Abnormalities of the corpus callosum are frequently missed on prenatal ultrasound scans. Imaging the entire corpus callosum is not routinely performed, but is important for accurate diagnosis. Indirect markers like the cavum septum pellucidum seen on axial views can indicate abnormalities, but have limitations. A midline sagittal view of the brain is needed to directly visualize the corpus callosum and rule out abnormalities, but this view is often omitted from routine scans. Careful imaging of the corpus callosum is important for evaluating cases of ventriculomegaly or other suspected central nervous system anomalies.

1. Abnormalities of corpus callosum
Dr.S.Lakshmy Ravi
Shri Lakshmi Clinic
Kaveripattinam

2. Callosal abnormality - incidence
Once thought to be a rare condition experts now
do not agree with this concept
National organisation for disorders of the corpus
callosum (NODCC) reports an incidence as high
as seven in 1000 children
Do we report such a high incidence
on antenatal ultrasound

3. An abnormality of corpus callosum is a frequently
missed malformation because imaging the entire corpus
callosum per se is not a part of our routine anomaly scan
Indirect markers of an evidence of abnormality of
callosum is easily obtained from routine axial views but
may sometimes be associated with pitfalls
Midline sagittal section of the brain is
generally not included in every anomaly
scan

4. Two structures of importance visualised in
the midsagittal view are the corpus
callosum and cerebellar vermis

5. Midsagittal view is inevitable in two CNS
anomalies
ACC DWM

6. The three standard views quoted in the anomaly
scan do not image the corpus callosum per se
 Transthalamic view
 Ventricular view
 Transcerebellar view
Axial views show only the cavum septum pellucidum
and not the corpus callosum

7. CAVUM SEPTUM PELLUCIDUM
The corpus callosum is in close anatomic and embryologic
relationship with underlying cavum septum pellucidum.

8. DIAGNOSIS OF CC ABNORMALITY
In the present scenario a suspicion of callossal
abnormality arises only by looking at the CSP.
Demonstration of the normal CSP is
considered sufficient in a routine anomaly scan
WHAT ARE THE PITFALLS IN IMAGING CSP

9. High riding third ventricle

10. High riding third ventricle

11. Fused frontal horns mimic the presence of CSP
Lobar holoprosencephaly and septo-optic dysplasia
are associated with agenesis of corpus callosum and CSP

12. Mimickers of CSP in callosal agenesis
 High riding third ventricle
 Fusion of the frontal horns
 Presence of small interhemispheric cyst
Ideal to image the CSP along
with frontal horns

13. Corpus callosum
splenium
body
genu
rostrum

14. Etiology of ACC
 Chromosomal abnormalities
 Inherited genetic factors - genetic syndromes
 Metabolic syndromes
 Maternal phenylketonuria
 Prenatal infections (rubella) and injuries
 Prenatal toxic exposures (alcohol,valproate)
 Structural blockage by cysts or other
abnormalities.

15. Embryology
Derived from the massa commisuralis which is an
embryologic structure formed by the fusion of lateral
margins of the groove that separates the primitive
telencephalic vesicle.
Agenesis is caused by disruption to development of
fetal brain between 3rd and 12th week

16. Absence of the corpus callosum
 prosencephalic cleavage failure (holoprosencephaly),
 an abnormal commissural plate formation (agenesis of
the anterior commisures),
 an abnormality in the area of the commissural plate
destined to form the corpus callosum (agenesis of the
corpus callosum),
 failure of cortical axons to reach the corpus callosum
analogue (agenesis of the corpus callosum),
 a destructive lesion of the corpus callosum

17. Stages leading to the formation of the corpus callosum.
The light blue line represents a time-line.
Numbers on top of the blue line represent days of gestation.
The different stages are represented by the multicolor line above the light blue line.
Pink: prosencephalic cleavage (28 to 35 days);
dark blue: commisural plate formation (36 to 73 days);
green: corpus callosum formation (74 to 115 days);
gray: corpus callosum growth (after 115 days).

