The BAHA

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The BAHA

• Home Study Course
• Otology and Neurotology
• Section 8 May 2007

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BAHA system is comprised of three parts

• Titanium fixture
• Connecting abutment
• Detachable sound processor

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How does it Work?

• The processor receives sound through the
  abutment and sends it to the functioning cochlea
  using the skull as a pathway to bypass the outer
  and middle ears

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Indications

• gt 5 years old
• Mixed or conductive hearing loss
• Bone conduction pure-tone average in the
  indicated ear is greater than or equal to 45 dB
  HL
• Monosyllabic word discrimination score 60
• For bilateral fittings candidates must have
  symmetrical bone conduction pure-tone averages
  between ears
• For single sided Deafness, candidates must have
  normal hearing in one ear (AC PTA gt 20 dB HL) and
  profound hearing loss in contralateral hear

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Candidates

• Chronic otitis media
• Congenital aural atresia
• Microtia
• Cholesteatoma
• Middle ear dysfunction or disease

• Acoustic neuroma tumors
• Tumor removal surgery
• Sudden deafness
• Neurologic degenerative disease
• Menieres disease
• Viral infection
• Trauma

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To anticipate a "high success rate" with BAHA

• Patients should have a PTA less than 45 dB,
  although improvements in hearing should still be
  expected for a PTA of up to 60 dB.
• (Hakansson B, Tjellstrom A, Carlsson P 
  Percutaneous vs. transcutaneous transducers for
  hearing by direct bone conduction.   Otolaryngol
  Head Neck Surg  1990 102339-344.)

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Operative Technique

• A. Posterior-based skin flap is elevated
• B. Flap is thinned until all hair follicles are
  removed from the flap center
• C. Soft tissues beneath and adjacent to the flap
  are excised to create a smooth transition from
  surrounding tissue to the thin central skin flap

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Operative Technique

• D. 3- to 4-mm hole is drilled in mastoid or
  retromastoid cortex.
• E and F, A countersink creates a recessed
  surface for implant placement.

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Operative Technique

• G. The hole is tapped
• H. Titanium screw is implanted
• I. Titanium screw is tightened in place

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Operative Technique

• H/I. The titanium screw is tightened into place
• K. The skin flap is replaced

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Operative Technique

• L/M. Metallic abutment for later attachment of
  the vibrating external hearing aid is attached to
  the screw
• N/O. A healing cap is placed to apply pressure
  to the skin flap

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The Evidence Base for the Application of
Contralateral Bone Anchored Hearing Aids in
Acquired Unilateral Sensorineural Hearing Loss in
AdultsBaguley DM, Bird J, Humphriss RL
Prevost ATClin Otolaryngol 2006
316-14Metanalysis
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Acquired Unilateral Sensorineural Hearing Loss
Leads to

• Impairment in sound localization
• Impairment in the discrimination of a signal in
  background noise

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Robust Hearing Handicap Inventory

• 72 - 83 severe Handicap
• Some articles populations were s/p sudden SNHL
• Two articles addressed unilateral SNHL s/p
  vestibular schwannoma surgery
• 17 states improved
• 58 states no change

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CROS Hearing Aid (Contralateral Routing of Signal)

• Sound is transmitted via a wire or FM link from a
  satellite microphone on the side of the poorer
  hearing ear into the better ear
• Improved contralateral hearing when sound
  originates from the poorer hearing side
• Impairs reception of better hearing side when
  sound originates from the better hearing side

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CROS Hearing Aid (Contralateral Routing of Signal)

• The ear mould on the good ear should be
  sufficiently open to not create a conductive loss
  on that side
• The gain response should be smooth over a wide
  frequency range and without excess gain at any
  frequency

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Three Situations (4 weeks each for habituation)

• Unaided
• CROS hearing aids
• BAHA

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Tested / Measured Benefits

• Abbreviated Profile of Hearing Aid Benefit
  (APHAB) questionnaire
• Ease of communication
• Background noise
• Reverberation
• Aversion
• Auditory localization testing (Speaker array)
• Speech discrimination testing (Hearing in Noise
  Test HINT or balance monosyllabic wordlist)

