Chapter 60: Fetal Neural Axis - Part 1

neural tube closure occurs within ___.

4 weeks

if the neural tube doesn’t close, it is termed ___.

neural tube defect

the CNS arises from the ectodermal neural plate around ____.

18 gestational days

the cephalic neural plate develops into the ___.

forebrain

the caudal end of the neural plate forms the ___.

spinal cord

the forebrain continues to develop into the ____.

prosencephalon

the midbrain becomes the ____.

mesencephalon

the hindbrain forms the ____.

rhombencephalon

when can the rhombencephalon be seen on ultrasound?

around 8-9 weeks

a cystic structure seen in the back of the brain in the early first trimester is likely the ___.

rhombencephalon

at birth, the spinal cord terminates at the level of _____.

L3

by adulthood, the spinal cord will terminate at the level of ___.

L2

where the spinal cord terminates; bunch of nerve fibers

cauda equina

when does neural function begin?

at 6 weeks of gestation

by ___ weeks, sensitivity has spread across the surface of the body except at the back and top of the head and movement of the extremities will be seen.

12

when does the fetus display suckling reflex?

6 months

between 4-5 months, the fetus can ____ and is capable of ____.

grip objects and capable of weak respiratory movements

at about 28 weeks, changes in brain wave patterns occur and we will see…

voluntary movements and breathing patterns start to resonate

what do many of congenital malformation of the CNS result from?

incomplete closure of neural tube

what is the most common neural tube defect?

anencephaly

there is a significant recurrence of anencephaly for women with…

history of prior pregnancy with open neural tube defect

what should anencephaly should be corresponded with?

Meckel-Gruber syndrome, trisomy 13, trisomy 18

what are risk factors for anencephaly?

maternal diabetes, environmental/dietary factors, teratogens

a structural defect of the uterus that could cause anencephaly

amniotic band syndrome

anencephaly means ___.

absence of the brain

what is anencephaly caused by?

a failure of the rostral end of the neural tube to close

superior portion of the neural tube

rostral end

in cases of anencephaly, the remnant brain is covered by a thick membrane called the ____.

angiomatous stroma or cerebrovasculosa

up to 50% of cases of anencephaly end in ___.

fetal demise

prenatal diagnosis of anencephaly is often made with sonography following a referral for ____.

elevated MSAFP

what are the sonographic findings of anencephaly?

absence of the brain and cranial vault, cerebrovasculosa, bulging fetal orbits

bulging fetal orbits, causing the fetus to give a froglike appearance corresponds to what abnormality?

anencephaly

other than absence of brain and cranial vault and bulging fetal orbits, what are some other sonographic findings?

polyhydramnios, existing spina bifida, cleft lip/palate, hydronephrosis, diaphragmatic hernia, cardiac defects, omphalocele, GI defects, talipes

talipes =

clubfoot

___ is considered a precursor to anencephaly.

acrania

acrania is a lethal anomaly that is also known as ___.

exencephaly

manifests as absence of cranial bones with presence of complete, although abnormal, development of the cerebral hemispheres

acrania

acrania occurs at the beginning of ____.

4th gestational week

acrania usually progresses to anencephaly as…

the brain slowly degenerates as a result of exposure to AF

acrania may be confused with anencephaly, but what should establish the diagnosis of acrania?

presence of significant brain tissue and lack of froglike appearance of the skull

what are the sonographic findings of acrania?

presence of brain tissue without the presence of bone structure, disorganization of brain tissue, possibly appears as a large protrusion of the head

if acrania appears with a large protrusion of the head, it could mimic ____ which would be a differential diagnosis.

osteogenesis imperfecta (Cloverleaf skull/skeletal dysplasia)

acrania may be associated with other anomalies including…

spinal defects, cleft lip/palate, talipes, cardiac defects, omphalocele, amniotic band syndrome

neural tube defect in which meninges alone or meninges and brain herniate through a defect in the calvarium

cephalocele

term used to describe herniation of meninges AND brain through defect

encephalocele

describes herniation of ONLY meninges

cranial meningocele

why are MSAFP levels likely low or normal in cases of a cephalocele?

because the brain matter is covered

what does the prognosis for the infant with a cephalocele look like?

varies based on size, location, involvement of other brain structures, and the presence of intracranial or extracranial malformations and microcephaly

is fetal death common in cases of cephaloceles?

yes

a ____ occurs when the protrusion is larger than the head from which it arises.

giant encehpalocele

what does the sonographic appearance of a cephalocele depend on?

location, size, involvement of brain structures

cephaloceles are classified as _____ cephaloceles when the defect lies between the lamboid suture and the foramen magnum.

occipital (posterior)

___ cephaloceles occur between the bregma and the lambda.

parietal (lateral)

___ cephaloceles lie between the anterior aspects of the anterior aspects of the ethmoid bone.

anterior

the ____ cephaloceles are always external lesions that occur near the root of the nose.

