Diagnostic ultrasound ( PDFDrive )

CHAPTER 34 The Fetal Brain 1199
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FIG. 34.26 Periventricular Nodular Heterotopia and Agenesis of the Corpus Callosum (ACC). (A) In fetus with ACC at 31 weeks, note
the very nodular lining of the ventricle wall (arrow). This represents accumulations of neurons that have failed to migrate to the cortex. Note the
separation of the hemispheres and abnormal orientation of interhemispheric sulci (hairy midline; arrowheads). (B) Transverse T2-weighted magnetic
resonance image in a different fetus at 35 weeks shows ACC and nodular heterotopias (arrows).
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FIG. 34.27 Open-Lip Schizencephaly. (A) There are large gaps in the parietal regions with no brain tissue at the periphery (arrowhead). There
is partial sparing of the frontal and occipital regions. (B) Coronal T2-weighted magnetic resonance image in a different fetus with absent septal
lealets (absent septum pellucidum) shows region of schizencephaly (arrow).
Agenesis and Dysgenesis of Corpus Callosum
Agenesis of the corpus callosum (ACC) is failure of normal
development of the corpus callosum and other commissures
that connect the let and right hemisphere. he prevalence of
ACC in neonates is about 1.4 per 10,000 live births but is higher
in developmentally disabled individuals. his likely is an underestimate
of the prenatal incidence because many afected fetuses
die in utero, and not all cases are postnatally diagnosed. 154,220
he corpus callosum is the largest of three commissures that
connect and allow communication between the cerebral hemispheres,
the other two being the anterior commissure and the
posterior hippocampal commissure. Any of these three commissures
may be absent singularly or in combination. Development
of the corpus callosum starts at about 12 weeks from the
lamina terminalis near the anterior end of the third ventricle; it
becomes detectable by about 15 weeks and is complete by about