Fetal Head and Brain Flashcards
When do neural tube defects occur?
when the embryonic neural tube fails to close
When should the neural tube normally close?
by 6 weeks
What are neural tube defects related to?
increased levels of maternal serum alpha fetoprotein (MSAFP)
What is an accurate diagnosis of NTD?
Ultrasound
*What has been proven to reduce the risk of developing NTD?
*folic acid (4mg)
What achieving combination of screening is used for neural tube defects?
-sonography, amniocentesis, and/or maternal screening
What lab values are combined for *maternal serum screening (triple screen)?
- Human chorionic gonadotropin
- Estriol
- Maternal serum alpha-fetoprotein (MSAFP)
Where is alpha-fetoprotein (AFP) initially produced?
-by the yolk sac, fetal gastrointestinal tract, and the fetal liver, respectively
What/where does AFP exit and what does this result in?
-exits the fetus through an opening in the neural tube if one is present (i.e. an opening in the cranium or spine), thus allowing for a greater amount to pass into the maternal circulation
What are elevated levels of AFP found in?
- neural tube defects
- omphalocele
- gastroschisis
- multiple gestations
- fetal demise
- incorrect gestational dating
What are the types of NTD?
- acrania: absence of cranial vault
- encephalocele
- hydrocephalus
- iniencephaly: short cervical spine
- schizencephaly: clefting of cerebral tissue
- spina bifida
- chiari malformation
*What is Acrania?
- anencephaly
- the most common neural tube defects
- defined as the absence of the cranial vault above the bony orbits
When is the cranium normally ossified?
-by 15 wks and should be easily visualized
What are the two main subtypes of acrania (differentiate)?
- Anencephaly: considered when there are no cerebral hemispheres present
- Exencephaly: denotes the presence of a normal amount of cerebral tissue
What are the sonographic findings of acrania/anencephaly?
1) absence of cranial vault
2) some cerebral tissue may be present
3) froglike facies or bulging eyes
4) can be identified as early as 12 wks
*Encephalocele?
- *meninges and brain tissue herniation through a bony defect in the calvarium
- *most common location is in the occipital region
- can also be distinguished by location
- may have frontal and parietal positions
- usually leads obstruction of flow of CSF
- poor prognosis
- can be part of Meckel Gruber syndrome & Pentalogy of Cantrell
What are the sonographic findings for encephalocele?
1) open cranial defect
2) small or obliterated cisterna magna
3) complex mass protruding from the cranium
4) abnormal appearance of intracranial structures
What are the different types of cephaloceles and their contents?
- meningocele-> meninges only
- encephalocele-> brain tissue only
- encephalomeningocele-> both meninges and brain tissue
- ecephalomeningocystocele-> meninges, brain tissue, and lateral ventricle
What is hydrocephalus?
- caused by abnormal CSF drainage or the brain producing too much CSF
- this lead to dilated lateral ventricles first then the other ventricles will dilate too
- obstructive hydrocephalus is the buildup of CSF within the ventricular system secondary to some type of obstruction
- *dilation of the lateral ventricles is the first sign of hydrocephalus > 10 mm width
What are the two main types of hydrocephalus?
- communicating hydrocephalus is apparent when the obstruction lies outside of the ventricular system
- non-communicating hydrocephalus is when the obstruction level is located within the ventricular system
What is ventriculomegaly?
- *dilation of the lateral ventricles, other ventricles are normal
- most common cranial abnormality
- suspicion of ventricular dilation occurs when the atrial diameter measures greater than 10 mm
What is the sonographic finding of the “dangling choroid” sign?
-it describes the echogenic choroid plexus, hanging limp and surrounded by CSF, within the dilated lateral ventricle
*How is ventriculomegaly described (in terms of degrees/severity) and etc.?
- mild: 10-15mm
- moderate: 16-20mm
- severe: >20mm
- frequently associated with other severe developmental abnormalities
- difficult to distinguish from hydrocephalus by sonography only
What is ventriculomegaly associated with?
- polyhydramnios
- myelomeningocele
- encephalocele
- dandy walker malformation
What is aqueduct stenosis?
- *the most common cause of hydrocephalus in utero
- the cerebral aqueduct (aqueduct of Sylvius), located between the 3rd and 4th ventricle of the brain, may be narrowed, thus preventing the flow of CSF from the 3rd to the 4th ventricle
What will the obstruction from aqueduct stenosis cause?
-will cause the 3rd ventricle and both lateral ventricle to expand, while the 4th ventricle remains normal
What is Arnold-Chiari Malformation?
- displacement of the brain structures of the posterior fossa through the foramen magnum into the cervical canal
- strong association with *open spina bifida
What does Arnold-Chiari malformation have a strong association with?
-*open spina bifida
What may spina bifida result in?
