Chapter 59, The Fetal Neural Axis Flashcards
Many of the congenital malformations of the CNS result from
incomplete closure of the neural tube
A wide range of defects resulting from incomplete closure of the neural tube may affect what?
the spine and/or brain
What is anencephaly?
neural tube defect characterized by the lack of development of the cerebral and cerebellar hemispheres and cranial vault
T/F: anencephaly is compatible with life?
false
What is the most common neural tube defect?
anencephaly
What is the overall incidence of anencephaly in pregnancies in the US?
1 in 1,000
Where is there a much higher prevalence of anencephaly?
the U.K.
Prevalence of gender and race related to anencephaly?
female prevalence of 4 to 1, white to black of 6 to 1
What is the cause of anencephaly?
failure of closure of the neural tube at the cranial end…result is the absence of the cranial vault, complete or partial absence of the forebrain (Which may partially develop then degenerate,) and the presence of the brain stem, midbrain, skull base, facial structures.
Up to ____% of cases of anencephaly result in fetal demise?
50%, remainder die at birth or shortly after
T/F: With anencephaly, early diagnosis is preferred?
True
T/F: Maternal serum alpha-fetoprotein levels are extremely high with anencephaly?
True, because of the absent skull and exposed tissue
Anencephaly may result from what?
Meckel-Gruber syndrome or a chromosomal abnormality like trisomy 13
T/F: There is an increased risk of anencephaly in patients with diabetes?
True
Environmental and dietary factors that may increase the prevalence of neural tube defects include:
- hyperthermia
- folate and vitamin deficiencies
- teratogenic levels of zinc
- amniotic band syndrome
Sonographic features of anencephaly include:
- absence of brain and cranial vault
- rudimentary brain tissue characterized as the cerebrovasculosa
- bulging fetal orbits, giving a froglike appearance
- polyhydramnios (may not be present until after 26 weeks.)
- coexisting spina bifida and/or craniorachisschisis
Related anomalies of anencephaly include:(7)
- cleft lip and palate
- hydronephrosis
- diaphragmatic hernia
- cardiac defects
- omphalocele
- GI defects
- talipes
Acrania is AKA:
exencephaly
What is acrania?
a lethal anomaly that manifests as complete or partial absence of the cranial bones with the presence of complete, although abnormal, development of the cerebral hemispheres
When does acrania occur?
the beginning of the 4th gestational week
T/F: Acrania is rare?
True
Disorders that may mimic acrania:
- anencephaly
- hypophosphatasia
- osteogenesis imperfecta (result in hypomineralization of the cranium.)
Sonographic features of acrania:
- presence of brain tissue without the presence of a calvarium
- disorganization of brain tissue
- prominent sulcal markings
What is cephalocele?
A neural tube defect in which the meninges alone or meninges and brain herniate through a defect in the calvarium
What is encephalocele?
used to describe herniation of the meninges and brain through the defect
What is cranial meningocele?
The herniation of only meninges
Cephaloceles occur at a rate of
1-3 in 10,000 live births
In 75% of cephalocele cases:
the cephalocele involves the occipital bone and is located in the midline, although it may also involve the parietal and frontal regions
The prognosis for the infant with a cephalocele varies based on:
- size
- location
- involvement with other brain structures
The sonographic features of cephaloceles include:
- an extracranial mass which may be fluid filled or contain solid components
- a bony defect in the skull
- ventriculomegaly (usually w/ encephalocele)
- polyhydramnios
Coexisting anomalies of cephalocele include:
- microcephaly
- agenesis of the corpus callosum
- facial clefts
- spina bifida
- cardiac anomalies
- genital anomalies
Chromosomal anomalies and syndromes ID’d with cephaloceles include:
- Trisomy 13
- Meckel-Gruber syndrome
What is Meckel-Gruber syndrome?
an autosomal-recessive disorder characterized by encephalocele, polydactyly and polycystic kidneys
What is spina bifida?
encompasses a wide range of vertebra defects that result from failure of neural tube closure (there is a cleft or opening in the spine)
What may protude through spina bifida?
the meninges and neural elements
What is a form of spina bifida that is covered with skin or hair?
spina bifida occulta
What is spina bifida occulta associated with?
a normal spinal cord and nerves and normal neurologic development
T/F: Spina bifida occulta is extremely difficult to detect in the fetus?
