• 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

Radiology Cases of Alobar Holoprosencephaly

Radiology Cases of Semilobar Holoprosencephaly

MRI of semilobar holoprosencephaly
Axial (above), coronal (below left) and sagittal (below right) T1 MRI without contrast of the brain shows fusion of the frontal lobes, partial development of the posterior falx and occipital horns and separation of the occipital lobes, absent septum pellucidum, and hypoplasia of the corpus callosum.

Radiology Cases of Lobar Holoprosencephaly

Radiology Cases of Septo-Optic Dysplasia