Congenital Diseases Associated with Central Nervous System Flashcards
What does the neural tube differentiate into?
- The brain
- Spinal cord
- Cranial and spinal nerves
- Eyes and other sensory organs
- Neural crest
When does neurulation occur and what do defects result in?
- Defects in neural tube formation will affect the formation of some or all of these structures.
- In humans, neurulation occurs between weeks 3 and 4.
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 stimulates the neurulation process?
The notochord
What happens when the neural tube closes?
It becomes patterned along the dorso-ventral and the rostro-caudal axes. This process is driven by secreted signalling molecules, which promote the specification of different CNS structures along each axis.
What are the derivatives of the neural tube along the cranio-caudal axis?
![](https://s3.amazonaws.com/brainscape-prod/system/cm/384/232/153/a_image_thumb.png?1646342190)
What congenital defects can arise from perturbation of different steps during CNS formation?
- Defects of early patterning of the CNS: holoprosencephaly
- Defects of neural tube closure: chraniorachischisis, exencephaly/anencephaly, spina bifida.
- Regional brain defects: rostro-caudal defects.
What is Holoprosencephaly (HPE)?
- A defect of dorso-ventral forebrain patterning
- HPE is a structural malformation of the forebrain characterised by impaired midline cleavage of the brain.
- HPE can be classified as alobar, semilobar or lobar, depending on the degree of severity of the midline defect.
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.
- For example, 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 do different conditions of defects in neural tube closure depend on?
Depending on the extent of the closure defect, or the region along the cranio-caudal axis where non-closure occurs.
What is Craniorachischisis?
- This is the most severe form of neural tube defect. The neural tube remains open along the whole body axis.
- Sometimes the forebrain closes normally, and the defect is then called rachischisis.