Congenital brain

1. Congenital Brain
Malformations
Mark Nicholas B. Reyes, M.D.
Radiology Resident
YL-II

2. Normal Development
• Post conceptual age at the time of imaging is essential
• Recognize milestones of development in relation of AOG
• Myelination begins at 5th fetal month (20 weeks AOG)
• 1 year of age, appearance of white matter myelination is similar to
that of an adult

3. Normal Development

4. Abnormalities of Midline Development
• Corpus callosum can appear thin in normal neonates
• Splenium should be at least as thick as the genu by 1 year of age
• Dysgenesis of corpus callosum

5. Dysgenesis of Corpus Callosum
• Spectrum that range from:
• Complete agenesis
• Partial agenesis or hypogenesis of corpus callosum

6. Dysgenesis of Corpus Callosum
• Complete agenesis
• Parallel orientation of the lateral ventricles
• Posterior horn (lateral ventricle) dilation
• Upturned anterior horns of the lateral ventricles
• Absence of cingulate sulcus

7. Dysgenesis of Corpus Callosum
• Complete agenesis

8. Dysgenesis of Corpus Callosum
• Partial agenesis
• Truncation of the AP dimension with the callosum appearing as two separate
commissures
• Frequently associated with interhemispheric cysts or lipomas

9. Dysgenesis of Corpus Callosum
• Partial agenesis

10. Holoprosencephaly
• Spectrum of malformations caused by abnormalities of differentiation
and midline cleavage of the prosencephalon during the 5th week AOG
• Hallmark:
• Abnormal communication of gray/white matter across the midline
• Facial dysmorphism is seen in up to 80%

11. Holoprosencephaly
• Spectrum of malformations:
• Alobar holoprosencephaly
• Semilobar holoprosencephaly
• Lobar holoprosencephaly

12. Holoprosencephaly
• Alobar holoprosencephaly
• Most severe of the subtypes
• Complete absence of cleavage with anterior displacement of the cerebral
tissues
• “pancake” configuration
• Large monoventricle expanding posteriorly into a dorsal cyst

13. Holoprosencephaly – Alobar subtype
- Absence of normal midline
structures and most of the parietal
and posterior cortex.
- Small frontal cortex is present,
with no evidence of midline fissure.
- Anterior flattening (“pancake”) of
cerebral tissue

14. Holoprosencephaly
• Semilobar holoprosencephaly
• Characterized by incomplete forebrain division
• Worse than lobar holoprosencephaly but better than alobar
holoprosencephaly
• Basic structure of the cerebral lobes are present, but are fused most
commonly anteriorly and at the thalami and there is partial diverticulation of
brain

15. Holoprosencephaly
• Semilobar holoprosencephaly
• Some differentiation of the posterior lateral ventricles

16. Holoprosencephaly
• Lobar holoprosencephaly
• Least severe of the subtypes
• Incomplete separation of the basal ganglia and partial separation of the basal
ganglia and partial separation of the frontal lobes
• Anterior falx cerebri can be partially present

17. Holoprosencephaly
• Lobar holoprosencephaly

18. Posterior Fossa Malformations
• Majority are categorized as:
• Chiari malformations
• Dandy-Walker continuum

19. Chiari Malformation
• A group of defects associated with congenital caudal displacement of
the cerebellum and brainstem
• Three subtypes were initially described
• Chiari I malformation
• Chiari II malformation
• Chiari II malformation

20. Chiari Malformation
• Chiari I malformation
• Characterized by cerebellar tonsillar protrusion below the foramen magnum
in the absence of an open spinal dysraphism or intracranial mass effect
• Tonsillar displacement of ≥ 5mm below the McRae line

22. Chiari Malformation
• Chiari I malformation
• Often are isolated abnormalities but may be associated with the following
imaging findings:
• Abnormal pointed morphology of the cerebellar tonsils
• Dorsal tilts of the dens
• Basilar invagination
• Effacement of the CSF spaces at the foramen magnum
• Syringomyelia

