Malformations of the nervous system.txt

Generally, the earlier in development an abnormality occurs, the more severe the malformation will be

• Abnormal closure of the neural tube (either failure to close or reopening)
• Disorders of forebrain formation, usually with abnormalities of neuronal migration
• Posterior Fossa abnormalities

the neural groove is open directly to air, can see arachnoid covering more laterally, and some overlying skin

• Both, the meninges and the spinal cord protrude through an opening
• they are covered by a layer of skin

only the meninges bulge out, covered by the skin

there is an opening in the skin that passes through meninges, spinal cord directly open to the outside, but no bulging out or herniation

• a continuous layer of skin covers a closure defect of posterior vertebral arch
• no herniation, but subcutaneous tissue contains an opening to the spinal cord

may lead to several malformations

• most common CNS malformation
• most frequently occurs in the lumbosacral area
• Has been related to folate deficiency early in pregnancy
• wide range of severity

• brain's analogue of meningomyelocele
• usually found in the occipital region or posterior fossa

• brain's analogue of spina bifida apart
• absence of brain and calvarium at the anterior end of the neural tube
• the disruption in development happens at ~28 days gestational age, and all that is left is a jumble of red area of disorganized neural tissue, meninges, choroid plexus and ependyma, which is referred to as the AREA CEREBROVASCULOSA

• holoproxencephaly
• Arhinencephaly
• Agenesis of the corpus callosum
• Cystic lesions

• defective separation of the prosencephalon into two cerebral hemispheres, thus a single ("hole" prosencephalon
• There are varying degrees of severity
• usually severe midline facial defects
• associated with trisomy 13 and trisomy 18
• jas been caused in animals by maternal ingestion of cyclopamine: inhibits sonic hedgehog (Shh) signaling during emgryogenesis

absence of the "smell brain" - loss of the olfactory bulbs and tracts, often associated with midline facial defects, such as cleft lip and palate

may accompany holoprosencephaly or be an isolated defect

• porencephaly
• hydranencephaly
• cavities in the brain due to tissue destruction or failure of formaion.

a cyst or cavity in a cerebral hemisphere of the brain through to the ventricle, open to the "outside"

a cyst or cavity in a cerebral hemisphere of the brain, but the opening does not completely open to the outside of the mass of brain or to the ventricles

cyst in brain open to the ventricles, but not outside of brain

• lissencephaly/agyria/pachygyria
• microgyria
• polymicrogyria
• heterotopias

• lack of gyral folding and sulcus formation
• different forms of lissencephaly attributed to specific genetic abnormalities
• mutations in gene encoding the MT-associated protein LIS-1

little tiny folds that only mimic gyri

clusters of neurons that don't make it all the way to their appropriate destinations

• The Arnold-Chiari malformation
• The Dandy-Walker malformation

• 1) elongation of the medulla and 4th ventricle
• 2) protrusion of the posterior portion of the cerebellar vermin through the foramen magnum
• 3) flattening and "beaching" of the quadrigeminal plate
• ** almost always associated with spina bifida, typically accompanied by a lumbosacral meningomyelocele
• most cases develop hydrocephalus

• Is characterized by an enlarged posterior fossa
• The cerebellar vermin is absent or rudimentary, and in its place is a midline cyst lined by ependyma
• the cyst represents the expanded 4th ventricle

a cavity in the spinal cord

• a term used to describe neurologic deficits which are noted soon after birth and don't progress. It has no unifying neuropathologic correlate
• may be caused by malformative or destructive lesions
• it may also follow perinatal hypoxia/ischemia
• ***discrete and non-progressive changes
• if an infant has neurologic symptoms that become worse, look for another explanation

• 1) periventricular hemorrhage: especially in very premature infants. occurs in the germinal matrix and may rupture into the ventricular cavities
• 2) periventricular leukomalacia: due to focal infarcts in the white matter
• 3) status marmoratus: an abnormal "marbling" of the deep gray matter due to hypoxic destruction of neurons in the perinatal period