- Etiology: abnormality of ventral induction with failure of cleavage of brain into 2 hemispheres, lobation of hemisphere occurs posterior to anterior – posterior brain can be separated but anterior brain still fused
- Imaging
— Alobar – monoventricle with holosphere, fused thalami, absent midline structures (falx + septum pellucidum + corpus callosum)
— Semilobar – partial development of posterior falx + occipital horns + separation of occipital lobes, absent septum pellucidum, callosal hypoplasia
— Lobar – falx is complete, partial frontal lobe fusion, occipital/temporal/parietal lobes well formed
— Septo-optic dysplasia – hypoplastic optic nerves/chiasm, absent septum pellucidum - Clinical: Septo-optic dysplasia – hypothalamic-pituitary dysfunction in 1/3rd, associated with schizencephaly / midline malformation / eye anomalies
Pediatric Imaging 