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SDL 2- CNS Malformations Neural Tube Defects Failure of a portion of the neural tube to close completely or reopening Abnormalities of meninges, neural tissue, ST bone Encephalocele: malformed CNS tissue extending through defect in cranium (most common in posterior fossa) 1/1000 births in american Caucasians Between 18-26 days Primary neurulation: brain and SC are developed, neural folds form and converge toward midline, form neural tube Neural fold proceeds rostrally and caudally and the ends of the tube remain open: neuropores Closure of neural pores happens around day 26 Encephalocele: failure of rostral neural tube to close Myelomeningocele: failure of caudal tube to close Most common encountered neural tube closure defect Spinal dysraphism: spina bifida cystic (myelomeningocele) and meningocele Failure of ectoderm to separate properly from the neural ectoderm and persistence of neural placode (flat plate of un-neurulated tissue) More common in female Risk factors: pregestational diabetes, inadequate maternal folic acid, in-utero exposure to anti-epileptic drugs Congenital spinal meningoceles: vertebral defect with cystic lesion of herniated dura and arachnoid (SC normal); 1/1000 Most are lumbosacral Increased CNS infection due to poor skin covering Lower extremity sensory and motor function normal to paraplegia (above L3) Chronic UTI, pyelonephritis 1/3 have apnea, swallowing difficulties, impaired head control, hydrocephalus Meningocele: neurologically normal with no hydrocephalus, no CNS infection increase Serum alpha-fetoprotein and prenatal ultrasound diagnosis Confirmed with amniocentesis, MRI with T2 weighted sequences can provide structural information Forebrain Anomalies Abnormalities of brain volume Megalencephaly: increased brain volume Microencephaly: decreased brain volume Most common; due to chromosomal abnormalities, fetal alcohol syndrome, HIV acquired in utero Neurons and glial cells that form the cerebral cortex migrate to cortex guided by adhesion molecules, cortical development entails the generatio of stem cells and their differentiation to neurons and glia, migration to cortex and organization to functional layers. 1. Neurons fail to migrate from the ventricles (periventricular heterotopias) or halfway (subcortical band heterotopia) 2. Neurons reach cortex, but large numbers do not (no normal cortical layers are formed, leading to formation of lissencephaly and cobblestoe cortex 3. Neurons may overshoot the cortex and end up in subarachnoid space 4. Late stage of migration and cortical migration is disrupted (polymicrogyri) Abnormal migration causes an abnormal gyral pattern Lissencephaly, cobblestone cortex and polymicrogyri are associated with psychomotor retardation and intractable seizures Most neuronal migration defects have some genetic basis; genotypes and phenotypes may overlap Lissencephaly: sulci are absent except for sylvian fissure Cortex is thick and consists of molecular and 3 neuronal layers Complete loss of LIS1 gene located on chrom 17p13 that forms a complex for cell migration, cell division and intracellular transport Complete loss of LISS1 gene is fatal, deletion of one copy causes lissencephaly SDL 2- CNS Malformations Lesions of LIS1 gene cause Miller-Dieker syndrome that is a combo of lissencephaly with dysmorphic facial features, visceral abnormalities and polydactyly Posterior Fossa Anomalies Aqueductal atresia and aqueductal stenosis: common causes of congenital hydrocephalus with Chiari type malformation Aqueductal atresia: occurs in utero or postnatally by thrombus formation from interventricular bleeding, infection, or other abnormalities that cause gliosis and obliterate the aqueduct X linked aqueductal stenosis by mutations in L1CAM gene on chromosome Xq28 that codes cell adhesion molecule Associated mental retardation, absence of cortical spinal tracts, agenesis of corpus callosum Chiari Malformations Type II: characterized by neural tube defects (usually lumbosacral meningomyelocele), abnormalities of posterior fossa and craniocervical junction and hydrocephalus Contents of posterior fossa reside in large foramen magnum (low insertion of tentorium and shallow posterior fossa) Cerebellum and brainstem are crowded and displaced into upper cervical canal Medulla elongated and may be folded dorsally, aqueduct and 4th ventricle are collapsed Associated aqueductal atresia Blocked CSF flow may lead to hydrocephalus (possible hydromyelia or syringomyelia) Type I: mild variant of type II, volume of posterior fossa is reduced overcrowding and herniation of cerebellar tonsils and dorsal cerebellum into spinal canal May also have syringomyelia and hydrocephalus (no associated NTD) Many patients are asymptomatic, other complain of dizziness, CN abnormalities and headache Dandy-Walker Malformation Complete or partial agenesis of the cerebellar vemis Hemispheres are connected by thin membrane of neural tissue that forms the fourth ventricle roof Obstruction of fluid from 4th ventricle; 4th ventricle thus enlarges and membrane that forms its roof balloons to create a large posterior fossa cyst that pushes the tentorium superiorly obstruction of cerebrovascular fluid hydrocephalus Neuro defecits and agenesis of corpus callosum and neuronal migration abnormalities Most are sporadic (there are rare familial cases associated with genetic abnormalities- trisomy 3, 9, 13, and 18) Syringomyelia Tubular formed cavity of SC that can affect cervical and upper thoracic segments Located I central gray matter of SC and enlarges over time Syrinx is lined by glial tissue and contains CSF-like fluid that accumulates and grows under pressure causing atrophy of gray and white matter of SC Symptoms show in 2nd to 3rd decades of life; patients may demonstrate dissociated anesthesia (segmental loss of pain and temp sensation), denervation, atrophy of muscle and kyphoscoliosis Pressure is relieved by shunting of syrinx fluid or laminectomy Often associated with type I Chiari malformations Multifactoral cause, may be seen both superiorly and inferior to SC tumors such as ependymoma, pyelocytic astrocytomas, and hemanngioblastomas SDL 2- CNS Malformations Vascular Malformations Developmental venous anomalies: AKA venous angiomas Radially arranged configuration of medullary veins (caput medusae) separated by normal brain parenchyma Usually supratentorial with a frontal lobe predominance Commonly present with seizures, progressive neurologic deficits and hemorrhage Most common autopsy series (2%); Benign Headache is most common complaint; diagnosis is by cerebral angiography (CT and MRI may also be helpful) Can be treated conservatively in majority of patients and headaches and seizures managed medically Capillary telangiectasias: Small lesions most common in the pons, middle cerebellar peduncles and dentate nuclei Multiple lesions are common and composed of small dilated capillaries with no smooth muscle or elastic fibers May be associated with microhemorrhage and gliosis Some associated with Osler0Weber-Rendu (hereditary hemorrhagic telangiectasia) Benign, usually silent and found on neuroimaging studies or at autopsy (MRI helpful), nonoperable Cavernous malformations: AKA cavernous angiomas/hemangiomas or cavernomas May be sporadic or inherited in familial pattern Characteristic mulberry appearance with engorged purplish clusters of vessels Tissue may demonstrate gliosis and hemosiderin-laden macrophages due to previous hemorrhages 30-40 years, men and women Symptomatic hemorrhage, seizures and progressive neurologic defecits may be associated Least common autopsy series (0.4%); Greater tendency toward neurologic sequelae Blood flow is limited, dx by angiography is difficult (MRI more helpful) Progressive neurologic deficit, intractable epilepsy and recurrent hemorrhage are indications for surgical removal Arteriovenous malformations: Greater tendency toward neurologic sequelae