What types of defects are there?
- Failure of neural tube closure
- CSF accumulation
- Problems with Gyri Formation
- Corpus Callosum
- Head size
- Split cord
List some abnormalities caused by failure of the neural tube?
Anencephaly (Ant neuropore doesnt close)
Encephalocoele (Rostral neural tube failure)
Spina Bifida (Caudal neuropore doesn’t close right leading to non-fused vertebral arches)
How does Anencephaly develop?
Anterior neuropore doesnt close so the skull doesnt form over the brain and (exposed to the outside) it degenerates –> Death
How does Encephalocoele develop?
The rostral neural tube fails causing a defect in the skull through which cerebral tissue herniates.
This can cause a varying degree of neurological deficits based on location and level of herniation
How does spina bifida develop?
Caudal neural tube fails to close properly so you end up with non-fused vertebral arches
(Often has herniation out the spinal column in the lower back)
What is the most minor form of spina bifida?
Spina Bifida Occulta
This occurs in 10% of peoples L5/6 vertebrae with usually no clinical symptoms.
Sometimes it has a dimple with a tuft of hair there.
What are the types of protrusion through the defect in spina bifida?
Collectively called Spina Bifida Cystica.
- Spina Bifida with Meningocele (Protrusion of meninges & CSF)
- Spinal Bifida with Meningomyelocle (Nerve roots/spinal cord also protrude causing loss of sensation and paralysis below lesion)
- Myeloschisis (Spinal cord open due to failure of neural folds to fuse - Complete loss of function/sensation below the lesion causing lower limb paralysis and bladder problems)
How can we prevent neural tube malformations?
- Folic Acid Supplements (Very important to neural tube for no apparent reason)
What screening methods are there for neural tube malformations?
Maternal Blood Screening:
- Raised Serum Alpha Fetoprotein
- AFP from foetal liver leaks into amniotic fluid through open neural tube and into maternal blood
- Raised AFP in amniotic fluid
- Anencephaly and Spina Bifida
What risk factors are there for neural tube malformations?
- Genetic Predisposition
- Nutrional (e.g. too little folate or too much Vit A)
- Environmental e.g. Hyperthermia or Drugs (e.g. Na Valproate)
What is Hydrocephalus?
CSF cant drain so it builds up resulting in an enlarged brain and cranium, usually due to blocked cerebral aqueduct.
What causes hydrocephalus?
- Prenatal Viral Infection
- Intraventricular Haemorrhage
- Spina Bifida Cystica
What do we call it if the Gyri/Sulci fail to develop?
Lissencephaly or “smooth Brain”.
What causes Lissencephaly?
Defective Neuronal Migration
What happens in Lissencephaly?
- Severe Mental Impairment
- Failure to Thrive
- Abnormal Muscle Tone
(Many die before 10)
Other than lissencephaly what conditions affect the gyri?
An excessive number of small gyri with a variable degree of neurological problems
What causes microcephaly and how does it present?
Genetics, drugs and infection e.g. Zika
Intellectual impairment Delayed Motor function/speech Seizures Balance/Co-ordination problems Hyperactivity
What congenital malformation affects the Corpus Callosum?
Agenesis of the Corpus Callosum (Partial or incomplete)
Effects range from subtle cognitive/social difficulties up to severe impairment, seizures and hypotonia etc
What causes CSF filled Cysts or cavities?
Due to postnatal stroke or infection
What causes Clefts or slits in the brain?
Genetics, in utero stroke or infection.
Spinal cord split longitudinally in two, associated with other vertebral anomalies.
Causes loss of sensation, weakness, scoliosis, hairy lower back and foot deformities.