Congenital Diseases Associated With The Central Nervous System Flashcards
What stimulates the neurulation process?
The notochord
What is the neural plate?
- It is initially a flat sheet of cells located along the dorsal portion of the developing embryo in direct continuation with the epidermis, and exposed to the extraembryonic medium.
- This sheet of cells will become a tube, and will end up being located inside the embryo.
What does the neural tube give rise to?
- Brain
- Spinal cord
- Cranial and spinal nerves
- Eyes and other sensory organs
- Neural crest
When is the neural tube formed?
In gastrulation at week 3/4
What happens as the neural tube closes?
Becomes patterned along the dorso-ventral and rostro-caudal axis
What is the closing of the neural tube driven by?
This process is driven by secreted signalling molecules, which promote the specification of different CNS structures along each axis
What are defects classified according to?
Stage thought to be affected
What are the classifications of neural tube defects?
- Early CNS patterning
- Neural tube closure
- Regional brain defects
What is an example of an early CNS patterning defect?
Holoprosencephaly (HPE)
What are the types of HPE’s?
- Alobar HPE
- Semilobar HPE
- Lobar HPE
- Microforms of HPE
What is Alobar HPE?
- Refers to the formation of a single ventricle, and the absence of interhemispheric fissure.
- Not only the brain, but also other CNS derivatives and face structures are affected in this from.
What is an example of Alobar HPE?
The separation of the eye field into two optic primordia does not occur, and the affected individuals also display cyclopia.
What is Semilobar HPE?
Shows partial cortical separation, rudimentary hemispheres and a single ventricle.
What is Lobar HPE?
Shows separate ventricles, but there is still incomplete frontal cortical separation.
What are microforms of HPE?
- Some milder forms of HPE have been described, which show much milder midline defects
- Sometimes only identifiable by a single maxillary median incisor or hypotelorism (close set eyes), and no brain malformation
What are Exencephaly and Anencephaly?
- These conditions refer to the lack of closure in the brain region.
- Lack of closure results in exencephaly (“brain exposed”).
- In this condition, the brain tissue remains exposed to the amniotic cavity and eventually degenerates, resulting in anencephaly (“lack of brain”).
What are some examples of neural tube closure defects?
- Chraniorachischsis
- Exencephaly
- Spina bifida
What is Spina Bifida?
- This defect refers to the malformation of the spine and/or spinal cord, usually in the lumbar area.
- It can be due to the failure in the closing of the neural tube during neurulation.
- It can also be due to defective formation of the vertebrae, resulting in the spinal cord being exposed and unprotected.
What are the types of Spina bifida?
Spina bifida can be classified as occulta, meningocele and myelomeningocele
What are regional brain disorders?
- Refers to diseases where whole elements of the CNS are missing or underdeveloped.
- They are often related to defective rostro-caudal CNS patterning.
- Gene-phenotype correlations are not very clear.
What is the difference between Spina bifida and anencephaly?
- Anencephaly is when the anterior (rostral) end of the neural tube remains open
- Spina bifida is when the posterior (caudal) end remains open
How many neural tube closure points are there?
- Three main and two others
Where is the first closure of the neural tube?
Between hindbrain and spinal cord
Where is the second closure of the neural tube?
Between forebrain and midbrain
