DOCSLIB.ORG

MR of Neuronal Migration Anomalies

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
MR of Neuronal Migration Anomalies 1009 MR of Neuronal Migration Anomalies A. James Barkovich 1,2 Migration anomalies are congenital malformations caused by insults to migrating Sylvester H. Chuang3 neuroblasts during the third to fifth gestational months. Included in this group are agyria, David Norman2 pachygyria, polymicrogyria, unilateral megalencephaly, schizencephaly, and gray matter heterotopias. Patients who have these conditions present clinically with developmental delay and seizures, and abnormal motor skills are noted in the more severely affected infants. To determine the utility of MR as a method for imaging in these patients, we used MR to evaluate 13 patients who had the full spectrum of migration anomalies. MR was more sensitive than CT in detecting these anomalies because of its better contrast between gray and white matter. We found that MR was particularly more sensitive in detecting schizencephaly, where recognizing the presence of gray matter lining the cleft is critical to distinguishing that disease from porencephaly, and in detecting polymicrogyria, where critical details of cortical architecture are obscured on CT by the overlying bone. Multiplanar capabilities were also found to be essential, since narrow clefts may not be detected when the imaging plane is parallel to the cleft. MR should be the primary imaging method for infants who have seizures or develop­ mental delay. Abnormalities of cell migration are characterized by ectopiC location of neurons in the cerebral cortex. This broad group of anomalies includes agyria, pachygyria, polymicrogyria, schizencephaly, unilateral megalencephaly, and gray matter heter­ otopias. All these entities have been characterized pathologically and in vivo by sonography and CT. MR is an imaging technique uniquely suited to study these This article appears in the November/Decem­ anomalies because of its exceptional differentiation between gray and white matter ber 1987 issue of AJNR and the January 1988 and its high-resolution multi planar display of anatomy. issue of AJR. In a review of 537 MR studies in the pediatric age group, we identified 13 Received March 13, 1987; accepted June 1, 1987. patients with migration anomalies. We review the salient features of these anom­ alies and their MR appearance. The relationship of the pathologic anatomy to The views expressed in this article are those of the authors and do not reflect the official policy or theories of pathogenesis is emphasized . position of the Department of the Army, Department of Defense, or the U.S. Government. Presented in part at the annual meeting of the Subjects and Methods American Society of Neuroradiology, New York, May 1987. Thirteen patients with migration anomalies were scanned, including two with lissencephaly, , Department of Radiology, Letterman Army four with schizencephaly, two with unilateral megalencephaly, two with isolated polymicro­ Medical Center, Presidio of San Francisco, CA gyria, and three with isolated gray matter heterotopias. The four patients with schizencephaly 94129-6700. Address reprint requests to Technical also had foci of polymicrogyria. One of the patients with unilateral megalencephaly had foci Publications Editor HSHH-ZCT. of ectopic gray matter. The patients' ages ranged from 4 months to 21 years, with a mean 2 Department of Radiology, Neuroradiology Sec­ of 6.6 years and a median age of 3.5 years. The mean age is skewed by two patients with tion, University of California School of Medicine, schizencephaly who were 17 and 21 years old. The patients were referred for imaging San FranCiSCO, CA 94143. because of seizures, mental retardation, developmental delay, or enlarging head size (see 3 Department of Radiology, Neuroradiology Sec­ Table 1). tion, Hospital for Sick Children, Toronto, Ontario M5G 1X8, Canada. Ten patients were examined on a 1.5-T GE Signa unit. Three patients were examined on a 0.35-T Diasonics MT/S scanner. Slice thickness was 5 mm with a 2.5-mm interslice gap. AJNR 8:1009-1017, November/December 1987 0195-6108/87/0806-1009 Spin echo (SE) images were obtained with a TR of 2000 msec and TE of 35-40 msec and © American Society of Neuroradiology 70-80 msec in the transverse and coronal planes and a TR of 600 msec and TE of 25 msec 1010 BAR KOVICH ET AL. AJNR :8, November/December 1987 TABLE 1: Summary of Patient Data Presenting Patient Age MR Diagnosis Symptoms· 1 4 mo S Lissencephaly 2 4y S,DD Lissencephaly 3 8y DD Polymicrogyria 4 2y S, DD Polymicrogyria 5 12 mo S, DD Schizencephaly (bilateral vertical clefts: one narrow, one wide); polymicrogyria in and adjacent to clefts 6 7 mo S,DD Schizencephaly (bilateral horizontal clefts: both narrow); polymicrogy­ ria and pachygyria in adjacent brain 7 17 Y S,DD Schizencephaly (unilateral horizontal wide cleft); polymicrogyria in and Cortical plate adjacent to cleft; ectopic gray matter 8 21 Y S Schizencephaly (unilateral vertical Fig. 1.