Chapter 60 Fetal Neural Axis Flashcards
CNS arises from the ectodermal neural plate around _____
18 days gestation
Cephalic neural plate develops into the
forebrain
the caudal end forms the
spinal cord
the forebrain develops into the
Prosencephalon
the mesencephalon develops into the
midbrain
the rhombencephalon develops into the
hindbrain
by the end of the 3rd week, the cephalic end of the neural tube bends into a ____ shape
c-shape
in the ____ week, the neural tube bends again
5th
The prosenceohalon divides into the
Telencephalon and diencephalon
Telencephalon becomes the
Cerebral hemispheres
Diencephalon becomes the
Thalamus
Rhombencephalon divides into the
Metencephalon and mylencephalon
Metencephalon becomes
Cerebellum and pons
Mylencephalon becomes
Medulla
Neural function begins at
6 weeks gestation
Between _____ the fetus can grip objects and is capable of weak respiratory movements
4-5 months
Fetus displays sucking reflux at ____
6 months
Most common neural tube defect
Anencephaly
Absence of brain and skull
Anencephaly aka aprosencephaly/atencephaly
Risk of anencephaly can be reduced by 50-70% with use of ______ supplements beginning 1 month before pregnancy
Folic acid
Caused by failure of the neural tube at the cranial end. Resulting in absent cranial vault, complete/partial absence of forebrain
Anencephaly
Prenatal diagnosis of anencephaly is often made with sonography, following a lab value of ___
Elevated AFP
Causes for anencephaly:
Diabetes, Meckel-Gruber syndrome
Sonographic findings of anencephaly:
Bulging fetal orbits—frog face appearance
Absence of skull
Acrania
Acrania is also known as
Exencephaly
Absence of cranial bones with the cerebral hemispheres still there(although abnormal)
Acrania
Acrania usually progresses to anencephaly because:
Brain slowly degenerates from exposure to amniotic fluid
How to distinguish acrania from anencephaly:
Presence of significant brain tissue and lack of frog-face appearance indicated acrania
Neural tube defect in which meninges alone or meninges and brain herniate through a defect in the skull
Cephalocele
Herniation of meninges AND brain through defect
Encephalocele
Herniation of only meninges through defect
Cranial meningocele
Cephalocele more commonly involves the _____ bone
Occipital
Sonographic features of cephalocele:
Extracranial mass
Ventriculomegaly
Autosomal recessive disorder characterized by encephalocele, polydactyl, polycystic kidney disease
Meckel-Gruber syndrome
Cephalocele may be confused with
Cystic hygroma
Chromosomal anomalies and syndromes associated with cephaloceles
Trisomy 13
Meckel-Gruber syndrome
Wide range of defects that result from failure of neural tube to close
Spina bifida
Spina bifida most commonly occurs along the ____ and ____ region
Lumbar and sacral
The term spina bifida means
There is an cleft/opening in the spine
Spina bifida occulta is extremely difficult to detect if
Defect is covered by skin
AFP is normal
Spinal opening covered in skin, commonly with a tuft of hair
Spina Bifida Occulta
Sounds bifida term used when defect only involves the protrusion of meninges
Meningocele
Sounds bifida term used when both meninges & neural elements protrude through defect(more common)
Meningomyelocele
Sounds bifida term used when defect is very large and severe
Rashcischisis
Raschischisis is associated with increased
AFP
Most fetus(90%) with myelomeningocele present with cranial defects associated with
Arnold-Chiari 2 malformation
Arnold-Chianti 2 malformation is ____ shaped appearance of the cerebellum
Banana
Arnold-Chiari 2 malformation leads to obliteration of the
Cisterna magna
Due to increased intracranial pressure during spina bifida, the skull will be ____ shaped
Lemon shaped
The best plane to evaluate the spine for spina bifida is:
Transverse
Normal spine should be triangular or circular, with spina bifida (meningomyelocele) the splaying of the posterior ossification centers makes a
V or U shape
Intracranial findings with spina bifida
Ventriculomegaly
Banana shaped cerebellum
Lemon shaped skull
Cisterna magna obliteration
Spina bifida is associated with chromosomal anomalies and syndromes like:
Trisomy 18
Maternal risk factors for spina bifida:
Diabetes, obesity, folic acid deficiency, hyperthermia
Rare, occiput is fused to the cervical region
Iniencephaly
Defect in occiput involving the foramen magnum, retroflexion of spine causes fetus to look upward: ____ sign. This is ____
Stargazing sign
Iniencephaly
cerebellar lobes “go for a walk”
Dandy-Walker Malformation
Agenesis or hypoplasia of the cerebelar vermis, resulting in 4th ventrical dilation and enlargement of posterior fossa
Dandy-Walker Malformation
50% of the time, Dandy-Walker Malformation is associated with
Agenisis of the corpus collosum
Dandy Walker Malformation encompasses 3 types of posterior fossa malformations:
Elevated tentorium(tent of the cerebellum)
Dialation of 4th ventricle & hypoplasia of cerebellar vermis w/o enlargement of posterior fossa
Megacisterna magna(large Cisterna magna)
Diagnosis of agenesis or hypoplasia of vermis shouldnt be made until ____ week
18 weeks gestation
Vermis begins to develop during
