FETAL BRAIN US IN THE SECOND TRIMESTER

C . G A R E L

D E P A R T M E N T O F R A D I O L O G Y , H Ô P I T A L D ’ E N F A N T S A R M A N D - T R O U S S E A U ,

P A R I S , F R A N C E

ESPR Helsinki 20191

CHARACTERISTICS OF THE FETAL BRAIN IN THE SECOND TRIMESTER

• Most developmental abnormalities involving the midline structures

and the posterior fossa are present in the 2nd trimester

• Some disorders may not be present in the 2nd trimester, due to:

• brain maturation

• late growth of certain structures

• late onset of certain developmental disorders

• late growth of certain abnormalities

• late onset of acquired disorders

ESPR Helsinki 20192

MIDLINE STRUCTURES

• The cavum septi pellucidi

• Visible from 15 WG and in all fetuses by 18 WG (US >> MR)

• Numerous normal variants

ESPR Helsinki 2019

shape size echogenicity septations3

ABSENCE OF SEPTUM PELLUCIDUM

ESPR Helsinki 2019

24 WG+4

31 WG + 5 34 WG + 2 2 months 25 d

Absence of septum

pellucidum

+ opercular dysplasia

and polymicrogyria

Diagnosis in the late 2nd T

or 3rd T

Other fetus

4

THE CORPUS CALLOSUM

ESPR Helsinki 2019

17.5 WG 20 WG 21 WG19 WG

22 WG

The corpus callosum is complete by 22 WG

23 WG

Morphology

US>> MR

5

AGENESIS OF THE CORPUS CALLOSUM

24 WG + 3

Complete agenesis

of the corpus callosum

Diagnosis in the 2nd T6

PARTIAL AGENESIS OF THE CORPUS CALLOSUM

23 WG + 5 29 WG + 6 32 WG + 6

32 WG + 6 6 months

Diagnosis in the 2nd T

7

AGENESIS OF THE CC + ASSOCIATEDABNORMALITIES

33 WG + 3

4 months

Partial agenesis

of the corpus

callosum +

subependymal

nodular

heterotopia

Diagnosis in the

late 2nd T or 3rd T

8

AGENESIS OF THE CC + ASSOCIATEDABNORMALITIES

24 WG + 2

Right Left

Partial agenesis of the

corpus callosum and

abnormal gyration

Diagnosis in the 2nd T

9

AGENESIS OF THE CC + ASSOCIATEDABNORMALITIES

31 WG + 1 1st twin 2nd twin

Partial agenesis

of the CC with

delayed gyration

Diagnosis in the

3rd T

10

AGENESIS OF THE CC + ASSOCIATEDABNORMALITIES

32 WG + 4

6 months

Partial agenesis of the CC

with marked hypoplasia of

the olfactory bulbs

Diagnosis in the 3rd T

11

POSTERIOR FOSSA

23 WG

21 WG 33 WG

Same morphology in the 2nd and 3rd T

except for hemispheres foliation

Morphological analysis: MRI >> US

28 WG 12

DEVELOPMENTAL ABNORMALITIES OF THE POSTERIOR FOSSA

27 WG

24 WG

23 WG

35 WG

20 days20 WG

Dandy-Walker malformation

No changes in morphology over time

and whatever the technique

13

24 WG

DEVELOPMENTAL ABNORMALITIES OF THE POSTERIOR FOSSA

33 WG 28 WG

2 months

Blake’s pouch

Same morphology over time unless

late fenestration of the Blake’s pouch occurs

14

22 WG + 3

DEVELOPMENTAL ABNORMALITIES OF THE POSTERIOR FOSSA

34 WG + 2

11 months24 days 4 months

Retrocerebellar arachnoid cyst

Marked increase in size between

US at 2nd and 3rd T

15

DEVELOPMENTAL ABNORMALITIES OF THE POSTERIOR FOSSA

26 WG + 3 31 WG + 2

31 WG + 2 5 months

Partial

Rhombencephalosynapsis

Same appearance in the

2nd and 3rd T

16

ABSENT DISORDERS DURING THE 2ND T DUE TO BRAIN MATURATION

30 WG + 6Type I lissencephaly

Microcephaly

Insula like 21 WG

No sulci

Diagnosis in the 3rd T

17

ABSENT DISORDERS DURING THE 2ND T DUE TO BRAIN MATURATION

27 WG 31 WG + 6 35 WG + 2

3 months

Partial agenesis of the CC

+ curvilinear pericallosal

lipoma

Non visibility of the lipoma

on fetal MRI

Diagnosis with US in the

3rd T, often missed in the

2ndT when small lipoma

18

ABSENT DISORDERS DURING THE 2ND T DUE TO BRAIN MATURATION

33 WG

34 WG + 1 4 days

Subependymal pseudocysts

secondary to involution of the

germinal matrix

Diagnosis mostly in the 3rd T

May be present in the 2nd T

mainly in case of damage of

the germinal matrix

19

CMVEARLY DAMAGE OF THE GERMINAL MATRIX

23 WG

24 WG

20

LATE GROWTH OF CERTAIN STRUCTURES

34 WG

Transverse cerebellar diameter = 30 mm, << 3rd centile

Normal TCD in the 2nd T

Growth of the cerebellum is particularly rapid in the 3rd T

Cerebellar hypoplasia may be overlooked in the 2ndT

21

LATE ONSET OF CERTAIN DEVELOPMENTAL DISORDERS

34 WG

34 WG + 2

Two cases of pontocerebellar hypoplasia

Small TCD

Small pons (no bulge or small bulge)

+/- small vermis

Normal PF in the 2nd T+++

Late onset of PCH

Most cases are discovered after birth

22

LATE GROWTH OF CERTAIN ABNORMALITIES

32 WG + 5 34 WG + 5 34 WG + 5

Immature teratoma of the roof of the

3rd ventricle

33 WG + 4

ATRT of the 4th ventricle

In both cases, normal US in the 2nd T

23

LATE ONSET OF ACQUIRED DISORDERS

35 WG + 2

Born at

36 WG + 4

2 days

Grade IV haemorrhage, may occur at any time during the

pregnancy. Normal US in the 2nd T 24

LATE ONSET OF ACQUIRED DISORDERS

Monochorionic diamniotic twin pregnancy. IUFD of the 2nd twin at 22 WG.

Normal US before 22 WG

27 WG

left right

29 WG

Bilateral ischaemic lesions of the white matter,

may occur at any time during the pregnancy. 25

MESSAGES

• Due to normal chronology of the cerebral development:

• Some abnormalities may be depicted as well in the 2nd or 3rd T (midline and some

abnormalities of the posterior fossa)

• Some abnormalities may not be present in the 2nd T (late development of the

cerebellum)

• Some abnormalities are not visible in the 2nd T (gyration and migration disorders)

• Moreover:

• Some developmental disorders may be visible very late, even after birth (ex

pontocerebellar hypoplasia)

• Some lesions may develop late and are not visible in the 2nd T (ex tumours)

• Some lesions may occur at any time of the pregnancy (ex haemorhage, ischaemic

damage)

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