-Schematic drawing shows relationship of the germinal matrix cleft with fused lips) in wall of lateral ventricle to the developing cortical plate. There is a one­ 9 2y S,DD, H Unilateral megalencephaly to-one correspondence between the site of cell proliferation within the germinal zone and its eventual destination within the cortical plate. Cor­ 10 8 Y S, DD Unilateral megalencephaly responding regions are connected by radial glial cells that span entire 11 7 Y S Heterotopic gray matter thickness of hemisphere. Neurons migrate along these radial cells, even­ 12 2 Y S Heterotopic gray matter tually arriving at predestined locations on the enlarged, convoluted cortical 13 3 Y S Heterotopic gray matter surface. (Adapted from [4].) • Abbreviations: S = seizures; DO = developmental delay; H = hemiplegia. in the axial, coronal, or sagittal plane, as indicated. The results of Leading these studies are included in the Discussion section. process Pathologic confirmation was not obtained. Migration anomalies were diagnosed from the characteristic gross morphology of the affected brains, which has been established from pathologic and CT experience. Radial fiber Discussion The phenomenon of neuronal migration has been known since the turn of the century [1]. The neurons that constitute the mammalian brain are generated in proliferative zones situated along the ventricular surface of the developing brain Trailing process [1-4]. At the end of the second gestational month, the neu­ rons migrate from their site of origin along radially aligned glial cells to relatively distant final positions [3, 4] (Figs. 1 and 2). At this point they differentiate further, grow axons and den­ drites, and develop synaptic contacts with other neurons [4]. The final position of the neurons within the cortex varies inversely with the time of cell origin. Those cells generated earlier migrate to the deeper cortical layers relatively Ciuickly Glial cell (3-4 days). The cells generated later end their migration in Germinal the more superficial cortex; this migration takes place over zone several weeks. The major cell migration activity lasts about 2 months, beginning in the eighth fetal week and ending at about week 16 [4, 5]. Smaller waves of cell migration continue up to week 25 . Any insult to the brain during this period results in a migration anomaly. The normal human cerebral cortex is six-layered, the sizes of the layers varying with the location. There is a marginal Fig. 2.-lIIustration of relationship of migrating neurons to fibers of the layer (I), external granular layer (II), external pyramidal layer radial glial cells. Migrating neuron is seen ascending the glial fiber (radial (III) , internal granular layer (IV), internal pyramidal layer (V), fiber) led by multiple pseudopodia. Any damage to radial glial fiber will presumably cause an arrest of cell migration at that point. (Adapted from and fusiform layer (VI) (Fig. 3). The common underlying feature [4].) AJNR :8. November/December 1987 MR OF MIGRATION ANOMALIES 1011 Fig. 3.-Cortical architecture in agyric (labeled lissencephaly) and pachygyric regions of brain as com­ pared with normal cortical architecture. , In agyric cortex there is a large cell­ ~ . "0. , sparse layer (open arrow) that sepa­ .,' 0 rates a disorganized cortex (outer cel­ lular layer) from a thick layer of ectopic · ' ····0 o neurons located medially. Pachygyric ", '. ~ -, :' . " • 0 .. .0 I> o~ . ' ' . 