In   this   tutorial   you   will   learn   about   the   anatomy   of   the   facial   nerve.   This   nerve  supplies  the  muscles  of  the  face  that  are  concerned  with  facial  expressions.  Smiling,  frowning,  blinking  the  eye  and  whistling  are  just  some  of  the  movements  that  the  facial  nerve  allows  us  to  do.    The  importance  of  the  facial  nerve  to  us  as  clinicians  is  that  diseases  of  the  ear  may  damage   it   and   cause   paralysis.   The   clinician   must,   therefore,   recognize   the  presence  of  paralysis  as   it   implies  serious  ear  disease  such  as  cholesteatoma.  The  state  of  facial  nerve  function  should  always  be  noted  when  we  examine  an  ear.    ANATOMICAL  OVERVIEW    The   facial  nerve   is  one  of   the  cranial  nerves.  Cranial  nerves  are  nerves   that  come  directly  out  of   the  brain.  These  are  different  to  the  nerves  that  move  our  arms  or  legs  as  those  nerves  come  out  of  the  spinal  cord.    There  are  twelve  cranial  nerves  and  they  do  jobs  like  moving  the  eyes,  moving  the  face,   moving   the   tongue   and   shoulders,   feeling   pain   in   the   face,   detecting   light,  balance  and  sound  and  many  other  jobs.  There  is  a  list  of  the  cranial  nerves  in  the  table  below.  You  don’t  have  to  worry  about  them  all  at  this  time  although  they  will  become  important  in  the  future.  For  now  just  take  a  look  at  the  sorts  of  things  that  cranial  nerves  do.    Cranial  Nerve  number  and  name  

List  of  functions  

   1  –  Olfactory  nerve   Detects  smells  2  –  Optic  nerve   Detects  light  for  seeing  3  –  Oculomotor  nerve   Moves  the  eyes  (up,  down)  4  –  Trochlear  nerve   Moves  the  eyes  (in)  5  –  Trigemminal  nerve   Gives  sensation  to  the  face  

Helps  with  chewing  Contracts  tensor  tympani  muscle  in  the  middle  ear  

6  –  Abducent  nerve   Moves  the  eyes  (out)  7  –  Facial  nerve   Moves  the  face  

Contracts  the  stapedius  muscle  in  the  middle  ear  Gives  taste  sensation  

8  –  Vestibulocochlear  nerve   Hearing  and  balance  9  –  Glossopharyngeal  nerve   Moves  the  throat  on  swallowing  

Senses  taste  Gives  middle  ear  sensation  

10  –  Vagus  nerve   Does  many  different  things  all  through  the  body  11  –  Accessory  nerve   Raises  the  shoulder  12  –  Hypoglossal  nerve   Moves  the  tongue    Table  of  cranial  nerves  and  their  functions.    The  next  few  pictures  show  the  cranial  nerves  as  they  appear  under  the  brain  and  in  real  life.  

 http://en.wikipedia.org/wiki/File:Brain_human_normal_inferior_view_with_labels_en-­‐2.svg#filelinks  

This   is   a   view   of   the  underside   of   the   brain  (inferior   side).   It   shows   the  cranial  nerves.    Notice   that   the   nerves   are  paired  –  that  is  that  there  is  one   on   each   side   of   the  brain.      All   of   the   nerves   come  directly  out  of  the  brain  but  only  one  does  not   leave   the  skull.   It   is   the   olfactory  nerve.    All   of   the   others   leave   the  skull   through   holes   in   the  bone   of   the   skull   called  foramina.  

 

 http://www.sci.uidaho.edu/med532/cranialnervestartpage.htm  

This   is   the   inferior   surface  of  an  actual  human  brain.  It  shows   the   cranial   nerves  emerging   from   the   brain.  They  are  white  in  colour.  

     The  course  of  the  facial  nerve  (the  pathway  that  it  follows  from  the  brain  into  the  facial  muscles)   is   very   complicated.   However,   what   is   important   for   us   is   that   it  passes  with  the  vestibulocochlear  nerve  into  the  inner  ear  (cranial  nerve  8),  it  then  passes  through  the  middle  ear  and  mastoid  before  leaving  the  skull.  Once  out  of  the  skull  it  travels  inside  the  parotid  salivary  gland  to  get  to  the  muscles  in  the  face.    In  other  words  the  facial  nerve  travels  through  areas  of  the  body  that  ear  clinicians  examine  and  test  every  day.  Diseases  such  as  cholesteatoma,  acute  otitis  media  and  acoustic  neuroma  can  affect  the  facial  nerve  so  we  must  know  about  the  nerve  and  be  able  to  examine  it.    

