Fetal Central Nervous System pt 1 Flashcards
______ begins with the formation of the neural plate, followed by an neural folds, and ultimate fusion and closure by six menstrual weeks
Neurulation
the neural tubes closes from the center temporarily leaving both ends open, they should be closed by ______ menstrual weeks, if not then it is a neural tube defect
six
how do you evaluate the fetal spine?
in transverse plane you must run the spine from the base of the skull to the coccyx
in sagittal plane asses the normal curvatures of the spine and the sacral caudal tapering
what 3 centers of ossification must you identify?
the round center (the vertebral body) and two centers of ossification posterior to the round (in which point posteriorly) they are posterior elements to the spine or the lamina
what structures must be documented of the fetal brian?
cavum septum pellucidum and lateral ventricles
this insures an in tact corpus callosum of the fetas and is evidenced by two parallel lines in the anterior aspect of the fetal cranium with a central lucency, these are at the midline
cavum septum pellucidum
these are filled with echogenic Choroid plexus
lateral ventricles
how do you measure the lateral ventricles?
at the atrium, or largest part of the ventricles, at the level of the thalami. Normal measurement is less than 10mm Do Not measure from the midline echogenic falx (this is a pitfall)
how is biparietal diameter (BPD) taken?
from outer side of the parietal bone in the near field to inner aspect of the parietal bone in the far field
how is the head circumference measured?
using ellipse button, taken at the level of the paired Thalami which look like a walnut
then angle inferiorly to see the cerebellum, cisterna magna, and nuchal fold in the posterior cranium
where is the cerebellum measured and what can it tell us?
at its widest point
it closely dates the pregnancy up until the third trimester
the ______ is a space at the midline posterior to the cerebellum and anterior to the echogenic fetal skull
cisterna magna
the measurement is taken from anterior to posterior
normal values are 2-12 mm
when and how is the nuchal fold (skin at the nape of the neck) measured?
it is measured in fetuses who are under 24 weeks gestation only!, the measurement is taken from the outer aspect of the echogenic skull to the edge of the skin
what is the normal value of the nuchal fold and what makes it thickened?
normal values are less than 6 mm, will be thickened in cases of chromosomal abnormalities like turners syndrome
these occur anywhere along the cranium or along the spine and will allow cerebrospinal fluid of the fetus to escape into the amniotic fluid, which results in elevation of amniotic fluid and in maternal serum levels of Alpha fetoprotein
neural tube defect
routine prenatal testing that reveals an elevated maternal serum ______ is an indication for targeted ultrasound to rule out a fetal neural tube defect
alpha-fetoprotein
______ can detect acetyl cholinesterase, which is elevated in the amniotic fluid when there is a neural tube defect
amniocentesis
______ is a congenital absence of the cerebral hemispheres and the cranial vault, occurs approximately one of every 1000 births
anencephaly
anencephaly occurs with failure of the neural tube to close by ______ days of gestation, it is characterized as an open defect which is covered by an angiomatous stroma rather than covered by ______ and ______ (the brainstem and the bony skull base is present)
24, skin and bone
what is anencephaly associated with?
polyhydramnios due to inefficient fetal swallowing and may also be associated with spina bifida
what is the US findings of anencephaly?
- absence of the fetal cranial vault (bones) and cerebral hemispheres
- the face and orbits are present and look very prominent (frog face)
- polyhydromnios will be present in 40-50% of cases
______ (also called exencephally) is a developmental abnormality in which the cranium is partially or completely absent but has development of abnormal brain tissue within, it is lethal and is also associated with elevated levels of maternal serum alpha-fatoprotein
Acrania
What are the sonographic findings of acrania?
No echogenic cranium with the presence of a large amount of brain tissue (seen at 12 weeks gestation, hard to see at 16 weeks d/t lack of an ossified cranium)
*an important note is that other bones of the fetus will be present
______ (also called cephalocele) is the herniation of the brain and meninges (covering of the brain and spinal cord) through a cranial defect, prognosis depends on how much brain is involved and other associations
Encephaloceles
Where are encephaloceles located?
Usually midline, **more common in the occipital region (know this), and maybe frontal or lateral
Consider amniotic band syndrome is they are asymmetric or in an atypical location
What are the sonographic findings of encephalocele?
- purely cystic extracranial mass which would indicate meningocele only
- solid mass with contiguous cranium which would indicate a cephalocele hydrocephalus
- polyhydramnios
This is a general term for lack of closure of the vertebral column, the prognosis really depends upon the level and the severity of the opening
Spina bifida
Spina bifida most commonly occurs in the ______ region
Lumbosacral
Fetuses with spina bifida may have what conditions?
Meningocele- herniation of meninges and cerebrospinal fluid through a spinal defect
Meningomyelocele- herniation of meninges and neural elements, the spinal cord, through the spinal defect
What are the sonographic findings of spina bifida?
(In transverse plane) paired posterior elements of spine will be parallel or point laterally (open)
May see a fluid filled sac posterior to the spine and skin interruption
(In sagittal) the soft tissue defect or discontinuity of the skin and muscle of the back
Arnold-Chiari malformation shows:
______- flattening of the temporal and frontal bones due to decreased intracranial pressure (on axial image, the cranium is shaped like a lemon)
Hydrocephalus, the ventricles measure greater than 10mm
______- obliteration of the cisterna manga by an abnormal configuration of the cerebellum (cerebellum looks like a banana)
Lemon sign, banana sign
_______ is a malformation in which the occipital is fused to the cervical region, cervical spina bifida and occipital encephalocele are present in this universally fatal defect
Iniencephally
What is the sonographic findings of iniencephally?
You get the stargazer appearance- the fetuses head is stuck in an upward hyperextension as if they are stargazing
There will also be occipital encephalocele and cervical spina bifida, most common abnormal structure is the fetal intracranial ventricular system
The paired lateral ventricles empty into the ______ via the paired for foramen of Monroe, these foramina are connections from each lateral ventricle into the single ______
Third ventricle (answer for both spaces)
The single third ventricle then communicates with the forth ventricle more inferiorly via the ______ or aqueduct of Sylvis
Cerebral aqueduct
From the forth ventricle, there are 2 lateral arpetures called ______ of ______
Foramen of Lushka
There is also a single median arpeture called the foramen of _______. The three foramina allow communication of cerebral spinal fluid to flow from the ventricular system around the brain and around the spinal cord
Magendie
It is the paired ______, located in the lateral ventricle that makes cerebrospinal fluid
Choroid plexuses
