18. Neural tube closure disorders
Disorders of closure of rostral neural
pore
Disorders of closureof caudal neural
pore
19. Cranial defects
Meningocele, meningoencephalocele, and
meningohydroencephalocele are all caused
by an ossification defect in the bones of the
skull. The most frequently affected bone is
the squamous part of the occipital
bone, which may be partially or totally
lacking. If the opening of the occipital bone
is small, only meninges bulge through it
(meningocele), but if the defect is
large, part of the brain and even part of the
ventricle may penetrate through the
opening into the meningeal sac
20. The latter two malformations are
known as meningoencephalocele and
meningohydroencephalocele
21.
22. Anencephaly
Exencephaly is characterized by failure of the
cephalic part of the neural tube to close. As a
result, the vault of the skull does not
form, leaving the malformed brain exposed.
Later this tissue degenerates, leaving a mass
of necrotic tissue. This defect is called
anencephaly, although the brainstem remains
intact. Since the fetus lacks the mechanism
for swallowing, the last 2 months of
pregnancy are characterized by hydramnios.
The abnormality can be recognized on a
radiograph, since the vault of the skull is
absent.
23.
24. Defects of caudal neuropore
Neural tube defects (NTDs), may
involve the
meninges, vertebrae, muscles, and
skin.
Spina bifida is a general term for
NTDs affecting the spinal region. It
consists of a splitting of the vertebral
arches and may or may not involve
underlying neural tissue. Two different
types of spina bifida occur:
25. ◦ Spina bifida occulta is a defect in the
vertebral arches that is covered by skin
and usually does not involve underlying
neural tissue. It occurs in the lumbosacral
region (L4 to S1) and is usually marked by
a patch of hair overlying the affected
region.
◦ Spina bifida cystica is a severe NTD in
which neural tissue and/or meninges
protrude through a defect in the vertebral
arches and skin to form a cyst like sac.
26. Occasionally the neural folds do not
elevate but remain as a flattened
mass of neural tissue (spina bifida
with myeloschisis or rachischisis).
27.
28.
29.
30.
31. Cerebral cleavage and neural
migration defects
Child with delayed devolopment and
seizures
Especially when child is dysmorphic
MRI is the investigaton of choice
After the imaging we have to see the MR
in a orderly fashion
◦ Midline structures
◦ Cerebral cortex and cortico white matter
junctions
◦ White matter
◦ Basal ganglia and ventricular system and
posterior fossa structures
32. Midline structures
Cerebral commisures are the most
common anomolies
Hypothalamus and pituatary
Midline leptomeninges
Large csf spaces in posterior fossa
33. Cerebral cortex
Is 2-3mm thick
Too thick polymicrogyria and
pachygyria
Greywhite matter junction irregular
polymicrogyria or cobble stone cortex
Abnormally thin perinatal or ishaemic
injury
34. White matter
Myelination appropriate or not
Diffuse layer of hypomyelination or
amyelination associated heterotopia or
polymicrogyria suggestive of CMV
Absent myelination may be localised
to a gyrus or may extend towards the
ependymal layer transmantle sign
characteristic of FCD
35. Posterior fossa
Brain stem and cerebellum
4 th V and vermis
Size of the pons with cerebellum
36.
37.
38. Callosal dysgenesis
Partial or complete absence corpus
callosum and hippocampal
commisures
Atrium or occipital horn dilatation
colpocephaly
Probst bundles
Vertical or posterior course ACAs
Most common presentation seizures
devolopmental delay and cranial
deformity and hypertelorism
43. HVR
◦ Variable vermian
hypoplasia
BPC
◦ Open 4th V
communicates with
cyst
MCM
◦ Enlarged
pericerebellar cisterns
communicate with sub
arachnoidspace
◦ Vermis and 4 th V
normal
44. Rhombencephalosynapsis
Etiology
◦ Unknown: 2 major theories
Failure of vermian differentiation
Vermian agenesis allowing hemisphere
continuity
Features
◦ Congenital continuity (lack of division) of
cerebellar hemispheres
◦ Usually with fusion of dentate nuclei and
superior cerebellar peduncles
45. ◦ Small, single hemisphere cerebellum with
continuous white matter (WM) tracts crossing
midline
◦ Diamond or keyhole-shaped 4th ventricle
◦ Absent primary fissure
Clinical features
◦ Variable neurological signs
◦ Ataxia, gait abnormalities, seizures
◦ Developmental delay
◦ RES discovered in near-normal patients at
autopsy
46.
47. Molar Tooth Malformations
(Joubert)
Hindbrain anomaly characterized by
dysmorphic vermis, lack of
decussation of superior cerebellar
peduncle, central pontine
tracts, corticospinal tracts
"Molar tooth" appearance of midbrain
on axial images
Etiology
◦ result from mutations of
ciliary/centrosomal proteins that can affect
cell migration, axonal pathway
48. Clinical features
◦ Most common signs/symptoms:
Ataxia, developmental delay, oculomotor
and respiratory abnormalities
49.
50.
51. Holoprosencephaly
Features
◦ Failure to delineate normal
prosencephalic midline with
absent/incomplete hemispheric and basal
cleavage
◦ Single ventricle
◦ Azygous ACA
◦ associated facial defects
52. Clinical features
Most common signs/symptoms
◦ Facial malformation (hypotelorism +++)
◦ Seizures and developmental delays
◦ Hypothalamic/pituitary malfunction
(75%, mostly diabetes insipidus), poor
body temperature regulation
◦ Dystonia and hypotonia: Severity
correlates with degree of BG
nonseparation
53.
54.
55. Heterotopic Gray Matter
Arrested/disrupted migration of groups
of neurons from periventricular
germinal zone (GZ) to cortex
Ectopic nodule or ribbon, isointense
with gray matter (GM) on every MR
sequence
Periventricular, subcortical/transcerebr
al, molecular layer
Band heterotopia
56.
57.
58. Lissencephaly
Features
◦ Disorders of cortical formation caused by
arrested neuronal migration, resulting in thick
4-layer cortex and smooth brain surface
◦ "Hourglass" or "figure eight" shape of
cerebral hemispheres
◦ 3 layers
Outer cellular layer → may be relatively
thin, smooth
Intervening cell-sparse layer
Deeper thick layer of arrested neurons mimicking
band heterotopia
59.
60. Schizencephaly
Features
◦ Transmantle gray matter lining clefts
◦ Ca++ when associated with CMV
Pathology
◦ Can be result of acquired in utero insult
affecting neuronal migration
◦ Infection (CMV), vascular insult, maternal
trauma, toxin
Types
◦ Closed lip
◦ Open lip
61.
62. Hemimegalencephaly
Features
◦ Hamartomatous overgrowth of part/all of
hemisphere
◦ Abnormal proliferation, migration, and
differentiation of neurons
◦ Embryology
Insult to developing brain causes development of
too many synapses, persistence of supernumerary
axons, and potential for white matter overgrowth
Localized epidermal growth factor (EGF) in cortical
neurons and glial cells may lead to excessive
proliferation
63. ◦ Large cerebral hemisphere, hemicranium
◦ Posterior falx and occipital pole "swing" to
contralateral side
◦ Lateral ventricle is large with abnormally
shaped frontal horn
64.
65. Polymicrogyria
Features
◦ Malformation due to abnormality in late
neuronal migration and cortical
organization
◦ Result is cortex containing multiple small
sulci that often appear fused on gross
pathology and imaging
◦ Neurons reach cortex but distribute
abnormally forming multiple small
undulating gyri
