CHAPTER 24- THE FETAL HEAD AND BRAIN (Penny)

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''dangling choroid'' sig describes the echogenic choroid plexus, hanging limp and surrounded by CSF, within the dilated lateral ventricle.

Vein of Galen Aneurysm

-A arteriovenous malformation that occurs within the fetal brain and is associated with congestive heart failure -anechoic mass within the midline of the brain that contains turbulent arterial and venous flow when interrogated with pulsed and color doppler. -fetal hydrops -cardiomegaly (caused by cardiac overload)

Hydranencephaly

-A fatal condition in which the entire cerebrum is replaced by a large sac containing CSF. the falx cerebri may be partially or completely absent whereas the brain stem and basal ganglia are maintained. the thalamus may be seen. THERE WILL BE NO CEREBRAL CORTEX IDENTIFIED.

Lobar holoprosencephaly

-The least severe form of the holoprosencephaly severe mental retardation. Trisomy 13-patau syndrome, is present in 50-70% of fetuses diagnosed with holoprosencephaly.

Agenesis of the Corpus Callosum and Cavum Septum Pellucidum

-bridge of tissue located within the midline of the brain that connects the two cerebral hemispheres. -completely formed by 18 weeks. -CSP, located inferior to the corpus callosum. most often if corpus callosum is absent, CSP is absent.

Fetal Intracranial Hemorrhage

-worry for premature infants weighing less than 1500 g or born before 32 weeks gestation. -Maternal use of cocaine, trauma and hx of amniocentesis. -most common risk factor; maternal platelet disorders. -most often in the germinal matrix - can also occur within the parenchyma of the brain.

Different types of cephaloceles and their contents

Meningocele - meninges only Encephalocele - brain tissue only Encephalomeningocele - meninges and brain tissue Encephalomeningocystocele - meninges, brain tissue, lateral ventricle

Arnold-Chiari II malformation - posterior fossa abnormality

Obliterated cisterna magna Banana shape cerebellum Lemon shape skull

corpus callosum - a thick band of tissue communicated with RT & LT halves of the brain

The cerebral hemisphere are linked in the midline by;

interhemispheric fissure

The cerebrum can be further divided into a right and left hemispheres by the;

Trisomy 18 (Edwards Syndrome)

The choroid plexus cyst could be associated with an increase risk of?

Sonographic Findings of Ventriculomegaly

Atrium of the lateral ventricle measures > 10 mm Atrial measurement > 15 mm is considered moderato Marked ventriculomegaly. Dangling choroid sign Dilatation of any part of the ventricular system

Transcerebella Measurement (posterior fossa)

The depth of the cisterna magna should not measure more than 10 mm or less than 22 in the transcerebellar plane. Measurement more than 10 mm is consistent with mega cisterna magna and Dandy-Walker complex whereas a measurement of less than 2 mm is worrisome for Arnold-Chiari II malformation.

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The resistance pattern of the MCA should be greater than that of the umbilical artery and thus should be compared when fetal shunting is suspected.

Holoprosencephaly

midline brain anomaly that is associated with not only brain aberrations but also atypical facial structures. -alobar, semilobar, lobar alobar holoprosencephaly is the most severe form, often result in neonatal death.

The Cavum Septum Pellucidum (CSP)

midline brain structure, anterior portion of the brain between the frontal horns of the lateral ventricles. anechoic box shaped structure in the axial scan plane. CSP should be seen between 18-37 weeks. CSP doesn't communicate with the ventricular system. its absence is associated with cerebral malformations including agenesis of the corpus callosum.