True
T/F: because spina bifida occulta is covered by skin, the maternal serum alpha-fetoprotein level will be normal.
True
When the defect involves only protrusion of the meninges it is termed ______.
meningocele
When the meninges ad neural elements protrude through the defect, this is called ____.
meningomyelocele
If the defect is very large and severe, it is termed _______
rachischisis
Meningoceles, meningomyeloceles, and rachischisis are commonly associated with:
increased maternal serum alpha-fetoprotein
Spina bifida is associated with varying degrees of neurologic impairment which may include
minor anethesia, paraparesis, or death
Fetuses with myelomeningoceles often present with
cranial defects associated with Arnold-Chiari (type 2) malformation
Describe Arnold-Chiari (type 2) malformation
presents invariably with hydrocephalus because of the cerebellar vermis, which becomes displaced into the cervical canal, giving the cerebellum a banana appearance and obliterates the cisterna magna. Also, caudal displacement of the cranial structures causes scalloping of the frontal skull bones, resulting in a lemon shape.
Sonographic findings of spina bifida include:
- 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
- talipes
- cephaloceles
- cleft lip and palate
- hypotelorism
- heart defects
- genitourinary anomalies
What should be documented once a spinal defect has been ID’d? (3)
- the level and extent of the defect
- the presence of absence of neural elements contained in the protruding sac
- associated intracranial findings
Associated sonographic cranial findings of spina bifida include:
- lemon-shaped head
- obliteration of cisterna magna
- inferior displacement of cerebellar vermis, giving cerebellum a banana shape
- ventriculomegaly
T/F: The lemon sign is specific to spina bifida.
False, seen in other CNS malformations like encephalocele and non-CNS malformations like thanatophoric dysplasia
Spina bifida has been associated with
- trisomy 18
- maternal diabetes
- hyperthermia
- folic acid deficiency
What does Dandy-Walker malformation manifest with?
Agenesis or hypoplasia of the cerebellar vermis with resulting dialation of the fourth ventricle.
When is Dandy-Walker thought to occur?
before the 6th or 7th week
What is thought to cause Dandy-Walker?
abnormal embryogenesis of the roof of the fourth ventricle
What % of the time is Dandy-Walker associated with other intracranial anomalies?
50%
What intracranial anomalies are associated with Dandy-Walker? (8)
- agenesis of the corpus callosum
- aqueductal stenosis
- microcephaly
- macrocephaly
- encephalocele
- gyral malformations
- heterotopias
- lipomas
What chromosomal anomalies are associated with Dandy-Walker?
Trisomies 13, 18, 21
What syndromes are associated with Dandy-Walker?
- Meckel-Gruber
- Walker-Warburg
- Aicardi’s
Sonographic features of Dandy-Walker include: (4)
- a posterior fossa cyst that can vary in size
- splaying of the cerebellar hemispheres as a result of the complete or partial agenesis of the cerebellar vermis
- enlarged cisterna magna
- ventriculomegaly
What does holoprosencephaly result from ?
abnormal cleavage of the prosencephalon
What is the incidence of holoprosencephaly?
1 in 10,000 to 20,000 live births
Holoprosencephaly is associated with chromosomal anomalies in ___% of cases
50%, But may also be a sporadic event or associated with syndromes, genetic factors and teratogens
What are the three forms of holoprosencephaly in descending severity?
- alobar
- semilobar
- lobar
Alobar holoprosencephaly is characterized by:
- singular monoventricle brain tissue that is small and may have a cup, ball, or pancake configuration
- fusion of the thalamus
- absence of the interhemispheric fissure, cavum septum pellucidum, corpus callosum, optic tracts, olfactory bulbs
Semilobar holoprosencephaly presents with:
- a singular ventricular cavit with partial formation of the occipital horns
- partial or complete fusion of the thalamus
- a rudimentary falx and interhemispheric fissure
- absent corpus callosum, cavum septum pellucidum, olfactory bulbs
Lobar holoprosencephaly presents with:
an almost complete division of the ventricles with a corpus callosum that may be normal, hypoplastic, or absent, although the cavum septum pellucidum will still be absent
What chromosomal anomaly has been associated with holoprosencephaly?
Trisomy 13
What syndromes have been associated with holoprosencephaly?