9th week
4th ventricle and cisterna magna are complete:
18 weeks
Extracranial abnormalities associated with Dandy-Walker Malformation(DWM):
Cardiac anomalies
Sonographic features of DWM:
Large posterior fossa cyst
Enlarged cisterna magna, ventriculomegaly
How would you differentiate a posterior fossa cyst from a subarachnoid cyst
PFC communicates with the 4th ventricle
Holoprosencephaly results from abnormal cleavage of
Prosencephalon
3 forms of holoprosencephaly
- Lobar(mild)
- Semi-lobar(middle)
- Alobar(worst)
Holoprosencephaly: Singular, monoventricle brain tissue that js small(may have cup, ball, pancake configuration). Absence of pretty much everything
Alobar
Alobar holoprosencephaly involves fusion of the ____
Thalamus
Holoprosencephaly: Singular ventricular cavity with partial formation of occipital horns, falx & interhemispheric fissure
Semi-lobar
Holoprosencephaly in which the corpus collosum may still be present
Lobar
Sonographic features of holoprosencephaly
C-shaped ventricle
Horseshoe shaped brain tissue surrounding that ventricle
Absent CSP
Facial clefts may be oresent with holoprosencephaly, most commonly they are
Medial or bilateral
Hypotelorism with normally placed nose with single nostril
Cebocephaly
Severe hypotelorism with probiscis superior to eyes
Ethmocephaly
Fibrous tract that connects the cerebral hemispheres that aids in learning and memory
Corpus collosum
Agenesis of the corpus callosum is thought to involve _____ or inflammatory lesions before 12 weeks
Vascular disruption
Maternal diseases contributing to a genesis of the corpus callosum
Diabetes
Sonographic features of agenesis of the corpus callosum
Teardrop shaped lateral ventricle
absent cavum septum pellucidum
Aqueductal stenosis results from obstruction or stenosis of the
Aqueduct of Sylvius
Sonographic features of aqueductal stenosis
Dilation of third ventricle, lateral ventricle enlargement
Rare arteriovenous malformation, predominantly occurs in males, associated with congenital heart defects
Vein of Galen Aneurysm
Vein of Galen aneurysm prognosis is especially poor when associated with
Hydrops or cardiac failure
Primary treatment for Vein of Galen aneurysm
Embolism
Vein of Galen aneurysm will show ____ flow with Doppler
Turbulent
Cystic space that may be a regularly shaped and located midline and posterosuperior to the third ventricle indicates:
Vein of Galen aneurysm
Choroid plexus cysts may be associated with
Trisomy 18
Cysts filled with CSF that communicate with the ventricular system or subarachnoid space. No known associated anomalies.
Porencephalic cysts/porencephaly
Post natal problems from porencephalic cysts/porencephaly may include
Seizures
Rare disorder characterized by clefts in the cerebral cortex
Schizencephaly
Schizencephaly is usually in the area of the _____
Sylvian fissure
Schizencephaly is linked with ___
Multiple assaults during pregnancy
In schizencephaly, _____ and ____ carry a wkrse prognosis
Open lip lesion and bilateral clefts
Sonographic features of schizencephaly
Ventriculomegaly
Fluid-filled cleft in cerebral cortex extending from ventricle to calvarium
Absent or reduced cerebral convolutions, brain lacks sulci and gyri, therefore is appears smooth
Lissencephaly
Diagnosis of lissencephaly cannot be made until
3rd trimester
Destruction of cerebral hemispheres by occlusion of the internal carotid arteries
Hydranencephaly
Coexisting chromosomal and stuctural anomalies associated with hydranencephaly
None
Hydranencephaly is associated with
Polyhydramnios
With hydranencephaly, brain ischemia may result from
Maternal hypotension
Sonographic features of hydranencephaly
Absense if normal brain tissue with almost complete replacement by CSF
Absent or partially absent falx
How do you differentiate hydranencephaly from hydrocephaly?
Look for the midline falx— if its gone it will be hydranencephaly
Hydranencephaly wont demonstrate the dangling choroid sign, hydrocephaly will
Dilation of the ventricles within the brain secondary to an increase in CSF volume
Ventriculomegaly/hydrocephalus
Ventriculomegaly/hydrocephalus can be either ____ or ______
Communicating or noncommunicating
Ventriculomegaly/hydrocephalus:
Obstruction cause by ventricular defect(aqueduct Sylvius):
Noncommunicating hydrocephalus
Ventriculomegaly/hydrocephalus:
Obstruction outside the ventricular system:
Communicating hydrocephalus
Associated abnormalities with ventriculomegaly/hydrocephalus:
Aqueductal stenosis
Vein of Galen aneurysm
Common causes of ventriculomegaly/hydrocephalus:
Spina bifida
Encephaloceles
Sonographic features of hydrocephalus/ventriculomegaly
Dangling choroid sign
What differentiates hydrocephalus/ventriculomegaly from hydranencephaly and holoprosencephaly?
Presence of complete falx, choroid plexus, 3rd & 4th ventricles
Abnormally small head that falls 2 standard deviations below the mean
Microcephaly
Factors linked with microcephaly
Alcohol abuse, heroin addiction, mercury poisoning
Microcephaly is usually associated with ______
Neurological deficits
Sonographic features of microcephaly
Abnormal measurements
Cerebral calcifications with congenital infections
Clover-leaf skull