Acrania

one of the most common neural tube defects. absence of the cranial vault above the bony orbits. -elevated MSAFP -fatal -frog like facies or bulging eyes -Some cerebral tissue may be present two types; - anencephaly(there are no cerebral hemispheres) -exencephaly(normal amount of cerebral tissue)

Lambdoidal suture

parietal bones and occipital bone

Squamosal sutures

parietal bones and temporal bones

Cephalocele

protrusions of intracranial contents through a defect in the skull The most common location is in the occipital region. common findings in Meckel-Gruber syndrome. possibly elevation of MSAFP -open cranial defect - (posterior) -small or obliterated cisterna magna -complex or simple appearing mass protruding from the cranium

Porencephaly

rare condition in which a cyst communicates with the ventricular system. can occur after fetus experiences hemorrhage within the one or both of the cerebral hemispheres. -communication with the lateral ventricle of the affected side.

The Corpus Callosum

should be completely intact between 18-20 weeks. connects two lobes of the cerebrum. fetal development of the corpus callosum is anterior to posterior. echogenic band of tissue within the midline of the brain connecting the two cerebral hemispheres.

Lissencephaly

smooth brain- no gyri within the cerebral cortex. Sono findings; lack of sulci and gyri within the cerebrum

Coronal suture

the frontal and two parietal bones

aqueductal stenosis

the most common cause of hydrocephalus in utero is;

Lambda

the posterior fontanel when completely filled with bone referred to as;

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With agenesis of the corpus callosum, the sulci tend to have a more perpendicular or radial arrangement, and often appear to have a ''spoke wheel'' pattern.

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With holoprosencephaly, there will be evidence of a horseshoe shaped monoventricle, and the lobes of the thalamus may be fused and echogenic in appearance.

fourth ventricle

With what structure does the posterior fossa cyst associated with DWM communicate?

Dandy-Walker malformation - posterior fossa abnormality

Enlargement of the cisterna magna >10 mm in the anteroposterior dimension Absent cerebellar vermis Enlarged fourth ventricle

Schizencephaly

The development of fluid-filled cleft within the cerebrum is consisted with;

between the two lobes of the thalamus

The third ventricle is located;

Head shape: Strawberry

Trisomy 18 - Edwards Syndrome

Germinal Matrix

a group of thin-walled blood vessels and cells within the subependymal layer of the ventricles.

Craniosynostosis

premature closure of sutures, leads to an irregular shaped skull.

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AFP exits the fetus through an opening in the neural tube if one is present allowing for a greater amount to pass into the maternal circulation. Elevated levels of AFP are also found with omphalocele, gastroschisis, multiple gestations, fetal demise and incorrect gestational dating.

there is absence of the corpus callosum, CSP, third ventricle, interhemispheric fissure and falx cerebri.

Alobar holoprosencephaly is diagnosed when;

Foramina of Monro

CSF moves from the lateral ventricles into the third ventricle through the;

Head shape: Lemon

Chiari II malformation

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Choroid plexus, which is mostly located within the atria of the lateral ventricles is responsible for producing cerebrospinal fluid (CSF)

Colpocephaly

Enlargement of the frontal horns and narrowing of the occipital horns is termed;

Sonographic Findings of Schizencephaly

Fluid filled clefts within the cerebrum Agenesis of CSP and corpus callosum Ventriculomegaly

Porencephaly

Following an intracranial hemorrhage, a cyst is noted within the cerebrum that communicates with the lateral ventricles. This is referred to as;

Cranial Bones and their locations

Frontal bone - anterior Parietal bones - superior and lateral Temporal bones - inferior and lateral Occipital bone - posterior Sphenoid bone - lateral Ethmoid bone - anterior (between orbits)

metopic suture

Frontal bone along the midline of the forehead

Apert syndrome (acrocephalosyndactyly)

Genetic disorder that includes craniosynostosis, midline facial hypoplasia and syndactyly;

Danny walker malformation

What cerebral malformation is as a result of agenesis or hypoplasia of the cerebellar vermis?

Trisomy 13 (Patau Syndrome)

What chromosomal aberration is most often associated with holoprosencephaly?

metopic suture (frontal suture)

What fetal suture is located within the frontal bone along the midline of the forehead?

