Fetal Neural Axis Flashcards
1
Q
What is the most common neural tube defect?
A
anencephaly
2
Q
What is the incidence of aprosencephaly?
A
1 in 1000 USA pregnancies
4x more often in females
6x more often in caucasians than african americans
3
Q
How does atelencephaly occur?
A
caused by failure of closure of neural tube at cranial end
result is absence of cranial vault, complete or partial absence of forebrain, presence of brain stem, midbrain, skull base, facial structures
remnant brain covered by thick membrane called angiomatous stroma or cerebrovasculosa
4
Q
Clinically, what does anencephaly look like?
A
high maternal serum alpha fetoprotein levels
5
Q
What are some causes of aprosencephaly?
A
meckel-Gruber, chromosomal (T-13, T-18), diabetes, environmental and dietary factors (folic acid), and amniotic band syndrome
6
Q
Sonographic findings of anencephaly include:
A
frog face sign
polyhydramnios, coexisting spina bifida and/or cranioarchischisis, cleft lip and palate, hydronephrosis, diaphragmatic hernia, cardiac defects, omphalocele, GI defects, talipes
my also be isolated
7
Q
What is acrania?
A
manifests as absence of cranial bones with presence of complete, although abnormal, development of cerebral hemispheres
8
Q
What are other names for anencephaly?
A
aprosencephaly and atelencephaly
9
Q
What is another name for acrania?
A
exencephaly
10
Q
When does acrania occur?
A
beginning of 4th gestational week
mesenchymal tissue fails to migrate and does not allow bone formation over cerebral tissue
11
Q
What does exencephaly result in?
A
progresses to anencephaly as brain slowly degenerates as result of exposure to AF
12
Q
What other anomalies may be associated with acrania?
A
spinal defects, cleft lip and palate, talipes (cleft foot), cardiac defects, omphalocele, amniotic band syndrome
13
Q
What is cephalocele?
A
neural tube defect in which meninges alone or meniges and brain herniate through in calvarium
14
Q
What is encephalocele?
A
term used to describe herniation of meninges and brain through defect
15
Q
What is cranial meningocele?
A
describes herniation of only meninges
16
Q
What bones are involved in cephalocele?
A
involved occipital bone
located in midline (75% of cases)
may also involve parietal, frontal, temporal regions, and other bones of calvarium
17
Q
Describe the different types of cephaloceles and what they include.
A
meninges only - meningocele
brian tissue only - encephalocele
meninges and brain tissue - encephalomeningocele
meninges, brain tissue and lateral ventricles - encephalomeningocystocele
18
Q
How are cephaloceles classified?
A
according to size of lesion
19
Q
Describe the different classifications of cephaloceles.
A
occipital: occur when defect lies between lambdoid suture and foramen magnum
parietal: occur between bregma and lambda
anterior: lie between anterior aspect of ethmoid bone
20
Q
What further classifications is anterior cephaloceles?
A
frontal and basal
frontal: always external lesions that occur near root of nose
basal: internal lesions that occur within the nose, pharynx, and orbit
21
Q
What is the sonographic appearance of a cephalocele?
A
extracranial mass, which may be fluid filled (cranial meningocele) or contain solid components (encephalocele); a bony defect in skull, ventriculomegaly, polyhydramnios
22
Q
Coexisting conditions along with cephaloceles includeL
A
microcephaly, agenesis of corpus callosum, facial clefts, spina bifida, cardiac anomalies, nad genital anomalies
23
Q
What chromosomal anomalies have been identified with cephaloceles?
A
trisomy 13 and Meckel Gruber syndrome
24
Q
What is spina bifida?
