temporal)bone)encephalocele… · 2016. 9. 15. ·...

Temporal  Bone  Encephalocele  Presenting  with  Conductive  Hearing  Loss

ABSTRACT

INTRODUCTION

CASE  REPORT DISCUSSION

CONCLUSIONS

Dennis  Bojrab  II,  MD1;  Robert  Hong,  MD1,2;  Aaron  Metrailer,  MD2;  Dennis  Bojrab,  MD1,2

1Wayne  State  University,  2Michigan  Ear  Institute

Outcome  Objectives:1.  Describe-­‐ Conductive  hearing  loss  has  numerous  potential  causes.  This  case  report  presents  a  patient  with  an  intact  tympanic  membrane,  aerated  middle  ear,  and  no  history  of  ear  disease  or  trauma  who  developed  unilateral,  conductive  hearing  loss  as  an  adult  secondary  to  temporal  bone  encephalocele.

2.  Recognize-­‐ In  a  patient  with  conductive  hearing  loss  and  partially  intact  acoustic  reflexes,  a  temporal  bone  encephalocele  impeding  movement  of  the  ossicles  in  addition  to  the  more  common  etiology  of  third  window  disorders must  be  considered.

Methods:We  present  a  case  report  of  a  50-­‐year-­‐old  woman  with  conductive  hearing  loss  and  aural  fullness  who  presented  to  our  clinic  in  late  2013.  She  initially  underwent  a  negative  middle  ear  exploration  for  suspected  otosclerosis.   Subsequently,  she  was  found  to  have  a  temporal  bone  encephalocele  with  resolution  of  conductive  hearing  loss  after  transmastoid  and  middle  cranial  fossa  repair.

Results:Temporal  bone  encephalocele  can  cause  conductive  hearing  loss  and  partially  absent  acoustic  reflexes  with  an  unremarkable  neurotological  examination  including  a  well  aerated  middle  ear.

Conclusion:This  case  demonstrates  the  role  of  imaging  and  importance  of  close  evaluation  for  temporal  bone  encephaloceles  when  evaluating  conductive  hearing  loss,  particularly  when  acoustic  reflexes  are  not  completely  absent.

Conductive  hearing  loss  is  the  result  of  any  process  that  attenuates  the  sound  energy  reaching  the  cochlea.  The  differential  diagnosis  for  conductive  hearing  loss  is  broad;  however  a  thorough  patient  history  in  conjunction  with  the  physical  examination,  audiologic  testing,  and  imaging  may  narrow  the  differential  diagnosis.  The  most  common  cause  of  progressive  conductive  hearing  loss  in  the  absence  of  chronic  otitis  media  is  otosclerosis,  yet  other  entities  causing  ossicular  chain  fixation,  ossicular  discontinuity,  and  third  window  phenomena  should  be  considered  [1].

In  this  report,  we  present  the  unusual  case  of  a  patient  who  underwent  middle  ear  exploration  for  presumed  otosclerosis,  but  who  was  ultimately  found  to  have  a  temporal  bone  encephalocele  as  the  etiology  of  conductive  hearing  loss. Preoperative  evaluation  did  not  reveal  any  specific  signs  or  symptoms  strongly  suggestive  of  this  diagnosis,  with  an  aerated  middle  ear  and  inconclusive  imaging  studies. Temporal  bone  encephaloceles  can  present  with  conductive  hearing  loss,  though  usually  in  the  context  of  persistent  middle  ear  effusion  or  otorrhea.  However,  as  this  case  demonstrates,  they  can  also  be  the  cause  of  conductive  hearing  loss  in  the  presence  of  a  normal  otoscopic  exam.

A  50  year  old  healthy  female  was  referred  for  evaluation  of  unilateral  hearing  loss.  The  patient  weighed  250  lbs  with  body-­‐mass  index  of  41.  Hearing  loss  began  6  months  prior  with  associated  aural  fullness.  She  denied  tinnitus,  vertigo,  disequilibrium,  sound  or  pressure-­‐induced  dizziness,  otorrhea,  otalgia,  history  of  ear  disease,  or  trauma.  She  also  denied  a  family  history  of  hearing  problems.

On  examination,  the  right  ear  tympanic  membrane  was  intact  and  the  middle  ear  aerated.  Tuning  fork  examination  was  consistent  with  a  significant  conductive  hearing  loss  in  the  right  ear. The  remaining  neurotological  examination  and  the  general  head  and  neck  examination  were  unremarkable.

