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Janica E. Walden, MD Neuroradiology University of North Carolina. Holoprosencephaly (HPE). Spectrum of congenital structural forebrain anomalies defined by different degrees of frontal lobe fusion Impaired midline cleavage of the embryonic forebrain

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Janica e walden md neuroradiology university of north carolina l.jpg

Janica E. Walden, MD

Neuroradiology

University of North Carolina


Holoprosencephaly hpe l.jpg
Holoprosencephaly (HPE)

  • Spectrum of congenital structural forebrain anomalies defined by different degrees of frontal lobe fusion

  • Impaired midline cleavage of the embryonic forebrain

  • “Face predicts brain”: severe midline anomaly = severe HPE

  • Clinical severity relates to degree of hemispheric and deep gray nuclei fusion


Etiology pathology l.jpg
Etiology & Pathology

  • Normal prosencephalic cleavage occurs at 4-6 weeks

  • HPE: disruption in dorsoventral axis patterning of secondary prosencephalon,

    • Result of mutations affecting signaling genes (Sonic hedgehog gene) which regulate neural tube patterning.

  • Extreme hypoplasia of neocortex

  • Dorsal cyst (especially in association with non-cleaved thalami) thought to represent expansion of partially blocked posterodorsal 3rd ventricle

  • Variable degree of fusion of diencephalon & basal ganglia/thalamus with incorporation into upper brainstem


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Epidemiology

  • Occurs in 1 to 1.4 per 10,000 live births

    • More common in early embryogenesis with high spontaneous miscarriage rates

  • Maternal factors include alcohol use, diabetes, retinoic acid

    • 1% risk to infants of diabetic mothers (200-fold increased risk than that of general population)

  • Male: female ratio = 1.4: 1


Facial anomalies l.jpg
Facial Anomalies

  • Severe facial anomalies correlate with severity of HPE in 80%

    • +/- midline clefting

    • premaxillary agenesis if severe

    • absent superior frenulum

    • +/- central incisor

    • proboscis

    • single nare; single nasal bone/absent inter-nasal sutures

    • caudal metopic suture

    • infants of diabetic mothers may have alobar HPE with near-normal facies



Clinical features l.jpg
Clinical Features nostril, small low set ears.

  • Most severe (classic alobar HPE) features include: cyclopia, proboscis, midline facial clefting, microcephaly

  • Severe of pituitary/hypothalamic dysfunction (75% especially diabetes insipidus) & disturbed body temperature regulation

    • Correlates with degree of hypothalamic non-separation

  • Seizures (50%) & mental retardation

    • Most severe with cortical malformations

  • Dystonia & hypotonia

    • Severity correlates with degree basal ganglia non-separation


Classification l.jpg
Classification nostril, small low set ears.

  • Defined by degree of frontal lobe fusion

  • Sylvian angle (of Barkovich) = lines drawn tangentially through Sylvian fissures

    • Anteriorly displaced Sylvian fissures results in increased Sylvian angle

    • The larger the Sylvian angle is the more severe frontal lobe hypoplasia is too

  • 3 types of HPE based on criteria (lobar, semilobar, and alobar), as well as a middle interhemispheric variant, septooptic dysplasia, and single central incisor


Alobar holoprosencephaly l.jpg
Alobar Holoprosencephaly nostril, small low set ears.

  • “Pancake” or “horseshoe” brain

  • Monoventricle

  • Large dorsal cyst

  • Fused diencephalon

  • Basal ganglia & thalami may form gray matter fusion mass

  • No interhemispheric fissure

  • No olfactory nerves


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Alobar HPE: note fused thalamic & hemispheres, monoventricle, absent interhemispheric fissure and venous sinsues, & azygous ACA.


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Fetal MRI shows alobar HPE. monoventricle, absent interhemispheric fissure and venous sinsues, & azygous ACA.


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MR T1 images in alobar HPE. monoventricle, absent interhemispheric fissure and venous sinsues, & azygous ACA.


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Diagnosis of HPE by Ultrasound monoventricle, absent interhemispheric fissure and venous sinsues, & azygous ACA.

  • Diagnosis of HPE by ultrasound can be made as early as 9 weeks gestational age.

  • Development of forebrain can be delineated in detail with ultrasound from 7 weeks on.

  • Alobar HPE may be detectable as early as the end of week 7

  • Non-visualization of the butterfly sign is very helpful in diagnosis


Semilobar holoprosencephaly l.jpg
Semilobar Holoprosencephaly monoventricle, absent interhemispheric fissure and venous sinsues, & azygous ACA.

  • Partial occipital/temporal horns

  • Moderate sized dorsal cyst

  • Fused diencephalon

  • Partial fusion of basal ganglia > thalami

  • Interhemipheric fissure present posteriorly

  • Absent of hypoplastic olfactory tracts and bulbs

  • Corpus callosum is rudimentary


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CT in semilobar HPE. monoventricle, absent interhemispheric fissure and venous sinsues, & azygous ACA.


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MRI in semilobar HPE. monoventricle, absent interhemispheric fissure and venous sinsues, & azygous ACA.


Lobar holoprosencephaly l.jpg
Lobar Holoprosencephaly monoventricle, absent interhemispheric fissure and venous sinsues, & azygous ACA.

  • Formed lateral ventricles

  • Small or no dorsal cyst

  • Fused diencephalon and/or fornices

  • +/- partial fusion of basal ganglia > thalami

  • Interhemispheric fissure nearly normal

  • Small or normal olfactory nerves


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MRI in lobar HPE. monoventricle, absent interhemispheric fissure and venous sinsues, & azygous ACA.


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Middle monoventricle, absent interhemispheric fissure and venous sinsues, & azygous ACA.Interhemispheric Variant

  • Sylvian fissures connect across midline over vertex (86%)

  • Interhemispheric fusion of posterior frontal/parietal lobes, with normal separation of anterior frontal/occipital lobes

  • Non-cleavage of thalami > basal ganglia

  • Heterotopias and cortical dysplasias common (86%)

  • Thought to reflect abnormal induction of embryonic roof plate

    • Classic HPE = abnormal induction of embryonic floor plate

    • May explain absence of craniofacial malformations

  • Spasticity, hypotonia, seizures, developmental delay


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MRI in midline intehemispheris variant of HPE. monoventricle, absent interhemispheric fissure and venous sinsues, & azygous ACA.


References l.jpg
References monoventricle, absent interhemispheric fissure and venous sinsues, & azygous ACA.

  • Sepulveda Waldo, Dezerega Victor, Be Cecilia. First-Trimester Sonographic Diagnosis of Holoprosencephaly. Journal of Ultrasound in Medicine 23: 761-765.

  • Hahn Jin, Barnes Patrick. Neuroimaging Advances in Holoprosencephaly: Refining the Spectrum of the Midline Malformation. American Journal of Medical Genetics 154C: 120-132.

  • Blaas H., Eriksson A., Salvesen K., et al. Brains and faces in holoprosencephaly: pre- and postnatal description in 30 cases. Ultrasound ObstetGynecol 2002; 19: 24-38.

  • Takanashi Jun-ichi, Barkovich A. James, Clegg Nancy, Delgado Mauricio. Middle InterhemisphericBariant of Holoprosencephaly Associated with Diffuse Polymicrogyria. AJNR 2003; 24: 394-397.

  • Simon Erin, Hevner Robert, Pinter Joseph, et al. The Middle Interhemispheric Variant of Holoprosencephaly. AJNR 2002; 23: 151-155.


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