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Lecture 10
Ultrasound Evaluation of the Fetal Neural Axis
Holdorf
OBSTETRICAL ULTRASOUND
PART I
Take-a-ways…
 The Banana Sign
 “Bent” Cerebellum
 The part of the brain at the back of the skull in
vertebrates. Its function is to coordinate and
regulate muscular activity.
 Absent Cisterna Magna
 One of three principal openings in the subarachnoid
space between the arachnoid and pia mater layers
of the meninges surrounding the brain. The
openings are collectively referred to as cisterns.
 The Lemon Sign
 Frontal bossing of the cranium
 Temporal bones
The Banana Sign explained:
 Seen on axial imaging through the posterior
fossa and is associated with Chiari II
Malformation. The Banana sign describes the
way the cerebellum is wrapped tightly around
the brain stem as a result of spinal cord
tethering and downward migration of
posterior fossa content. The cisterna magna
gets obliterated and the shape of the
cerebellum takes on the appearance of a
banana. This sign persists into the second and
third trimesters.
The Lemon sign explained:
 The lemon sign is the medial inward
displacement and scalloping of the frontal
bones of the fetal calvarium. This is often
associated with an open spina bifida (seen
under ultrasound as the widening and
flattening of the posterior elements of the
spine.
The formation of the Neural
Axis
The stuff that is always on
the boards…
The lateral, 3rd, and 4th
ventricles
Ventriculomegaly
 Ventriculomegaly is a brain condition that
occurs when the lateral ventricles become
dilated. The most common definition uses a
width of the atrium of the lateral ventricle
of greater than 10 mm. This occurs in
around 1% of pregnancies. When this
measurement is between 10 and 15 mm,
the ventriculomegaly may be described as
mild to moderate.
Ventriculomegaly
 When the measurement is greater than
15mm, ventriculomegaly may be classified as
more severe.
 Enlargement of the ventricles may occur for a
number of reasons, for example due to loss of
brain volume (perhaps due to infection or
infarction), or due to impaired outflow or
absorption of cerebrospinal fluid from the
ventricles.
 Often, however, there is no identifiable
cause. This diagnosis is generally found in
routine fetal anomaly scans at 18–22 weeks
gestation. It is one of the commonest
abnormal brain findings on prenatal
ultrasound, occurring in around 1-2 per 1000
pregnancies.
 In many cases of mild ventriculomegaly,
however,
there
is
resolution
of
ventriculomegaly during the pregnancy.
 Ventriculomegaly is also known to be
associated with other malformations such as
agenesis of the corpus callosum (a broad
band of nerve fibers joining the two
hemispheres of the brain), spina bifida, and
heart defects.
 Fetuses with both isolated ventriculomegaly
and with other anomalies have an increased
risk of having a chromosomal abnormality,
including that of Down Syndrome .
Anencephaly
 Cephalic disorder that results from a neural tube
defect that occurs when the cephalic (head) end
of the neural tube fails to close, usually between
the 23rd and 26th day of pregnancy, resulting in
the absence of a major portion of the brain, skull,
and scalp. Children with this disorder are born
without a forebrain, the largest part of the brain
consisting mainly of the cerebral hemispheres
(which include the isocortex, which is responsible
for higher level cognition, i.e., thinking). The
remaining brain tissue is often exposed - not
covered by bone or skin.
Anencephaly
Spina bifida
 (Latin: "split spine") is a developmental birth
defect involving the neural tube: incomplete
closure of the embryonic neural tube results
in an incompletely formed spinal cord.
 In addition, the vertebrae overlying the open
portion of the spinal cord do not fully form
and remain unfused and open.
Spina Bifida
 The spinal opening allows the abnormal
portion of the spinal cord to protrude through
the opening in the bones.
 There may or may not be a fluid filled sac
surrounding the open spinal cord.
 Other
neural tube defects include
anencephaly, a condition in which the portion
of the neural tube which will become the
cerebrum does not close, and encephalocele,
which results when other parts of the brain
remain unfused
 Spina bifida malformations fall into three categories: spina
bifida occulta, spina bifida cystica (myelomeningocele), and
meningocele.