19. 26%
5%
5%
4%
13%
26%
4% 13%
4%
corpus callossal abnormality
isolated
IUGR - TORCH
schizencephaly
interhemispheric cyst
lissencephaly
Other CNS malformation
Midfacial hypoplasia
ventriculomegaly - partial Acc
acrocallosal syndrome
Collection of 23 cases detected at our centre over a
period of four years

20. Agenesis of corpus callosum
 Axons form but are
unable to cross the
midline because of the
absence of massa
commissuralis.They
form aberrant
longitudinal fibre
bundles that run along
the medial hemispheric
walls.(Probst bundles)
 Axons and their parent
cell bodies fail to form in
the cerebral
cortex.Probst bundles are
not seen . This type is
associated with
lissencephaly and has a
poor prognosis.
Sonographic appearance of ACC is often a
diverse spectrum and are not strictly confined

21. Presence and absence of Probst bundles

22. Absence
of corpus
callosum
Failure of
axonal cross
over
Longtitutidinal
callossal
bundles
Probst bundles
indenting
lateral
ventricle
Absence of
cingulate
gyrus
Sulci extend
dorsally into
3rd ventricle
Radial
arrangement
of sulci
Roof of 3rd
ventricle
widens
Extends into
interhemispher
ic fissure
Interhemispher
ic cyst
Bodies of
lateral
ventricles
stay parallel
Dilation of
posterior and
occipital
horns
Tear drop
shaped
ventricles
colpocephaly
Architectual distortion in brain

23. Sonographic
markers of
ACC

24. Absence of the hypoechoic band of tissue in the midsagital plane
is the only diagnostic sign for definitive diagnosis for ACC
Abnormal appearance of CSP in axial plane should only
prompt us to look into the midsagittal and coronal planes

25. Normal course of pericallossal artery

26. ABNORMAL COURSE OF PERICALLOSAL ARTERY

27. Could be an isolated
malformation or may
be a part of spectrum
of anomalies
Abnormalities of corpus callosum

28. Suspicion of ACC and DWV

29. Suspicion confirmed
in the midsag plane
normal

30. Compare and contrast

31. 20 wk fetus - probable diagnosis from midsag
view

32. Arnold - Chiari malformation

33. Ventriculomegaly
Agenesis of corpus callosum is associated
with 3% of cases with ventriculomegaly
Imaging the corpus callosum in the midsagital
plane should never be missed in evaluating cases
with ventriculomegaly

34. Ventriculomegaly- partial ACC

35. ACC with interhemispheric cyst
 Type I
- cyst is a diverticulum of ventricular system and thus
communicates with the ventricles
 Type II
- multiple cysts are present that do not communicate
with the ventricles often associated with subcortical
heterotopia

36. Twin gestation for routine anomaly scan

37. NORMAL CSP - FETUS A ABSENT CSP – FETUS B

38. ACC with multiple small interhemispheric cyst

39. Postnatal followup

40. Routine anomaly scan reported normal
presenting with a cystic lesion in 3rd trimester

42. ACC with large interhemispheric cyst

43. ACC in schizencephaly

44. 2nd gravida - 15 week scan reported normal
presenting at 28 weeks

45. Impression
28 week live gestation with 5 weeks growth lag
Symmetric IUGR
Minimal unilateral ventriculomegaly
Inadequate imaging of CSP
? Intracerebral midline cyst
Single umbilical artery
Normal umbilical and MCA flow doppler

46. Midsagittal view showing absent corpus callosum and
dilated 3rd ventricle

47. ACC - sequelae of intrauterine infection
• Normal karyotype
Infection screening - High
titres of CMV and Rubella
Evaluation of fetus - symmetric IUGR
For chromosomal abnormality & intrauterine infection

48. Postnatal images

49. Primi,consanguinous marriage
for routine evaluation at 22 weeks

51. Impression
22 week live gestation with
HC falling below 5th percentile
Bilateral ventriculomegaly
Focal dilation of lateral ventricle ? communication with
interhemispheric cyst
Abnormal sulcation of fetal brain - underdeveloped brain

52. ACC IN LISSENCEPHALY

53. Lissencephaly
Increased subarachnoid
space in parasagital view

54. Acrocallosal syndrome
Involvement of acra - extremity
Callosal abnormality

55. Acrocallosal syndrome
 Rare congenital disorder involving absence or partial
formation of corpus callosum and polydactyly
 Described by Schinzel - Schinzel acrocallosal syndrome
 Acra - fingers and toes poly/syndactyly
 Autosomal recessive pattern of inheritance
 Each baby has a 25% risk of being affected

56. Primi, consanguinous marriage

58. Primi,consanguinous marriage,for routine
evaluation

61. Importance of midsag view in diagnosis of ACC

62. Spectrum of
callossal anomalies
in midsag view

63. In a nutshell
 Always image the CSP along with the
frontal horns in every anomaly scan
 Abnormal appearance of CSP in axial plan
should prompt us to look into the
midsagittal and coronal planes for a
definitive diagnosis
 In any suspected intracranial abnormality
please do image the corpus callosum in
midsagital plane

64. Ultrasound and MRI