A
means there is a cleft or opening in the spine
25
Describe spina bifida occulta
when the spinal defect is covered with skin or hair
associated with normal spinal cord and nerves and normal neurologic development
(MSAF level is normal)
26
What is a menigocele?
when the spinal defect involves only protrusion of meninges
27
What is meningomyelocele?
when both meninges and neural elements protrude through the spinal defect
28
What is rachischisis?
when the spinal defect is very large and severe - can be open
29
What is spina bifida associated with?
varying degrees of neuologic impairment such as minor anesthesia, paraparesis, and death
also associated with Arnold-Chiari type II malformation in fetuses with myelomeningoceles
associated with chromosomal abnormalities including Trisomy 18
30
What are some sonographic findings of spina bifida?
flattening of frontal bones (lemon sign), obliteration of cisterna magna, inferior displacement of cerebellar vermis (banana sign), ventriculomegaly
31
What sonographic findings are associated with spina bifida?
club foot, cephaloceles, cleft lip and palate, hypotelorism, heart defects, genitouriniary anomalies
32
What are maternal risk factors for spina bifida?
maternal diabetes, obesity, hyperthermia, folic acid deficiency, and family history
33
What are the risks of inutero surfical repair of the type of spina bifida?
premature delivery, maternal death, fetal death
34
What is Dandy Walker Malformation?
ageneisis or hypoplasia of cerebellar vermis with resulting dilations on fourth ventricle and enlargement of posterior fossa
35
What are the three main types of posterior fossa malformations?
```
Dandy Walker Malformation (DWM) with an elevated tentorium
Dandy Walker varient (DWV) manifests with cystic dilation of the fourth ventricle and hypoplasia of the cerebellar vermis without an enlarged posterior fossa
Megacisterna magna (MCM) is defined as an enlarged cistern magna
```
36
When can diagnosis of DWM be made?
not made prior to 18 weeks gestation
| because communications between the fourth ventricle and cistern magna not complete intil the 18th week
37
What other intracranial anomalies are assoiciated with DWM?
agenesis of corpus callosum, aqueductal stenosis, microcephaly, macrocephaly, encephalocele, gyral malformations, heterotopias, and lipomas
38
What other chromosomal anomalies are associated with DWM?
trisomies 13, 18, 21, and triploidy, Meckel-Gruber, Walker-Warburg, Aicardi
also linked to congenital infections and maternal diabetes
39
What is the prognosis of DWM?
depends on presence or absence of associated anomalies and on degree of hypoplasia of cerebellar vermis, as correlates with severity of mental retardation
mortality depends highly on other anomalies
many infants have subnormal IQ, some have normal function
40
What are extracranial anomalies associated with DWM?
cardiac anomalies, polydactyly, facial clefts, urinary tract anomalies
41
Sonographically, what does DWM look like?
posterior fossa cyst, splaying of cerebellar hemispheres as result of complete or partial agenesis of cerebellar vermis, enlarged cisterna magna caused by cerebellar vermis anomaly and posterior fossa cyst, ventriculomegaly
42
Differentials for DWM include:
arachnoid cyst, but identification of splayed cerebellar hemisoheres may help to confirm DWM
cerebellar hypoplasia should also be included in the differential diagnosis when cisterna magna enlarged
43
What are the three forms of holoprosencephaly?
alobar, semilobar, and lobar
| identification of specific form depends on degree of failed hemispheric division
44
What occurs with alobar holoprosenecephaly?
singular monoventricle brain tissue that is small; cup, ball, and pancake configuration; fusion of thalamus; absence of interhemisphereic fissure; absence of CSP; absence of corpus callosum; absence of optic tracts; absence of olfactory bulbs
45
What occurs with semilobar holoprosencephaly?
singular ventricular cavity with partial formation of occipital horns; partial or complete fusion of thalamus; rudimentary falx and interhemispheric fissure; absent corpus callosum; absent CSP; absent olfactory bulbs
46
What configuration of the brain is seen with alobar holoprosencephaly?
pancake, cup, or ball
47
Which form of holoprosencephaly is most severe and which is least severe?
most: alobar
least: lobar
48
What is seen with lobar holoprosencephaly?
