Middle interhemispheric variant of holoprosencephaly: A rare midline malformation

Abstract

Middle interhemispheric variant (MIH) of holoprosencephaly (HPE) or syntelencephaly is a rare variant of HPE characterized by abnormal midline union of the posterior frontal and parietal lobes with variable fusion of thalami. It varies from classic HPE in embryopathogenesis, severity of fusion of brain structures, associated craniofacial anomalies and clinical presentation. We report a case of MIH in a 5-year-old girl, who presented with severe developmental delay and discuss the features differentiating it from other more common forms of HPE.

Keywords: Holoprosencephaly; middle interhemispheric variant; syntelencephaly.

Figure 1

Clinical photograph of the patient. (a) Frontal view shows metopic prominence, bushy eyebrows with synophrys, broad nasal root, telecanthus, and shallow philtrum, (b) Lateral view shows metopic prominence with flat nasal bridge

Figure 2

Magnetic resonance images of the patient. (a) Axial T1-weighted image shows abnormal orientation of sylvian fissures (arrows), which are connected across the midline and nonseparation of posterior frontal and parietal lobes (arrowheads), (b) Axial T2-weighted image at the level of basal ganglia shows normal separation of basal and anterior frontal lobes and occipital lobes. The basal ganglia and thalami are also well separated. The frontal horns are hypoplastic with absent septum pellucidum, (c) Sagittal T2-weighted image shows agenesis of body of corpus callosum (arrows) with normal splenium and genu, (d) Parasagittal T2-weighted image shows vertical orientation of sylvian fissure (arrows) and vertical course of middle cerebral artery (arrowhead)