0. • cortex is more organized into normal 0 _ 0 00 ; ' ,0- ; 0 : " I) 0 cortical layers and cell-sparse layer o o . (closed arrow) is thinner and populated by more cells. In general. there is a thinner layer of heterotopic neurons in the pachygyric cortex. (Adapted from [11].) LISSENCEPHALY PACHYGYRIA NOR MAL of the migration anomalies is an abnormal location of neurons within the layer of necrosis [11]. The cortex remains thick both within and outside of the cortex. In general the cortex is because it encompasses the radial columns of migrating cells thickened by a large, disorganized layer of neurons whose that are arrested in mid-migration. The subcortical white migration has been prematurely halted. The subcortical layer matter is thin because the organization phase during which of white matter is thinned because organization of the neu­ axonal and dendritic connections are established is markedly rons, which subsequently stimulates axonal growth, has not diminished (Fig. 4). occurred [1-4]. Dobyns and associates [9, 10, 12] have recently described It was generally believed that migration anomalies were this entity as a series of "syndromes with lissencephaly." They sporadic events that occurred
Load more

Recommended publications
  • Bhagwan Moorjani, MD, FAAP, FAAN • Requires Knowledge of Normal CNS Developmental (I.E
    1/16/2012 Neuroimaging in Childhood • Neuroimaging issues are distinct from Pediatric Neuroimaging in adults Neurometabolic-degenerative disorder • Sedation/anesthesia and Epilepsy • Motion artifacts Bhagwan Moorjani, MD, FAAP, FAAN • Requires knowledge of normal CNS developmental (i.e. myelin maturation) • Contrast media • Parental anxiety Diagnostic Approach Neuroimaging in Epilepsy • Age of onset • Peak incidence in childhood • Static vs Progressive • Occurs as a co-morbid condition in many – Look for treatable causes pediatric disorders (birth injury, – Do not overlook abuse, Manchausen if all is negative dysmorphism, chromosomal anomalies, • Phenotype presence (syndromic, HC, NCS, developmental delays/regression) systemic involvement) • Predominant symptom (epilepsy, DD, • Many neurologic disorders in children weakness/motor, psychomotor regression, have the same chief complaint cognitive/dementia) 1 1/16/2012 Congenital Malformation • Characterized by their anatomic features • Broad categories: based on embryogenesis – Stage 1: Dorsal Induction: Formation and closure of the neural tube. (Weeks 3-4) – Stage 2: Ventral Induction: Formation of the brain segments and face. (Weeks 5-10) – Stage 3: Migration and Histogenesis: (Months 2-5) – Stage 4: Myelination: (5-15 months; matures by 3 years) Dandy Walker Malformation Dandy walker • Criteria: – high position of tentorium – dysgenesis/agenesis of vermis – cystic dilatation of fourth ventricle • commonly associated features: – hypoplasia of cerebellum – scalloping of inner table of occipital bone • associated abnormalities: – hydrocephalus 75% – dysgenesis of corpus callosum 25% – heterotropia 10% 2 1/16/2012 Etiology of Epilepsy: Developmental and Genetic Classification of Gray Matter Heterotropia Cortical Dysplasia 1. Secondary to abnormal neuronal and • displaced masses of nerve cells • Subependymal glial proliferation/apoptosis (gray matter) heterotropia (most • most common: small nest common) 2.
    [Show full text]
  • Approach to Brain Malformations
    Approach to Brain Malformations A General Imaging Approach to Brain CSF spaces. This is the basis for development of the Dandy- Malformations Walker malformation; it requires abnormal development of the cerebellum itself and of the overlying leptomeninges. Whenever an infant or child is referred for imaging because of Looking at the midline image also gives an idea of the relative either seizures or delayed development, the possibility of a head size through assessment of the craniofacial ratio. In the brain malformation should be carefully investigated. If the normal neonate, the ratio of the cranial vault to the face on child appears dysmorphic in any way (low-set ears, abnormal midline images is 5:1 or 6:1. By 2 years, it should be 2.5:1, and facies, hypotelorism), the likelihood of an underlying brain by 10 years, it should be about 1.5:1. malformation is even higher, but a normal appearance is no guarantee of a normal brain. In all such cases, imaging should After looking at the midline, evaluate the brain from outside be geared toward showing a structural abnormality. The to inside. Start with the cerebral cortex. Is the thickness imaging sequences should maximize contrast between gray normal (2-3 mm)? If it is too thick, think of pachygyria or matter and white matter, have high spatial resolution, and be polymicrogyria. Is the cortical white matter junction smooth or acquired as volumetric data whenever possible so that images irregular? If it is irregular, think of polymicrogyria or Brain: Pathology-Based Diagnoses can be reformatted in any plane or as a surface rendering.
