Ch. 24: The Fetal Head and Brain (Content)

True or false: an absent CSP is a normal anatomical variant.

*FALSE*. An absent CSP is associayed with many cerebral malformations, including agenesis of the corpus callosum and holoprosencephaly.

True or false: an MCA RI >1.0 is abnormal.

*False*. < 1.0 is abnormal. The MCA should be high resistance. Low resistance indicates fetal hypoxia and brain sparing.

True or false: the cisterna magna is the smallest cistern in the brain.

*False*. It is the largest cistern, posterior to the cerebellum. (Hint: "magna" is Latin for "great")

True or False: holoprosencephaly affects only the brain.

*False*. It will affect the face, as well. I.e. cyclopia, probiscis, anophthalmia, hypotelorism, cleft lip, cebocephaly.

What predisposing factors lead to intracranial hemorrhage in utero?

*Maternal platelet disorders* Maternal cocaine use Trauma Amniocentesis

True or false: intracranial hemorrhage can lead to porencephaly and hydrocephalus.

*True*.

True or false: spina bifida may present with hydrocephalus.

*True*.

True or false: the CSP does not communicate with the ventricular system.

*True*.

True or false: porencephaly communicates with the ventricular system.

*True*. Arachnoid cysts are the ones that do not communicate.

True or false: HC is taken at the same level as the BPD.

*True*. Make sure to encompass the entire cranium as best as possible.

True or false: the CSP will close in late gestation, i.e. after 37 weeks.

*True*. It usually closes before or shortly after birth.

True or false: Alobar Holoprosencephaly will have a fused thalamus and horseshoe-shaped monoventricle.

*True.*

Describe the anatomy of the lateral ventricles:

- 3 horns: frontal, temporal, occipital - Body, located between frontal and occ. horns - Trigone/Atrium: where occ. horn, temp. horn, and body meet - Choroid Plexus in Atrium

Name 3 sonographc findings of Acrania (including anenceph and exencaph):

1. Absent cranial vault 2. Minimal cerebral tissue 3. Froglike facies or bulging eyes

What are the three types of Holoprosencephaly?

1. Alobar (most severe) 2. Semilobar 3. Lobar (can be consistent with life)

Name 4 Sonographic findings of Ventriculomegaly

1. Atrium >10 mm 2. Atrium >15 mm is moderate/marked 3. Dangling choroid 4. Dilitation of any part of the vent. system

Name 4 Sonographic findings of Aqueductal Stenosis

1. Atrium >10 mm 2. Atrium >15 mm is moderate/marked 3. Dangling choroid 4. Dilitation of the LVs and 3rd ventricle. 4th vent. is normal

Name 3 abnormal skull shapes:

1. Dolichocephaly: elongated (AKA schaphocephaly) 2. Brachycephaly: rounded 3. Strawberry (Lemon, cloverleaf)

Name 3 sonographic signs of DWM:

1. Enlarged CM >10 mm 2. Enlarged 4th vent. 3. Absent/hypoplastic cerebellar vermis. (Ventriculomegaly, absent CSP/CC, holopros, cephaloceles)

NAme 2 sonographic signs of Mega CM:

1. Enlarged CM >10 mm 2. Normal cerebellum and 4th vent.

Name 3 sonographic signs of Schizencephaly:

1. FLuid filled clefts in the brain 2. Agen of the CSP and CC 3. Ventriculomegaly

How do cephaloceles appear sonographically?

1. Open cranial defect 2. Small/absent CM 3. Complex/simple mass protruding from cranium

What are the three brain mantle shapes that may manifest in alobar holoprosencephaly?

1. Pancake (flattened anterior mantle) 2. Cup (anterior mantle, does not cover monoventricle) 3. Ball (covers the monoventricle)

Name the Meningeal layers from inner to outer:

1. Pia Mater 2. Arachnoid Mater (Membrane) 3. Dura Mater

What structural changes occur with spina bifida and Arnold-Chiari?

1. Scalloped frontal bones (Lemon) 2. Banana sign cerebellum 3. Obliterated CM 4. (Myelo)meningocele 5. Enlarged interthalamic adhesion 5. Colpocephaly

Name 3 conditions an absent CSP/CC is associated with:

1. T18 2. T13 3. DWM (Holopros, Apert syndrome, T8, aqueductal stenosis)

When is the corpus callosum fully formed

18 weeks

How fast does the cerebellum grow between 14 and 21 weeks?

About 1 mm/week This goes nicely with gestational age. A 16 week fetus should have a ~16 mm cerebellum

What is the Occipitofrontal Diameter measurement?

An anterior posterios measurement taken from the middle of the midline frontal bone to the middle of the midline occipital bone. Taken at same level as HC and BPD. It is used to obtain a "corrected-BPD."

Name the 4 fontanelles

Anterior (frontal) Posterior (occipital) Anterolateral (sphenoidal) Posterolateral (mastoid)

Where is the Cavum Septum Pellucidum (CSP)?

Anterior midline of the cerebrum, between frontal horns of the LVs. Should ALWAYS be seen between 18 and 37 weeks.

What is the most common cause of hydrocephalus?

Aqueductal stenosis (cerebral aqueduct)

Where do you measure the LV? What is a normal measurement?

