2. HOLOPROSENCEPHALY
0 Absence of brain tissue in the midline
0 Fusion of lateral ventricles to form a single chamber
0 Eye field area fails to separate

3. Schizencephaly
0 Formation of clefts in cerebral hemisphere
0 Loss of brain tissue may also occur

4. Defects in ossification of skull
bones
0 Most common is that of sq.part of occipital bone
0 If opening is small, only the herniation of meninges
takes place(Meningocele)
0 If large , cranial tissue may also be
involved(Meningoencephalocele)
0 If ventricles also
involved(Meningohydroencephalocele)

5. Exencephaly
0 Failure of closure of neural folds in cephalic region
0 Vault of skull is absent
0 Nervous tissue is exposed, degenerates and becomes
necrotic---anencephaly
0 Swallowing reflex absent— Hydramnios present

6. Craniorachischisis
0 If NTD(Failure of closure) extends upto the spinal
cord—craniorachischisis----Anencephaly occurs

7. Hydrocephalus
0 Abn.accumulation of CSF in ventricles
0 Most common cause is the obstruction in aqueduct of
Sylvius
0 Pressure on brain and skull bones---
opening/widening of skull---large sized skull
0 Sometimes thinning of brain tissue and bones also
occurs

8. Arnold-Chiari Syndrome
0 Caudal displacement and herniation of cerebellar
structures

9. Microencephaly
0 Underdevelopment of brain and overlying skull
0 CAUSES:
0 Fetal insults by
0 DRUGS
0 RADIATION
0 TERATOGENS
0 INFECTIONS(Rubella,Toxoplasmosis,Cytomegalovirus
)
0 Maternal alcohol abuse

10. ABSENCE OF CORPUS
CALLOSUM
0 Without much functional disturbence

11. ABSENCE OF CEREBELLUM
0 Only a little difficulty in coordination