    [Show full text]
  • Description Treatment
    Description Megalencephaly, also called macrencephaly, is a condition in which an infant or child has an abnormally large, heavy, and usually malfunctioning brain. By definition, the brain weight is greater than average for the age and gender of the child. Head enlargement may be evident at birth or the head may become abnormally large in the early years of life. Megalencephaly is thought to be related to a disturbance in the regulation of cell production in the brain. In normal development, neuron proliferation - the process in which nerve cells divide to form new generations of cells - is regulated so that the correct number of cells is produced in the proper place at the appropriate time. In a megalencephalic brain, too many cells are produced either during development or progressively as part of another disorder, such as one of the neurofibromatoses or leukodystrophies. Symptoms of megalencephaly include delayed development, seizures, and corticospinal (brain cortex and spinal cord) dysfunction. Megalencephaly affects males more often than females. Unilateral megalencephaly or hemimegalencephaly is a rare condition that is characterized by the enlargement of one side of the brain. Children with this disorder may have a large, asymmetrical head accompanied by seizures, partial paralysis, and impaired cognitive development. Megalencephaly is different from macrocephaly (also called megacephaly or megalocephaly), which describes a big head, and which doesn’t necessarily indicate abnormality. Large head size is passed down through the generations in some families. Treatment There is no standard treatment for megalencephaly. Treatment will depend upon the disorder with which the megalencephaly is associated and will address individual symptoms and disabilities.
    [Show full text]
  • Megalencephaly and Macrocephaly
    277 Megalencephaly and Macrocephaly KellenD.Winden,MD,PhD1 Christopher J. Yuskaitis, MD, PhD1 Annapurna Poduri, MD, MPH2 1 Department of Neurology, Boston Children’s Hospital, Boston, Address for correspondence Annapurna Poduri, Epilepsy Genetics Massachusetts Program, Division of Epilepsy and Clinical Electrophysiology, 2 Epilepsy Genetics Program, Division of Epilepsy and Clinical Department of Neurology, Fegan 9, Boston Children’s Hospital, 300 Electrophysiology, Department of Neurology, Boston Children’s Longwood Avenue, Boston, MA 02115 Hospital, Boston, Massachusetts (e-mail: [email protected]). Semin Neurol 2015;35:277–287. Abstract Megalencephaly is a developmental disorder characterized by brain overgrowth secondary to increased size and/or numbers of neurons and glia. These disorders can be divided into metabolic and developmental categories based on their molecular etiologies. Metabolic megalencephalies are mostly caused by genetic defects in cellular metabolism, whereas developmental megalencephalies have recently been shown to be caused by alterations in signaling pathways that regulate neuronal replication, growth, and migration. These disorders often lead to epilepsy, developmental disabilities, and Keywords behavioral problems; specific disorders have associations with overgrowth or abnor- ► megalencephaly malities in other tissues. The molecular underpinnings of many of these disorders are ► hemimegalencephaly now understood, providing insight into how dysregulation of critical pathways leads to ►
    [Show full text]
  • Congenital Disorders of Glycosylation from a Neurological Perspective
    brain sciences Review Congenital Disorders of Glycosylation from a Neurological Perspective Justyna Paprocka 1,* , Aleksandra Jezela-Stanek 2 , Anna Tylki-Szyma´nska 3 and Stephanie Grunewald 4 1 Department of Pediatric Neurology, Faculty of Medical Science in Katowice, Medical University of Silesia, 40-752 Katowice, Poland 2 Department of Genetics and Clinical Immunology, National Institute of Tuberculosis and Lung Diseases, 01-138 Warsaw, Poland; [email protected] 3 Department of Pediatrics, Nutrition and Metabolic Diseases, The Children’s Memorial Health Institute, W 04-730 Warsaw, Poland; [email protected] 4 NIHR Biomedical Research Center (BRC), Metabolic Unit, Great Ormond Street Hospital and Institute of Child Health, University College