- a mass that protrudes from the spine
- cerebellum will become displaced inferiorly and posteriorly and appear curved in the presence of spina bifida, which is referred to as the *“banana” sign
What happens to the frontal bones with spina bifida? sign?
-frontal bones become flattened and will yield a lemon shape to the cranium, which is referred to as the *“lemon” sign (scalloping of the frontal bones)
What is the result of the cerebellum being displaced inferiorly?
-*the cisterna magna is completely obliterated or <2mm
What is colpocephaly?
-when the frontal horns ar small and slit like, while the occipital horns are enlarged
What are the sonographic findings of Arnold-Chiari malformation?
- lemon sign: lemon shaped cranium w/ flattened frontal bones
- banana sign: banana shaped cerebellum
- obliterated cisterna magna
- colpocephaly
- enlarged massa intermedia
- hydrocephalus
- open spinal defect
What is schizencephaly associated with?
- *associated with the development of fluid-filled clefts within the cerebellum
- associated with: agenesis of corpus callosum, agenesis of cavum septum pellucidum, and ventriculomegaly
What is the sonographic appearance of schizencephaly?
is that of a cerebrum containing clefts filled with anechoic cerebrospinal fluid
What is hydranencephaly?
- a fatal condition in which the entire cerebrum is replaced by large sac containing cerebrospinal fluid
- *will be no cerebral cortex identified
- the falx cerebri may be partially or completely absent, while the brainstem and basal ganglia are maintained and surrounded by cerebrospinal fluid
What are the causes of hydranencephaly?
- bilateral occlusion of the internal carotid arteries w/ subsequent destruction of the cerebral hemispheres
- intrauterine infections such as cytomegalovirus and toxoplasmosis lead to the destruction of the cerebral hemispheres
- hydranencephaly can be difficult to differentiate with the sonographic findings of hydrocephalus and alobar holoprosencephaly
What is important to note with both hydrocephalus and holoprosencephaly?
-there will be a rim of cerebral tissue maintained, while with hydranencephaly there is no cerebral mantle present
What is the typical outcome of hydranencephaly?
-it is typically a fatal condition, with death occurring in the first year of life
What is holoprosencephaly?
-it is a midline brain anomaly that is associated with not only brain aberrations but also atypical facial structures
How may holoprosencephaly be detected?
-with endovaginal imaging as early as the first trimester
What is holoprosencephaly commonly seen with?
*with Trisomy 13 (Patau syndrome)
What are the 3 main types of holoprosencephaly?
-alobar, semilobar, and lobar
Which forms of holoprosencephaly are most consistent with life and death?
- lobar form can be consistent with life
- alobar is most severe form, often resulting in neonatal death
When is alobar holoprosencephaly diagnosed?
- when there is absence of corpus callosum, cavum septum pellucidum, 3rd ventricle, interhemispheric fissure and falx cerebri
- will also be evidence of a horseshoe shaped monoventricle and the lobes of the thalamus will be fused and echogenic in appearance
- conversely, the cerebellum and brainstem remain intact
What remains intact with alobar holoprosencephaly?
-the cerebellum and brainstem
What is cyclopia?
a condition in which the orbits are fused and contain a single eye, and proboscis, a false nose situated above the orbits, are two of the most disturbing external findings associated with holoprosencephaly
What is a proboscis?
fleshy, tongue like appendage that is typically located within the midline above the orbits in association with cyclopia and holoprosencephaly
What are other facial anomalies that may be detected during a fetal sonogram?
- anophthalmia
- hypotelorism
- median cleft lip
- cebocephaly (close set eyes and a nose with a single nostril
What are the fetal head shapes and their associated anomalies?
- lemon: Chiari II malformation
- strawberry: trisomy 18
- cloverleaf: thanatophoric dysplasia
- microcephaly (small head): TORCH infections, Trisomy 13 and 18, Meckel-Gruber Syndrome, fetal alcohol syndrome
- macrocephaly (large head): hydrocephalus, hydranencephaly, intracranial tumors, familial inheritance, Beckwith-Weidemann syndrome
- brachycephaly (short & wide): craniosynostosis, trisomy 21, trisomy 18
- dolichocephaly (long & narrow): craniosynostosis
What is Dandy-Walker malformation (DWM)?
- splaying of cerebellar lobes by dilated 4th ventricle
- partial or compete absence of the cerebellar vermis
- fluid filled space in the posterior fossa
- CM > 10mm
- associated with maternal diabetes, infection, alcohol abuse, coumadin usage
What is actually a classification within a larger group of anomalies referred to as the Dandy-Walker complex?
DWM (dandy walker malformation)
Dandy Walker complex is a a spectrum of what?
posterior fossa abnormalities that involve the cystic dilation of the cisterna magna and 4th ventricle
*What are the sonographic findings of DWM?
1) enlarged cisterna magna (>10mm) that communicates with a distended 4th ventricle through a defect in the cerebellum
