EP05.32: Prenatal ultrasound features of the middle interhemispheric variant of holoprosencephaly: a case report

A 32-year-old woman, gravida 1, para 0, came to our institution for prenatal diagnosis. A level 3 ultrasound at 31 weeks of gestation revealed: thalamus in transverse plane bilateral anterior and posterior corners of ventricles were connected, and the hyaloid septum and corpus callosum were not shown in the median sagittal plane. Prenatal MRI suggested: bilateral ventricles in the cephaloaxial plane were communicating in the anterior, somatic and posterior corners of the ventricles, the hyaline septum cavity was absent in the midsagittal plane, and the corpus callosum was completely absent. Depending on the degree of brain separation and the site of fusion, the holoprosencephaly (HPE) is divided into two categories: classic HPE and middle interhemispheric variant of holoprosencephaly (MIH). The classic HPE is characterised by a pronounced ventral fusion of the brain; MIH is rarer and is mostly characterised by dorsal fusion of the brain (posterior frontal and parietal lobes), with prefrontal and occipital lobes present. Ultrasound images of lobar HPE and MIH both showed anterior horn communication of the lateral ventricles and the absence of the septum cavity. The main points of differentiation between the lobar HPE and MIH were that in the former, dysplasia of the corpus callosum was more often seen in the genu and splenium, while in the latter, dysplasia of the corpus callosum was more often seen in the body; and that only the anterior horn of the lateral ventricle communicates in the former, while in the latter most of the communication of the lateral ventricle is found in the posterior horn and the body. MIH is very similar to lobar HPE, isolated absence of septum pellucidum, and optic septal dysplasia, which are difficult to differentiate in clinical practice. MRI is helpful for differential diagnosis, but it is difficult to confirm the diagnosis in the prenatal period due to the influence of the intrauterine environment and fetal movement.