London, London SE1 9RT, UK; [email protected] * Correspondence: [email protected]; Tel.: +48-606-415-888 Abstract: Most plasma proteins, cell membrane proteins and other proteins are glycoproteins with sugar chains attached to the polypeptide-glycans. Glycosylation is the main element of the post- translational transformation of most human proteins. Since glycosylation processes are necessary for many different biological processes, patients present a diverse spectrum of phenotypes and severity of symptoms. The most frequently observed neurological symptoms in congenital disorders of glycosylation (CDG) are: epilepsy, intellectual disability, myopathies, neuropathies and stroke-like episodes. Epilepsy is seen in many CDG subtypes and particularly present in the case of mutations
    [Show full text]
  • Optic Nerve Hypoplasia Plus: a New Way of Looking at Septo-Optic Dysplasia
    Optic Nerve Hypoplasia Plus: A New Way of Looking at Septo-Optic Dysplasia Item Type text; Electronic Thesis Authors Mohan, Prithvi Mrinalini Publisher The University of Arizona. Rights Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author. Download date 29/09/2021 22:50:06 Item License http://rightsstatements.org/vocab/InC/1.0/ Link to Item http://hdl.handle.net/10150/625105 OPTIC NERVE HYPOPLASIA PLUS: A NEW WAY OF LOOKING AT SEPTO-OPTIC DYSPLASIA By PRITHVI MRINALINI MOHAN ____________________ A Thesis Submitted to The Honors College In Partial Fulfillment of the Bachelors degree With Honors in Physiology THE UNIVERSITY OF ARIZONA M A Y 2 0 1 7 Approved by: ____________________________ Dr. Vinodh Narayanan Center for Rare Childhood Disorders Abstract Septo-optic dysplasia (SOD) is a rare congenital disorder that affects 1/10,000 live births. At its core, SOD is a disorder resulting from improper embryological development of mid-line brain structures. To date, there is no comprehensive understanding of the etiology of SOD. Currently, SOD is diagnosed based on the presence of at least two of the following three factors: (i) optic nerve hypoplasia (ii) improper pituitary gland development and endocrine dysfunction and (iii) mid-line brain defects, including agenesis of the septum pellucidum and/or corpus callosum. A literature review of existing research on the disorder was conducted. The medical history and genetic data of 6 patients diagnosed with SOD were reviewed to find damaging variants.
    [Show full text]
  • Polymicrogyria (PMG) ‘Many–Small–Folds’
    Polymicrogyria Dr Andrew Fry Clinical Senior Lecturer in Medical Genetics Institute of Medical Genetics, Cardiff [email protected] Polymicrogyria (PMG) ‘Many–small–folds’ • PMG is heterogeneous – in aetiology and phenotype • A disorder of post-migrational cortical organisation. PMG often appears thick on MRI with blurring of the grey-white matter boundary Normal PMG On MRI PMG looks thick but the cortex is actually thin – with folded, fused gyri Courtesy of Dr Jeff Golden, Pen State Unv, Philadelphia PMG is often confused with pachygyria (lissencephaly) Thick cortex (10 – 20mm) Axial MRI 4 cortical layers Lissencephaly Polymicrogyria Cerebrum Classical lissencephaly is due Many small gyri – often to under-migration. fused together. Axial MRI image at 7T showing morphological aspects of PMG. Guerrini & Dobyns Malformations of cortical development: clinical features and genetic causes. Lancet Neurol. 2014 Jul; 13(7): 710–726. PMG - aetiology Pregnancy history • Intrauterine hypoxic/ischemic brain injury (e.g. death of twin) • Intrauterine infection (e.g. CMV, Zika virus) TORCH, CMV PCR, [+deafness & cerebral calcification] CT scan • Metabolic (e.g. Zellweger syndrome, glycine encephalopathy) VLCFA, metabolic Ix • Genetic: Family history Familial recurrence (XL, AD, AR) Chromosomal abnormalities (e.g. 1p36 del, 22q11.2 del) Syndromic (e.g. Aicardi syndrome, Kabuki syndrome) Examin - Monogenic (e.g. TUBB2B, TUBA1A, GPR56) Array ation CGH Gene test/Panel/WES/WGS A cohort of 121 PMG patients Aim: To explore the natural history of PMG and identify new genes. Recruited: • 99 unrelated patients • 22 patients from 10 families 87% White British, 53% male ~92% sporadic cases (NB. ascertainment bias) Sporadic PMG • Array CGH, single gene and gene panel testing - then a subset (n=57) had trio-WES.
