Abnormalities of the Fetal Central Nervous System Prenatal US Diagnosis with Postnatal Correlation - Fisiha Fikiru.ppt

Obstetrics Ultrasound
Fetal CNS abnormality

1. Abnormalities of the Fetal Central
Nervous System: Prenatal US Diagnosis
with Postnatal Correlation
Fish Fikiru7/23/2024 1

2. Abnormalities of the Fetal Central
Nervous System: Prenatal US Diagnosis
with Postnatal Correlation
Prepared By -Fisiha Fikiru (Senior MRT)
Arbaminch University, Ethiopia
RADዩጵያ

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RADዩጵያ

4. Outline
i.Introduction.
ii.Standard Sonographic Examination of the Fetal CNS.
iii.Characterization of major CNS anomalies.
iv.Conclusion.
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5. Introduction

6. I. Introduction -Congenital CNS Anomalies
Thesecondmostcommonmalformations.
0.1%–0.2%inlivebirthsand3%–6%instillbirths.
EarlyandaccuratediagnosisatprenatalUSistherefore
essential.
Sensitivityandspecificityof72.2%and100%respectively.
Knowledge of normal intracranial anatomy andlogical
sonographicapproachcan improve depiction of abnormal
findings.
TimelyandAccurateDiagnosis.
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7. Anatomic survey of the fetus and its r/s
to gestational age –what can be seen
and cannot be seen !!
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TheAveragegestationalageforthedetectionanomaliesare
notthesameforallanomalies.
Example–Anencephaly.
–BilateralRenalAgenesis.
Thebestcompromisehastobemadeb/ntheearliest
gestationalageatwhichitispossibletovisualizethe
anatomicstructure,theearliestgestationalagetodetect
anomalyandtheearliestgestationalagetoaccurate
diagnosis.

8. This shows for each anatomic structure the earliest gestational age (blue +)
at which it is possible to visualize it and the ideal gestational age (black +) for
its visualization.

9. Ultrasound screening for fetal brain malformations is
performed at 18 –22weeks’ gestation.
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10. Standard Sonographic
Examination of the Fetal CNS

11. II. Standard Sonographic Examination of the
Fetal CNS.
The CNS displays remarkable embryological and developmental
changes throughout gestation.
Standard approach of examination and evaluation of the CNS
should be followed.
Abdominal ultrasound VsTransvaginal scan for fetal CNS.
Transverse scanning planes VsCoronal VsSagittal views.
Four standard recommended view —provide an overview
of fetal intracranial anatomy.
Transthalamic, Transventricular, and Transcerebellar.
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12. Con’t…Standard Sonographic Examination of the Fetal CNS
-Essential elements surveyed in the head and neck include
Lateral cerebral ventricles,
Choroid plexus,
Midline falx,
Cavum septipellucidi,
Cerebellum,
Cisterna magna,
Upper lip, and nuchal fold.
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AXIAL PLANE
Figure -Four
standard views are
used in prenatal US
assessment of the
head:
a.Transventricular
view,
b.Transthalamic
View,
c.Transcerebellar
view.

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A.Transventricular View
Most cephalad axial scan plane of the fetal head.
It allows visualization of the sonolucent lateral ventricles
with the echoic choroid plexuses, filling the ventricular
bodies and atria and of the Cavum Septi Pellucidi (CSP).
To exclude the presence of ventriculomegaly.
Morphologic evaluation of the cerebral ventricles.

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Ventriculomegaly(Hydrocephalus)

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AXIAL PLANE
Transventricular View

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Transventricular View

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Transventricular View

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Transventricular View

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Transventricular View
Frontal Horn

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Fig -Transventricular view: Axial US image of a fetus at 18 weeks
gestation depicts ventriculomegaly. The lateral ventricle (calipers) normally
measures less than 10 mm across the atrium of the posterior horn at all
gestational ages. The near-field ventricle (dashed arrow in b and c) is
usually poorly seen because of reverberation artifact from the ossified
skull.

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Fig -Transventricular view: Axial US image of a fetus at 26 weeks gestation
shows the classic dangling choroid sign (solid arrow) of ventriculomegaly,
whereby the more anterior choroid plexus is tethered medially, and the
posterior choroid falls in a dependent fashion.

