• 1 in 10,000 births
  • Disturbance in separation of embryonic prosencephalon into two separate cerebral hemispheres
  • Associated with chromosomal abnormalities, maternal diabetes
  • 3 types based on severity: alobar, semilobar, interhemispheric variant (syntelencephaly)
Alobar holoprosencephaly
  • Complete or near complete failure of separation of cerebral hemispheres
  • Often seen in stillborn
  • Infants that survive show abnormal reflexes, tone and seizures
  • Severe midline facial deformities – cyclops, single eye on a stalk, midline clefts, hypotelorism
  • Medial and ventral brain not formed
  • Septum pellucidum is absent
  • Imaging
    • Crescent shaped holoventricle continuous with large dorsal cyst
    • Cerebrum as a pancake like mass with no interhemispheric fissure, corpus callosum or falx cerebri
    • Fused basal ganglia and hypothalamus
    • Arterial supply directly from internal carotid arteries
    • Hydrocephalus eventually develops and shunt is required
Semilobar holoprosencephaly
  • Less severe
  • Posteriorly interhemispheric fissure partially formed
  • Anteriorly hemispheres fused
  • Midline facial abnormalities mild
  • Children present late with delayed milestones or hydrocephalus
  • Frontal lobes fused
  • Thalami partially separated
  • Single ventricle
  • Posterior corpus callosum is partially present
  • Rudimentary temporal horns
  • Hippocampi underdeveloped
Interhemispheric variant (syntelencephaly)
  • Mild learning and visual impairments
  • Anterior frontal and posterior occipital lobes separated
  • Posterior frontal and parietal lobes fused with absent interhemispheric fissure, falx and corpus callosum