(almost complete division of ventricles with corpus callosum that may be normal, hypoplastic or absent)
CSP will still be absent
49
What specific triploidy is associated with holoprosencephaly?
trisomy 13
| however, trisomy 18 and troploidy have been identified and anomalies of chromosomes 7,3,and 11
50
What syndromes are associated with holoprosencephaly? What else is it associated with?
meckel-gruber syndrome; alcardi's syndrome; fryns syndrome; hydrolethalus syndrome
teratogens; radiation exposure; oral contraceptives and aspirin during pregnancy
51
What are the sonographic features of holoprosencephaly?
common c-shaped ventricle that may or may not be enlarged; brain tissue with horseshoe shape as it surrouds monoventricle; fusion of thalamus with absence of third ventricle; absence of interhemispheric fissure; dorsal sac with expansion of monoventricle posteriorly; absence of corpus callosum; absence of CSP
other assoications include hydrocephaly, microcephaly, polyhydramnios, and IUGR; renal cysts/dysplasia, omphalocele, cardiac defects, spina bifida, talipes, GI anomalies
52
What are facial anomalies associated with holoprosencephaly?
cyclopia; hypoteleroism; an absent nose; a flattened nose with a single nostril (cebocephaly); a proboscis
53
What is cebocephaly?
combination of hypotelorism (eyes too close) with normally placed nose with single nostril
54
What is ethmocephaly?
severe hypotelorism with proboscis superior to eyes
55
What is the corpus callosum?
a fibrous tract that connects the cerebral hemispheres
| aids in learning and memory; begings tp develop at 12 weeks gestation and not complete until 20 weeks
56
What is dysgenesis of the corpus callosum?
it describes range of complete to partial absence of callosal fibers that cross the midline
57
Describe another name for agenesis of the corpus callosum?
callosal agenesis
occurs sporadically, may be associated with other CNS malformations; may be transmitted in autosomal-dominant or autosomal-recessive manner; X-linked syndromes have been identified
58
What anomalies/syndromes are associated with callosal agenesis?
trisomies 13, 18 (both most common), 11, 8, 21, and triploidy
aicardi, apert, opitz, joubert syndromes
extracranial anomalies (cardiac malformations, diaphragmatic hernia, lung agenesis or dysplasia, absent or dysplastic kidneys)
59
What are maternal risk factors for ACC (agenesis of corpus callosum)?
diabetes, infections, alcohol abuse
60
What is the prognosis of ACC?
depends on high incidence of associated anomalies
is an isolated event
may be asymptomatic or associated with mental retardation and/or seizures
61
Describe the sonographic appearance of ACC.
absence of corpus callosum; elevation and dilation of third ventricle; widely separated lateral ventriclar frontal horns with medial indentation of medial walls; dilated occipital horns (colpocephaly), giving lateral ventricles teardrop shape; absence of CSP
62
Associated sonographic findings with ACC include:
CNS anomalies: holoprosencephaly, DWM, cranial lipoma, arnold-chiari malformation, septo-optic dysplasia, hydrocephlay, encephalocele, porencephaly, microcephaly, lissencephaly
63
What results from Aqueductal Stenosis?
from obstruction, atresia, or stenosis of aqueduct of sylvius, causing ventriculomegaly
64
Where is the aqueduct of sylvius located?
connection of 3rd and 4th ventricle
65
Describe the flow of cerebral spinal fluid within the brain.
formed from the choriod plexus, flow starts in the lateral ventricles and then travels through two channels to the 3rd ventricle; from 3rd ventricle through aqueduct of sylvious to 4th ventricle and then goes through foramia into the subarachnoid space surrounding the brain and spinal cord
66
Describe the physiology behind aqueductal stenosis.
when aqueduct of sylvius is obstructed, the proximal areas will be dilated (3rd ventricle and lateral ventricles) while distally (4th ventricle) remains a normal appearance
67
What may cause aqueductal stenosis?
intrauterine infections; cranial masses and ventricular hemorrhage also contributing factors
usually x-linked and has autosomal-recessive inheritance
68
What is the prognosis of aqueductal stenosis?
varies with associated anomalies - usually poor prognosis
about 90% of survivors have IQ <70
infants with x-linked aqueductal stenosis profoundly mentally retarted
69
The sonographic appearance of aqueductal stenosis is...
ventricular enlargement of lateral ventricles; third ventriclar dilation; flexion and adduction of thumb (in x-linked form)
70
What is the vein of galen aneurysm?
rare congential vascular malformations; consist of a tangled mass of dilated vessels supplied by an enlarged artery; characterized by shunting of arterial flow into an enlarged cerebral vein
71
What may vein of galen aneurysm be associated with?
