wk)

Posterior (11th wk)

Incidental, Seizure disorder,

Developmental disorder

Corpus Callosum agenesis

Corpus callosum agenesis

Complete corpus callosum agensis

Partial corpus callosum agenesis

Splenium & rostrum absent

Genu & body present

Common congenital brain disorder

COMPLETE AGENESIS

Complete absence of corpus callosum (CC) = agenesiso Hippocampal commissure (HC) absento Anterior commissure (AC) often present

Coronal

o “Viking helmet” or “moose

head” appearance

o “High-riding” third ventricle

o Probst bundles

IMAGING

Axial

• o Parallel lateral ventricles

• nonconverging, widely separated

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

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

Enlarged righthemisphere, hemicranium

Enlarged WM in the corona radiata

Hyperintense WM

Hemimegaloencephaly

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

-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.

Subcortical heterotropia

focal subcortical mass of heterotopic gray matter

Thin overlying cortex

Band Heterotopia

Double cortex syndromeAffects Females

ImagingBand of GM deep to cortex

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

Classic Lissencephaly

CT APPEARANCE

• smooth, nearly agyric surface

• shallow sylvian fissures (Axial)

Classic Lissencephaly

MRI APPEARANCE

• Thin cortical ribbon

• Hyperintense cell-sparse zone

• Thickened cortex

• Agyria

Type 2 Lissencephaly

Cobblestone appearance Associated with muscular dystrophy syndromes

Abnormalities of Postmigrational Development

Polymicrogyria• Irregular cortex with multiple small

convolutions • Shallow sulci• Irregular GWM interface• Similar to Lissencephaly type II

Schizencephaly

• Cleft extending from ventricle to the pial surface lined by gray matter

• Types

Close lipped

Open lipped

Open lipped Schizencephaly

ANOMALIES OF VENTRAL PROSENCEPHALON DEVELOPMENT

• Holoprosencephaly and variants

• Septo-optic dysplasia

HOLOPROSENCEPHALY Incomplete separation of the two hemispheres

‘Holo’ –Single

alobar holoprosencephalysemilobar holoprosencephaly lobar Holoprosencephaly

Can effect diencephalic structures

Alobar Holoprosencephaly

• single midline monoventricle

absent midline structures

• absent septum pellucidum

• agenesis or hypoplasia of the corpus callosum

• absent interhemispheric fissure and falx cerebri

• More cephalad

• occurs in-utero

• Causes

Infarction, Infection, hypoxic ischemic encephalopathy

• The falx is usually present

Differential - Hydranencephaly

Semilobar holoprosencephaly

• absence of septum pellucidum

• monoventricle with partially developed

occipital and temporal horns

• rudimentary falx cerebri: absent anteriorly

• incompletely formed interhemispheric

fissure

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

Syntelencephaly• middle interhemispheric variant

(MIHV), is a mild subtype of holoprosencephaly 

Mids frontal and parietal lobes are fused across the midline

Septooptic dysplasia

• Optic nerve hypoplasia 

• Absence of septum pellucidum

• Two-thirds of patients hypothalamic-pituitary dysfunction. 

THANK YOU

Normal brain development

Neurulation(neural tube formation & dysjunction)

Regionalization (vesicle formation &

cleavage)

Cortico-genesis(histogenesis &

migration)

Proliferation

Migration

Organization

Myelination