Which of the following is not associated with a defect in neural migration:
Ans is 'd' i.e. Focal cortical brain maldevelopment with ballooning Neuronal migration DisordersThis group of disorders is characterized by defective movement of neurons from the peace of origin along the lining of the lateral ventricle, to the eventual peace of residence in the correct laminar position within the cerebral cortex.Depending upon the timing of the insult, the cortex will completely lack gyri and sulci (lissencephaly), may have a few coarse gyri (pachygyria), may have multiple small gyri (microgyria or polymicrogyria), or have fragments of gray matter present in an abnormal location of the brain (heterotopias).Affected individuals typically display mental retardation and epilepsy.SchizencephalyThis is the presence of unilateral or bilateral clefts within the cerebral hemispheres due to an abnormality of morphogenesisLissencephaly (Agyria)Lissencephaly, or agyria, literally means smooth brain is characterized by the absence of cerebral convolutions and a poorly formed sylvian fissure, giving the appearance of a 3-4 mo fetal brain. CT and MRI scans typically show a smooth brain with an absence of sulci (figure of 8 appearance).PachygyriaPolymicrogyriaHeterotopiaCongenital disorders of the brain and spine are extremely complex and are best studied by correlating with the embryological development.Stage 1: Dorsal Induction: Formation and Closure of the NeuralTubeFailure: defects of neural tube closure-AnencephalyCephaloceleArnold ChiariSpinal dysraphismStage 2: Ventral Induction: Formation of the Brain Segments and FaceThree vesicles (prosencephalon, mesencephalon, and rhombencephalon) form the cerebrum, mid-brain, cerebellum, and lower brain stem. Division into two hemispheres.Failure: defects in formation of brain vesicles + faceHoloprosencephalyCorpus callosum agenesisDandy WalkerSepto-optic dysplasiaFacial anomalies Stage 3: MigrationNeuronal migration from germinal matrix to the cortex. Cortical organization.Disorders: defects of neural migration.Stage 4: MyelinationFailure: developmental delay, dysmyelinating disease
Lissencephaly
Schizencephaly
Polymicrogyria
Focal cortical brain maldevelopment with ballooning
Brain Imaging: Anatomy, Trauma, and Tumors