Computed Aided Tomography Case Histories—Brain D Karthikeyan, Deepa Chegu
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_FM1Computed Aided Tomography Case Histories BRAIN
_FM2Computed Aided Tomography Case Histories BRAIN
SECOND EDITION
D Karthikeyan DMRD DNB Consultant Radiologist Bharat Heart Scans Chennai, India Deepa Chegu DMRD Consultant Radiologist Bharat Scans Chennai, India
_FM3Published by
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Computed Aided Tomography Case Histories—Brain
© 2008, D Karthikeyan
All rights reserved. No part of this publication and CD ROM should be reproduced, stored in a retrieval system, or transmitted in any form or by any means: electronic, mechanical, photo copying, recording, or otherwise, without the prior written permission of the author and the publisher
First Edition: 2003
Second Edition: 2008
9788184482935
Typeset at JPBMP typesetting unit
Printed at Ajanta Offset
_FM4PREFACE TO THE SECOND EDITION
Computed Tomography is an indispensable tool in neuroimaging. This collection of CT images has been selected to show the variable manifestation of common and uncommon neuropathologies with correlative MR images. These cases are intended to familiarize radiology residents and clinicians to commonly encountered clinical scenarios.
D Karthikeyan
Deepa Chegu
_FM5PREFACE TO THE FIRST EDITION
Computed Tomography is a complex, rapidly evolving modality, which has recently developed newer applications in all areas of diagnostic radiology. This collection of brain CTs has been carefully selected to show variable manifestations of common pathology as well as unusual cases highlighting the role of Helical CT. The discussions have been kept brief conforming to the case file format with a problem-solving approach. These cases are intended to familiarize clinicians and radiologists to commonly encountered clinical scenarios.
The depth of medical knowledge and the scope of image interpretation expected from the radiologist and the clinician has soared over the last two decades. It is our sincere hope that this Computed Aided Tomography Case Histories Series (CATCH) will be of use to enhance our interpretation skills for better patient care.
D Karthikeyan_FM6_FM7_FM8_FM9_FM10
_FM11ACKNOWLEDGEMENTS
We thank our teachers and colleagues from Barnard Institute of Radiology and SRMC, Chennai.
We thank all our clinical associates who helped us in this academic endeavour.
We thank our family and friends who constantly encourage us.
_FM12CONGENITAL ANOMALIES OF BRAIN  
INTRODUCTION
Malformations of the CNS are relatively common, constituting between 5-10% of all the malformations and about one-third of those diagnosed after birth. These malformations vary in clinical severity.
The induction of a malformation is thought to depend on a specific insult to the developing brain. Only in this century have some of these insults (e.g. infectious agents, toxins, hypoxic ischaemic agents, and chromosomal abrerrations) have been identified.
We present a few cases, which were diagnosed on CT.
 
Comments on Embryology
Dorsal induction is the first stage in the formation and closure of the neural tube. This occurs at weeks 3 - 4 gestation.
The first phase of neurulation leads to the formation of the neural tube which will be the foundation for the brain and spinal cord.
The second phase and third phase of dorsal induction involving canalisation and retrogressive differentiation leads to the formation of the caudal part of the neural tube
During neurulation (phase 1), there is formation of embryonic ectoderm dorsal to the noto cord, and this thickens to form a neural plate.
The neuroectoderm will invaginate along its central axis to form the neural groove with neural folds on either side. This will then close like a zipper to form the neural tube.
_FM13
 
SECONDARY NEURULATION
There is formation of mesenchyme with neurocutaneous separation.
Leads to formation of neural arches, paravertebral muscles.
Dysfunction of neurocutaneous separation leads to anomalies.
In stage 2 of ventral induction, there is formation of the brain and face by the formation of vesicles. At 4-10 weeks.
Three main vesicles form. These are the prosencephalon (which eventually forms the cerebral hemispheres) and the thalamus, the mesencephalon (which forms the midbrain), and the rhombencephalon (which will form the pons, cerebellum, and medulla). During this time, the face also develops such that facial anomalies may accompany brain anomalies during ventral induction.
Developmental Sequence of Brain Regions
Three-vesicle stage
Five-vesicle stage
Brain region
Prosencephalon
Telencephalon
Diencephalon
Cerebral hemisphere
Diencephalon
Optic nerve and retina
Mesencephalon
Mesencephalon
Mesencephalon
Rhombencephalon
Metencephalon
Pons
Cerebellum
Myelencephalon
Medulla oblongata
_FM14
 
CELLULAR PROLIFERATION AND DIFFERENTIATION
  • 2-4 months, formation of neural cells (neuroblasts, fibroblasts, astrocytes, endothelial cells)
  • Choroid plexus is formed
  • Radial glial fibres play an important role in neural migration.
_FM15
 
CELLULAR MIGRATION AND INVOLUTION
At 5 months, neural cells migrate from germinal matrix to pial surface through radial glial fibres—inside out. Thus, cortical layers are formed deep to superficial.
 
INSULTS TO FORMED BRAIN—RESULT IN HYDRENCEPHALY, PORENCEPHALY, INFARCTION
Dysgenesis: Disturbed development of the forebrain with a closed neural tube (e.g. anencephaly, aprosopia, cyclopia, holoprosencephaly, arhinencephaly, olfactogenital dysplasia).
Dysraphias: Disturbance of neural tube closure.
Cranial dysraphias:
Total cranioschisis (= anencephaly)
Partial cranioschisis (= meroencephaly)
Encephaloceles (of the convexity and base)
_FM16Dysgenesis of the corpus callosum, commisural dysgenesis, monoventricle.
Rhombocerebellar dysraphias:
Encephaloceles, meningoceles (occipital and cerebellar)
Cerebellar hypoplasia, Dandy-Walker cyst
Arnold-Chiari malformation
Aqueductal stenosis.
Disturbances of migration: Schizencephalic porencephaly, dysgyrias such as agyria, macrogyria, microgyria, micropolygyria, perisylvian aplasia.
Phakomatoses: Dysplasias with blastomatous dissemination, e.g. neurofibromatosis, tuberous sclerosis, Hippel- Lindau disease, Sturge-Weber disease, Louis-Bar´s telangiectatic ataxia.
Disturbances of cerebral volume: Primary microcephaly, macrocephaly.
Hydrocephalus.
Applied Embryology—Synopsis
Congenital 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 Neural Tube
Weeks 3-4
Three phases: Neurulation, canalization, retrogressive differentiation
Failure: Anencephaly
Cephalocele
Chiari
Spinal dysraphism
Stage 2: Ventral Induction: Formation of the Brain Segments and Face
Weeks 5-10
Three vesicles (prosencephalon, mesencephalon, and rhombencephalon) form the cerebrum, midbrain, cerebellum, and lower brainstem
Division into two hemispheres
Failure: Holoprosencephalies
Corpus callosum agenesis
Dandy-Walker
Facial anomalies
Stage 3: Migration and Histogenesis
Neuronal migration from germinal matrix to the cortex
Cellular differentiation
Months 2-5
Disorders: Heterotopias, agyria-pachyria, polymicrogyria, vascular malformations, teratomas, phakomatosis
Stage 4: Myelination
Inferior to superior; posterior to anterior
5-15 months; matures by 3 years
Failure: Developmental delay, dysmyelinating disease.