DEVELOPMENTAL ABNORMALITIES AND PERINATAL BRAIN INJURY
Neural tube defects are the most common
developmental central nervous system abnormalities. They result
from defective closure of the neural tube, and they tend to occur at the 2
extremities of the neuraxis. Folate deficiency is involved in the pathogenesis.
•
Anencephaly
is the
absence of cranial vault. It is incompatible with life; babies die soon after birth.
•
Neural
tube defects of the spinal cord may take a variety of forms. Significant defects lead to paraplegia and urinary
incontinence from birth.
•
Spina bifida occulta is a bony defect of the
vertebral arch.
•
Meningocele is a bony defect with outpouching
of meninges.
•
Meningomyelocele is a defective formation of
the bony arch with cystic outpouching of meninges, spinal cord, and spinal
roots.
•
Myelocele is a defective bony arch
with complete exposure of the spinal cord
Syringomyelia is an ependymal-lined, CSF-filled channel parallel to and
connected with the central canal in the spinal cord. (Hydromyelia means the
central canal is dilated with CSF.) About 90% of cases are associated with
Arnold-Chiari type 2; the remaining 10% are posttraumatic or associated with
intraspinal tumors. Syrinx (the cyst) enlarges progressively and destroys the
spinal parenchyma. Symptoms include paralysis and loss of sensory functions.
Perinatal brain injury is
injury to the brain during prenatal or immediately post-natal period. This is
the most common cause of cerebral palsy, and it occurs most frequently in
premature babies.
•
Germinal matrix hemorrhage is hemorrhage localized in
the germinal matrix due to its fragile vessels.
•
Periventricular leukomalacia causes infarcts in watershed
areas (periventricu-lar white matter in the fetus).
•
Multicystic encephalopathy refers to multiple brain
infarcts occurring early in pregnancy.
Fetal alcohol syndrome is characterized by structural abnormalities
(microcephaly, agenesis of the corpus callosum, cerebellar hypoplasia),
functional impairments including learning disabilities, and neurological
impairments including epilepsy.
Cerebellar malformations have
chromosomal, single-gene and complex inheritance. FOXCI deletions and
duplications are associated with cerebellar vermis hypoplasia, mega-cisterna
magna and Dandy-Walker malformation, the most common human cerebellar
malformation.
Dandy-Walker malformation is a non-communicating hydrocephalus with
dilation of the fourth ventricle and hypoplasia of the cerebellar vermis.
Arnold-Chiari
malformations
• Type 1 (common) is a downward displacement of cerebellar tonsils
and the medulla through the foramen magnum. This lesion is mostly asymptomatic.
• Type 2 is due to a faulty craniospinal junction, resulting in a
small pos-terior fossa, with abnormal development of the cerebellar vermis and
medulla leading to downward displacement. It is mostly symptomatic because of
compression of the fourth ventricle with obstructive hydro-cephalus
• Other frequently related manifestations include syringomelia and
lum-bar meningomyelocele.
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