The Fetal Head and Brain

The neural plate is the

Structure that will form into the central nervous system (developed by 4.5 wks)

The neural tube becomes the

Spine and brain

The brain is divided into 3 vesicles called the

Prosencephalon (forebrain)

Mesencephalon (midbrain)

Rhombencephalon (hindbrain)

The prosencephalon will mature into

Telencephalon and diencephalon

The telencephalon will form the

Cerebral hemispheres, lateral ventricles, and third ventricle

The diencephalon will become the

Thalamus and hypothalamus

The mesenchephalon will become the

Midbrain, superior parts of brainstem

The rhombencephalon will become the

4th ventricle and medulla oblongata and cerebellum

Cranial bones

Fetal cranial sutures (connective tissue that lies btw cranial bones)

Premature fusion of sutures is termed

Craniosynostosis

Fontanelles/ soft spots

The opening in the base of cranium through which the spinal cord travels is the

Foramen magnum

Meninges of the brain

The brain can be divided into 2 parts:

Cerebrum and cerebellum

The cerebrum is the largest part of the brain and the normal cerebrum contains multiple:

Sulc: grooves within brain

Gyri: folds in cerebral cortex (wrinkly outer layer)

The cerebrum has 4 main cerebral lobes

The cerebrum is divided into a right and left hemisphere by

Interhemispheric fissure

Midline brain anatomy

Bilateral brain structures

What is the falx cerebri

A double fold of dura mater, located in the interhemispheric fissure and seperates the cerebral hemispheres

What is the corpus callosum

Connects the cerebral hemispheres and allows communication between them

The corpus callosum (developed btw 18-20wks) develops form anterior to posterior and has 4 parts termed the

The absence of the corpus callosum is referred to as

Agenesis of the corpus callosum

Anterior portion of brain between frontal horns of the lateral ventricles

Cavum septum pellucidum CSP

Sonographically, the Cavum Septum Pellucidum (CSP) will present

“Box shaped” structure in axial/transverse plane

Should be seen between 18 and 37 weeks

The CSP does NOT communicate with the ? And its absence is associated with?

Ventricular system.

Multiple cerebral malformations including agenesis of corpus callosum

The two lobes of thalamus are located and connected by?

Located on Both sides of third ventricle and conencted by massa intermedia/ interthalamic adhesion

The paired lateral ventricles are located?

Both sides ot the falx celebri

Within the atria of both lateral ventricles lies the choroid plexus, which is

Mass of cells responsible for production of cerebrospinal fluid ( CSF )

Cerebal ventricle system

Lateral ventricle measurement

Measured in axial plane at level of atrium. Should not measure more than 10mm (ventriculomegaly)

The lateral ventricles communicate with the third ventircle at the ?

Foramen of monro/ interventricular foramina

The third ventricle connects to the 4th ventricle inferiorly by means of a long tubelike structure via the?

Aqueduct of sylvius or cerebral aqueduct.

The 4th ventricle is located

Anterior to cerebellum

The foramina of luschka of the 4th ventricle allows CSF from 4th ventricle to travel to

Subarachnoid space

The median aperture of 4th ventricle aka the foramen of magendie allows CSF to travel to

Cisterna magna and subarachnoid space

What is the cisterna magna?

Located in the posterior fossa of cranium, it is the largest cistern in the head

The cisterna magna is sonographically located

Posterior to cerebellum between the cerebral vermis and inner surface of occipital bone

The depth of the cisterna magna should not measure

More than 10 mm or less than 2 mm in trans cerebellar plane

CM meas of more than 10mm is consistent with

Mega cisterna magna and dandy-walker complex

CM meas of less than 2mm is worrisome for

Arnold chiari 11 malformation

The cerebellum is located in the posterior fossa of the cranium and consists of two hemispheres: right and left. These two hemispheres are joined by the

Cerebellar vermis

The cerebellum appears

Normal cerebellum is dumbbell or figure 8 shaped

2 hemispheres should be symmetric although hypoplasia of one hemisphere may occur, causing one to appear smaller than normal

The transcerebellar diameter (TCD)

TCD= gestational week of fetus

Measured at transverse plane at level of cisterna magna and thalamus

What is the cephalic index?

