C11: Neural Tube Pathology Flashcards
Where would we see the 4 ventricle when scanning?
On the anterior and inferior edge of the cerebellum
How would you angle the probe from the posterior fossa view p the see the 4th ventricle
Inferior
What is hydrocephalus
What commonly causes it?
An increase in CSF that results in enlargement of the ventricles
Usually due to obstruction long the path of the CSF
What is the most common cranial anomaly
Hydrocephalus
What happens in aqueduct stenosis? What does it cause
- CSF can’t flow from the 3rd and 4th ventricle
- lateral and 3rd ventricles are enlarged
- 4th ventricle is normal
- larger ventricles lead to hardly any brain mantel developing
Aqueduct stenosis is a cause of intRAventricular obstruction hydrocephalus
How will the choroid appear w/ aqueduct stenosis
Posterior choroid will be dangling
Anterior choroid will be resting on mid line
What does it mean if you can see the 3rd ventricle on US
It means that it’s enlarged
What can cause extraventricular obstruction hydrocephalus
Spinal bifida
Excess CSF
Dandy walker malformation
How can spinal bifida cause extracellular obstruction hydrocephalus
Which ventricles does it effect
CSF can’t flow normally through the spinal canal and backs up into the ventricles
Effects all ventricles
Where do we measure the ventricles
What is the upper limit of normal
At the atria or parietal occipital fissure
Upper is 10mm
What should the measurement from the medial ventricle wall to the choriod be?
<3mm
What is true hydrocephalus
CSF obstruction
What are the true causes of true hydrocephalus
Neural tube defect
Aqueduct stenosis
Dandy walker malformations
What is ventriculomegaly
Caused by brain atrophy which allows the ventricles more room to expand… NOT DUE TO OBSTRUCTION
If you see hydrocephalus, which view of the brain should you assess
The posterior fossa view
Look at cisterna magna and cerebellum to assess for:
- obliterated cisterna magna
- deformed cerebellum (banana)
- lemon sign
When would the lemon sign be seen
2nd trimester
When does the lemon sign occur
Results when cranial contents are pulled towards the spine w/ Arnold chiari II malformations
How does the lemon sign appear of US
Frontal bones caved in
When does the lemon sign disappear
In 3rd trimester due to the resulting hydrocephalus from the enlarging ventricles of the blocked CSF
Where are the most common places for a neural tube defect
Lumbosacral area
What type of Arnold chiari do we see on ultrasound
Type 2… other types are so lethal that fetus will die very early on
The higher up the neural tube defect goes, is this better or worse in terms of deficits of the baby
Worse
Describe dandy walker malformation. What characteristics should you look for
- enlarged cisterna magna and absent cerebellar vermis
- cisterna magna communicates w/ the 4th ventricle through the defect in the cerebellum (absent vermis)
- ventricles can be enlarged due to pressure in the posterior fossa
What is a dandy walker variant
Partial agenesis of the vermis w/ smaller cisterna magna and minimal dilation of the ventricles
-associated w/ many syndromes
What is DWM associated w/
-Intellectual impairment and fetal death
- agenesis or corpus callosum
- heart defects
- genitourinary defects
- polydactyly
The risk of DWM increases w/ what 3 things?
Maternal viral infection
Alcohol consumption
Maternal diabetes (type 1 only)
What’s the differential diagnosis for DWM and how does it appear
Arachnoid cyst in posterior fossa
-fluid collection in the layers of the arachnoid membrane
What can the nuchal fold be assessed (wks) and why
B/w 16-20 wks because babies may have large fat deposits in this are after 20 wks
What is acrania
Absent skull
What is Anencephaly
No or destroyed cerebral cortex
What is exencephaly
Some cerebral cortex but it’s abnormal
May be an early stage of anencephaly
Why is it problematic that brain tissue is exposed to amniotic fluid
The amniotic tissue is damaged by the amniotic fluid which leads to exencephaly
What does acranial lead to?
Leads to exencephaly and then anencephaly
What are the US features of exencephaly
Facial structures and orbits are present No skull above the orbits Polyhydramnios usually baby can’t swallow) Active fetus Frog like face
Exencephaly can’t be diagnosed before how many wks
prognosis?
12-13 wks
fatal
Can you still have a normal CRL w/ anencephaly?
Yes
