Holoprosencephaly

Etiology:
— Cleavage failure – lateral: cerebral hemispheres and transverse: diencephalon and telencephalon
— Is continuum from alobar (severe) to semilobar to lobar (mild)
— 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 MRI Alobar Holoprosencephaly:
— Severe craniofacial anomalies
— Monoventricle with holosphere: often midline dorsal cyst
— Absent midline structures (septum pellucidum, falx cerebri, interhemispheric fissure, corpus callosum)
— Fused thalami and basal ganglia
Imaging MRI Semilobar Holoprosencephaly:
— Variable craniofacial anomalies
— Rudimentary ventricles with occipital and temporal horns
— Absent septum pellucidum
— Partial midline structures (posterior falx cerebri, interhemispheric fissure, splenium of corpus callosum present)
— Partially separated thalami and basal ganglia
— Separation of occipital lobes
Imaging MRI Lobar Holoprosencephaly:
— Absent or mild craniofacial anomalies
— Squared off frontal horns of lateral ventricles
— Absent septum pellucidum
— Present midline structures (well-formed falx cerebri, interhemispheric fissure with mild inferior frontal fusion, body and splenium of corpus callosum present)
— Separated thalami and basal ganglia
— Partial frontal lobe fusion with occipital and temporal and parietal lobes well formed
— Azygous anterior cerebral artery
Imaging MRI Septo-optic Dysplasia:
— Hypoplastic optic nerves and chiasm
— Hypoplasia or absence of septum pellucidum
Note Associations: Hypothalamic – pituitary dysfunction in 60-70%, ectopic posterior pituitary gland, migrational anomalies – schizencephaly or gray matter heterotopia, overlap with lobar holoprosencephaly, white matter atrophy leads to ventriculomegaly, corpus callosal agenesis, Chiari II malformation, cephalocele
DDX:
Complications:
Treatment:
Clinical: Alobar holoprosencephaly usually do not survive long after birth