CNS Development Anomalies PDF

# Developmental Anomalies ## I. Neural Tube Defects - Arise from incomplete closure of the neural tube. - Neural plate invaginates early in gestation to form the neural tube, which runs along the cranial-caudal axis of the embryo. - The wall of the neural tube forms central nervous system ti...

# Developmental Anomalies ## I. Neural Tube Defects - Arise from incomplete closure of the neural tube. - Neural plate invaginates early in gestation to form the neural tube, which runs along the cranial-caudal axis of the embryo. - The wall of the neural tube forms central nervous system tissue, the hollow lumen forms the ventricles and spinal cord canal, and the neural crest forms the peripheral nervous system. - Associated with low folate levels prior to conception. - Detected during prenatal care by elevated alpha-fetoprotein (AFP) levels in the amniotic fluid and maternal blood. - Anencephaly is absence of the skull and brain (disruption of the cranial end of the neural tube). - Leads to a 'frog-like' appearance of the fetus. - Results in maternal polyhydramnios since fetal swallowing of amniotic fluid is impaired. - Spina bifida is failure of the posterior vertebral arch to close, resulting in a vertebral defect (disruption of the caudal end of the neural tube). - Spina bifida occulta presents as a dimple or patch of hair overlying the vertebral defect. - Spina bifida presents with cystic protrusion of the underlying tissue through the vertebral defect. - Meningocele - protrusion of meninges. - Meningomyelocele - protrusion of meninges and spinal cord. ## II. Cerebral Aqueduct Stenosis - Congenital stenosis of the channel that drains cerebrospinal fluid (CSF) from the 3rd ventricle into the 4th ventricle. - Leads to accumulation of CSF in the ventricular space; most common cause of hydrocephalus in newborns. - CSF is produced by the choroid plexus lining the ventricles. - Flows from the lateral ventricles into the 3rd ventricle via the interventricular foramen of Monro. - Flows from the 3rd ventricle into the 4th ventricle via the cerebral aqueduct. - Flows from the 4th ventricle into the subarachnoid space via the foramina of Magendie and Luschka. - Presents with enlarging head circumference due to dilation of the ventricles (cranial suture lines are not fused). ## III. Dandy-Walker Malformation - Congenital failure of the cerebellar vermis to develop. - Presents as a massively dilated 4th ventricle (posterior fossa) with an absent cerebellum; often accompanied by hydrocephalus. ## IV. Arnold-Chiari Malformation (Type I) - Congenital downward displacement of cerebellar vermis and tonsils through the foramen magnum. - Obstruction of CSF flow commonly results in hydrocephalus. - Often associated with meningomyelocele.