At the level of the Trigone/Atrium It should be ≤10 mm

What is the Cephalic Index?

BPD/OFD x 100 75-85 is mesocephalic, or normal >85 is brachycephaly <75 is dolichocephaly

What is Macrocephaly associated with?

Beckwith-Wiedemann Syndrome Hydrocephalus Hydranencephaly Intracranial tumors Familial Inheritance

What is the normal measurement for the cisterna magna?

Between 2 and 10 mm >10 mm is assoc. with Dandy-Walker and mega cisterna magna. <2 mm is assoc. with Arnold-Chiari II

Where is the 3rd ventricle located?

Between the Thalami lobes

What do experts think cause hydranencephaly?

Bilateral occlusion of the ICAs Intrauterine infections (Cytomegalovirus and Toxoplasmosis)

What condition is a vein of Galen aneurysm associated with?

CHF (and thus hydrops and cardiomegaly)

Describe the flow of CSF

CP → LVs → Interventricular Foreman → 3rd Vent → Cerebral Aqueduct → 4th Vent → Apertures or Spinal cord

What is most often found intracranially in the presence of TORCH?

Calcifications in the the ventricles Ventriculomegaly

Name the 5 fetal sutures

Coronal: | | frontal and parietal bones Sagittal: | | parietal bones Lambdoidal: | | parietal and occipital bones Squamosal: | | parietal and temporal bones Metopic: midline frontal bone

What is a brain with alobar holoprosencephaly missing?

Corpus Callosum CSP 3rd Ventricle Interhemispheric Fissure Falx cerebri

What is thought to cause Dany-Walker malformation?

Developmental abnormality of the 4th ventricle

Where is the thalamus located?

Either side of the third ventricle, with the massa intermedia (interthalamic adhesion) running through the 3rd ventricle, connecting the lobes. Do not confuse with the peduncles.

Which vitamin helps reduce the risk of NTDs?

Folate

Name the 8 cranial bones

Frontal Parietal (2) Temporal (2) Occipital Sphenoid Ethmoid

Where do most intracranial hemorrhages occur? (fetal and neonatal)

Germinal matrix

What is another name foe the Foramen of Monro?

Interventricular Foramina

What causes porencephaly?

Ischemic events and vascular occlusion

Name the apertures in the 4th ventricle. What is their function?

Lateral Apertures (2; Foramina of Luschka) Median Aperture (Foramen of Magendie) They allow CSF to flow into the subarachnoid space and the cisterna magna.

Which condition has agyria?

Lissencephaly

What substance is elevated in the presence of NTDs?

MSAFP

What is the difference between DWM and Mega CM?

Mega CM will have a normal 4th ventricle and intact vermis, whereas DM will have an enlarged 4th vent and absent vermis.

How does the corpus callosum appear sonographically?

Midline echogenic band of tissue connecting the cerebral hemispheres.

Where us the 4th ventricle located?

Midline, anterior to the cerebellum

Describe the level at which BPD is measured:

Must contain the CSP, thalamus, and falx cerebri. Rounded, symmetric skull bones. NO CEREBELLUM. Leading edge to Leading edge

Noncommunicating vs Communicating Hydrocephalus

Noncommun.: obstruction within ventricular system Commun.: obstruction outside ventricular system.

Where are most cephaloceles located?

Occipital bone

What is the function of the fourth ventricle in the brain?

Primarily to cushion the brain.

Which posterior, anechoic brain structure maybe be noted in the first trimester?

Rhombencephalon

What are the two most common NTDs?

Spina bifida Anencephaly

What is Microcephaly associated with?

TORCH Trisomy 13 and 18 Meckel-Gruber Fetal Alcohol Syndrome

What is the most common intracranial tumor in utero?

Teratoma

What is hydranencephaly?

The entire cerebrum is replaced with a large sac filled with CSF. There is no cerebral mantle. The falx will be partially or complete absent, but the brain stem, basal ganglia and possibly thalamus are still present.

Why does an absent CSP also typically mean an absent CC?

They develop at the same time.

Choroid plexus cysts are associated with...

Trisomy 18

When can you start measuring BPD?

Typically 13 or 14 weeks

Where are the cerebellar tonsils?

Undersurface of the cerebellum. They become distorted with Spina bifida and Arnold-Chiari.

What is the most common cranial anomaly?

Ventriculomegaly

What's the difference between Hydrocephalus and Ventriculomegaly?

Ventriculomegaly: the enlargement of the ventricles Hydrocephalus: dilatation of the ventricular system due to increased CSF, causing increased intraventricular pressure. May be reserved for very severe ventriculomegaly caused by an obstruction.

What is the sunburst sign?

agenesis of corpus callosum causing the sulci to have a sunburst appearance, meaning they run perpendicular to the CC rather than parallel.

What is the normal sonographic appearance of the cerebellum? a. banana sign b. dumbbell shaped c. v-shaped d. none of the above

b. dumbbell shaped

When does the corpus callosum develop?

between 12-22 weeks. Should be completely intact by 18-22 weeks.

The ______ connects the 3rd and 4th ventricles. a. Aqueduct of Sylvius b. Cerebral Aqueduct c. Central Canal d. a and b

d. a and b (Aqueduct of Sylvius/Cerebral Aqueduct)