 The most common location of the malformations is the
lumbar and sacral areas of the spinal cord. Myelomeningocele
is the most significant form and is that which leads to
disability in most affected individuals. The terms spina bifida
and myelomeningocele are usually used interchangeably.
 Spina bifida can be surgically closed after birth, but this
does not restore normal function to the affected part of the
spinal cord and an individual with this condition will have
dysfunction of the spinal cord and associated nerves from
the point of the open defect and below. Intrauterine
surgery for spina bifida has also been performed and the
safety and efficacy of this procedure is currently being
investigated.
Holoprosencephaly
 A type of cephalic disorder. This is a disorder
characterized by the failure of the prosencephalon
(the forebrain of the embryo) to develop.
 During normal development the forebrain is formed
and the face begins to develop in the fifth and sixth
weeks of human pregnancy. (The condition also
occurs in other species, as with Cy, the Cyclops
kitten.)
 Holoprosencephaly is caused by a failure of the
embryo's forebrain to divide to form bilateral
cerebral hemispheres (the left and right halves of the
brain), causing defects in the development of the
face and in brain structure and function.
Holoprosencephaly
Dandy-Walker syndrome
 DWS, or
Dandy-Walker complex, is a
congenital brain malformation involving the
cerebellum and the fluid filled spaces around
it.
 The Dandy-Walker complex is a genetically
sporadic disorder that occurs one in every
25,000 live births, mostly in females.
Dandy-Walker
Syndrome/absent pons
and cerebellum in 7y/o
 The key features of DWS are an enlargement of
the fourth ventricle, the space containing
cerebrospinal fluid between the medulla and the
cerebellum, a partial or complete absence of the
cerebellar vermis, the posterior midline area of
cerebellar cortex responsible for coordination of
the axial musculature, and cyst formation near
the internal base of the skull.
 An increase in the size of the fluid spaces
surrounding the brain as well as an increase in
pressure may also be present. The syndrome can
appear dramatically or develop unnoticed.
And now…the other stuff
Chapter 10 outline
Neural Tube Defects (NTD)
 Spina Bifida
 Anencephaly
 Encephalocele
 Iniencephaly
Intracranial Abnormalities












Hydrocephaly (Ventriculomegaly)
Hydranencephaly
Holoprosencephaly
Porencephaly
Dandy-Walker Syndrome
Agenesis of the Corpus Callosum
Schizencephaly
Lissencephaly
Choroid Plexus Cysts
Choroid Plexus Papillomas
Microcephaly
Intracranial Tumors
Terminology
Rachischisis: Completely open spine with Herniation
and or destruction of the spinal cord
Spina Bifida occulta: Failure of closure of the vertebral
column
without
any
associated
external
abnormalities. Rarely associated with neurologic
complications.
Spina Bifida Apperta: Failure of closure of the vertebral
column with apparent external abnormalities and
neurologic complications
Meningocele: Herniation of the meninges through a
schisis defect
Myelomeningocele: Herniation of the mengenges and
neural tissue through a schisis defect.
Neural Tube Defects
 On the boards since 1991. There are MANY
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questions regarding NTDs…study this!!!!
A gamut of CNS anomalies may result from a failure
of the normal process of Neurulation (Embryology).
The lesions are frequently open.
This allows CSF to pour into the amniotic cavity,
causing elevation of the maternal serum and
amniotic fluid levels of AFP.
Routine prenatal testing that reveals elevated
MSAFP levels is and indication for a level II
sonogram.
When the sonogram does not find the cause of
elevated AFP, an amniocentesis is recommended.
Spina Bifida
Is a general term for lack of closure of the vertebral column.
Prognosis depends on the severity of the lesion.
Pathology
 Presence of a Myelomeningocele, a protruding sac which may
contain meninges and spinal cord.
 May occur anywhere along the spinal column but lumbar region is
most common.
 Variable in size and content.
 Sonographic findings in Transverse view:
 Splaying of posterior ossification centers into a U or V shape.
 When sac is intact, a cystic structure may be seen extending from
the back. Appearances include a small cystic structure, a cyst with
septations and or solid matter.
 Sonographic Findings on Sagittal View:
 Splaying of parallel lateral ossification centers
 Soft tissue defect or discontinuity of skin and
muscle of posterior back
An image of a Myelomeningocele in Transverse view
Splayed ossification centers in transverse view.
