Central Nervous System
| Structures | Neural Canal Remnant | |
|---|---|---|
| Telencephalon | Cerebral hemispheres, most of basal ganglia | Lateral ventricles |
| Diencephalon | Thalamus, hypothalamus, subthalamus, epithalamus (pineal gland), retina and optic nerve | Third ventricle |
| Mesencephalon | Midbrain | Cerebral aqueduct |
| Metencephalon | Pons, cerebellum | Fourth ventricle |
| Myelencephalon | Medulla Spinal cord | Central canal |
| Condition | Types | Description | |
|---|---|---|---|
| Anencephaly | — | Failure of anterior neuropore to close Brain does not develop Incompatible with life Increased AFP during pregnancy and AChE | |
| Spina bifida | Spina bifida occulta (Figure A) | Failure of posterior neuropore to close, or to induce bone growth around it. Mildest form Vertebrae fail to form around spinal cord No increase in AFP Asymptomatic; tuft of hair over defect. | |
| Spina bifida with meningocele (Figure B) | Meninges protrude through vertebral defect Increase in AFP | ||
| Spina bifida with meningomyelocele (Figure C) | Meninges and spinal cord protrude through vertebral defect; seen with Arnold-Chiari Type II Increase in AFP | ||
| Spina bifida with myeloschisis (Figure D) | Most severe Spinal cord can be seen externally Increase in AFP and AChE | ||
 | |||
| Arnold-Chiari malformation | Type I | Most common Mostly asymptomatic in children Downward displacement of cerebellar tonsils through foramen magnum Frequent association with syringomyelia | |
| Type II | More often symptomatic Downward displacement of cerebellar vermis and medulla through foramen magnum Compression of IV ventricle → obstructive hydrocephaly Frequent lumbar meningomyelocele | ||
| Dandy-Walker malformation | Failure of foramina of Luschka and Magendie to open → dilation of IV ventricle Agenesis of cerebellar vermis and splenium of the corpus callosum | ||
| Hydrocephalus | Most often caused by stenosis of cerebral aqueduct CSF accumulates in ventricles and subarachnoid space Increased head circumference | ||
| Holoprosencephaly | Incomplete separation of cerebral hemispheres One ventricle in telencephalon Seen in trisomy 13 (Patau) | ||
| Abbreviation: AFP, α-fetoprotein | |||
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