ALOBAR HOLOPROSENCEPHALY
HPE(Holoprosencephaly) is characterized by a failure of transformation of the prosencephalon into cerebral hemispheres with separate lateral ventricles. HPE has many associated anomalies, both of the nervous system and face. HPE is also associated with malformations in other body systems, particularly when it has a chromosomal etiology.
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 (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).
(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 (there are partially separated cerebral hemispheres and a single ventricular cavity).
(3) Lobar (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).
(4) Middle Interhemispheric Variant (MIHV) -- where the middle of the brain (posterior frontal and parietal lobes) are not well separated.
(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 (there are partially separated cerebral hemispheres and a single ventricular cavity).
(3) Lobar (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).
(4) Middle Interhemispheric Variant (MIHV) -- where the middle of the brain (posterior frontal and parietal lobes) are not well separated.
Children diagnosed with HPE may have a microcephaly, hydrocephalus, variable degrees of mental retardation, epilepsy, endocrine abnormalities, or abnormalities of other organ systems such as cardiac, skeletal, genitourinary, and gastrointestinal. Mildly affected children may exhibit few symptoms and may live a normal life.
The cause of HPE is currently unknown. Often, no specific cause can be identified. Suggested risk factors include maternal diabetes, infections during pregnancy (syphilis, toxoplasmosis, rubella, herpes, cytomegalovirus), and various drugs taken during pregnancy (alcohol, aspirin, lithium, thorazine, anticonvulsants, hormones, retinoic acid). Women with previous pregnancy loss and first trimester bleeding are also more likely to have a child diagnosed with HPE.