Audiologic  testing  revealed  a  right  mixed  hearing  loss  with  an  air-­‐bone  gap  at  all  frequencies  (most  pronounced  at  2000  to  4000  Hz)  and  type  A  tympanograms  bilaterally  (Figure  1).  Right  ipsilateral  acoustic  reflexes  were  absent. Left  contralateral  reflexes  were  present  at  500  Hz,  1000  Hz,  and  2000  Hz,  and  absent  at  4000  Hz  (Figure  2).  A  high  resolution  CT  scan  of  the  temporal  bone  was  obtained  to  evaluate  for  the  possibility  of  cochlear  otosclerosis  (given  the  mixed  hearing  loss)  as  well  as  a  third  window  disorder  (given  the  presence  of  acoustic  reflexes).   CT  imaging  was  essentially  normal,  with  no  evidence  of  cochlear  otosclerosis  or  a  third  window  disorder. The  tegmen  appeared  thin  in  places  but  was  not  clearly  dehiscent. Scant  opacification  was  noted  in  the  mastoid.

The  patient  elected  to  have  a  right  middle  ear  exploration  to  address  the  conductive  hearing  loss. Intraoperatively,  no  specific  ossicular  abnormality  was  identified. Scant  middle  ear  fluid  was  present  and  the  possibility  of  an  encephalocele  with  associated  CSF  (cerebrospinal  fluid)  otorrhea  was  entertained,  though  an  encephalocele  was  not  directly  visualized. A  small  amount  of  fluid  was  collected  and  sent  for  beta-­‐2  transferrin  (though  this  test  was  ultimately  negative).

Given  the  intraoperative  findings,  a  magnetic  resonance  imaging  (MRI)  of  the  brain  was  ordered  postoperatively  to  evaluate  for  possible  encephalocele  (Figure  3). Possible  encephalocele  was  identified,  and  there  appeared  to  be  more  extensive  opacification  of  the  mastoid  compared  to  the  preoperative  CT  scan. A  repeat  CT  scan  of  the  temporal  bone  was  obtained,  again  suggesting  increased  opacification  of  the  mastoid,  as  well  as  an  area  of  tegmen  dehiscence  (Figure  4). As  such,  the  patient  underwent  a  combined  transmastoid  and  middle  cranial  fossa  repair,  with  intraoperative  confirmation  of  the  encephalocele  and  CSF  leak. Postoperatively,  the  patient  had  an  uneventful  recovery,  with  postoperative  audiogram  demonstrating  resolution  of  conductive  hearing  loss.

A  patient  who  presents  with  progressive  conductive  hearing  loss  without  evidence  of  chronic  otitis  media  is  often  presumed  to  have  an  ossicular  etiology  of  hearing  loss,  most  commonly  otosclerosis. However,  more  recently,  third  window  disorders  such  as  superior  semicircular  canal  dehiscence  have  been  demonstrated  to  cause  similar  hearing  loss  [1].  Third  window  disorders  include  dehiscence  of  any  semicircular  canal,  dilated  vestibular  aqueduct,  inner  ear  malformations  causing  dehiscence  of  the  cochlea  or  vestibule,  and  Paget’s  disease  of  the  temporal  bone  [2].  Patients  with  an  enlarged  vestibular  aqueduct  or  superior  semicircular  canal  dehiscence  can  present  with  conductive  hearing  loss  as  the  primary  complaint  [3].

Given  the  multiple  possible  diagnoses,  acoustic  reflex  testing  is  an  important  tool  in  the  armamentarium  of  an  otolaryngologist  in  the  evaluation  of  conductive  hearing  loss  in  the  setting  of  a  normal  ear  exam.  Its  use  is  advocated  to  help  differentiate  between  ossicular  and  third  window  etiologies  prior  to  middle  ear  surgery,  with  the  presence  of  reflexes  necessitating  additional  workup  for  third  window  disorders  to  minimize  the  risk  of  negative  middle  ear  explorations  [4].

In  the  acoustic  reflex  test  the  reflex  arch  starts  with  stimulation  of  the  cochlea,  which  in  turn  stimulates  the  cochlear  nerve,  ventral  cochlear  nuclei,  superior  olive,  facial  nerve,  and  finally  causing  the  stapedius  muscle  to  contract.  In  patients  with  conductive  hearing  loss  that  has  progressed  to  the  point  of  considering  surgery,  the  reflexes  are  typically  absent  with  otosclerosis.   In  contrast,  acoustic  reflexes  may  be  present  when  superior  semicircular  canal  dehiscence  or  enlarged  vestibular  aqueduct  is  responsible  for  the  conductive  hearing  loss  [5,  6]. When  at  least  one  reflex  is  present,  CT  imaging  of  the  temporal  bone  is  advocated  to  evaluate  for  3rd window  etiologies  [4]. We  suggest  that  careful  attention  should  also  be  paid  to  the  tegmen  on  such  imaging,  as  a  temporal  bone  encephalocele  overlying  the  ossicles  may  also  lead  to  such  hearing  loss  and  result  in  a  significantly  different  recommendation  for  surgery

The  presence  of  middle  cranial  floor  defects  occurs  in  20-­‐33%  of  adult  temporal  bones,  but  the  occurrence  of  encephaloceles  is  much  less  common  [7]. Depending  on  the  location  and  size  of  the  encephalocele,  patient  presentation  can  be  quite  variable. Several  studies  have  shown  that  encephaloceles  can  cause  a  conductive  hearing  loss  [8]. Other  articles  had  both  pre  and  post-­‐encephalocele  repair  audiology  testing,  which  revealed  that  the  conductive  hearing  loss  either  stayed  relatively  stable  or  improved  [9,  10].