- Meckel-Gruber
- Aicardi’s
- Fryns
- hydrolethalus syndrome
Teratogens reported to produce holoprosencephaly include: (5)
- alcohol
- phenytoin
- retinoic acid
- maternaal diabetes
- congenital infections
Sonographic features of holoprosencephaly include: (11)
- common C-shaped ventricle that may be enlarged
- brain tissue wth a horseshoe shape as it surrounds the monoventricle
- fusion of the thalamus with absence of 3rd ventricle
- absence of interhemispheric fissure
- a dorsal sac with expansion of the monoventricle posteriorly
- absence of the corpus callosum
- absence of the cavum septum pellucidum
- hydrocephaly
- microcephaly
- polyhydramnios
- IUGR
Holoprosencephaly is often associated with ___ anomalies.
facial
Facial anomalies with holoprosencephy include: (5)
- cyclopia
- hypotelorism
- an absent nose
- a flattened nose with a single nostril
- proboscis
Cebocephaly consists of a combination of
hypotelorism with a normally placed nose with a single nostril
Ethmocephaly consists of
severe hypotelorism with a proboscis superior to the eyes
What facial clefts are most common with holoprosencephaly?
-median or bilateral
What defects can be ID’d in the presence of holoprosencephaly?
- renal cysts or dysplasia
- omphalocele
- cardiac defects
- spina bifida
- talipes
- GI problems
________ anomalies must be considered if holoprosencephaly is present
Chromosomal , esp Trisomy 13
What is the corpus callosum?
a fibrous tract that connects the cerebral hemispheres and aids in learning and memory
Dysgenesis of the corpus callosum describes:
a range of complete to partial absence of the callosal fibers that cross the midline, forming a connection between the two hemispheres
Likely cause of agenesis of the corpus callosum?
a vascular disruption of inflammatory lesion before 12 weeks
Agenesis of the corpus callosum is associated with other CNS malformations, including: (5)
- hydrocephals
- gyral anomalies
- heterotopias
- Dandy-Walker malformation
- Holoprosencephaly
Chromosomal anomalies that may accompany agenesis of the corpus callosum include:
- Trisomies 13, 18, 8
- Triploidy
What syndromes are associated with agenesis of the corpus callosum? (4)
- Aicardi
- Apert
- Opitz
- Joubert
Sonographic findings of agenesis of the corpus callosum: (15-just kill me now)
- absence of cavum septum pellucidum
- widely seperated lateral ventricular frontal horns with medial indentation of media walls
- elevation and dilation of 3rd ventricle
- small frontal horns and dilated occipital horns (colpocephaly), giving lateral ventricles teardrop shape
- holoprosencephaly
- DWM
- cranial lipoma
- Arnold-Chiari malformation
- septo-optic dysplasia
- hydrocephaly
- encephalocele
- porencephaly
- microcephaly
- lissencephaly
- “sunburst” of cerebral sulci
What is colpocephaly?
small frontal horns and dilated occipital horns
Abnormalities associated with agenesis of the corpus callosum
- cardiac malformation
- diaphragmatic hernia
- lung agenesis or dysplasia
- absent/dysplastic kidneys
What does aqueductal stenosis result from?
- obstruction
- atresia
- stenosis of the aqueduct of Sylvius causing ventriculomegaly
The aqueduct of Sylvius connects
the 3rd and 4th ventricle
Sonographic findings of aqueductal stenosis: (3)
- ventricular enlargement of lateral ventricles
- third ventricular dilation
- flexion and adduction of the thumb
What is a rare arteriovenous malformation?
an aneurysm of the vein of Galen
T/F: Vein of Galen aneurysm is considered a sporatic event and has a male prodominance?
True
What has a Vein of Galen aneurysm been associated with? (3)
- congenital heart defects
- cystic hygromas
- hydrops
Sonographic findings with Vein of Galen aneurysm: (4)
- cystic space that may be irregular in shape and is located midline and posteriosuperior to the third ventricle
- turbulent flow with Doppler evaluation
- fetal cardiomegaly
- nonimmune hydrops
What are choroid plexus cysts?
round or oval anechoic structures found within the choroid plexus, containing cerebrospinal fluid and cellular debris that is trapped within the neuroepithelial folds
When will choroid plexus cysts often resolve?