Hydranencephaly

a fluid filled cranium with absence of cerebral tissue is consistent with;

Arachnoid granulations / arachnoid villi

are responsible for the reabsorption of CSF into the venous system.

The Cerebellum

consist of RT and LT hemispheres that are coupled at the midline by cerebellar vermis. They become distorted with spina bifida and Arnold Chiari malformations.

Dandy-Walker Malformation

spectrum of posterior fossa abnormalities that involve the cystic dilatation of the cisterna magna and fourth ventricle. -abnormality in the roof of the fourth ventricle.

Fetal Intracranial Tumors

the most common - teratoma; contains tissues such as hair, sebum and fat - appear as complex masses and that distort the normal shape of brain. Choroid plexus papillomas - found within the choroid plexus and produce an increase in the production of CSF - leads to ventriculomegaly corpus callosum lipomas may be present with agenesis of the corpus callosum - appear as echogenic mass

CSP

typically be absent with agenesis of the corpus callosum;

Choroid Plexus Cyst

typically regress by the end of the third trimester. association with Trisomy 18. located within the choroid plexus of the lateral ventricle, measure more than 2 mm , appear round and anechoic, and have smooth walls.

lobes of the thalamus

what would not be normally located within the midline of the fetal brain?

Neural Tube Defects and The Brain

when the embryonic neural tube fails to close. Anencephaly and spina bifida are the most common neural defects.

noncommunicating hydrocephalus

when the obstruction lies inside the ventricular system

communicating hydrocephalus

when the obstruction lies outside the ventricular system

Fourth ventricle

would not be included in the correct level for an HC measurement;

Agenesis of the Corpus Callosum and Cavum Septum Pellucidum

Apert syndrome, holoprosencephaly, DWM, aqueductal stenosis, trisomy 18,8,13 are linked to

Anterior or Frontal

Bordered by the frontal and parietal bones Closure : by 18 months

Anterolateral or sphenoidal

Bordered by the frontal, parietal and sphenoid bones Closure: by 2 yr

Posterolateral or mastoid

Bordered by the mastoid and occipital bones Closure : b 2 yr

Occipitofrontal Diameter

Can be used in conjunction with the BPD to obtain the corrected BPD.

Head shape: Dolichocephaly - elongated

Craniosynostosis

Ventriculomegaly (Hydrocephalus)

Dangling choroid sign is associated with;

Foramina of Luschka

Lateral foramina out of 4th ventricle

Embryologic Development of the Fetal Brain

4.5 weeks - neural plate - the structure that will form the central nervous system has developed. The neural plate will give rise to the neural tube, which will become the spine and the brain.

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A cephalic index of less than 75 denotes a dolichocephalic shape, whereas index of more than 85 denotes a brachiocephalic shape.

Aqueductal Stenosis

Cerebral aqueduct (aqueduct of Sylvius) located between the third and fourth ventricles of the brain, may be narrowed preventing the flow of CSF from the third to the fourth ventricle. -third ventricle and both lateral ventricles will expand, fourth ventricle will remain normal.

Head Shape: Brachycephaly - round

Craniosynostosis Trisomy 21 and 18

Sonographic Findings of Dandy Walker Malformation

Enlargement of cisterna magna >10 mm in anteroposterior dimension communication of the enlarged cisterna magna with a dilated fourth ventricle agenesis or hypoplasia of the cerebellar vermis and varying degrees of ventriculomegaly

Mega cisterna magna - posterior fossa abnormality

Enlargement of the cisterna magna > 10 mm in the anteroposterior dimension. Normal cerebellum

Sonographic Findings of Mega Cisterna Magna

Enlargement of the cisterna magna >10mm in the anteroposterior dimension normal cerebellum and fourth ventricle

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If the cerebellar vermis is absent and the fourth ventricle is enlarged, then DWM must be suspected.

cyclopia monoventricle fused thalamus

Sonographic features of alobar holoprosencephaly;

Fontanelles or ''soft spots'' evaluation for intracranial hemorrhage or suspected brain anomalies.