Soft tissue defect or discontinuity of skin and muscle of posterior
back on Sagittal view.
Spina Bifida Continued…
Intracranial
 Lemon sign-frontal bossing of cranium
 Banana sign-dislocated cerebellum and
obliteration of the cistern magna
 Chiari type II malformation-variable displacement
of cerebellum, 4th ventricle and medulla oblongata
through the foramen magnum
The lemon and Banana signs
The lemon sign
ANENCEPHALY
 Anencephaly occurs at 2-3 weeks when the
anterior neuropore fails to fuse.
 Pathology
 Absence of cranial vault and cerebral hemispheres
(functioning brain)
 Portions of midbrain and brain stem may be present
 Other features include bulging eyes, macroglossia and
a very short neck.
 Sonographic findings
 Fetal head should be identifiable by 12 weeks,
definitively by 15 weeks.
 Major portions of cranium and intracranial structures
are absent: orbits and face are usually present
 Associated Polyhydramnios in half the cases
Anencephaly
Encephalocele
 Protrusion
of the intracranial contents
through a bony defect of the skull can also be
called a cephalocele.
 Occipital encephaloceles are most frequent.
There is a defect in the cranium.
Pathology
 Boney defect in calvarium with herniation of
brain and or meninges outside of cranium
 Classified as occipital, frontal, or parietal
 Hydrocephalus is present 80 % of the time in
occipital lesions.
Sonographic findings
 Mass extending from calvarium, may be totally
cystic,
have
some
meninges
(cranial
Meningocele,
or
may
contain
brain
(encephalocele)
 Cranial disruption is occasionally seen
 Associated with hydrocephalus, Polyhydramnios
Encephalocele
Iniencephaly
 Iniencephaly is a dramatic NTD characterized
by an exaggerated spinal Lordosis, cervical
Rachischisis and an occipital encephalocele
Sonographic findings
 Exaggerated, hyperextension of the fetal
head
 Demonstration of cervical spina bifida
Iniencephaly
Iniencephaly

A type of cephalic disorder. It is a rare neural tube defect that
combines extreme retroflexion (backward bending) of the head
with severe defects of the spine.
 The affected infant tends to be short, with a disproportionately
large head. Diagnosis can be made immediately after birth
because the head is so severely retroflexed that the face looks
upward. The skin of the face is connected directly to the skin of
the chest and the scalp is directly connected to the skin of the
back. Generally, the neck is absent.
 Most individuals with iniencephaly have other associated
anomalies such as anencephaly, encephalocele (a disorder in
which part of the cranial contents protrudes from the skull),
hydrocephalus, cyclopia, absence of the mandible (lower jaw
bone), cleft lip and palate, cardiovascular disorders,
diaphragmatic hernia, and gastrointestinal malformation. The
disorder is more common among females.
Iniencephaly
Intracranial Abnormalities
Hydrocephaly AKA Ventriculomegaly
 Dilatation of the ventricular system secondary to the
increase in the amount of CSF.
Classifications
 Aqueductal Stenosis is the cause 43% of the time
 Hydrocephalus caused by narrowing of the aqueduct of
Sylvius (3rd ventricle outflow)
 Communicating hydrocephalus is the cause 38% of the time
 Dilatation of all ventricles and subarachnoid space caused
by an obstruction to CSF follow outside the ventricular
system.
 Dandy-Walker Syndrome is the cause 12% of the time
 Idiopathic in 7% of the time Cause unknown
Bilateral ventriculomegaly
diagram of the ventricular system, showing the lateral
ventricle, the third ventricle, and the fourth ventricle.
Ventriculomegaly cont…
Sonographic findings
In the first trimester
 CSF seen in the lateral ventricle and possibly compressing
choroid plexus
In the 2nd and 3rd trimester
 Normal ventricular configuration…just dilated
 Presence of excess fluid in lateral ventricles, with an atrial
measurement exceeding 10mm
 Dangling choroid plexus
 Observe brain echogenicity-echogenic foci in parenchyma may
suggest intrauterine infection
 Can have Polyhydramnios, abnormal fetal lie, fetal ascites,
encephalocele, and Dandy-Walker.