-22-26 weeks
Choroid plexus cysts have been associated with:
aneuploidy, esp. trisomies 18 and 21
Sonographic features of choroid plexus cysts: (5)
- cysts ranging from 0.3 to 2 cm
- unilateral or bilateral cysts
- solitary or multiple
- unilocular or multilocular
- enlargement of the ventricle with large cyst
What is porencephaly?
cysts filled with CSF that communicate with the ventricular system or subarachnoid space
What can porencephalic cysts result from?
hemorrhage, infarction, delivery trauma, or inflammatory changes on the nervous system
Sonographic features of porencephalic cysts include: (3)
- a cyst within the brain parenchyma without mass effect
- communication of the cyst with the ventricle or subarachnoid space
- reduction in size of the affected hemisphere, may cause a midline shift and contralateral ventricular enlargement
What is schizencephaly?
a rare disorder characterized by clefts in the cerebral cortex (clefts may be unilateral, or bilateral, open-lip or closed-lip defects.)
What is schizencephaly associated with?
congenital infections, drugs and other toxic exposures, vascular accidents, metabolic abnormalities
T/F: prognosis for patients with schizencephaly varies?
true
Sonographic features of schizencephaly include:
- a fluid-filled cleft in the cerebral cortex extending from the ventricle to the calvarium
- ventriculomegaly
- agenesis of the CSP and corpus callosum (50% of time)
What is lissencephaly?
When the surface of the brain lacks normal sulci and gyri and appears smooth
When can lissencephaly be diagnosed?
3rd trimester
What can lissencephaly be associated with?
mild ventriculomegaly and abnormal corpus callosum
What is hydraencephaly?
destruction of the cerebral hemispheres by occlusion of the internal carotid arteries. Brain parenchyma is destroyed, replaced by CSF.
What parts of the brain are spared with hydraencephaly? (5)
- midbrain
- cerebellum
- basal ganglia
- choroid plexus
- thalamus
What causes hydraencephaly?
congenital infection or ischemia or cocaine abuse
What can cause brain ischemia?
- maternal hypotension
- twin-to-twin embolization
- vascular agenesis
Sonographic features of hydraencephaly: (6)
- absence of normal brain tissue, almost completely replaced by CSF
- an absent/partially absent falx
- presence of midbrain, basal ganglia, cerebellum
- choroid plexus may be ID’d
- macrocephaly may occur
- polyhydramnios
What is ventriculomegaly?
dilation of the ventricles within the brain
What is hydrocephalus?
when ventriculomegaly is coupled with enlargement of the fetal head
The incidence of hydrocephalus is
0.3 -1.5 per 1,000 live births
Enlargement of the ventricles occurs with obstruction of
CSF
Noncommunicating hydrocephalus is
an obstruction caused by a ventricular defect (ie. aqueductal stenosis)
Communicating hydrocephalus is
when the obstruction may be outside of the ventricular system, such as with arachnoid cysts
Rarely ventriculomegaly results from an overproduction of CSF by a
choroid plexus papilloma
Common causes of ventriculomegaly: (2)
spina bifida and encephaloceles
What may present with hydrocephalus? (5)
- DWM
- agenesis of corpus callosum
- lissencephaly
- schizencephaly
- holoprosencephaly
Sonographic features of ventriculomegaly:
- lateraly ventricular enlargement exceeding 10 mm
- a ‘dangling choroid sign’
- possible dilation of the 3rd and 4th ventricles
- fetal head enlargement when the BPD and HC measurements exceed those for the established gest. age
What is microcephaly?
An abnormally small head that falls 2 standard deviations below the mean (occurs because the brain is reduced in size)
What is the incidence of isolated microcephaly?
1 per 1,000 births
About _____% of children with microcephaly are mentally retarded?
85%
Son. diagnosis of microcephaly depends upon:
an accurate assessment of fetal age
Diagnosis of microcephaly before ___ weeks of age is impossible.
24
Sonographic features of microcephaly: (5)
- small BPD
- small HC
- abnormal HC/AC and HC/FL ratios
- disorganized brain tissue
- ventriculomegaly
Microcephaly is associated with: (5)
- Trisomies 13, 18, 21, 22
- triploidy
What syndromes have been linked to microcephaly? (3)
- Meckel-Gruber
- Pena-Shokeir
- Neu-Laxova
What is the most common intracranial tumor found in utero?
teratoma
What do teratomas contain?
hair, sebum, fat
teratomas appear as what?
complex masses that distort the normal architecture of the brain.