Spaces that exist between the forming fetal bones are referred to as;

Head shape: Microcephaly - small

TORCH infection Trisomy 13 and 18 Meckel-Gruber syndrome Fetal Alcohol Syndrome

Falx cerebri

The double fold of dura mater that divides the cerebral hemispheres is the;

Anterior to the cerebellar vermis

The fourth ventricle is located;

intracranial calcifications

fetal cranial findings with TORCH infections;

Mega cisterna magna

A cisterna magna that measure 15 mm and a normal appearing cerebellum is most likely;

Thanatophoric dysplasia

A cloverleaf shaped skull is relate to;

Arnold-Chiari II malformation

A lemon-shaped skull is related to;

Mesocephaly

A normal shaped skull is termed;

Trisomy 18 (Edwards Syndrome)

A strawberry shaped skull is commonly associated with;

Sonographic Findings of Aqueductal Stenosis

Atrium of the lateral ventricle measures > 10 mm Atrial measurement > 15 mm is considered moderato Marked ventriculomegaly. Dangling choroid sign Dilatation of the lateral ventricles and the third ventricle; the fourth will remain normal.

Sonographic Findings of Porenchephaly

Cystic mass that communicates with the lateral ventricle Most often unilateral

Sonographic Findings of Hydranencephaly

Fluid filled cranium Absent/partially absent falx cerebri Maintained brain stem & basal ganglia No identifiable cerebral cortex

Sonographic Findings of Alobar Holoprosencephaly

Horseshoe shaped monoventricle Fused echogenic thalami Normal cerebellum and brain stem Absence of CSP, interhemispheric fissure, falx cerebri, corpus callosum, third ventricle

Head shape: Macrocephaly - big

Hydrocephalus Hydranencephaly Intracranial tumors Familial inheritance Beckwith-Wiedemann Syndrome

The Cerebrum

Largest part of the brain. contains multiple sulci and gyri. 6 cerebral lobes; the frontal lobe, two temporal lobes, two parietal lobes and the occipital lobe.

Sonographic Findings of Arnold-Chiari II Malformation

Lemon sign- lemon shaped cranium with flattened frontal bones. Banana sign- banana shaped cerebellum Obliterated cisterna magna Colpocephaly Enlarged massa intermedia Hydrocephalus Open spinal defect

The effects of fetal infections on the brain

Maternal serum screening for intrauterine infection resulting from; Toxoplasmosis Other agents Rubella Cytomegalovirus Herpes simplex virus cytomegalovirus is the most common.

Sonographic Findings of Agenesis of the Corpus Callosum and Cavum Septum Pellucidum

Partial or complete absence of the corpus callosum and absence of the CSP (after 18 weeks) 'Sunburst sign' - radial arrangement of the sulci which produces a 'spoke wheel' pattern. Colpocephaly- small frontal horn and enlarged occipital horns (tear drop shaped lateral ventricles) Elevated and dilated third ventricle.

Doppler of the Middle Cerebral Artery

Shown effective at evaluating hypoxia in a fetus that is measuring small for date. the normal cerebral circulation yields a high-impedance doppler pattern with continuous forward flow.

Enlarged massa intermedia Hydrocephalus Obliteration of the cisterna magna

Some of the sonographic findings of Arnold-Chiari II malformation;

Head shape: Cloverleaf

Thanatophoric dysplasia.

