Module 5: Fetal Neuo Pathology Flashcards
Where is CSF produced?
Choroid plexus
What is the choroid plexus?
A collection of cells located in the ventricles that produce CSF
Where in the ventricles is the choroid plexus located?
- Floor of lateral ventricles
- Roof of 3rd ventricle
- Posterior wall of 4th ventricle
Trace the flow of CSF from the lateral ventricles
Lateral ventricles through interventricular foramen to 3rd ventricle through cerebral aqueduct to the 4th ventricle and then exits medially to the magendi and laterally to the two luschka and from there it flows into the subarachnoid space and circulates with the spine and brain respectively.
What is another name for the interventricular foraman?
Foramen of Monro
What is another name for the cerebral aqueduct?
The aqueduct of Sylvius
What structures does CSF flow through to circulate the brain and spine?
Spine = Magendi (medial)
Brain = Two Luschka (lateral sides)
Where is the 4th ventricle located?
Inferiorly to cerebellum
What is the most common cranial anomaly?
Hydrocephalus
What is hydrocephalus?
Increase in CSF causing enlarged ventricles
What is “true” hydrocephalus?
Hydrocephalus caused by a CSF obstruction
What is ventriculomegaly?
Enlarged ventricles resulting from brain atrophy (small brain = more room for ventricles to fill up).
Not “true” hydrocephalus
What are the causes of “true” hydrocephalus?
- Neural Tube Defect (NTD)
- Aqueductal stenosis
- Dandy Walker Malformation
What is an aqueduct stenosis?
When CSF cannot flow from the 3rd to 4th ventricle
What ventricles are enlarged in the presence of an aqueduct stenosis?
The lateral and 3rd are enlarged
The 4th is normal
What are the causes of extraventricular obstruction causing hydrocephalus? (3)
- Spina Bifida - flow obstructed in spine, backs up all ventricles
- Excess CSF - excessive secretion from a choroid plexus
- Dandy Walker Malformation
How do you assess the ventricular size?
Measure atrial diameter, size doesn’t change much from 15-35 weeks
What is the normal measurement and upper limit of the ventricles?
Normal = 7mm
Upper limit = 10 mm
How does the Choroid appear in a normal ventricle?
Hyperechoic, less than 3 mm from the medial ventricle wall and the choroid plexus should not appear to “dangle” in the atria of the ventricle
What does the position of the Choroid Plexus depend on?
Gravity
If hydrocephalus is present, how likely is an additional anomaly?
70-80%
What structures are seen in the posterior fossa view?
- Cisterna Magna
2. Cerebellum
How does an obliterated cisterna magna appear on US?
Cerebellum right up agains posterior skull
What is the banana sign?
Deformed cerebellum shaped like a banana due to downward displacement through the foramen magna from spina bifida with Arnold Chiari Malformation
What is the lemon sign?
Indicates the frontal bones have caved in due to Spina Bifida with Arnold Chiari II Malformation
When is the lemon sign seen and when does it disappear?
Seen in 2nd trimester
Disappears in 3rd due to hydrocephalus from enlarging ventricles
What is Dandy Walker Malformation characterized by? (3)
- Enlarged cisterna magna
- Agenesis of the cerebellar vermis (connection between cerebellum) causing a communication between the cisterna magna and the 4th ventricle
- Enlarged ventricles due to pressure in posterior fossa
What is the Dandy Walked Variant?
Partial agenesis of the cerebellar vermis causing a smaller cisterna magna than full blown and minimal dilation of the ventricles. (Associated with many syndromes)
What is the most important condition DWM is assoicated with?
Agenisis of the corpus callosum
What is DWM associated with?
- Agenisis of the corpus callosum
- Fetal death
- Intellectual Impairment
- Heart defects
- Genitourinary
- Polydactyly
What is genitourinary?
The genital/urinary system
What factors increase the risk of DWM? (3)
- Viral infection
- Alcohol
- Diabetes
What is the normal value for the cisterna magna?
Less than 1 cm
What 3 structures must be included in the cerebellar view?
- Cavum septi pellucidi
- Peduncles
- Cerebellum
What is the DDx for DWM?
Arachnoid cyst in posterior fossa
How does the corpus callosum develop?
It starts to develop at 12 weeks, starting from anterior to posterior and is complete at 20 weeks
How can agenisis of the corpus callosum vary?
- It can be complete or partial
- Developmental or acquired
What is agenisis of the corpus callosum associated with?
- DWM
- CNS abnormalities (gyral/gyri dysplasia)
- Facial, limb and genitourinary system anomalies
What is dysplasia?
Abnormal cells
How does agenesis of the corpus callosum appear on US?
- Absence of Cavum Septi Pellucidi
2. Enlargement of occipital horns only (pointed anterior horns like a tear drop).
What is the enlargement of the occipital horns called?
Colpocephaly
What are CPC’s?
Choroid Plexus Cysts
What are CPC’s assoicated with?
Most disapper in 2nd trimester BUT 1 in 200 are associated with Trisomy 18
CPC’s = figure 8 for T18 (two cysts)
How do CPC’s appear?