Tool for head shape indication calculated by

CI = BPD/OFD x 100

A CI of less than 75 denotes a

Dolichocephy/spachocephaly (elongated and narrow)

A CI of more than 85 denotes

Brachycephaly (short and round)

The normal-to-medium sized skull is termed

Mesocephalic

Fetal head shapes and associated anomalies

Lemon: chiari 2 malformation

Strawberry: trisomy 18

Cloverleaf: thanotophoric dysplasia

Microcephaly: torch infection, trisomy 13 or 18, meckel-gruber syndrome

Macrocephaly: hydro or hydranecephaly, beckwith- wiedeeman syndrome

Brachycephaly: trisomy 21

Dolichocephaly: craniosynostosis

Ventriculomegaly is the most common cranial abnormality and occurs when atrial diameter of lateral ventricle measures?

More than 10 mm

What are the sonographic findings of vetriculomegaly?

Atrium of LV meas >10mm

Atrial meas >15mm is considered moderate to marked ventriculomegaly

Dangling choroid sign

Dilation of any part of ventricular system

How does hydrocephalus differ from ventriculomegaly

Hydrocephalus is the dilation of ventricular system secondary to an obstruction

What are the 2 types of hydrocephalus?

Communicating hydrocephalus (obstruction outside of ventricular system)

Noncommunicating hydrocephalus (obstruction is located within ventricular system)

What is the most common cause of hydrocephalus in utero

Aqueductal stenosis

what is aqueductal stenosis?

when the cerebral aqueduct/aqueduct of sylvius is narrowed, thus preventing the flow of CSF from the third to the fourth ventricle.

sonographic findings of aqueductal stenosis

Atrium of the lateral ventricle measures greater than 10 mm

Atrial measurement greater than 15 mm is considered moderate to marked ventriculomegaly

Dangling choroid sign

Dilatation of the lateral ventricles and the third ventricle;

the fourth ventricle remains normal

what is hydranencephaly and what happens with this condition

fatal condition in which the entire cerebrum is replaced by a large sac containing CSF;

what are possible causes of hydranencephaly

bilateral occlusion of the internal carotid arteries with subsequent destruction of the cerebral hemispheres.

TORCH infections (cytomegalovirus or toxoplasmosis)

Sonographic Findings of Hydranencephaly

Fluid-filled cranium

Absent or partial absence of the falx cerebri

Maintained brainstem, basal ganglia, and, perhaps, the thalamus

No identifiable cerebral cortex

Hydranencephaly can be difficult to differentiate with the sonographic findings of severe ventriculomegaly and alobar holoprosencephaly. It is important to note that with both severe ventriculomegaly and holoprosencephaly,

there will typically be a rim of cerebral tissue maintained, whereas with hydranencephaly, there is no cerebral mantle present

what is Holoprosencephaly

a group of brain abnormalities consisting of varying degrees of lateral ventricle fusion, absence of the midline structures, and associated facial anomalies

what are the three main types of holopresencephaly

alobar (cortex can resemble “pancake” “cup” or “ball”) this is the most severe form

semilobar

lobar

Alobar holoprosencephaly is diagnosed when there is absence of the

corpus callosum

CSP

third ventricle

interhemispheric fissure

falx cerebri

There will also be evidence of a horseshoe-shaped monoventricle

and the lobes of the thalamus may be fused and echogenic in appearance

Facial anomalies associated with alobar holoprosencephaly

Cyclopia (fusion resulting in one single eye)

Hypotelorism (close eyes)

Proboscis (false nose)

(Median) cleft lip

Anophthalmia (absence of one or both orbits)

Cebocephaly (closely spaced eyes, one nostril, missing upper lip, irregular head shape)

Infants with lobar holoprosencephaly may experience

extreme mental retardation

in 50% to 70% of fetuses diagnosed with holo-prosencephaly also have

Trisomy 13/ Patau syndrome

Sonographic Findings of Alobar Holoprosencephaly

Horseshoe-shaped monoventricle

Fused echogenic thalami

Absence of the CSP, interhemispheric fissure, falx cerebri, corpus callosum, and third ventricle

Normal cerebellum and brainstem

Facial anomalies (e.g., cyclopia, proboscis, cebocephaly, facial clefts, hypotelorism)

What is dandy-walker complex

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

what other midbrain anomalies associated with dandy-walker malformation

agenesis of the corpus callosum, ventriculomegaly, holoprosencephaly, and cephaloceles

If the cerebellar vermis is absent and the fourth ventricle is enlarged, then

DWM must be suspected.