This  case  demonstrates  that  close  evaluation  for  temporal  bone  encephaloceles  is  important  when  evaluating  conductive  hearing  loss  and  this  diagnosis  should  be  considered  prior  to  middle  ear  exploration,  particularly  when  acoustic  reflexes  are  present. In  this  case,  the  encephalocele  was  touching  the  heads  of  the  ossicles,  leading  to  a  conductive  hearing  loss  that  was  not  corrected  until  the  encephalocele  was  repaired  via  a  combined  transmastoid/middle  cranial  fossa  approach.  To  our  knowledge  this  is  the  first  report  of  a  case  with  conductive  hearing  loss,  a  normal  otoscopic  exam,  and  presence  of  at  least  some  acoustic  reflexes  where  the  final  etiology  of  hearing  loss  was  determined  to  be  an  encephalocele.

There  are  multiple  potential  diagnoses  for  an  adult  patient  presenting  with  progressive  conductive  hearing  loss.  In  addition  to  a  thorough  history  and  examination,  it  may  also  be  important  to  obtain  audiometric  and  radiologic  evaluation.  In  this  report,  the  patient  had  no  history  of  ear  disease  or  trauma,  an  unremarkable  otoscopic  examination  who  presented  with  worsening  conductive  hearing  loss  because  of  an  encephalocele  impeding  normal  ossicular  movement.  Now  temporal  bone  encephalocele  must  also  be  considered  when  evaluating  a  patient  with  conductive  hearing  loss  and  partially  intact  acoustic  reflexes.  

Figure  1This  is  the  patient’s  pre-­operative  audiogram  revealing  mixed  hearing   loss  in  the  right  ear,  with  an  air-­bone  gap  at  all  frequencies,  most  pronounced  at  2000  to  4000  Hz.  

Figure  2This  is  the  patient’s  pre-­operative  tympanogram  and  acoustic  reflexes.  Bilateral    type  A  tympanograms.  Right  ipsilateral  acoustic  reflexes  were  absent.    Left  contralateral   reflexes  were  present  at  500  Hz,  1000  Hz,  and  2000  Hz,  and  absent  at  4000  Hz

Figure  3T1  coronal  MRI  scan  post  contrast  demonstrating  encephalocele  involving  epitympanum  

Figure  4Coronal  CT  scan  revealing  tegmen  dehiscence  and  encephalocele  in  the  region  of  the  epitympanum  coming  into  contact  with  the  ossicles.

1. Ebert,  C.S.,  Jr.,  A.M.  Zanation,  and  C.A.  Buchman, Another  cause  for  conductive  hearing  loss  with  present  acoustic   reflexes. Laryngoscope,  2008. 118(11):  p.  2059-­‐61.2.  Merchant,  S.N.  and  J.J.  Rosowski, Conductive  hearing  loss  caused  by  third-­‐window  lesions  of  the  inner  ear.Otol Neurotol,  2008. 29(3):  p.  282-­‐9.3.  Gopen,  Q.,  et  al.,Enlarged  vestibular  aqueduct:  review  of  controversial  aspects. Laryngoscope,  2011. 121(9):  p.  1971-­‐8.4.  Hong,  R.S.,  et  al., Acoustic  Reflex  Screening  of  Conductive  Hearing  Loss  for  Third  Window  Disorders. Otolaryngol Head  Neck  Surg,  2015.5. Halmagyi, G.M., et al., Superior semicircular canal dehiscence simulating otosclerosis. J Laryngol Otol, 2003. 117(7): p. 553-7.6. Wieczorek, S.S., et al., Enlarged vestibular aqueduct syndrome

mimicking otosclerosis in adults. Am J Otolaryngol, 2013. 34(6): p. 619-25.7. Kapur, T.R. and W. Bangash, Tegmental and petromastoid defects in the temporal bone. J Laryngol Otol, 1986. 100(10): p. 1129-32.8. Stucken, E.Z., S.H. Selesnick, and K.D. Brown, The role of obesity in spontaneous temporal bone encephaloceles and CSF leak. OtolNeurotol, 2012. 33(8): p. 1412-7.9. Semaan, M.T., et al., Transmastoid extradural-intracranial approach for repair of transtemporal meningoencephalocele: a review of 31 consecutive cases. Laryngoscope, 2011. 121(8): p. 1765-72.10. Nahas, Z., et al., Spontaneous meningoencephalocele of the temporal bone: clinical spectrum and presentation. Arch OtolaryngolHead Neck Surg, 2008. 134(5): p. 509-18.