TY  - CHAP
M1  - Book, Section
TI  - Structural and Functional Organization of the Central Nervous System
A1  - Martin, John H.
PY  - 2016
T2  - Neuroanatomy Text and Atlas, 4e
AB  - CLINICAL  CASE  |  Horizontal  Gaze  Palsy  With  Progressive  ScoliosisHorizontal  gaze  palsy  with  progressive  scoliosis  (HGPPS)  is  an  extremely  rare  genetic  syndrome.  It  is  the  result  of  mutation  in  the  ROBO3  gene,  essential  for  normal  axon  guidance  in  many  developing  neurons,  including  those  of  the  corticospinal  tract  and  the  medial  lemniscus.  Mutations  in  this  gene  are  associated  with  a  failure  of  axonal  crossing  in  certain  regions  of  the  brain.  Because  it  is  so  rare,  this  syndrome  is  not  likely  to  be  encountered  in  routine  medical  practice.  Nevertheless,  by  examining  brain  images  from  patients  with  HGPPS,  we  have  the  opportunity  to  see  how  brain  structure  changes  when  decussation  does  not  occur.  Further,  by  assessing  their  neurological  signs  and  the  results  of  electrophysiological  testing,  we  have  the  opportunity  to  see  how  mutation  can  affect  the  way  sensory  and  motor  information  is  processed  by  the  brain.A  12-year-old  boy  with  a  genetically  determined  mutation  of  the  ROBO3  gene  was  examined  for  somatic  sensory,  limb  motor,  and  ocular  motor  functions.  Sensory  testing  did  not  reveal  impairment.  He  has  mild  gait  instability  and  a  tremor  during  reaching  (intention  tremor).  He  is  able  to  follow  a  visual  stimulus  moving  vertically  with  his  eyes.  He  is  unable  to  follow  a  horizontal  moving  stimulus.  His  eyes  remain  fixated  in  the  forward  direction,  bilaterally.Figure  2–1A1  is  a  midsagittal  magnetic  resonance  imaging  (MRI)  from  a  person  with  HGPPS.  Brain  tissue  is  shades  of  gray  (gray  matter  darker  than  white  matter)  and  cerebrospinal  fluid,  black.  The  bracket  is  located  dorsal  to  the  pons  and  medulla.  Cerebrospinal  fluid  penetrates  into  this  region  on  the  midline  because  there  is  a  shallow  groove  (sulcus).  Note  that  this  is  not  present  in  the  control  MRI  (Figure  2–1B1).  The  transverse  MRI  through  the  upper  medulla  (A2)  reveals  an  abnormally  flattened  appearance  in  the  patient  with  HGPPS  compared  with  the  control  brain  (B2).  A  section  through  the  caudal  medulla  reveals  an  aberrant  deep  midline  groove  (A3,  arrow;  B3).Neurophysiological  testing  was  conducted  to  assess  the  integrity  of  the  touch  and  corticospinal  motor  pathways  (see  Figure  2–2).  To  determine  the  function  of  the  sensory  pathway,  the  skin  is  electrically  stimulated  and  the  overall  change  in  on-going  neuronal  activity  of  parietal  lobe  (ie,  EEG)  is  recorded.  Recording  the  EEG  in  the  region  of  the  somatic  sensory  cortex  in  response  to  electrical  stimulation  of  skin  revealed  ipsilateral  activation,  not  the  customary  contralateral  activation.  To  determine  the  function  of  the  corticospinal  tract,  transcranial  magnetic  stimulation  (TMS)  is  used  to  activate  the  motor  cortex,  and  the  evoked  change  in  muscle  activity  is  recorded.  TMS  of  the  motor  cortex  activated  muscles  on  the  ipsilateral  side,  not  the  typical  contralateral  side.Finally,  diffusion  tensor  imaging  (DTI;  this  is  discussed  in  Box  2–2)  was  performed  on  the  patient's  MRIs  in  order  to  follow  the  corticospinal  tract.  This  method  permits  imaging  of  neural  pathways  in  the  brain.  Figure  2–1A4  shows  the  DTI  image  from  a  HGPPS  patient.  There  are  two  parallel  pathways.  The  arrow  points  to  the  caudal  medulla,  where  the  decussation  normally  occurs.  Furthermore,  there  are  no  other  decussations  along  the  ...
SN  - 
PB  - McGraw-Hill Medical
CY  - New York, NY
Y2  - 2024/04/18
UR  - neurology.mhmedical.com/content.aspx?aid=1129848843
ER  -