An image measuring the atrial measurement exceeding 10mm
a “Dangling”
choroid plexus.
DEFINE FILLY’s RULE

Ventriculomegaly is a brain condition that occurs when the lateral
ventricles become dilated. The most common definition uses a width of
the atrium of the lateral ventricle of greater than 10 mm. This occurs in
around 1% of pregnancies. When this measurement is between 10 and
15 mm, the ventriculomegaly may be described as mild to moderate.
When the measurement is greater than 15mm, the ventriculomegaly
may be classified as more severe. Enlargement of the ventricles may
occur for a number of reasons, such as loss of brain volume (perhaps due
to infection or infarction), or impaired outflow or absorption of
cerebrospinal fluid from the ventricles. Often, however, there is no
identifiable cause. The interventricular foramen may be congenitally
malformed, or may have become obstructed by infection, hemorrhage,
or rarely tumor, which may impair the drainage of cerebrospinal fluid,
and thus accumulation in the ventricles. This diagnosis is generally found
in routine fetal anomaly scans at 18–22 weeks gestation. It is one of the
more common abnormal brain findings on prenatal ultrasound,
occurring in around 1–2 per 1000 pregnancies. In many cases of mild
ventriculomegaly, however, there is resolution of ventriculomegaly
during the pregnancy
DEFINE FILLY’s RULE
Hydranencephaly
 Means “water, no brain”. Total or near total
absence of the cerebral hemispheres. Cause
could be intrauterine infarction secondary to
bilateral ICA occlusion or malformation.
Sonographic findings
 Microcephaly
 Large anechoic areas in cranial vault
 Variable presence of 3rd ventricle
 Polyhydramnios
Hydranenephaly
HOLOPROSENCEPHALY (this is
always on the boards)
Three classifications
1. Alobar (Most severe)
 Large single cavity with minimal amount of cerebral
tissue surrounding it, fused thalami, and facial
syndrome with hypotelorism and other craniofacial
anomalies
2. Semilobar
 More cerebral tissue is present. Occipital lobe is
present. Associated cleft palate and cleft lip
3. Lobar
 Interhemispheric fusion is developed, but there is
variable degree of fusion and CSP is absent
Sonographic findings
 Fetal cranium appears as a large cystic space
with some peripheral cerebral tissue
 Presence of a single midline ventricle
 Craniofacial abnormalities including a
proboscis, severe hypotelorism, Cycolpia
 Appearance varies with severity of
malformation.
. Alobar (Most severe)
 In Holoprosencephaly, remember this
hint…”THE FACE PREDICTS THE BRAIN”.
Porencephaly
The presence of cystic areas within the cerebral
parenchyma. The etiology is believed to be
the result of lysis of in-utero intracranial
hemorrhage or cystic encephalomalacia.
Sonographic findings
 Simple cystic structures within the cerebral
parenchyma.
Porencephaly
 A type of cephalic disorder involving an extremely rare disorder
of the central nervous system involving a cyst or cavity in a
cerebral hemisphere. The cysts or cavities are usually the
remnants of destructive lesions, but are sometimes the result of
abnormal development.
 Porencephaly most likely has a number of different, often
unknown causes, including absence of brain development and
destruction of brain tissue.
 More severely affected infants show symptoms of the disorder
shortly after birth, and the diagnosis is usually made before age
1. Signs may include delayed growth and development, slight or
incomplete paralysis, decreased muscle tone, seizures and
macrocephaly or microcephaly.
 Individuals with porencephaly may have poor or absent speech
development, epilepsy, hydrocephalus, spastic contractures
(shrinkage or shortening of muscles), and mental retardation.
Porencephaly
Dandy-Walker Syndrome
Indicates the association of the following:
 Large Cistern Magna
 Ventriculomegaly of varying degree
 Cerebellar Vermain Agenesis (complete or partial), through
which the 4th ventricle communicates with the cystic
structure in the posterior fossa.
 There is obstruction of the 4th ventricle outflow and
subsequent cystic enlargement of the posterior fossa.
