L8-Congenital Malformation & Hydrocephalus (2)

8/17/2019 L8-Congenital Malformation & Hydrocephalus (2)

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Know the common types of congenital malformations of the CNS

and have a basic knowledge of their pathological features.

Correlate CNS normal development with the classification ofcongenital CNS malformations.

Appreciate the role of folate deficiency as an etiological factor in

neural tube defects and understand the role of Alpha feto-proteinmeasurement and ultrasound in antenatal diagnosis of neuraltube defects.

Understand the various mechanisms that lead to thedevelopment of hydrocephalus.

ist and classify the main causes of hydrocephalus.


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!he incidence of CNS malformations" giving rise tomental retardation" cerebral palsy" or neural tubedefects" is estimated at #$ to %$

&alformations of the brain are more common in the

setting of multiple birth defects

'ecause different parts of the brain develop at differenttimes during gestation (and afterwards)" the timing of anin*ury will be reflected in the pattern of malformation


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+renatal or perinatal insults may either cause,

◦ failure of normal CNS development

◦

tissue destruction

Although the pathogenesis and etiology of many malformationsremain unknown" both genetic and environmental factors areclearly at play

◦ CNS malformatio ca be caused by &utatio s affectingmolecules in pathways of neuronal and glial, evelopment &igration Connection

◦ Additionally" some toic compounds and infectious agentsare known to have teratogenic effects


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• !he volume of brain may be abnormally large (megalencephaly ) or

small (microencephaly ). &icroencephaly" by far the more common ofthe two" is usually associated with a small head as well

• /t can occur in a wide range of clinical settings" including,

• chromosome abnormalities

• fetal alcohol syndrome

• human immunodeficiency virus # (0/1-#) infection ac2uired in utero• All causes are associated with a decreased number of neurons

destined for the cerebral corte. isruption of normal neuronalmigration and differentiation during development can lead to a

disruption of the normal gyration and si-layered neocortical

architecture


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Lissencephaly (agyria) or, in case of more patchy involvement, pachygyria is characterized by an absence of normal gyration and asmooth-surfaced brain. The cortex is abnormally thickened and isusually only four-layered. Single-gene defects have been identied in

some cases of lissencephaly.

• !ortical sulci are absent except,usually, for the Sylvian ssure

• The cortex is thick and consists of

the molecular and three neuronallayers

• The deepest of these layers isalso the thickest and mostcellular, presumably comprised of

neurons that migrated a certaindistance from the ventricles butfailed to reach their normaldestinations

• There is a small amount of

myelinated "hite matter bet"eenthe abnormal cortex and the


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Among the earliest stages in brain development is theformation of the neural tube" the inside of which will becomethe ventricular system and the wall of which will become thebrain and spinal cord

• 3ailure of a portion of the neural tube to close" or reopening

after successful closure" may lead to one of severalmalformations. All are characteri4ed by abnormalities involvingsome combination of neural tissue" menginges" and overlyingbone or soft tissues

•

Collectively" neural tube defects are the most fre2uent CNSmalformations


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• &yelomeningocele is an etension of CNS tissue through adefect in the vertebral column

• !hey occur most commonly in the lumbosacral region

• +atients have motor and sensory deficits in the loweretremities and problems with bowel and bladder control

• !he symptoms derive from the abnormal spinal cord in thisregion" and are often compounded by infections etendingfrom thin or ulcerated overlying skin


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At the other end of the developing brain" anencephaly is amalformation of the anterior end of the neural tube" withabsence of the brain and top of skull

An encephalocele is a diverticulum of malformed CNS

tissue etending through a defect in the cranium◦ /t most often involves the occipital region or the

posterior fossa


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• !he most common malformations in this region of the

brain result in either misplaced or absent cerebellum

• !ypically" these are associated with hydrocephalus.

• !he Arnold-Chiari malformation (Chiari type //malformation) consists of,• A small posterior fossa• A misshapen midline cerebellum• ownward etension of vermis through the foramen

magnum• 0ydrocephalus•

A lumbar myelomeningocele


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• After being produced by the choroid pleus within the

ventricles" cerebrospinal fluid (CS3) circulates through theventricular system and eits through the foramina ofuschka and &agendie

• CS3 fills the subarachnoid space around the brain andspinal cord" contributing to the cushioning of the nervous

system within its bony confines

• !he arachnoid granulations are responsible for theresorption of CS3

• !he balance between CS3 generation and resorptionkeeps the volume of this fluid stable


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• 0ydrocephalus refers to the accumulation of ecessiveCS3 within the ventricular system

• &ost cases occur as a conse2uence of impaired flow orimpaired resorption of CS3

• /n rare instances (e.g." tumors of the choroid pleus)"overproduction of CS3 may be responsible

• 5hen hydrocephalus develops in infancy before closure ofthe cranial sutures" there is enlargement of the head


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0ydrocephalus developing after fusion of the sutures" incontrast" is associated with epansion of the ventricles andincreased intracranial pressure" without a change in head

circumference

/f there is an obstacle to the flow of CS3 within theventricular system" then a portion of the ventriclesenlarges while the remainder does not. !his pattern is

referred to as noncommunicating hydrocephalus and ismost commonly seen with masses at the formamen of&onro or a2ueduct of Sylvius

/n communicating hydrocephalus all of the ventricularsystem is enlarged6 here the cause is most often reducedreabsorption of CS3


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Abnormal buildup of cerebrospinal fluid (CS3) in theventricles of the brain

/t can result from congenital and ac2uired etiologies.

!he fluid is often under increased pressure (but notalways) and can compress and damage the brain.


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0ypersecretio of CS3, e.g. choroid pleus tumor

7bstructive hydrocephalus

◦ 7bstruction of the foramina of &onro e.g. colloid cyst

◦ 7bstruction of the third ventricle e.g. pilocytic astrocytoma◦ 7bstruction of the a2ueduct e.g. a2ueductal stenosis or atresia and

posterior fossa tumors

◦ 7bstruction of the foramina of uschka or impairment of flow from thefourth ventricle (Chiari malformation" meningitis" subarachnoidhemorrhage" posterior fossa tumors).

◦ 3ibrosis of the subarachnoid space e.g. meningitis" subarachnoidhemorrhage" meningeal dissemination of tumors

-efective filtratio of CS3, postulated for low-pressure hydrocephalus.


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#ene$ %eningocele

#ene$ &olymicrogyria

'hat is the dierence bet"eenmicrocephaly and microencephaly

#ene$ *ydrocephalus +x acuo

L8-Congenital Malformation & Hydrocephalus (2)

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