Class 15: NTD Flashcards
what are neural tube defects?
anomalies of the fetal head, neck, spine
causes of NTD?
may result from genetic mutation or be acquired
what is the most common NTD?
anencephaly/acrania
what is anencephaly
the absence of cerebral hemispheres & overlying skull & scalp – no forebrain
only the midbrain & hindbrain are present with anencephaly. T/F?
true
what weeks can anencephaly be seen on US TV?
9-10 weeks
what is the most common congenital anomaly of the CNS?
anencephaly
which parts of the world is anencephaly more common in?
where spina bifida is common (UK)
which part of the population does anencephaly more commonly occur in? male or female?
females
in anencephaly, what is the US appearance of the cranial vault & intracranial contents?
absent
in anencephaly, what is the US appearance of the eyes?
eyes are present, but bulging
US appearance of the neck with a fetus with anecephaly?
short neck
oligohydramnios is present in half the cases of anencephaly. T/F?
false – polydramnios is present
why is polyhydramnios common with fetuses with anencephaly?
due to problems with swallowing amniotic fluid
5 causes of NTD?
- chromosomal abnormalities
- diabetes mellitus
- folic acid deficiency
- amniotic band syndrome
- hyperthermia
what is the most common cause of NTD?
chromosomal abnormalities
lab values for NTD?
high levels of alpha feto protein
fetuses with anencephaly take on a ___-like appearance
frog
any NTD with exposure to ___ can cause degeneration of brain tissue
amniotic fluid
what is acrania?
the absence of cranial bones but with the presence of abnormal brain tissue
what can acrania lead to?
anencephaly if the brain tissue is exposed to amniotic fluid
what is hydranencephaly?
the total or near total absence of the cerebral hemispheres; cerebral parenchyma is destroyed & replaced by CSF
hydranencephaly is usually not associated with chromosomal abnormalities. T/F?
true
hydranencephaly is usually associated with other structural anomalies. T/F?
false
hydranencephaly is a lethal condition. T/F?
true
what are 2 causes of hydranencephaly?
- bilateral obstruction of the ICA leads to tissue necrosis of brain & is replaced by CSF
- congenital infection
US appearance of hydranenncephaly?
- no cerebral parenchyma
- large anechoic areas surrounding midbrain
what is holoprosencephaly?
failure of prosencephalon to divide into double lobes of cerebral hemispheres
holoprosencephaly is associated with hypertelorism deformities. T/F?
false – hypotelorism
3 types of holoprosencephaly?
- alobar
- semilobar
- lobar
what is the most severe type of holoprosencephaly?
alobar
what is the mildest type of holoprosencephaly?
lobar
what is alobar holoprosencephaly?
complete failure of prosencephalon to divide into 2 hemispheres – unable to see IHF
US appearance of alobar holoprosencephaly?
absent CSP, monoventricle & fused thalami
what abnormalities are associated with alobar holoprosencephaly?
craniofacial abnormalities
what is semilobar holoprosencephaly?
partial separation of cerebral tissue
US appearance of semilobar holoprosencephaly?
abset CSP, present occipital lobe
what abnormalities are associated with semilobar holoprosencephaly?
cleft palate & lip
what is lobar holoprosencephaly?
nearly complete separation of cerebral hemispheres
US appearance of lobar holoprosencephaly?
abset CSP
what is cebocephaly?
hypotelorism & normally placed nose with 1 nostril
what is ethmocephaly?
hypotelorism with proboscis superior to eyes
how do facial clefts form?
due to the failure of lip fusion prior to 35 days from conception
other names for dandy walker malformation?
dandy walker syndrome, dandy walker cyst, dandy walker variant
features of dandy walker malformation?
- agenesis/incomplete formation of vermis
- dilation of 4th ventricle & enlargement of posterior fossa
cause of dandy walker malformation?
obstruction at lushka & magendie foramen
US appearance of dandy walker malformation?
cystic dilation of 4th ventricle & subsequent dilation of 3rd & lateral ventricles
cerebellar lobes splayed apart
what is a cephalocele?
a herniation of meninges with or without brain tissue through a skull defect
what is an encephalocele?
a herniation of meninges, CSF, and brain tissue
most common location for a cephalocele to occur?
occipital region
hydrocephalus is present in ___ of cases with cephalocele
80%
spina bifida is present in ___ of cases with cephalocele
7-15%
cephalocele is associated with polyhydramnios. T/F?
true
US appearance of encephalocele?
heterogenous – has meninges & brain tissue present
what is hydrocephalus?
an abnormal increase in fluid in cerebral ventricles
what is another name for hydrocephalus?
ventriculomegaly
effects for ventriculomegaly?