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B. TransthalamicView
Classicplaneinwhichthebiparietaldiameter(BPD)and
thefetalheadcircumference(HC)aremeasured.
TheCSP,thethalamiandthesymmetryofthe
cerebralhemispherescanbeassessed.
Variousmidlinemalformationsassociatedwithabsence
oftheCSPcanbedetectedonthisview.
Holoprosencephaly and complete agenesis of the corpus
callosum, both featuring absence of the CSP and abnormal
lateral ventricles.

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AXIAL PLANE
Transthalamic View

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Transthalamic View

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Transthalamic View

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AXIAL PLANE
TranscerebellarView

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C. Transcerebellar View
Usedtoassesstheposteriorcranialfossaandtherelated
structures,namelythecerebellum,thecisternamagna
andthefourthventricle.
Itisthereforepossibleonthisviewtodemonstratethe
anomaliesofthesestructures,suchasabnormalwidthof
theposteriorcranialfossa(ChiariIImalformation,Dandy–
Walkercontinuum)and/orthepresenceofa‘cyst’inthe
posteriorfossa.

29. Asforthecisternamagna,thedistancebetweenthe
posteriormarginofthecerebellarvermisandtheinternal
occipitalbonesurfaceshouldbemeasured.Thenormal
rangeis3–10mm.
Thescreeningexaminationforthedetectionofposterior
fossaabnormalitiesshouldnotbeperformedbefore19–21
weeks’gestation.
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C. Transcerebellar View

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TranscerebellarView

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TranscerebellarView

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Fig -Posterior fossa or transcerebellar view: Axial US image of a fetus at
18 weeks gestation at the level of the thalamus or midbrain with the
transducer tilted inferiorly toward the occiput depicts normal anatomy,
including the cisterna magna (calipers), which should measure less than 10
mm, the bilobed cerebellum (dashed arrows), the cerebellar vermis
(arrowheads), which is slightly more echogenic, and the thalami (T).

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Fig -Falx view.

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Fig -Cavum view.

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39. Characterization of major
CNS anomalies

40. I.Developmental Anomalies
a. Neural tube defects
b. Neuronal migration disorders.
II.Posterior fossa Disorders
a. Dandy-Walker malformation
variants
b. Chiari II malformation.
III. Ventricular Anomalies
a. Aqueductal stenosis.
IV.Midline Disorders
a. Spectrum of
Holoprosencephaly.
b. Agenesis of the corpus
callosum.
c. Septo-optic Dysplasia.
V.Vascular Anomalies
a. Vein of Galen malformations.
VI.Miscellaneous Disorders
a. Hydranencephaly,
b. Porencephaly, tumors, and
intracranial hemorrhage.
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CNS abnormalities can be organized into six main
categories at prenatal US.

41. III. Characterization of major anomalies
IV.Midline Disorders
Multiplecongenitalmalformationscanresultfrom
incompleteseparationofthetwohemispheres
andabnormalformationofthecorpuscallosum.
Thesemalformationsconstitutesomeofthemost
commonbrainabnormalitiesandmayresultinfetal
demise.
Theyarefrequentlyassociatedwithmidlinefacial
anomalies,leadingtotheadagethat“facepredicts
brain.”
Midlineanomaliesencompassesaheterogeneousgroup
ofconditions.
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42. IV.Midline Disorders
IVc.Agenesis of the Corpus Callosum
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43. Corpus Callosum
Thelargestcommissuralwhitematterbundle.
(it extends from the frontal lobe anteriorly to above the
collicularplate posteriorly)
Abroadshapedbandofwhitefibersthatconnectthe
cerebralhemispheres.Itconsistsofthe
Rostrum–anteriorandinferior.
Genu–anterior.
Body-b/ngenuandsplenium.
Splenium–posterior.
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45. IV.Midline Disorders
IVc. Agenesis of the Corpus Callosum
Introduction
Hypoplasia, Hyperplasia, Agenesis, and Dysgenesis.
Agenesis of the corpus callosum (ACC) can be complete (CACC)
or partial (PACC).
Incidence
From 0.3–0.7% in the general population to 2–3% in the
developmentally disabled population.
Pathogenesis
Formation of the corpus callosumand organogeneticsequence.
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46. Ultrasound Diagnosis
ACC -commonly associated with a hypoplasticor absent
cavum septipellucidi.
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47. Suspicion of ACC (Indirect sign of ACC)
Absent cavum septi pellucidi
Colpocephaly.
Hypoplasia of the cingulus.
Increased separation of the hemispheres with a prominent
interhemispheric fissure.
Parallel bodies of the LV which are shifted laterally and an
abnormal third ventricle (dilated, elevated or dorsally
displaced).
Gyri –“sunray appearance” on the sagittal plane.
Color Doppler study may show an abnormal course of
percallosal arteries.
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Fig -Axial gray-scale US image of a fetus at 18 weeks gestation
shows absence of the CSP (arrow) between the frontal horns of
the lateral ventricles

