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Holoprosencephaly
There is frontal fusion (which constitutes the holoprosencephaly) and occipital division (which makes the case: semilobar).
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Holoprosencephaly

OVERVIEW
  • Holoprosencephaly occurs when the prosencephalon (the embryonic forebrain) fails to divide into the doubled lobes of the brain.
  • This results in a single-lobed brain with severe skull and facial defects.
    • Typically, the malformations are too severe for the fetus to even reach birth; however, the disorder is on a broad spectrum.
FREQUENCY
  • 1/250 during early embryo development.
  • 1/10,000 to 1/20,000 at term.
CLASSIFICATIONS:
  • Alobar -- no division, associated with severe facial defects.
  • Semilobar, partial division (intermediate severity).
  • Lobar, prominent, but incomplete separation of the lobes (the least severe form).
Notable craniofacial characteristics
  • Median cleft lip (aka premaxillary agenesis) (the least severe finding)
  • Cyclopia: a single eye located at what is otherwise the root of the nose (the most severe finding)
  • Microcephaly
  • Midface flattening
  • Hypotelorism (closely spaced eyes)
  • Flat nasal bridge
  • Single maxillary central incisor
Genetics
  • Less than 1/3 of cases are caused by gene mutation (eg, SHH (sonic hedgehog)); at least 9 genes mutations have been discovered.
  • The remainder of cases are due to other genetic and/or environmental factors.
    • Trisomy 13
    • Fetal alcohol syndrome
References
  • Geng, Xin, and Guillermo Oliver. “Pathogenesis of Holoprosencephaly.” The Journal of Clinical Investigation 119, no. 6 (June 1, 2009): 1403–13. https://doi.org/10.1172/JCI38937.
  • Raam, Manu S, Benjamin D Solomon, and Maximilian Muenke. “Holoprosencephaly: A Guide to Diagnosis and Clinical Management.” Indian Pediatrics 48, no. 6 (June 2011): 457–66.
  • Solomon, Benjamin D., Andrea Gropman, and Maximilian Muenke. “Holoprosencephaly Overview.” In GeneReviews®, edited by Margaret P. Adam, Holly H. Ardinger, Roberta A. Pagon, Stephanie E. Wallace, Lora JH Bean, Karen Stephens, and Anne Amemiya. Seattle (WA): University of Washington, Seattle, 1993. http://www.ncbi.nlm.nih.gov/books/NBK1530/.

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