Fetal Central Nervous System pt 1

Question 1

______ begins with the formation of the neural plate, followed by an neural folds, and ultimate fusion and closure by six menstrual weeks

Answer 1

Neurulation

Question 2

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

Answer 2

six

Question 3

how do you evaluate the fetal spine?

Answer 3

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

Question 4

what 3 centers of ossification must you identify?

Answer 4

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

Question 5

what structures must be documented of the fetal brian?

Answer 5

cavum septum pellucidum and lateral ventricles

Question 6

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

Answer 6

cavum septum pellucidum

Question 7

these are filled with echogenic Choroid plexus

Answer 7

lateral ventricles

Question 8

how do you measure the lateral ventricles?

Answer 8

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)

Question 9

how is biparietal diameter (BPD) taken?

Answer 9

from outer side of the parietal bone in the near field to inner aspect of the parietal bone in the far field

Question 10

how is the head circumference measured?

Answer 10

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

Question 11

where is the cerebellum measured and what can it tell us?

Answer 11

at its widest point

it closely dates the pregnancy up until the third trimester

Question 12

the ______ is a space at the midline posterior to the cerebellum and anterior to the echogenic fetal skull

Answer 12

cisterna magna
the measurement is taken from anterior to posterior
normal values are 2-12 mm

Question 13

when and how is the nuchal fold (skin at the nape of the neck) measured?

Answer 13

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

Question 14

what is the normal value of the nuchal fold and what makes it thickened?

Answer 14

normal values are less than 6 mm, will be thickened in cases of chromosomal abnormalities like turners syndrome

Question 15

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

Answer 15

neural tube defect

Question 16

routine prenatal testing that reveals an elevated maternal serum ______ is an indication for targeted ultrasound to rule out a fetal neural tube defect

Answer 16

alpha-fetoprotein

Question 17

______ can detect acetyl cholinesterase, which is elevated in the amniotic fluid when there is a neural tube defect

Answer 17

amniocentesis

Question 18

______ is a congenital absence of the cerebral hemispheres and the cranial vault, occurs approximately one of every 1000 births

Answer 18

anencephaly

Question 19

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)

Answer 19

24, skin and bone

Question 20

what is anencephaly associated with?

Answer 20

polyhydramnios due to inefficient fetal swallowing and may also be associated with spina bifida

Question 21

what is the US findings of anencephaly?

Answer 21

• 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

Question 22

______ (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

Answer 22

Acrania

Question 23

What are the sonographic findings of acrania?

Answer 23

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

Question 24

______ (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

Answer 24

Encephaloceles

Question 25

Where are encephaloceles located?

Answer 25

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

Question 26

What are the sonographic findings of encephalocele?

Answer 26

• purely cystic extracranial mass which would indicate meningocele only
• solid mass with contiguous cranium which would indicate a cephalocele hydrocephalus
• polyhydramnios

Question 27

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

Answer 27

Spina bifida

Question 28

Spina bifida most commonly occurs in the ______ region

Answer 28

Lumbosacral

Question 29

Fetuses with spina bifida may have what conditions?

Answer 29

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

Question 30

What are the sonographic findings of spina bifida?

Answer 30

(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

Question 31

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)

Answer 31

Lemon sign, banana sign

Question 32

_______ 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

Answer 32

Iniencephally

Question 33

What is the sonographic findings of iniencephally?

Answer 33

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

Question 34

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 ______

Answer 34

Third ventricle (answer for both spaces)

Question 35

The single third ventricle then communicates with the forth ventricle more inferiorly via the ______ or aqueduct of Sylvis

Answer 35

Cerebral aqueduct

Question 36

From the forth ventricle, there are 2 lateral arpetures called ______ of ______

Answer 36

Foramen of Lushka

Question 37

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

Answer 37

Magendie

Question 38

It is the paired ______, located in the lateral ventricle that makes cerebrospinal fluid

Answer 38

Choroid plexuses