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Fig -Color Doppler scan showing the
normal course of the pericallosal artery.
Fig -Agenesis of the corpus callosum: the
semicircular loop of the pericallosal artery
is absent; the same image reveals sulci
and gyri radiating superiorly from the
region of the third ventricle.

50. Definitive Diagnosis (Direct Sign)
Absence of the corpus callosum.
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The presence of these anomalies can be
recognized only from the late 2
nd
trimester
onwards, with late development of the sulci
and gyri on sagittal plane only.

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Fig -Sagittal scan of a normal fetal brain
showing the entire corpus callosum
Fig -Sagittal scan of the fetal brain
demonstrating absence of the corpus
callosum .

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Fig -Coronal scans of the fetal brain demonstrating
(a) absence of the corpus callosum and the presence
of an interhemispheric cyst communicating with the
third ventricle and (b) the presence of a midline
lipoma.

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Fig -Partial agenesis of the corpus callosum: three-dimensional
ultrasound image (midsagittal plane) of the fetal brain showing partial
formation of the corpus callosum.

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Fig -Magnetic resonance image
(MRI) sagittal view of the normal
fetal brain (T2-weighted)
Fig -Complete agenesis of the
corpus callosum: MRI (sagittal
view, T2-weighted) of the fetal
brain showing complete absence
of the corpus callosum and the
third ventricle communicating
with the interhemispheric fissure.
Fig -Sagittal T1-
weighted MR image
shows an
intracranial lipoma as a
posterior midline mass

55. Ddx for ACC.
Borderline ventriculomegaly
Association with other malformations
Risk of associated brain anomalies.
Risk of associated extra-CNS abnormalities is high (up-to
60%).
Risk of chromosomal anomalies.
This is relatively high (20% of cases): trisomy 13 and 18.
Risk of non-chromosomal syndromes.
This is high.
Obstetric management –
Should ACC be diagnosed in a fetus, karyotyping is mandatory,
because of the high risk of a chromosomal anomalies..
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56. Prognosis, survival and quality of life.
Noneurologicproblems,despitetheabsenceofcallosal
fibers.
Regardlessoftheassociatedanomalies,significant
neurodevelopmentaldelaydevelopsinaconsistent
proportionofcases(15–28%).
Subtleneuropsychologic,perceptual,andmotordefects
canemergelaterinlife,sinceallindividualswith
CACC/PACChavesomeneuropsychologicalsymptom.
Most need special education.
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57. III. Characterization of major anomalies
II. Posterior cranial fossa malformations
The classification of cerebellar malformations is controversial –no
widely accepted agreementhas been reached, despite many
attempts.
However, based on a morphologic ultrasound approach, it is at
least possible to differentiate posterior fossa anomalies into two
broad categories:
(i)Cystic malformations, characterized by the presence of an
evident CSF collection in the posterior fossa resulting from
active expansion of CSF spaces, and
(ii)Non-cystic malformations, in which either there is no increase
of CSF or the widening of the spaces is passive, i.e. resulting
from defective cerebellar development.

58. (I) Cystic Posterior Fossa
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Inthefetus,cysticanomaliesareeasilyrecognizableinthe
axialtranscerebellarplane.
Differentialdiagnosiscanbeparticularlydifficultbecausethe
recognitionofthesubtleanatomicfeaturesthatdifferentiate
themmaybechallengingorsometimesimpossible.
This is why a midsagittal section of the fetal brain is
required for accurate anatomic assessment of the posterior
fossa.
Cystic anomalies of the posterior fossa –DWM,
DWv, BPC, MCM and AC.

