“1 in 1,300 fetuses at 12 weeks’ gestation. 1 in 10,000 births.
Abnormalities from incomplete cleavage of the forebrain observed in the standard transverse sections of the brain.
There are 4 types:
Alobar: fusion of the cerebral hemispheres with a single ventricle.
Semilobar: cerebral hemispheres and lateral ventricles are fused anteriorly but separated posteriorly.
Lobar: cerebral hemispheres are separated both anteriorly and posteriorly, but there is partial fusion of the frontal horns of the lateral ventricles, absence of septum pellucidum and abnormalities of the corpus callosum, cavum septum pellucidum and olfactory tract. The main differential diagnosis is septo-optic dysplasia and therefore an attempt should be made to examine optic chiasm and optic nerves by MRI.
Syntelencephaly, the anterior and occipital areas of the brain are fully cleaved as in the lobar type, but unlike this, there is no parietal cleavage and therefore the Silvian fissures are vertically oriented and abnormally connected across the midline over the vertex of the brain.” Read More