    [Show full text]
  • Reportable BD Tables Apr2019.Pdf
    April 2019 Georgia Department of Public Health | Division of Health Protection | Maternal and Child Health Epidemiology Unit Reportable Birth Defects with ICD-10-CM Codes Reportable Birth Defects in Georgia with ICD-10-CM Diagnosis Codes Table D.1 Brain Malformations and Neural Tube Defects ICD-10-CM Diagnosis Codes Birth Defect ICD-10-CM 1. Brain Malformations and Neural Tube Defects Q00-Q05, Q07 Anencephaly Q00.0 Craniorachischisis Q00.1 Iniencephaly Q00.2 Frontal encephalocele Q01.0 Nasofrontal encephalocele Q01.1 Occipital encephalocele Q01.2 Encephalocele of other sites Q01.8 Encephalocele, unspecified Q01.9 Microcephaly Q02 Malformations of aqueduct of Sylvius Q03.0 Atresia of foramina of Magendie and Luschka (including Dandy-Walker) Q03.1 Other congenital hydrocephalus (including obstructive hydrocephaly) Q03.8 Congenital hydrocephalus, unspecified Q03.9 Congenital malformations of corpus callosum Q04.0 Arhinencephaly Q04.1 Holoprosencephaly Q04.2 Other reduction deformities of brain Q04.3 Septo-optic dysplasia of brain Q04.4 Congenital cerebral cyst (porencephaly, schizencephaly) Q04.6 Other specified congenital malformations of brain (including ventriculomegaly) Q04.8 Congenital malformation of brain, unspecified Q04.9 Cervical spina bifida with hydrocephalus Q05.0 Thoracic spina bifida with hydrocephalus Q05.1 Lumbar spina bifida with hydrocephalus Q05.2 Sacral spina bifida with hydrocephalus Q05.3 Unspecified spina bifida with hydrocephalus Q05.4 Cervical spina bifida without hydrocephalus Q05.5 Thoracic spina bifida without
    [Show full text]
  • Massachusetts Birth Defects 2002-2003
    Massachusetts Birth Defects 2002-2003 Massachusetts Birth Defects Monitoring Program Bureau of Family Health and Nutrition Massachusetts Department of Public Health January 2008 Massachusetts Birth Defects 2002-2003 Deval L. Patrick, Governor Timothy P. Murray, Lieutenant Governor JudyAnn Bigby, MD, Secretary, Executive Office of Health and Human Services John Auerbach, Commissioner, Massachusetts Department of Public Health Sally Fogerty, Director, Bureau of Family Health and Nutrition Marlene Anderka, Director, Massachusetts Center for Birth Defects Research and Prevention Linda Casey, Administrative Director, Massachusetts Center for Birth Defects Research and Prevention Cathleen Higgins, Birth Defects Surveillance Coordinator Massachusetts Department of Public Health 617-624-5510 January 2008 Acknowledgements This report was prepared by the staff of the Massachusetts Center for Birth Defects Research and Prevention (MCBDRP) including: Marlene Anderka, Linda Baptiste, Elizabeth Bingay, Joe Burgio, Linda Casey, Xiangmei Gu, Cathleen Higgins, Angela Lin, Rebecca Lovering, and Na Wang. Data in this report have been collected through the efforts of the field staff of the MCBDRP including: Roberta Aucoin, Dorothy Cichonski, Daniel Sexton, Marie-Noel Westgate and Susan Winship. We would like to acknowledge the following individuals for their time and commitment to supporting our efforts in improving the MCBDRP. Lewis Holmes, MD, Massachusetts General Hospital Carol Louik, ScD, Slone Epidemiology Center, Boston University Allen Mitchell,
    [Show full text]
  • CONGENITAL ABNORMALITIES of the CENTRAL NERVOUS SYSTEM Christopher Verity, Helen Firth, Charles Ffrench-Constant *I3
    J Neurol Neurosurg Psychiatry: first published as 10.1136/jnnp.74.suppl_1.i3 on 1 March 2003. Downloaded from CONGENITAL ABNORMALITIES OF THE CENTRAL NERVOUS SYSTEM Christopher Verity, Helen Firth, Charles ffrench-Constant *i3 J Neurol Neurosurg Psychiatry 2003;74(Suppl I):i3–i8 dvances in genetics and molecular biology have led to a better understanding of the control of central nervous system (CNS) development. It is possible to classify CNS abnormalities Aaccording to the developmental stages at which they occur, as is shown below. The careful assessment of patients with these abnormalities is important in order to provide an accurate prog- nosis and genetic counselling. c NORMAL DEVELOPMENT OF THE CNS Before we review the various abnormalities that can affect the CNS, a brief overview of the normal development of the CNS is appropriate. c Induction—After development of the three cell layers of the early embryo (ectoderm, mesoderm, and endoderm), the underlying mesoderm (the “inducer”) sends signals to a region of the ecto- derm (the “induced tissue”), instructing it to develop into neural tissue. c Neural tube formation—The neural ectoderm folds to form a tube, which runs for most of the length of the embryo. c Regionalisation and specification—Specification of different regions and individual cells within the neural tube occurs in both the rostral/caudal and dorsal/ventral axis. The three basic regions of copyright. the CNS (forebrain, midbrain, and hindbrain) develop at the rostral end of the tube, with the spinal cord more caudally. Within the developing spinal cord specification of the different popu- lations of neural precursors (neural crest, sensory neurones, interneurones, glial cells, and motor neurones) is observed in progressively more ventral locations.