Sonographic findings
 Large midline cystic structure in posterior fossa
 Enlargement of posterior fossa
 Assoc. with ventriculomegaly and Polyhydramnios
Dandy-Walker Syndrome/fluid
filled spaces in the
posterior fossa
Agenesis of the Corpus Callosum
 Absence of the corpus callosum results from a
chromosomal abnormality. May be complete or
partial. Is frequently associated with other
syndromes and or anomalies.
Sonographic findings
 Absent Cavum septum Pellucidum
 Lateral ventricles displaced upward and outward
with a teardrop shape.
 Enlarged occipital horn
 3rd ventricle enlarged and displaced superiorly.
The corpus Callosum
 The corpus callosum (from Latin: "tough
body"), is a wide, flat bundle of neural fibers
beneath the cortex at the longitudinal
fissure. It connects the left and right cerebral
hemispheres and facilitates inter-hemispheric
communication. It is the largest white matter
structure in the brain.
Teardrop ventricle with Agenesis of
the Corpus Callosum
Schizencephaly
 Abnormal clefts in the cerebral hemispheres.
 The brain appears split into anterior and
posterior parts
Schizencephaly
 A rare developmental disorder characterized by abnormal slits, or
clefts, in the cerebral hemispheres.
 Schizencephaly can be distinguished from porencephaly by the
fact that in schizencephaly the cyst is lined by heterotopic grey
matter while a porencephalic cyst is lined by white matter.
Individuals with clefts in both hemispheres, or bilateral clefts, are
often developmentally delayed and have delayed speech and
language.
 Individuals with smaller, unilateral clefts (clefts in one
hemisphere) may be weak on one side of the body and may have
average or near-average intelligence.
 Patients with schizencephaly may also have varying degrees of
microcephaly, mental retardation, hemiparesis (weakness or
paralysis affecting one side of the body), or quadriparesis
(weakness or paralysis affecting all four extremities), and may
have reduced muscle tone (hypotonia). Most patients have
seizures and some may have hydrocephalus.
Schizencephaly/destructive brain
lesion
Lissencephaly
 The surface of the brain lacks the normal sulci and
gyri and appears smooth. Diagnosis is not made until
the 3rd trimester.
Choroid Plexus cyst
 The significance is an infrequent association with
aneuploidy (Trisomy 18). Can be lateral, bilateral,
small, large…
Choroid plexus Papillomas
 Are benign tumors of the choroid plexus. Most
frequently are unilateral and occur at the level of the
atrium of the lateral ventricle. They are frequently
associated with hydrocephalus
Lissencephaly
Choroid Plexus cyst
Microcephaly
 Considered a symptom of many etiologic
disturbances. Defined as a small head
circumference below 3 standard deviations of
normal.
Sonographic findings
 Small HC (other parameters are normal)
 Sloping forehead, and disproportion between
size of face and skull
Microcephaly
Intracranial tumors
 Rare.
 Teratomas are the most common.
 Prognosis is dismal
Sonographic findings
 Loss of normal intracranial architecture
 Presence of space-occupying lesion
Intracranial Tumor
Homework
1. Rhombencephalon: what is it, and how is it
visualized by ultrasound?
2. The ventricular system: Draw and label the
ventricle system
3. Choroid plexus: what are they, what do they
do, and where are they located in the brain?
4. Ventriculomegaly: how is it defined? Show this
with an image. What is measured? What are
the upper limits of normal? What
measurement is considered abnormal?
5. Define hydrocephalus
6. Is hydrocephalus usually isolated? Explain
7. Are there any surgical options available for
the parents of the fetus diagnosed with
intrauterine hydrocephalus?
8. Spina Bifida: Define occulta and aperta.
9. What is myeolmeningocele?
10.What is Arnold-Chiari or Chiari Type II
malformation?
11. What is the banana sign?
12. What is the lemon sign?
13. Define a Cephalocele.
14. What is a cranial Meningocele?
15. What is an encephalocele?
16. Define Holoprosencephaly.
17. What is agenesis of the Corpus Callosum?
18. What is Dandy-Walker Complex?
19. What is porencephaly?
20. What is Hydranencepahly?
21. What is Microcephaly?
22. Is there such a thing as intracranial
calcification? Explain.
23. Please discuss the occurrence of choroid
plexus cysts.