Hypoechoic or anechoic cysts within choroid plexus
How big must a CPC be to be significant?
Greater than or equal to 3 mm
What is Acrania and how common is it?
Absent skull
1/1000 births
What is anecephaly?
No cerebral cortex
What is exencephaly?
Some cerebral cortex but abnormal
Why is exencephaly dangerous?
Amniotic fluid damages brain tissue
How does Acrania/anencephaly/exencephaly appear on US?
- Face and orbits present
- No calvaria (skull) above orbits
- Very active fetus
- Usually polyhydramnios
What is polyhydramnios?
Excess of amniotic fluid
What is the DDx for anencephaly?
- Amniotic band syndrome
2. Large encephalocele
What is Amniotic band syndrome?
When strands in the amniotic sac wrap around parts of the baby hindering development
What is encephalocele?
Protrusion of intracranial structures through defect in the skull (may contain only meninges or brain as well)
How do you decipher between acrania/anencephaly/exencephaly and amniotic band syndrome on US?
Look for other amputations, waving membraine or if fetus seems stuck to a side wall (all = amniotic band)
How do you decipher between acrania/anencephaly/exencephaly and encephalocele?
Look for cranial bones (bones = encephalocele)
What is the condition marked by a variable absence of cerebrum and the filling of remaining space with CSF?
Hydranencephaly
Why does Hydranencephaly occur?
- Occlusion of ICA’s
- Infection
- Hemorrhage
- Destruction and reabsorption of brain matter
How does hydranencephaly appear on US?
Intact thalami which are never fused, irregular brain matter
What is the prognosis of hydranenecehaly?
Fatal
What is the DDx of hydranencephaly?
- Severe hydrocephalus - would be smooth along cranium
2. Alobar holoprosencephaly - would have fused thalami
What is the term for when brain tissue is destroyed by hemorrhage or infarct?
Porencephalic cysts
Where are porenecephalic cysts located?
The destroyed brain becomes cystic usually along the periventricular halo close to the lateral ventricles (may or may not communincate)
What is the DDx for porencephalic cysts?
- DWM
- Arachnoid cyst
- Hydrocephaly (if it communicates)
What are arachnoid cysts?
Fluid filled collections in the layers of the arachnoid membrane (well defined cyst on US that may resemble a mass)
Where do arachnoid cysts occur in the cranium and what are they associated to?
Can occur anywhere, not associated with anything
What is the DDx of arachnoid cysts and what is the prognosis?
- Dandy Walked Variant if occurs in the posterior fossa
2. Porencephalic cyst
Where do most encephalocele’s occur?
Midline of the occiput
What condition is linked to increased AFP?
Encephalocele
How can you tell the difference between meninges or brain tissue within an encephalocele?
Meninges = cystic structure Brain = Encapsulated echogenic mass with cystic areas
What is cystic hygroma?
Clusters of cysts in the lymphatic drainage system of the head and neck
What is the DDx of encephalocele?
- Cystic hygroma - septations in cystic area should be seen
- Teratoma
What abnormality is encephalocele associated with?
Meckel-Gruber syndrome
What is schizencephaly?
Symmetrical clefts in the parietal or temporal lobes that extend from the ventricles to the cortical surface that split brain into anterior and posterior segments
What is a smooth brain with no sulci or gyri called?
Lissencephaly
Why does lissencephaly occur?
Abnormal migration of neurons from the germinal matrix
When can lissencephaly be diagnosed?
3rd trimester
What is microcephaly?
Small head with sloping forehead and ventriculomegaly seen in late pregnancy
What is considered microcephaly?
Greater than 3 standard deviations below the mean head would plot well below 5th percentile
What causes microcephaly?
- Aphyxia
- Infections (cytomegalovirus CMV)
- Drugs
- Alcohol
- Irraciation (pasteurized milk, etc)
What is vein of galen aneurism?
A variety of arteriovenous malformations drain into the vein of galen and result in distension as a single midline fluid collection (3rd trimester)
Where is the vein of galen aneurysm located?
Dilated midline collection posterior to the thalamus and mid brain, between the posterior horns of lateral ventricles
How can galen malformation be diagnosed?
Using colour doppler to show flow inside the cyst
What is cardiomyopathy?
Disease of heart muscle (due to AV shunting), heart failure
What is the most common brain lesion?
Teratomas
How do teratomas appear on US?
Large, echogenic masses with cystic spaces and occasional calcifications
What is craniosynostoses?
Bizarre fusion of cranial sutures before brain is finished growing
What is the marker for craniosynostoses on US?
Cloverleaf
What is dolichocephalic?
Long skull
CL is less than 75
What is one cause for Dolichocephalic?
Breech baby
What is Brachiocephalic?
Short skull
CI greater than 85%
How do you find the CI?
Divide BPD by OFD
What should you consider if the brain is expecially clear?
Poor mineralization (bones not ossified) and skull can be compressed
What syndrome are encephalocele associated with?
Meckel-Gruber Syndrome
What is Meckel-Gruber Syndrome?
An autosomal recessive condition that is lethal and characterized by:
- Encephalocele
- Cystic renal dysplasia (large echogenic kidneys)
- Polydactyly
