RT Book, Section
A1 Martin, John H.
SR Print(0)
ID 1189286631
T1 Structural and Functional Organization of the Central Nervous System
T2 Neuroanatomy: Text and Atlas, 5e
YR 2021
FD 2021
PB McGraw Hill
PP New York, NY
SN 9781259642487
LK neurology.mhmedical.com/content.aspx?aid=1189286631
RD 2024/04/23
AB CLINICAL  CASE  |  12-Year-Old  Boy  With  Horizontal  Gaze  Palsy  With  Progressive  ScoliosisA  12-year-old  boy  presented  with  an  inability  to  follow  a  horizontal  moving  visual  stimulus.  His  eyes  remain  fixated  in  the  forward  direction,  bilaterally.  He  is  able  to  follow  a  visual  stimulus  moving  vertically  with  his  eyes.  Testing  for  somatic  sensory  function  did  not  reveal  any  change  in  sensation.  Limb  motor  testing  revealed  mild  gait  instability,  a  tremor  during  reaching,  and  progressive  scoliosis.Figure  2–1A1  is  a  midsagittal  magnetic  resonance  imaging  (MRI)  scan  from  the  patient.  This  is  a  T1-weighted  image.  Brain  tissue  is  represented  as  shades  of  gray  (gray  matter  darker  than  white  matter)  and  cerebrospinal  fluid,  black.  MRI  revealed  several  midline  structural  defects  in  the  pons  and  medulla.  The  bracket  (Figure  2–1A1,  B1)  is  located  dorsal  to  the  pons  and  medulla.  Cerebrospinal  fluid  penetrates  into  this  region  on  the  midline  because  of  the  presence  of  a  shallow  groove  (sulcus).  Note  that  this  sulcus  is  not  present  in  the  healthy  person’s  MRI  (Figure  2–1B1).  The  MRIs  in  the  transverse  plane  (second  and  third  rows)  are  T2-weighted  images,  where  cerebrospinal  fluid  and  fluid  within  the  eyes  appear  white.  The  MRI  through  the  upper  medulla  (A2)  reveals  an  abnormally  flattened  appearance  in  the  patient  compared  with  the  healthy  brain  (B2).  The  image  through  the  caudal  medulla  reveals  an  aberrant  deep  midline  groove  (A3,  arrow;  B3).Diffusion  tensor  imaging  (DTI;  this  is  discussed  in  Box  2–2)  was  performed  on  the  patient’s  MRI.  This  method  permits  imaging  of  neural  pathways  in  the  brain.  On  this  image  we  can  follow  the  corticospinal  tract,  the  principal  motor  control  pathway,  which  originates  from  the  motor  cortex.  Figure  2–1A4  shows  the  DTI  image  from  the  patient.  There  are  two  parallel  pathways.  The  arrow  points  to  the  caudal  medulla,  where  the  motor  pathway  decussation  normally  occurs.  Furthermore,  there  are  no  other  decussations  along  the  pathway.  B4  is  a  DTI  from  a  healthy  person.  The  arrow  points  to  the  decussation  of  the  corticospinal  tract  in  the  caudal  medulla  where  we  see  the  tracts  from  each  side  traversing  to  the  other.  We  will  learn  about  these  pathways  in  later  chapters.Finally,  clinical  neurophysiological  testing  was  conducted  to  assess  the  integrity  of  the  touch  and  motor  pathways  (see  Figure  2–2).  To  determine  the  function  of  the  sensory  pathway,  the  skin  is  electrically  stimulated  and  the  neural  response  is  recorded  with  electrodes  placed  on  the  scalp  over  the  region  of  the  somatic  sensory  cortex.  This  test  revealed  an  ipsilateral,  not  the  customary  contralateral,  response.  To  determine  the  function  of  the  corticospinal  tract,  transcranial  magnetic  stimulation  (TMS)  is  used  to  activate  the  motor  cortex  and  the  motor  pathway.  In  the  patient,  TMS  of  the  motor  cortex  produced  an  ipsilateral  muscle  response,  not  the  typical  contralateral  response  observed  in  healthy  subjects.After  reading  the  conclusion  and  explanations  below,  you  should  be  able  to  answer  the  following  questions.1.  At  what  dorsoventral  level  do  the  axons  of  the  sensory  and  motor  pathways  normally  cross  the  midline?2.  Is  the  crossing  of  all  central  nervous  system  axons  prevented  in  this  genetic  syndrome?3.  Does  DTI  ...