    [Show full text]
  • Chiari Type II Malformation: Past, Present, and Future
    Neurosurg Focus 16 (2):Article 5, 2004, Click here to return to Table of Contents Chiari Type II malformation: past, present, and future KEVIN L. STEVENSON, M.D. Children’s Healthcare of Atlanta, Atlanta, Georgia Object. The Chiari Type II malformation (CM II) is a unique hindbrain herniation found only in patients with myelomeningocele and is the leading cause of death in these individuals younger than 2 years of age. Several theories exist as to its embryological evolution and recently new theories are emerging as to its treatment and possible preven- tion. A thorough understanding of the embryology, anatomy, symptomatology, and surgical treatment is necessary to care optimally for children with myelomeningocele and prevent significant morbidity and mortality. Methods. A review of the literature was used to summarize the clinically pertinent features of the CM II, with par- ticular attention to pitfalls in diagnosis and surgical treatment. Conclusions. Any child with CM II can present as a neurosurgical emergency. Expeditious and knowledgeable eval- uation and prompt surgical decompression of the hindbrain can prevent serious morbidity and mortality in the patient with myelomeningocele, especially those younger than 2 years old. Symptomatic CM II in the older child often pre- sents with more subtle findings but rarely in acute crisis. Understanding of CM II continues to change as innovative techniques are applied to this challenging patient population. KEY WORDS • Chiari Type II malformation • myelomeningocele • pediatric The CM II is uniquely associated with myelomeningo- four distinct forms of the malformation, including the cele and is found only in this population. Originally de- Type II malformation that he found exclusively in patients scribed by Hans Chiari in 1891, symptomatic CM II ac- with myelomeningocele.
    [Show full text]
  • Classification of Congenital Abnormalities of the CNS
    315 Classification of Congenital Abnormalities of the CNS M. S. van der Knaap1 A classification of congenital cerebral, cerebellar, and spinal malformations is pre­ J . Valk2 sented with a view to its practical application in neuroradiology. The classification is based on the MR appearance of the morphologic abnormalities, arranged according to the embryologic time the derangement occurred. The normal embryology of the brain is briefly reviewed, and comments are made to explain the classification. MR images illustrating each subset of abnormalities are presented. During the last few years, MR imaging has proved to be a diagnostic tool of major importance in children with congenital malformations of the eNS [1]. The excellent gray fwhite-matter differentiation and multi planar imaging capabilities of MR allow a systematic analysis of the condition of the brain in infants and children. This is of interest for estimating prognosis and for genetic counseling. A classification is needed to serve as a guide to the great diversity of morphologic abnormalities and to make the acquired data useful. Such a system facilitates encoding, storage, and computer processing of data. We present a practical classification of congenital cerebral , cerebellar, and spinal malformations. Our classification is based on the morphologic abnormalities shown by MR and on the time at which the derangement of neural development occurred. A classification based on etiology is not as valuable because the various presumed causes rarely lead to a specific pattern of malformations. The abnor­ malities reflect the time the noxious agent interfered with neural development, rather than the nature of the noxious agent. The vulnerability of the various structures to adverse agents is greatest during the period of most active growth and development.
    [Show full text]