Syntélencéphalie: variant inter hémisphérique médian de l´holoprosencéphalie

Holoprosencephaly (HPE) is a congenital malformation occurring very early in pregnancy and due to abnormal diverticulation of the prosencephalon. This defect in primary brain cleavage may be total or partial, which explains the anatomopathological variants of holoprosencephaly. The main forms of holoprosencephaly include alobar, semilobar and lobar HPE. Syntelencephaly also known as middle interhemispheric variant (MIHV) is a very rare type of HPE. While in the three most common variants, cleavage defect has antero-posterior gradient of severity, syntelencephaly does not follow this rule. The latter is characterised by abnormal communication between cerebral hemispheres in the posterior and parietal frontal regions, with normal inter-hemispheric separation of the anterior frontal lobes, of the occipital regions and central grey nuclei. The trunk of the corpus callosum is achieved at the level of the knee of the corpus callosum (allowing differentiation from lobar HPE) and of the splenium. An azygos cerebral artery is common, consisting of a fusion of the A1 segments of the anterior cerebral arteries to form a single arterial trunk. Other cerebral malformations may be associated with syntelencephaly, the most frequent being cortical dysplasia and grey matter heterotopia. Facial abnormalities are less common in syntelencephaly compared to classic forms of HPE. Prognosis depends mainly on these malformative associations in the brain and other organs, and even on chromosomal aberrations.