what is the difference between mega cisterna magna and DWM

the fourth ventricle is normal with mega cisterna magna and enlarged with DWM

Sonographic Findings of Dandy–Walker Malformation

Enlargement of the cisterna magna greater than 10 mm

Communication of the enlarged cisterna magna with a dilated fourth ventricle

Agenesis or hypoplasia of the cerebellar vermis

splayed lobes

Varying degrees of ventriculomegaly

Sonographic Findings of Mega Cisterna Magna

Enlargement of the cisterna magna greater than 10 mm

Normal cerebellum and fourth ventricle

The congenital lack of corpus callosum and CSP is termed

agenesis of the corpus callosum, and CSP. There can be partial or complete absence of the corpus callosum. Most often, if the corpus callosum is absent, the CSP will be absent as well

agenesis of corpus callosum and csp has been linked to as many as 50 to 200 different syndromes and anomalies such as

Apert syndrome (genetic disorder that includes craniosynostosis, midline facial hypoplasia, and syndactyly)

holoprosencephaly

DWM

aqueductal stenosis

trisomy 18

trisomy 8

trisomy 13

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.

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/ “spoke-wheel” pattern

Colpocephaly—(teardrop-shaped lateral ventricles)

Elevated and dilated third ventricle

what is Schizencephaly

development of fluid-filled clefts within the cerebrum, may be described as open lip or closed lip, with open lip being more readily identified in utero

Sonographic Findings of Schizencephaly

Fluid-filled clefts within the cerebrum

Agenesis of the CSP and corpus callosum (50% of the time)

Ventriculomegaly

what is porencephaly

a rare condition in which a cyst communicates with the ventricular system. Porencephaly can occur after the fetus has experienced hemorrhage within one or both of the cerebral hemispheres.

porencephaly may be caused by

ischemic events or vascular occlusion within the brain

Arachnoid cysts can be confused with porencephaly. It is important to note that

arachnoid cysts will not communicate with the ventricular system.

Sonographic Findings of Porencephaly

Cystic mass that communicates with the lateral ventricle

Most often unilateral

what is lissencephaly

“smooth brain.” It is a condition in which there are no gyri within the cerebral cortex. Agyria, and the absence of sulci within the brain, is not typically diagnosed until the third trimester or postnatally and almost always carries a poor prognosis.

Sonographic Findings of Lissencephaly

Lack of sulci and gyri within the cerebrum

what are Choroid plexus cysts

cysts located within the choroid plexus of the lateral ventricles. These are frequently encountered during a routine sonographic examination and typically regress by the end of the third trimester, although there is an association with trisomy 18

Sonographic Appearance of a Choroid Plexus Cyst

Anechoic, round, smooth-walled cyst located within the choroid plexus of the lateral ventricle

Among the list of neural tube defects are

cephaloceles, various spinal dysraphisms, anencephaly, and spina bifida;

with Anencephaly and spina bifida the most common

Screening for neural tube defects is achieved by a combination of

sonography, amniocentesis, and/or maternal serum screening

Alpha-fetoprotein (AFP) is initially produced by the

yolk sac, fetal gastrointestinal tract, and the fetal liver. AFP exits the fetus through an opening in the neural tube if one is present

what test is especially helpful for detecting neural tube defects?

maternal serum alpha-fetoprotein (MSAFP)

increased levels of AFP may not always indicate that a neural tube defect is present. Elevated levels of AFP are also found with

omphalocele, gastroschisis, multiple gestations, fetal demise, and incorrect gestational dating.

what is acrania

one of the most common neural tube defects. Acrania is defined as the absence of the cranial vault above the bony orbits. It can be further divided into two main subtypes depending on the amount of cerebral tissue present, anencephaly and exencephaly.

Clinical Findings of Acrania/Anencephaly

Elevated MSAFP

Sonographic Findings of Acrania/Anencephaly

Absent cranial vault

Some cerebral tissue may be present

“Froglike” facies or bulging eyes

Possible fetal movement and active fetal heart

what is Arnold–Chiari II or Chiari II malformation

group of cranial abnormalities associated with the neural tube defect spina bifida

Spina bifida may result in a mass that protrudes from the spine. This mass can be referred to as a

meningocele or myelomeningocele, depending on its contents

The most common location of spina bifida is within the

distal lumbosacral region

A posterior fossa abnormality such as Chiari II malformation should be suspected if the

cisterna magna is not visualized.

The lateral ventricles will also be distorted in shape.

Colpocephaly (teardrop shaped lateral ventricles)