The document summarizes several congenital brain anomalies that can occur during early development of the forebrain, including meroencephaly, anencephaly, and holoprosencephaly. Meroencephaly is characterized by failure of the rostral neuropore to close in the fourth week, resulting in brain tissue being exposed or extruding from the cranium. Anencephaly is a term for when only a rudimentary brainstem remains. Holoprosencephaly is caused by defects in the median plane during the third week and results in a small, merged forebrain.

1. Development of forebrain

12. Meroencephaly

13. Meroencephaly
• failure of the rostral neuropore to close during
the fourth week
• forebrain primordium is abnormal and
development of the Most of the embryo's brain is
exposed or extruding from the cranium-
exencephaly.
•.

14. • abnormal structure and vascularization of the
embryonic exencephalic brain-nervous tissue
degenerates.
• Remaining brain appear as a spongy, vascular
mass; mostly hindbrain structures

15. • often called anencephaly(Gr. an, without,
+ enkephalos, brain);a rudimentary brainstem
and functioning neural tissue are always present
in living infants.
• meroencephaly (Gr.meros, part) is the better
term

16. • common lethal anomaly, occurring at least once
in every 1000 births.
• most common serious anomaly seen in stillborn
fetuses
• Female preponderance- 2-4 times>males
• always associated with acrania (absence of the
calvaria) and may be associated

17. • suspected in utero when there is an elevated
level of AFP in the amniotic fluid
• easily diagnosed by ultrasonography and MRI
fetoscopy, and radiography because extensive
parts of the brain and calvaria are absent.
• Associated polyhydramniosis- common

18. Microcephaly

19. Holoprosencephaly

20. Holoprosencephaly
• severe and relatively common
• Maternal diabetes and teratogens, such as high
doses of alcohol, can destroy embryonic cells in
the median plane of the embryonic disc during
the third week→ defective formation of the
forebrain.
• infants have a small forebrain, merged lateral
ventricles