Holoprosencephaly (HPE) Fetal MRI

Step-by-step decision

Choose step by step as prompted; reaching an endpoint gives the management recommendation. You can go back a step or restart anytime.

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Full pathway

1. [Decision] Degree of forebrain cleavage (DeMyer) + face
   Degree of forebrain cleavage (DeMyer classification) + face? (HPE = a disorder of forebrain cleavage. Common feature = absent cavum septi pellucidi. The face predicts the brain (facial anomaly is a clue). Severe forms detectable early on ultrasound, fetal MRI second-line to confirm the type + face + associated anomalies; chromosomes (trisomy 13 common).)
   • Lobar / middle interhemispheric variant (mostly cleaved, falx present, absent cavum septi pellucidi, azygos anterior cerebral artery) → Lobar / middle interhemispheric variant
   • Semilobar (frontal fusion, falx/interhemispheric fissure posterior only, partial thalamic separation, H-shaped monoventricle) → Semilobar · poor prognosis
   • Alobar (monoventricle + dorsal cyst, fused thalami, no falx/interhemispheric fissure, severe facial anomaly) → Alobar (most severe) · non-viable
2. [End] Lobar / middle interhemispheric variant
   Lobar / middle interhemispheric variant (MIH): mostly cleaved, falx and interhemispheric fissure present, absent cavum septi pellucidi (square frontal horns), azygos anterior cerebral artery; fetal MRI to confirm (differentiate from isolated absent cavum septi pellucidi/septo-optic dysplasia) + chromosomes + genetic counseling; survives but often with epilepsy/developmental and endocrine impairment (the middle interhemispheric variant has a slightly better prognosis).
3. [End] Semilobar · poor prognosis
   Semilobar: frontal fusion, interhemispheric fissure/falx posterior only, partial thalamic separation, H-shaped monoventricle, absent anterior CC, mild facial anomaly (hypotelorism/cleft lip); poor prognosis, often dies in infancy; fetal MRI to confirm + chromosomes + multidisciplinary counseling.
4. [End] Alobar (most severe) · non-viable
   Alobar (most severe): holoventricle + large dorsal cyst, fused thalami/basal ganglia, no falx/interhemispheric fissure/cavum septi pellucidi, severe facial anomaly (cyclopia/proboscis/hypotelorism); differentiate from hydrocephalus/hydranencephaly/Dandy-Walker (HPE has fused thalami, absent falx); non-viable, chromosomes (trisomy 13) + genetic counseling.

Source guidelines & references

• Holoprosencephaly DeMyer classification and fetal MRI (GeneReviews; StatPearls)

This pathway is our own synthesis of the decision logic in the guidelines above (not the guideline verbatim); thresholds and workflows change as guidelines update — in practice follow the latest guideline, your institution's protocol and the individual patient.

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