This brain malformation can range from mild to severe and is classified into four types:
(1) Alobar (severe) – where the brain is not divided and there are severe abnormalities.
(2) Semi-Lobar (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.
(3) Lobar (mild) – where the brain is divided and there are some mild abnormalities.
(3a) Lobar Subtype: Septopreoptic HPE (very mild) – only a small area of the brain is fused and the abnormalities are very mild; children with this subtype usually have good motor function.
(4) Middle Interhemispheric Variant (MIHV) – where the middle of the brain (posterior frontal and parietal lobes) are not well separated.