CSP, thalamus and falx cerebri

The BPD is obtained in the axial plane at the level of the;

CSP

The anechoic midline brain structure located between the frontal horns of the lateral ventricles is the;

Bregma

The anterior fontanel when completely filled with bone, is referred to as;

Corpus Callosum

The band of tissue that allows communications between the right and left cerebral hemispheres is the;

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The cerebellum will become displaced inferiorly and posteriorly and appear curved in the presence of spina bifida, which is referred to as the ''banana sign''

10 mm

The cisterna magna should not exceed ____ in the transcerebellar plane;

Colpocephaly

The condition in which the frontal horns are small and the occipital horns are enlarged is referred to as;

Third ventricle

The interthalamic adhesion (massa intermedia) passes through the;

Lissencephaly

The lack of sulci within the fetal cerebrum is a reliable indicator of;

innermost; pia matter middle ; arachnoid membrane outermost ; dura mater

The meninges are three protective tissues later that cover the brain and spinal cord;

HC

The most accurate measurement for estimating gestational age is;

aqueductal stenosis

The most common cause of hydrocephalus in utero is;

Alobar holoprosencephaly

The most severe form of holoprosencephaly is;

Cerebellar vermis

The structure located between the two lobes of the cerebellum is the;

Agenesis of the corpus callosum

The sunburst of the cerebral sulci is a sonographic finding of;

aqueduct of sylvius (cerebral aqueduct)

The third ventricle communicates with the fourth ventricle at the;

Suspicion of ventricular dilation occurs when the atrial diameter measures more than 10 mm.

Ventriculomegaly is the most common cranial abnormality.

Holoprosencephaly

What cerebral abnormality are atypical facia features most commonly associated with?

The Ventricular System

composed of 4 ventricles- provide cushioning for brain each ventricle lined by a membrane called the ependyma. The paired lateral ventricles are located on both sides of the falx cerebri within the cerebral hemispheres. Each lateral ventricle consist of; frontal, temporal and occipital horn.

Shizencephaly

development of fluid filled clefts within the cerebrum. Several associated anomalies such as agenesis of the corpus callosum and CSP, and ventriculomegaly.

Arnold-Chiari II Malformation & Spina Bifida

group of cranial abnormalities associated with the neural tube defect spina bifida. -mass protrudes from the spine (meningocele or myelomeningocele) -The most common location of spina bifida is lumbrosacral region. -Elevated MSAFP

lateral ventricles

is located on both sides of the midline;

Falx cerebri - double fold of dura mater

is located within the interhemispheric fissure - echogenic linear formation coursing through the midline of fetal brain

The Thalamus

located both sides of the third ventricle. The massa intermedia or interthalamic adhesion passes through the third ventricle to connect two lobes of the thalamus. Shouldn't be confused with the cerebral peduncles.

The Cisterna Magna

located in the posterior fossa of the cranium. Largest cistern in the head. anechoic fluid filled space, posterior to the cerebellum.

sagittal suture

two parietal bones

Aqueduct of Sylvius or cerebral aqueduct

The third ventricle connects to the fourth ventricle inferiorly by means of a long, tubelike structure called;

Posterior or occipital

Bordered by the occipital and parietal bones Closure : by 6 months

Prosencephalon (forebrain) Mesencephalon (midbrain) Rhombencephalon (hindbrain)

Brain is divided into 3 primary vesicles termed;

Lemon sign

The frontal lines become flattened and will yield a lemon shape to the cranium which is referred to as the ''lemon sign'' often referred to as scalloping of the frontal bones.

atrium. the calipers are placed at the level of the glomus of the choroid plexus.

The lateral ventricle is measure in the transaxial plane at the level of the;

above 1.0 index lower than 1.0 is considered abnormal

The middle cerebral artery / umbilical artery resistive index is normally;

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The normal cerebellum is a dumbbell shaped or figure 8 shaped structure noted in the posterior cranium of the fetus.

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The sonographic intracranial findings consistent with intrauterine infections are the calcifications around the ventricles and ventriculomegaly.

Causes of Neural Tube Defects (NTDs)

maternal diabetes valproic acid (seizure med) chromosomal anomalies Trisomy 18 -Edwards syndrome Trisomy 13- Patau syndrome triploidy

Foramen of Magendie

median aperture of fourth ventricle through which CSF flows into the cisterna magna and subarachnoid space