The  anatomy  of  the  Facial  nerve  (Cranial  nerve  7).    When  we  describe  the  course  of   the   facial  nerve  we  divide   it   into  segments1.    We  will  look  at  three  of  these:  the  intracranial  segment,  the  intratemporal  segment  and  the  extratemporal  segment.    The  intracranial  segment.    This  segment  is  that  part  of  the  nerve  that  lies  inside  the  skull  itself  before  it  passes  into   the  middle   ear.   Once   the   nerve   has   left   the   brain   it   passes   into   the   internal  acoustic   meatus   (IAM).   In   the   IAM   it   runs   with   the   cochlear   nerve   and   the  vestibular  nerves.      

 

This   is   a   picture   looking   up  through   the   internal   acoustic  meatus  on  the  right  side.    Imagine   that   you   are   standing  inside  the  head  looking  out  into  it.    Superiorly  there  are  two  holes.  The  anterior  one   takes   the   facial  nerve  and   the   posterior   one   takes   the  superior  vestibular  nerve.    Inferiorly   and   anteriorly   is   the  spiral   foramina   that   takes   the  cochlear  nerve  while  posteriorly   is  the   foramen   for   the   inferior  vestibular  nerve.    

 

This   diagram   is   a   simpler   way   of  looking  at  the  anatomy.    S,   I,  A,  and  P  are  superior,   inferior,  anterior  and  posterior.    VII   is   Cranial   nerve   7   –   the   facial  nerve.  SV   and   IV   are   the   superior   and  inferior  vestibular  nerves    C  is  the  cochlear  nerve      

Figure:  Two  pictures  that  show  the  IAM  and  how  the  nerves  pass  through  it.    Acoustic  neuromas  and  fractures  of  the  temporal  bone  can  damage  the  nerve  in  this  segment.  

                                                                                                               1  The  facial  nerve  is  a  long  nerve  that  travels  through  many  anatomical  areas.  This  is  just  like  the  Mekong:  it  starts  in  China  then  travels  through  Burma,  Laos  and  Thailand.  Then  it  travels  through  Cambodia  and  at  the  end  it  travels  through  Vietnam.  It’s  the  same  river  in  every  place  but  we  can  think  of  it  in  shorter  segments  just  like  the  facial  nerve.  

Once   the   nerve   passes   into   its   foramen   it   leaves   the   intracranial   segment   and  enters  the  intratemporal  segment.    The  intratemporal  segment.    This  is  the  segment  of  the  nerve  that  lies  inside  the  middle  ear  and  mastoid.  This  is  a  very  important  part  of  the  nerve  because  it  is  the  part  that  is  affected  by  middle  ear  diseases   such  as  otitis  media  and  cholesteatoma.  These  are  diseases   that  you  see  all  of  the  time.    In   the  middle  ear   the   facial  nerve  starts  anteriorly  and   then  runs  posteriorly  and  then  inferiorly.  It  is  a  complicated  course  that  passes  by  the  promontory,  the  tensor  tympani,   the   stapes,   and   the  pyramid  of   the   stapedius  muscle.     You  only  need   to  know   all   of   this   when   you   are   actually   operating   on   the   ear   so   don’t   worry   too  much  about  all  of  these  new  names.      

 

You  saw  this  picture  in  the  tutorial  on   the   middle   ear.   It   shows   the  middle   ear   seen   without   a  tympanic  membrane   and  with   the  scutum  removed.    The  following  picture  is  similar  but  it   has   also   had   the   ossicles  removed  so   that  all   you  can   see   is  the  medial  wall  of  the  middle  ear.  

 The  picture  below  shows  a   facial  nerve   in   the  middle  ear   in  a  yellow  colour.  The  facial  nerve  enters  the  middle  ear   just  superior  to  the  cochlea  at  A.   It  then  passes  posteriorly   in   the  middle   ear   to   lie   just   superior   to   the   oval  window   (B).   At   this  point  it  turns  inferiorly  so  that  it  comes  to  lie  posterior  to  the  oval  window  and  the  round  window  (C).    

   While   in   the  middle   ear   the   facial   nerve   gives   off   two   special   nerves.   One   is   the  nerve  to  stapedius  and  the  other  is  the  chorda  tympani.  The  nerve  to  stapedius  is  responsible  for  making  stapedius  muscle  contract  when  the  ear  is  exposed  to  very  loud   sound   (acoustic   reflex).   The   chorda   tympani   carries   taste   information   from  the  tongue  to  the  brain.    From   posterior   to   the   oval   window   the   nerve   travels   inferiorly   and   out   of   the  temporal  bone  at  the  stylomastoid  foramen.  It  is  then  in  its  extratemporal  segment.    The  extratemporal  segment.    This  is  where  the  nerve  divides  into  five  branches.  Each  of  these  is  responsible  for  moving  a  part  of   the   face.   In   the   image  below  you  can  see   these  branches  on   the  side  of  the  face.  The  ones  that  move  the  muscles  in  the  face  are  shown  in  yellow.    

