Holoprosencephaly (HPE) is a congenital anomaly in which there is incomplete development of the brain. In utero, the developing forebrain (prosencephalon) fails to divide into two separate hemispheres and ventricles. Specifically, there is incomplete cleavage into right and left hemispheres; into the telencephalon and diencephalons; and into the olfactory and optic bulbs and tracts. Based on the level of cleavage, Holoprosencephaly is classified into 4 subtypes: Alobar, Semilobar, Lobar and MIHV.
Holoprosencephaly can range from mild to severe and is classified into four types:
Alobar Holoprosencephaly (severe)--where the brain is not divided and there are severe abnormalities (there is an absence of the interhemispheric fissure, a single primitive ventricle, fused thalami, and absent third ventricle, olfactory bulbs and tracts and optic tracts).
Semi-Lobar Holoprosencephaly (moderate)--where the brain is partially divided and there are some moderate abnormalities; where there are two hemispheres in the rear but not the front of the brain (there are partially separated cerebral hemispheres and a single ventricular cavity).
Lobar Holoprosencephaly (mild)--where the brain is divided and there are some mild abnormalities (there is a well developed interhemispheric fissure however there is some fusion of structures).
Middle Interhemispheric Variant of Holoprosencephaly (MIHV) -- where the middle of the brain (posterior frontal and parietal lobes) are not well separated.
Contributed by MOM Maria Valencia - to read more, please check out Maria's FB Page