Why we scan the Corpus Callosum (CC)?
The Corpus Callosum represents the major commissure between the two cerebral hemispheres; it extends from the frontal lobe anteriorly to above the collicular plate posteriorly.
Developmental abnormalities of the CC include hypoplasia, hyperplasia, agenesis, and dysgenesis. Agenesis of the corpus callosum can be complete or partial (or hypogenesis).
The Diagnostic plane is the midsagittal plane of the fetal brain which is informative yet difficult to obtain, where the fetus has to be either breech or transverse presentation.
This plane passes through the fetal brain midline structures:
- Third Ventricle: a squared echo-spared area.
- Fourth Ventricle: indents the cerebellar vermis posteriorly.
- The Corpus Callosum: superior to the cavum septum pellucidum and the triangular velum cistern.
In Ultrasound the CC appears as a thin echoic area interposed between the hyperechogenic triangular velum cistern above and the large cavum septum pellucidum below.
Time of scan in the second trimester anomaly scan confirmation of normal corpus callosum is mandatory (recurrence rate is 5%).
Management of cases of agenesis of corpus callosum requires karyotyping.
Prognosis of agenesis of the corpus callosum is unfavourable as most of them suffer from neurodevelopmental delay, seizures. A final point that should be made is that even when the outcome is good, subtle neuropsychologic, perceptual, and motor defects can emerge later on.