Congenital malformations of the
nervous system
Birth defects of spinal cord
• Most of them are the neural tube defects (NTD)
– result from failure of fusion of one or more neural arches
of the developing vertebrae during the 4th week.
– affect the tissues overlying the spinal cord (meninges,
vertebral arches, muscles, skin).
– Spina bifida
• Spina bifida occulta
• Spina bifida cystica
Dermal sinus
• Failure of the surface ectoderm (future skin) to detach from
the neuroectoderm and meninges.
• Dimple in the skin of the sacral region of the back.
Spina bifida occulta
•
•
•
•
Failure of the fusion of neural arches in the median plane.
Occurs in the L5 or S1 vertebra in %10 of the normal people.
Most minor form - a small dimple with a tuft of hair.
Usually no symptoms.
Spina bifida cystica
• Protrusion of the spinal cord and/or meninges through defects in
the vertebral arches.
1. Spina bifida with meningocele (meningeal cyst contains
meninges).
2. Spina bifida with meningomyelocele (meningeal cyst contains
spinal cord).
–
common in lumbosacral region
Symptoms of spina bifida cystica include varying degrees of
neurologic deficit depending on the position and extent of the lesion.
• Loss of sensation at corresponding dermatome
• Complete/partial skeletal muscle paralysis
• Sphincter paralysis (lumbosacral lesion)
3. Myeloschisis (rachischisis)
–
–
–
–
most severe type of spina bifida
the neural folds fail to elevate and fuse
spinal cord is represented as a flattened mass of neural tissue
neural deficit caudal to lesion
Etiology of Neural Tube Defects
• Genetic, environmental, nutritional factors
• Low maternal vitamin B12 levels
• Valproic acid in first 4 weeks (meningomyelocele)
Folic acid (400µg/day)
Birth defects of brain
• Because of the complexity of its embryologic history,
abnormal development of the brain is common (3/1000
births)
• Results from the defects in the cranium (NTD)
• Birth defects of the brain can also be caused by
– alterations in the histogenesis of the nervous tissue.
– developmental failures of the associated structures.
• Abnormal histogenesis of brain can result in mental and
motor deficiency.
– Exposure to certain viruses and high levels of radiation (816 week)
– Prenatal factors
• Maternal infection or thyroid disorder
• Rh factor incompatibility
• Genetic conditions
Cranium bifidum
• Herniation of intracranial contents through a defect in the
cranium.
• 1/2000
• Most common in the occipital region
meningocele
meningoencephalocele
meningohydroencephalocele
Meroencephaly (anencephaly)
•
•
Failure of the rostral neuropore to close during the 4th week
Associated with
–
–
–
–
–
incomplete development of calvaria (acrania)
partial absence of the brain
exencephaly
rachischisis
facial abnormalities
• 1/1000 birth
• 2-4 times more
common in girls
stillborn fetus
polyhydramnios
DIOGNOSIS
•
•
•
•
Serum alpha fetoprotein (AFP)
Amniocentesis
USG
MRI
Craniorachischisis
Microcephaly
• Calvaria and brain are small, face is normal size
• Ressults from the reduction in brain growth
• Low pressure from the growing brain leads to the small size of the
neurocranium
Etiology
Genetical factors
Large amounts of ionizing
radiation
Cytomegalovirus, Rubella virus
Toxoplasma gondii
Maternal alcohol abuse
Hydrocephalus
• Enlargement of the head
• There is excess CSF in the ventricular system
• Result from
• Impaired circulation and absorption of CSF
• Congenital aqueductal stenosis
• Subarachnoid hemorrhage
• Increased production of CSF (choroid plexus adenoma)
Holoprosencephaly
• Defective formation/ failure of
cleavage of the forebrain
• Facial abnormalities
• 1:250 fetuses
• Maternal diabetes, high doses
of alcohol during the 3rd week
• Shh is a holoprosencephaly
related gene
References
1.
2.
3.
4.
The Developing Human: Clinically Oriented Embryology by Keith L. Moore, T.
V. N. Persaud and Mark G. Torchia (2013). 9th ed. Elsevier Saunders,
Philadelphia. ISBN: 978-0-8089-2444-9
Langman’s Medical Embryology by T.W. Sadler (2012). 12th ed. Lippincott
Williams & Wilkins, Philadelphia. ISBN: 978-1-4511-4461-1
Human Embryology by Larsen WJ (2001). 3rd ed. Churchill Livingstone,
Philadelphia. ISBN: 978-0-443-06583-5
Human Embryology and Developmental Biology by Bruce M. Carlson (2009).
4th ed. Mosby, Elsevier, Philadelphia. ISBN: 978-0-323-05385-3