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alobar holoprosencephaly

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).


- cerebral anomalies

  • 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)
  • exophtalmy
  • hypotelorism

- nasal malformations

  • single nostril
  • arhinia

- facial clefts

  • 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

- endocrine dysgenesis

Case records

- Case #12063: Isolated alobar holoprosencephaly
- Case #13535: Associated alobar holoprosencephaly

See also

- holoprosencephalies

  • semi-lobar holoprosencephaly
  • lobar holoprosencephaly

- holoprosencephaly sequence