2. Congenital Malformations: Failure to Form

Question 1

5 basic categories

Answer 1

1. Failure to form
2. Failure to cleave
3. Failure to Migrate
4. Developmental Failure mimics
5. Herniation Syndromes

Question 2

Formation of Coprpus Callosum

Answer 2

Forms FRONT to BACK (then rostrum last)

Therefore, hypoplasia of the corpus callosusm is usually absence of the splenium (Genu intact

Question 3

Answer 3

Colpocephaly (asymmetric dilatation of the occiputal horns..

With agenesis of the corpus callosum = Colpocephaly is shown

When you see colocephaly, think

1. Corpus callosum ageneis
2. Pericallosal lipoma

Question 4

Dysgenesis / Agenesis of the Corpus Callosum

Answer 4

Why are the lateral ventricles widely spaced when you have no corpus callosum?

There are thses things called “Probst bundles” - densly packed White matter tracts destined to cross the CC but can’t (because it isn’t there)

Instead - they run parallel to the interhemispheric fissure - making the ventricles look widely spaced

Question 5

Dysgenesis / Agenesis of the Corpus Callosum associations

Intracranial Lipoma

Answer 5

The most classic associafion with CC Agenesis.

50% found in the interhemispheric fissure
25% quadrigeminal cisterns

• They are congenital malformations, not neoplasms
• T1 = most helpful (most non bleedingthings in teh brain - not T1 bright)

rarely treated

Question 6

Anencephaly

Answer 6

Defect at the top of head

The Top of the Head is Absent (Above the Eyes)

Reduced/Absent = cerebrum and cerebellum.

Present = The hindbrain

Not compatible with life

Question 7

Iniencephaly

Answer 7

Neural Tube defect.
Defect at the level of the cervical spine

Deficient occipital bone + Defect - cervical region

Inion = back of head/neck

EXTREME retroflexion of the head
Enlarged foramen magnuma
Jacked up spines
Visceral problems

Usually not compatible with life

Question 8

Answer 8

Classic image appearance of Anencephaly

“Frog Eyes”

coronal plane (due to absent cranial bone /
brain with bulging orbits).

Polyhydramios - hard to swallow without a brain

AFP elevated (true with all open neural tube defects)

Question 9

Answer 9

Classic image appearnce of Iniencephaly

“Star Gazing Fetus”

Contorted - hyperextended cervical spine, short neck, upterned face

AFP elevated (true with all open neural tube defects)

Question 10

Answer 10

Encephalocele

Brain + Meninges herniate through a defect in the cranium

Locations: Most common - midline in the OCCIPITAL region

MOST classic association: Chiari III

Question 11

Failure to form = Cerebellar Vermis

What are the types?

Answer 11

1. Rhomboencephalosynapsis.
2. Joubert Syndrome

Question 12

Rhomboencephalosynapsis

Answer 12

Absent Vermis = abnormal FUSION of the cerebellum

Small 4th ventrilce, rounded fastigial point, absent primary fissure

Associations: Holoprocencephaly spectrum

Question 13

Answer 13

Rhomboencephalosynapsis

“Trasnversely oriented single lobes cerebellum”

Vertical lines across the cerebellum

Question 14

Joubert Syndrome

Answer 14

Vermis - ABSENT or SMALL
Small Cerebellum

Abscence of pyramidal decussation

Large 4th ventricle (Batwing shaped)
vs Rhombencephalosynapsis - small

Absent Fastigial point
Absent Primary fissure

Assoc: Retinal Dysplasia (50%)
Multicystic Dysplastic Kidney
Liver Fibrosis (COACH Syndrome

Question 15

Answer 15

Joubert Syndrome

“Molar Tooth” Appearance for the superior cerebellar peduncles