1. Disorders of neural tubeclosure,diverticulation,cleavage andcellular migration

2. Over view of embryology Disorders of neural tube closure Disorders of diverticulation, cleavageand cellular migration 3. CNS Embryology 4. Flexures 5. Spinal cord 6. Medulla oblongata 7. Pons 8. Mid brain 9. Ventricles 10. Cortex 11. Diencephalon 12. Basal ganglia 13. Commisures 14. Neural tube closure disorders Disorders of closure of rostral neuralpore Disorders of closureof caudal neuralpore 15. Cranial defects Meningocele, meningoencephalocele, andmeningohydroencephalocele are all causedby an ossification defect in the bones of theskull. The most frequently affected bone isthe squamous part of the occipital bone,which may be partially or totally lacking. Ifthe opening of the occipital bone is small,only meninges bulge through it(meningocele), but if the defect is large,part of the brain and even part of theventricle may penetrate through theopening into the meningeal sac 16. The latter two malformations areknown as meningoencephalocele andmeningohydroencephalocele 17. Anencephaly Exencephaly is characterized by failure of thecephalic part of the neural tube to close. As aresult, the vault of the skull does notform, leaving the malformed brain exposed.Later this tissue degenerates, leaving a massof necrotic tissue. This defect is calledanencephaly, although the brainstem remainsintact. Since the fetus lacks the mechanismfor swallowing, the last 2 months ofpregnancy are characterized by hydramnios.The abnormality can be recognized on aradiograph, since the vault of the skull isabsent. 18. Defects of caudal neuropore Neural tube defects (NTDs), mayinvolve themeninges, vertebrae, muscles, andskin. Spina bifida is a general term forNTDs affecting the spinal region. Itconsists of a splitting of the vertebralarches and may or may not involveunderlying neural tissue. Two differenttypes of spina bifida occur: 19. Spina bifida occulta is a defect in thevertebral arches that is covered by skinand usually does not involve underlyingneural tissue. It occurs in the lumbosacralregion (L4 to S1) and is usually marked bya patch of hair overlying the affectedregion. Spina bifida cystica is a severe NTD inwhich neural tissue and/or meningesprotrude through a defect in the vertebralarches and skin to form a cyst like sac. 20. Occasionally the neural folds do notelevate but remain as a flattenedmass of neural tissue (spina bifidawith myeloschisis or rachischisis). 21. Cerebral cleavage and neuralmigration defects Child with delayed devolopment andseizures Especially when child is dysmorphic MRI is the investigaton of choice After the imaging we have to see the MRin a orderly fashion Midline structures Cerebral cortex and cortico white matterjunctions White matter Basal ganglia and ventricular system andposterior fossa structures 22. Midline structures Cerebral commisures are the mostcommon anomolies Hypothalamus and pituatary Midline leptomeninges Large csf spaces in posterior fossa 23. Cerebral cortex Is 2-3mm thick Too thick polymicrogyria andpachygyria Greywhite matter junction irregularpolymicrogyria or cobble stone cortex Abnormally thin perinatal or ishaemicinjury 24. White matter Myelination appropriate or not Diffuse layer of hypomyelination oramyelination associated heterotopia orpolymicrogyria suggestive of CMV Absent myelination may be localisedto a gyrus or may extend towards theependymal layer transmantle signcharacteristic of FCD 25. Posterior fossa Brain stem and cerebellum 4 th V and vermis Size of the pons with cerebellum 26. Callosal dysgenesis Partial or complete absence corpuscallosum and hippocampalcommisures Atrium or occipital horn dilatationcolpocephaly Probst bundles Vertical or posterior course ACAs Most common presentation seizuresdevolopmental delay and cranialdeformity and hypertelorism 27. Dandy-Walker malformation Classic Dandy Walker malformation HVR BPC MCM 28. Classic DWM Cystic dilatation of4thV Torcular lambdoidinv HVR 29. HVR Variable vermianhypoplasia BPC Open 4th Vcommunicates withcyst MCM Enlargedpericerebellar cisternscommunicate with subarachnoidspace Vermis and 4 th Vnormal 30. Rhombencephalosynapsis Etiology Unknown: 2 major theories Failure of vermian differentiation Vermian agenesis allowing hemisphere continuity Features Congenital continuity (lack of division) ofcerebellar hemispheres Usually with fusion of dentate nuclei andsuperior cerebellar peduncles 31. Small, single hemisphere cerebellum withcontinuous white matter (WM) tracts crossingmidline Diamond or keyhole-shaped 4th ventricle Absent primary fissure Clinical features Variable neurological signs Ataxia, gait abnormalities, seizures Developmental delay RES discovered in near-normal patients atautopsy 32. Molar Tooth Malformations(Joubert) Hindbrain anomaly characterized bydysmorphic vermis, lack ofdecussation of superior cerebellarpeduncle, central pontinetracts, corticospinal tracts "Molar tooth" appearance of midbrainon axial images Etiology result from mutations ofciliary/centrosomal proteins that can affectcell migration, axonal pathway 33. Clinical features Most common signs/symptoms: Ataxia,developmental delay, oculomotor andrespiratory abnormalities 34. Holoprosencephaly Features Failure to delineate normalprosencephalic midline withabsent/incomplete hemispheric and basalcleavage Single ventricle Azygous ACA associated facial defects 35. Clinical features Most common signs/symptoms Facial malformation (hypotelorism +++) Seizures and developmental delays Hypothalamic/pituitary malfunction (75%,mostly diabetes insipidus), poor bodytemperature regulation Dystonia and hypotonia: Severitycorrelates with degree of BGnonseparation 36. Heterotopic Gray Matter Arrested/disrupted migration of groupsof neurons from periventriculargerminal zone (GZ) to cortex Ectopic nodule or ribbon, isointensewith gray matter (GM) on every MRsequence Periventricular, subcortical/transcerebral, molecular layer Band heterotopia 37. Lissencephaly Features Disorders of cortical formation caused byarrested neuronal migration, resulting in thick4-layer cortex and smooth brain surface "Hourglass" or "figure eight" shape ofcerebral hemispheres 3 layers Outer cellular layer may be relatively thin, smooth Intervening cell-sparse layer Deeper thick layer of arrested neurons mimicking band heterotopia 38. Schizencephaly Features Transmantle gray matter lining clefts Ca++ when associated with CMV Pathology Can be result of acquired in utero insultaffecting neuronal migration Infection (CMV), vascular insult, maternaltrauma, toxin Types Closed lip Open lip 39. Hemimegalencephaly Features Hamartomatous overgrowth of part/all ofhemisphere Abnormal proliferation, migration, anddifferentiation of neurons Embryology Insult to developing brain causes development of too many synapses, persistence of supernumerary axons, and potential for white matter overgrowth Localized epidermal growth factor (EGF) in cortical neurons and glial cells may lead to excessive proliferation 40. Large cerebral hemisphere, hemicranium Posterior falx and occipital pole "swing" tocontralateral side Lateral ventricle is large with abnormallyshaped frontal horn 41. Polymicrogyria Features Malformation due to abnormality in lateneuronal migration and corticalorganization Result is cortex containing multiple smallsulci that often appear fused on grosspathology and imaging Neurons reach cortex but distributeabnormally forming multiple smallundulating gyri