-male predominance-
usually isolated
been associated with congentital heart defects, cystic hygromas, and hydrops
can be associated with neurologic damage resulting from ischemia, hemorrhage, or mass effect
72
What is the prognosis of vein of galen aneurysm?
generally poor - especially when assoicated with hydrops and cardiac failure
when symptoms present later in older children and young adults, prognosis generally good
73
What is the treatment of vein of galen aneurysm?
embolization
74
What is the sonographic appearance of vein of galen aneurysm?
cystic space (may be irregular in shape and located midline and posterosuperior to third ventricle), turbulent flow with doppler evaluation
cardiomeglay, nonimmune hydrops
ventriculomegaly with resultant macroencephaly may develop
75
What are differential diagnoses to vein of galen aneurysm?
arachnoid cysts (doppler evaluation will reveal no blood flow within) and porencephalic cysts (distiguished by abscence of blood flow and cysts communication with ventricle)
76
What is a choroid plexus cysts?
round or ovoid anechoic structures found within choroid plexus
contain CSF and cellular debris trapped within neruoepithelial folds
77
What are choroid plexus cysts associated with?
usually isolated but can be associated with other anomalies
| identified in association with aneuploidy - most common with trisomy 18 and less common in trisomy 21
78
When do choroid plexus cysts resolve?
typically resolve on their own by 22 to 26 weeks
79
What is the sonographic appearance of choroid plexus cysts?
cyst within choroid plexus ranging in size from 0.3-2cm
| unilateral or bilateral; solitary or multiple; unilocular or multilocular; enlargement of ventricle with large cyst
80
What is porencephalic cysts?
porencephaly
cysts filled with CSF that communicate with ventricular system or subarachnoid space
affected brain parenchyma undergoes necrosis, brain tissue is resorbed, and a cystic lesion remains
81
What may porencephaly result in?
hemorrhage, infection, delivery trauma, or inflammatory changes in nervous system
82
What is the prognosis for porencephalic cysts?
depends on degree of damage of tissue
| most cases will have come level of impairment
83
List postnatal problems associated with porencephaly.
seizures, developmental delays, motor deficits, visual and sensory problems, hydrocephalus
84
What are the sonographic features of porencephalic cysts?
cyst within brain parenchyma without mass effect; communication of cyst with ventricle or subarachnoid space; reduction in size of affected hemisphere; may cause midline shift and contralateral ventricular enlargement
85
What is a differetial diagnosis of porencephaly? What may help with differentiation?
arachnoid cysts
| lack of mass effect seen with porencephaly may aid in differentiating
86
What is schizencephaly?
a rare disorder characterized by clefts in cerebral cortex; thought to result from abnormal migration of neurons
87
What types of clefts can there be with schizencephaly?
unilateral or bilateral; open-lip or closed-lip (usually in area of sylvian fissure)
clefts can extend from ventricle to outer surface of brain and are lined with abnormal gray matter
88
What is schizencephaly associated with?
congenital infections, drugs, other toxic exposures, vascular accidents (blood interupted to brain), metabolic abnormalities, aneuploidy
89
Describe the prognosis of schizencephaly.
varies with mild to severe outcomes
open-lip lesions and bilateral clefts carry a worse prognosis
long term effects include blindness; motor deficits may include spastic quadriparesis, hemiparesis, hypotonia
seizures, mental retardation and language impairment are possible
hydrocephalus may be progressive and require shunt in place
90
What is the sonographic appearance of schizencephaly?
fluid filled cleft in cerebral cortex extending from ventricle to calvarium; absence of CSP and corpus callosum
hydrocephaly can be seen when ventriculomegaly present; microcephaly has been observed
91
What is hydrancephaly?
destruction of cerebral hemispheres by occlusion of internal carotid arteries
brain parenchyma destroyed and replaced by CSF
92
What brain structures are preserved with hydrancephaly?
posterior communicating arteries (within circle of willis); midbrain and cerebellum present; basal ganglia, choriod plexus, thalamus may be spared
93
What is associated with hydrancephaly?
