Case of the Month
Section Editor: Nicholas Stence, MD
Children's Hospital Colorado, Aurora, CO
February 2022
Next Case of the Month Coming March 8...
Middle Interhemispheric Variant of Holoprosencephaly
- Background:
- Holoprosencephaly is a severe brain malformation caused by abnormal separation of the forebrain. It affects 1 in 16,000 live births.
- Classic holoprosencephaly spectrum includes—with decreasing severity—alobar, semilobar, and lobar forms.
- The middle interhemispheric variant (MIHV) of holoprosencephaly, syntelencephaly, was first described in 1993. It is a distinct clinical and neuroradiologic entity within the holoprosencephaly spectrum, closer to the lobar form, with nonseparation of the posterior frontal and parietal regions and normal separation of the anterior frontal and occipital regions.
- Prior to the first description of the MIHV, most of the cases were labelled as lobar holoprosencephaly.
- Accurate radiologic diagnosis is challenging and important to generate prognostic information.
- Clinical Presentation:
- Patients with MIHV have the mildest clinical findings within the holoprosencephaly spectrum.
- Neurologic signs: Mild-to-moderate spasticity is the most common motor symptom followed by hypotonia, developmental delay, epilepsy, and abnormal movements.
- Oromotor dysfunction: Feeding and swallowing difficulties
- No or mild midline craniofacial anomalies: Ocular hypotelorism, sharp nasal bridge, single maxillary central incisor
- Endocrine disorders: Diabetes insipidus, growth hormone deficiency, adrenal hypoplasia, hypogonadism, or thyroid hypoplasia
- Dysautonomic dysfunction: Instability of temperature, heart and/or breath rate
- Key Diagnostic Features:
- Posterior frontal and parietal regions cortical nonseparation, absent interhemispheric fissure and falx in the posterior frontal and parietal regions
- Absent corpus callosum body, variably present genu, present splenium
- Normal or hypoplastic anterior ventricles horns, formed third ventricle, present dorsal cyst in 25%
- Fused thalamus in 33–50%
- Separated basal ganglia
- Separated hypothalamus
- Absent septum pellucidum
- Some patients fall within the spectrum of septo-optic dysplasia and show complete absence of the septum pellucidum and hypoplasia of the optic nerves and chiasm.
- Additional findings:
- An often abnormally connected Sylvian fissure across the midline over the vertex
- Cortical dysplasia and heterotopic gray matter
- Azygous anterior cerebral artery
- Differential Diagnoses:
- Lobar holoprosencephaly: Basal frontal cortical nonseparation, interhemispheric fissure and falx hypoplastic anteriorly and present posteriorly
- Treatment:
- Screening evaluations for hypothalamic and endocrinologic dysfunctions
- Pharmaceutical interventions such as intrathecal baclofen pumps and oral trihexyphenidyl, as well as physical and occupational therapy and surgical interventions for spasticity
- Gastrostomy tube in patients with oromotor dysfunction
- Antiepileptic medications
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