Monday 23 April 2007
In alobar HPE, the brain consists of a single spherical forebrain structure with a single ventricle. A large cyst which communicates with the ventricle is present in the posterior-dorsal part of the brain. Alobar HPE is incompatible with survival.
The brain in alobar HPE is small and the gyral pattern and cortical architecture are abnormal. The eyes, which evaginate from the forebrain in the fourth week, are small and malformed or there is only one eye (cyclopia).
Because the olfactory nerves which are part of the rhinencephalon are absent, the term arrhinencephaly has also been applied to this malformation. However, in alobar HPE, there is much more missing than the olfactory brain.
The brain malformations are accompanied by severe midline facial anomalies (holoprosencephaly sequence).
- small single forebrain ventricle
- no interhemispheric division
- absence of olfactory bulbs and tracts
- absence of corpus callosum
- non separation of deep gray nuclei
severe facial dysmorphism
- proboscis (a trunk-like structure above the single eye)
- single nostril
- medial cleft lip
- medial cleft palate
- medial nasolabiopalatal cleft
midline skeletodental anomalies (malformations of midline structures anterior to the sella turcica comprising suture development and cartilage development)
- partial absence of the intermaxillary suture (in the region anterior to the central incisor)
- absence of the internasal suture
- partial absence of the metopic suture (caudal part)
- single midline nasal bone
- midline maxillary central incisor
- short nasal septum
- absence of crista galli
- partial absence of cartilaginous tissue anterior to the sella turcica
- semi-lobar holoprosencephaly
- lobar holoprosencephaly