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.
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
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
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
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).
18.
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
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
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
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
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
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
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
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
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
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