23. Chiari Malformation
• Chiari I malformation

24. Chiari Malformation
• Chiari II malformation
• Comprises a constellation of imaging findings in the brain associated with an
open spinal dysraphism
• Characterized by myelomeningocele and a small posterior fossa with descent
of the brainstem, cerebellar tonsils, and vermis through the foramen magnum
• Can be identified by prenatal ultrasound

25. Chiari Malformation
• Chiari II malformation
• Prenatal ultrasound may present with bifrontal concavity of the calvarium
(lemon sign) and a flattened cerebellum wrapping around the brainstem
(banana sign)

26. Chiari Malformation
• Chiari II malformation
• Postnatal imaging findings:
• Small posterior cranial fossa with downward sloping tentorium and herniation of
cerebellar tissue into the cervical canal
• Tectal beaking
• Falx insufficiency (marked by interdigitating hemispheric sulci)

27. Chiari Malformation
• Chiari II malformation

28. Chiari Malformation
• Chiari III malformation
• Rare
• Characterized by a cervico-occipital encephalocele containing posterior fossa
contents

29. Chiari Malformation
• Chiari III malformation

30. Dandy-Walker Continuum
• Group of posterior fossa malformations characterized by varying
degrees of vermian hypoplasia and malposition in association with
posterior fossa cysts

31. Classic Dandy-Walker Malformation
• Triad of:
• complete or partial agenesis of the vermis
• Cystic dilation of fourth ventricle
• Enlarged posterior fossa with upward displacement of the tentorium
• Obstructive hydrocephalus is a common complication but is not a part
of the malformation itself

33. Classic Dandy-Walker Malformation
• Hypoplastic vermis or Dandy Walker variant
• Tegmento-vermian angle > 18 degrees without enlargement of the posterior
fossa
• Normal neurodevelopmental outcome in patients with isolated vermian
hypoplasia

34. Classic Dandy-Walker Malformation
• Tegmento-vermian angle

35. Classic Dandy-Walker Malformation
• Blake pouch remnant
• Blake pouch is an embryonic structure that perforates to form the foramen of
Magendie and foramina of Luschka
• Delayed or incomplete perforation results in a Blake pouch remnant or cyst
causing upward displacement of an otherwise normally formed cerebellar
vermis

36. Classic Dandy-Walker Malformation
• Blake pouch remnant
• Considered normal up to 20 wees of gestational age
• Can present in isolation or may be associated with other anomalies
• Depending of the degree of nonperforation, can result in obstructive
hydrocephalus

37. Classic Dandy-Walker Malformation
• Dilated fourth ventricle is seen
freely communicating with
infracerebellar posterior fossa
cyst. The cerebellar vermis is
upward displaced with no
hypoplasia.

38. Classic Dandy-Walker Malformation
• Mega cisterna magna
• Result of a delayed fenestration
of Blake pouch
• Defined as isolated enlargement
of the cisterna magna (>10mm)
with a normal tegmento-
vermian angle and is considered
anormal variant

40. Joubert Syndrome and Related Disorders
(JSRD)
• Heterogenous group of disorders mostly resulting from mutations of
genes encoding ciliary proteins.
• The classic neuroimaging findings include vermian hypoplasia and the
“molar tooth sign”
• Additional associated anomalies include polydactyly, colobomas, and
polycystic kidneys

41. Joubert Syndrome and Related Disorders
(JSRD)
• Molar tooth sign refers to the appearance of the midbrain in an axial
section in which the elongated superior cerebellar peduncles give
the midbrain an appearance reminiscent of a molar or wisdom tooth.

42. Rhombencephalosynapsis
• Incomplete separation of the cerebellar hemispheres in associated
with partial or complete absence of the vermis
• MR demonstrates transversely oriented continuous folia and
flattened fastigial recess.
• 65% have coexisting aqueductal stenosis

43. Rhombencephalosynapsis

44. Thank You