polyhydramnios
94
What is the cause of hydrancephaly?
cause involves congenital infection or ischemia;
infections assoications include cytomegalovirus and toxoplasmosis
brain ischemia may result from maternal hypotension, twin-to-twin embolization, or vascular agenesis; has been assoicated with cocaine use
95
The prognosis of hydrancephaly is:
grave, with death occuring at birth or shortly after
96
Sonographically, what does hydrancephaly look like?
absence of normal brain tissue with almost complete replacement by CSF
absent or partially absent falx; presence of midbrain, basal ganglia, cerebellum; choroid plexus may be identified; macrocephaly may occur
97
What are the differentials for hydrancephaly?
hydrocephalus and holoprosencephaly
98
What is hydrocephalus?
ventriculomegaly - dilation of ventricles within brain coupled with enlargement of fetal head
99
What causes ventriculomegaly?
occurs with obstruction of CS flow
obstruction may be caused by ventricular defect like aqueductal stenosis (noncommunicating hydrocephalus)
obstruction may be outside of ventricular system (with arachnoid cyst) - communicating hydrocephalus
100
What is associated with ventriculomegaly?
aqueductal stenosis, arachnoid cysts, vein of galen aneurysms; DWM, ACC, schizencephaly, holoprosencephaly, musculoskeletal anomalies; congenital infections (toxoplasmosis and cytomegalovirus)
common causes include spina bifida and encephaloceles; intracranial neoplasms (teratoma) may cause ventricular dilation
101
Describe the difference between communicating and non-communicating hydrocephalus.
communicating hydrocephalus is when obstruction occurs outside of the ventricular system (such as with arachnoid cyst)
non-communicating hydrocephalus is when obstruction is caused by a centricular defect (like aqueductal stenosis)
102
Describe the progression of ventriculomegaly.
progresses from occipital horns into temporal then to frontal ventricular horns
103
When is the ventricle considered dilated?
when the diamter exceeds 10mm
104
What is the prognosis for hydrocephalus?
mortality rate is high
outcome depends largely on presence and severity of associated anomalies
prognosis improved in those with isoloated ventriculomegaly
survivors may require ventricular shunting to improve survival and intellectual outcome
105
Sonographically, what does ventriculomegaly look like?
lateral ventricular enlargement (>10mm); dangling choroid sign; possible dilation of 3rd and 4th ventricles; fetal head enlargement
106
With suspected centriculomegaly, what obstetric management should be done?
amniocentesis (to rule out chromosomal anomalies_, lab tests (rule out congenital infections)
fetus should be surveyed for associated anomalies and for defects involving face, heart, kidneys, abdominal wall, thorax, and limbs
107
What are differentials with hydrocephalus?
hydranencehpaly and holoprosencephaly
to differentiate, document complete falx and presence of choroid plexus in lateral ventricles, as well as seperate 3rd and 4th ventricles
108
What is microcephaly?
abnormally small head that falls two standard deviations below the mean
this occur because brain is reduced in size
109
What is the cause of microcephaly?
more commonly caused by associated anomaly
my result from inheritance of either autosomal-dominant or autosomal-recessive pattern
may also occur with chromosomal aberrations and various brain anomalies
teratogens linked with microcephaly
110
What is the prognosis of microcephaly?
depends to a degree on cause
| 85% of children with microcephaly are mentally retarted
111
When may microcephaly be diagnosed?
after 24 weeks
because microcephaly may manifest later in pregnancy, diagnosis before 24 weeks may be nearly impossible
(monthly serial measurements should be done with an at risk fetus)
112
What is the sonographic appearance of microcephaly?
small BPD, small HC, abnormal HC/AC and HC:FL ratios
| disorganized brain tissue and ventriculomegaly
113
What is cranial anomalies are associated with microcephaly? Other associations?
porencephaly, agensis of corpus callosum, craniosyntosis, holoprosencephaly, lissencephaly, schizencephaly, macrogyria, microgyria, agyria, kleeblattschadel defect (cloverleaf skull)
also associated with trisomies 13 (most common), 18,21,22, triploidy; meckel-gruber syndrome