frontal

____ cephaloceles are internal lesions that occur within the nose, the pharynx, or the orbit.

basal

what are the sonographic findings of a cephalocele?

an extracranial mass which may be fluid filled or contain solid components; a bony defect in the skull; ventriculomegaly; smaller than expected HC/BPD; polyhydramnios

ventriculomegaly is more commonly identified in what type of cephalocele?

encephalocele

coexisting anomalies with cephaloceles include…

microcephaly, agenesis of the corpus callosum, facial clefts, spina bifida, cardiac anomalies, genital anomalies

if there is anything abnormal, check the ___.

heart

what are chromosomal anomalies and syndromes that have been identified with cephaloceles?

trisomy 13 and Meckel-Gruber syndrome

what might a cephalocele be confused with?

cystic hygromas

frontal encephaloceles are difficult to distinguish from ___.

facial teratomas

wide range of vertebral defects that result from failure of neural tube closure

spina bifida

what may protrude through a spina bifida defect?

meninges and neural elements

spina bifida defect may occur anywhere along the vertebral column but most commonly along which region(s)?

lumbar and sacral

what does the term spina bifida mean?

there is a cleft, or opening, in the spine

when the spina bifida defect is covered with skin or hair, it is referred to as _____.

spina bifida occulta

the open form of spina bifida is termed __.

spina bifida aperta

what are the two forms of spina bifida aperta?

meningocele and myelomeningocele

the closed form of spina bifida is termed ___.

spina bifida occulta

why is spina bifida occulta extremely difficult to detect in a fetus?

because the defect is covered by skin and the maternal serum AF level will be normal

when spina bifida defect involves ONLY protrusion of the meninges, it is termed ___.

meningocele

term used when the spina bifida defect involves both meninges and neural elements protruding through defect

myelomeningocele

which is more common, myelomeningocele or meningocele?

myelomeningocele

open neural tube defects are commonly associated with ___.

increased MSAFP

spina bifida is associated with varying degrees of…

neurologic impairment, minor anesthesia, paraparesis (paralyzed), or death

fetuses with myelomeningoceles often present cranial defects associated with _____.

Arnold-Chiari II malformation

malformation where the cerebellum dips down into the spinal cord, forming the banana sign

Arnold-Chiari II malformation

Arnold Chiari II changes the shape of the ____, giving it a banana appearance.

cerebellum

Arnold Chiari II leads to obliteration of ____.

cisterna magna

caudal displacement of cranial structures causes scalloping of the frontal bones of the skull, making the fetal head resemble a ____.

lemon

Arnold Chiari II produces the “banana” and “lemon” signs and changes the shape of the cerebellum. The displacement of brain structures causes a ____.

decrease in the size of the BPD

spina bifid is associated with ____.

ventriculomegaly

ventriculomegaly is a ventricle measurement of ___.

greater than 10 mm

those with spina bifida and corresponding ventriculomegaly are usually delivered ___.

early and by C-section

prognosis of spina bifida for the infant varies greatly according to…

type, size, location of defect

what are the sonographic findings of spina bifida?

splaying of the posterior ossification centers with a V or U configuration, protrusion. of a saclike structure that may be anechoic or contain neural elements, a cleft in the skin

in cases of spina bifida, after the spinal defect is identified, what should be documented?

level and extent of the defect, presence or absence of neural elements contained in the protruding sac, associated intracranial findings

sonographic findings that are associated with spina bifida include…

talipes, cephaloceles, cleft lip/palate, hypotelorism, heart defects, genitourinary anomalies

spina bifida has been associated with multiple syndromes and chromosomal anomalies, including ___.

trisomy 18

spina bifida can occur in fetuses exposed to ____.

teratogens (valproic acid)

what are some risk factors that have been associated with spina bifia?

maternal diabetes, maternal obesity, maternal HTN, hyperthermia, folic acid deficiency

___ or ___ are considered a significant risk factor for occurrence of spina bifida.

family history of spina bifida or anencephaly

defect that may have varying degrees of severity; manifests with agenesis or hypoplasia of cerebellar vermis with resulting dilation of the 4th ventricle and enlargement of posterior fossa

dandy-walker malformation

CSF drains from the choroids to the ____ → ____ → ____

3rd ventricle, aqueduct of Sylvius, 4th ventricle

when does the development of the cerebellar vermis begin?

9th week of gestation

when are communications between the 4th ventricle and the cisterna magna completed?

18th week of gestation

when should diagnosis of agenesis and hypoplasia of the cerebellar vermis be made?

not before the 18th week of gestation

DWM is associated with other intracranial anomalies 50% of the time, including…

ventriculomegaly, agenesis of the corpus callosum, aqueductal stenosis, holoprosencephaly, microcephaly, macrocephaly, encephalocele, gyral malformations, heterotopias, lipomas