- flattening of the brain parenchyma
- intraparenchymal effusion
3 classifications of hydrocephalus?
- aqueductal stenosis/noncommunicating hydrocephalus
- communicating hydrocephalus
- overproduction of CSF
what can cause overproduction of CSF?
choroid plexus papilloma – can cause choroid plexus to make more CSF
measurement of cisterna magna with dandy walker malformation?
> 10 mm/1cm
what is another name for noncommunicating hydrocephalus?
aqueductal stenosis
what is aqueductal stenosis?
obstruction INSIDE ventricular system – there is no communication between ventricular system & subarachnoid space
what is communicating hydrocephalus?
obstruction OUTSIDE ventricular system (ex subarachnoid space)
US appearance of choroid plexus with ventriculomegaly?
hanging/dangling choroid plexus
US appearance of ventricles with hydrocephalus?
dilated ventricles (ventriculomegaly)
measurement of lateral ventricles with ventriculomegaly?
> 10 mm/1cm
US appearance of fetal head with hydrocephalus?
enlargement of head leads to overestimation of GA
what is arnold chiari malformation?
a common type of hydrocephalus where the cerebellum is pulled through the CM
where does the spinal cord normally start & end?
starts at the foramen magnum & ends at L2
with arnold chiari malformation, where does the spinal cord start & end?
pushed down on foramen magnum & starts at CM; ends below L2
what 2 conditions is arnold chiari malformation associated with?
spina bifida
hydrocephalus
US appearance of arnold chiari malformation?
- fruit bowl sign – cerebellum = banana shape; narrow frontal bone = lemon sign
- dilated lateral ventricles = severe bat wing sign
- dilated 3rd ventricle
- no CSP
microcephaly means that the head circumference of the fetus is ___ standard deviations below the mean
2
3 causes of microcephaly?
- trisomies (13, 18, 21)
- environmental teratogens
- uterine infections
effects of microcephaly?
mental retardation
choroid plexus cysts may be transient & ___ by the end of the ___ trimester
resolve; 2nd
when may choroid plexus cysts be associated with trisomy 18?
5% are associated with edward’s syndrome if unresolved by the 2nd half of pregnancy
choroid plexus cysts are an increased risk of abnormal karyotype if they are ___ that measure ___
bilateral; > 10 mm
is cystic hygroma benign or malignant?
benign
what is cystic hygroma?
a lymphatic obstruction/malformation that leads to fluid filled sacs
most common location for cystic hygroma?
80% of the time they are found in the posterolateral portion of the neck
what condition is associated with cystic hygroma?
turner’s syndrome
what is turner’s syndrome?
a chromosomal abnormality in which female only has 45X instead of 46XX
the following are characteristics of what condition?
- infantile sexuality
- pterigium colli
- elbow malformation
- low birth weight
- short stature
- edema on hands & feet
- loose skin folds on neck
- prominent ears
turner’s syndrome
US appearance of cystic hygroma?
uni/multilocular cystic mass
what is the 2nd most common NTD?
spina bifida
what is spina bifida?
a spinal defect in which the vertebral arches don’t fuse properly
most common location of spina bifida?
lumbar sacral
2nd most common location of spina bifida?
cervical
3 types of spina bifida?
- meningocele
- meningomyelocele
- occult spina bifida
what is meningocele?
spina bifida type in which only meninges protrude
what is meningomyelocele?
spina bifida type in which meninges & spinal cord protrude
what is occult spina bifida?
a small defect without protrusion
which type of spina bifida has poor prognosis?
meningomyelocele
what 4 conditions are associated with spina bifida?
- arnold chiari
- bladder, bowel dysfunction
- lower extremities paralysis
- hydrocephalus