 

You  can   see   that   they   supply  muscles   around   the   eye   so  that   you   can   raise   your  eyebrows  or  close  your  eyes.      They   go   to   the   muscles  around  the  lips  and  allow  you  to   smile   and   keep   your   lips  closed.      They   also   go   into   the   neck  muscles.    

 

Facial  Palsy    If  a  disease  within  the  middle  ear  (such  as  cholesteatoma)  damages  the  nerve  the  face  will  become  weak  because  the  muscles  will  not  move.  Below  is  a  picture  of  a  patient  trying  to  smile.      

 

Notice   how   the   right   side   of   his   face  moves   normally   but   that   the   left   side  does   not   move   at   all.   He   has   a  weakness  of  the  left  facial  nerve  of  the  type   that   could   be   caused   by   middle  ear  disease.      The  medical  term  for  this  weakness  is  palsy.  

Patients  with   complete   facial   nerve   palsy   cannot   blink   and   this  means   that   their  eyes   can   become   damaged   and  may   even   become   blind.   Looking   after   the   eye   is  important   and   it  must   be   kept   closed  with   an   eye  patch  until   the  nerve   starts   to  recover  its  function.  Eye  drops  are  also  useful  to  prevent  drying  of  the  eye’s  surface.    There  are  many  diseases   that   can   cause   facial  nerve  palsy  apart   from  middle  ear  diseases.  A   list   of   the  diseases   that   you  may   encounter   is   shown   in   the   table  but  there  are  many  other  rarer  causes.       Infections  1   Acute  otitis  media   Bacterial  infection  2   Cholesteatoma   Skin   growing   into   ear   and   getting   infected  with  

bacteria  3   Ramsay  Hunt  Syndrome   Varicella  zoster  virus  infection  4   Bell’s  Palsy   Herpes  Simplex  virus  (probably)  5   Malignant  otitis  externa   Bacterial  infection  6   Leprosy   Bacterial  infection  -­‐  Mycobacterium  leprae  7   HIV   Virus  8   Tuberculosis   Bacterial  infection  –  mycobacterium  tuberculosis  9   Malaria   Parasite  infection           Tumours  1   Cancers  in  parotid  gland    2   Acoustic  neuroma             Others  1   Cerebrovascular  incidents  (stroke)  2   Fractured  temporal  bone  3   Pregnancy  and  diabetes      A  stroke  looks  different  to  the  other  causes  because  the  forehead  can  move  even  on  the  weak  side  of   the   face.  Look  at   the  patient  below.  He  has  weakness  on   the   left  

side  of  his  face.  In  the  left  picture  he  has  an  asymmetric  smile  and  weaker  closure  of   the   left   eye.  However,   he   can   raise   his   eyebrows  on   the   left   (right   picture).   In  other  words  his   forehead  has  been  spared  any  weakness.  This   is  characteristic  of  strokes.    

 http://www.gla.ac.uk/ibls/US/cal/anatomy/calfacialnerve/clinicalfeat.htm  

 Examining  the  facial  nerve    Examining  the  face  is  easy.  Ask  the  patient  to  raise  their  eyebrows,  close  their  eyes  tightly,   to  smile  and   to  whistle  or  puff   their  cheeks  out.  Look  at  both  sides  of   the  face  when  they  are  doing  this  and  compare  them.  Make  a  record  of  what  you  see.    Learning  points    

1. Whenever  you  see  a  patient  with  ear  disease  you  should  examine  the  facial  nerve.   This   is   particularly   true   of   patients   with   perforations   and  cholesteatomas  

2. The  opposite  is  also  true;  whenever  you  see  a  patient  with  a  facial  palsy  you  must  examine  the  ear  because  the  cause  of  the  palsy  may  be  an  ear  disease  

3. Always  keep  a  written  record  of  what  you  see  4. If  you  see  a  patient  with  middle  ear  disease  and  a  facial  palsy  they  need  to  

see  an  ear  surgeon  as  an  emergency  5. Always  protect  the  eye  while  a  facial  palsy  is  present  because  blindness  is  a  

possibility  due  to  scarring  of  the  eye’s  surface  6. A  stroke  can  look  very  similar  but  the  forehead  will  not  be  weak