59. III. Characterization of major anomalies
II. Posterior cranial fossa malformations
I . Cystic Posterior Fossa
A. Dandy–Walker Malformation
-Amalformation consisting of a cystic enlargement of the
fourth ventricle associated with partialor complete
agenesis of the vermis.
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60. Dandy–Walker Malformation
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The four characteristic signs identifying classic DWM are:
(i)Complete or Partial Agenesis of the vermis;
(ii)Cystic Dilatation of the Fourth ventricle;
(iii)Enlarged Posterior Fossa with upward displacement of the Tentorium;
(iv)Anticlockwise Rotation of the HypoplasticVermis.

61. Dandy–Walker Malformation
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Epidemiology
-Incidence –1:25,000 –1:30,000.
-1% -4% of all cases of hydrocephalus.
-Slight female predominance
Pathophysiology
ThepathophysiologicalmechanismunderlyingtheDandy–Walkercomplex
isnotclearlyelucidated.Initially,itwasproposedthatcongenital
obstructionoftheforaminaofLuschkaandMagendieresultedincystic
dilatationofthefourthventricleandtheresultingmalformedposterior
fossa.
In later studies investigators have suggested that it is a manifestation of
abnormal development of the rhomboencephalon, with incomplete
formation of the vermis, or due to a defect within the telachoroidea, which
leads to cystic dilation of the fourth ventricle.

62. Ultrasound Diagnosis
-ThefirststepsinreachingacorrectdiagnosisofDWMare
differentiationbetweenadilatedfourthventricleand
extraventricularcystsanddistinguishingamongavarietyof
cerebellarvermiandysgenesissyndromes
(i)Complete or Partial Agenesis of the vermis;
(ii)Cystic Dilatation of the Fourth ventricle;
(iii)Enlarged Posterior Fossa with upward displacement of
the Tentorium;
(iv)Anticlockwise Rotation of the HypoplasticVermis.
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Dandy–Walker Malformation

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Fig -Axial gray-scale US image of a fetus at 21
weeks gestation shows a dilated cisterna magna
(arrow) communicating with the fourth ventricle
(arrowhead).
Fig -Axial FLAIR MR image
obtained after delivery on the
1st day of life demonstrates a
dilated cisterna magna (arrow)
communicating with the fourth
ventricle.

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Fig -Axial scan of the posterior fossa showing
a cystic dilatation of the fourth ventricle
(arrows) and a V-shaped cerebellum due to a
vermian defect.
Fig -Sagittal scan of the posterior fossa showing
an upward displacement of
the tentorium (TN), a cystic dilatation of the
fourth ventricle (thin arrow), and a rotation
(curved arrow) of a partially agenetic vermis;
the big arrow indicates the corpus callosum.

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Association with other Malformations

66. Risk of chromosomal anomalies.
This is high, with up to 35% of cases being associated with aneuploidy,
mainly trisomies18 and 13.
Risk of non-chromosomal syndromes.
This is high.
Postnatal treatment.
There is obviously no treatment of the primary vermianlesion. The
virtually ubiquitous secondary obstructive hydrocephalus may be
treated with a cystoperitonealshunt.
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67. Prognosis, survival and quality of life.
DWM is associated with late-onset hydrocephalus in about 80%
of cases.
If hydrocephalus develops, whether in utero or in the neonatal
period, there is a mortality rate of over 60%, with most survivors
having a low IQ.
In most DWM series, approximately 40% of the children were
intellectually normal, 40% were severely retarded, and 20% had
borderline mental retardation.
However, a review of DWM outcome has shown that isolated
forms have a better intellectual prognosis and lower mortality.
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68. Conclusion

69. FetalCNSabnormalitiesarealeadingcauseofinutero
mortalityandpostnatalmorbidity,andaccurate
prenataldiagnosiswithUSisessentialforappropriate
management.
Thiscanbeaccomplishedbyusingstandardizedviews
tohelpidentifynormalanatomyanddepictfeaturesof
commonanduncommonanomalies.
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70. END