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Conclusions

• BAHA gt CROS gt unaided conditions for speech
  discrimination in noise and subjective
  questionnaire measures of auditory abilities

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ConsensusWhen contralateral BAHA is utilized in
acquired sensorineural hearing loss

• Patients do not experience improved auditory
  localization abilities
• Speech discrimination in noise abilities are
  improved with BAHA over CROS aid and unaided
  conditions
• When subjective measures of auditory benefit are
  considered an improvement with BAHA over CROS aid
  and unaided conditions are observed

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Why do neither of the aids allow for sound
localization?

• Following unilateral deafferentation of the
  auditory pathway, plastic changes occur such that
  the functioning cochlea activates both the
  ipsilateral and contralateral pathways. This may
  be apparent as early as three weeks after hearing
  loss. However, is it possible to rewire the
  pathway back to its original configuration.

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Critical Review of Literature

• In all studies, the BAHA was applied last
• Patients are more likely to prefer the second
  hearing aid
• The additional month of bilateral hearing,
  regardless of the mechanism, could contribute to
  improved hearing
• Patient selection
• Niparko BAHAs were performed in a group that
  rejected CROS aids
• Hol et al. BAHAs were performed in a group that
  rejected bone conduction headband device trial

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Critical Review of Literature

• Time for habituation of CROS aids vs. BAHA
• Summative effect?
• Only tried for 4 week intervals?
• Each study compares the aided to the unaided.
  They do not compare aided (CROS) to aided (BAHA)
• Does not determine degree of hearing handicap of
  unaided patients
• Double-reporting of patients
• Underpowered

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Critical Review of Literature To discuss further

• Insert BAHA titanium screw at time of vestibular
  schwannoma excision in patients who hear well
  preoperatively?
• Why? Why not?

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Perioperative Complications with the
Bone-Anchored Hearing AidShirazi MA, Marzo S
and Leonetti JP. Otolaryngol HNS 2006 134
236-239.Retrospective Review
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Population

• 58 patients - 30 Female28 Male
• Mean age 48 years ( 8 80 )

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Population

• Indication Number of Patients
• Sudden unilateral sensorineural hearing loss
  25
• Mixed hearing loss / chronic otitis media 17
• Unilateral sensorineural hearing loss secondary
  13
• to acoustic neuroma
• Unilateral sensorineural hearing loss secondary
  3
• to Menieres disease

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Complications

• Complication of Cases 11
  (19) Management
• Loss of skin graft 6 (10) Local
  wound care
• Skin growth over abutment 3 (5)
  Office debridement
• Revision under GETA
• Implant extrusion 2 (3)
  Reimplantation

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The most important factor in obtaining a
trouble-free bone-anchored hearing aid
(BAHA) site isA. Having thin, immobile,
hairless skin around the abutment B. Using
a 4-mm fixture flangeC. Using a longer abutment
The longest D. Performing surgery in two stages
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To Prevent Loss of Skin Graft

• Have thin, immobile, hairless skin around the
  abutment - This allows for placement of the
  fixture in a tissue bed that has minimal local
  tissue reaction to the implant and thereby
  minimizes chance of skin graft loss, infection or
  extrusion
• Ensure that the skin graft is firmly attached to
  the underlying periosteum
• Ensure that the fixture and skin penetrating
  abutment are firmly secured

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To prevent growth of skin graft over the abutment

• Use longest implant possible
• Obtain adequate removal of surrounding soft
  tissue
• Approximate the surrounding skin edges to the
  periosteum

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To prevent implant extrusion

• Allow patients with poor wound healing and thin
  bones to have six months of osseointegration
• Fix any coagulopathies that the patient may have
  pre-operatively
• Maintain proper hemostasis to prevent hematoma
  formation
• Use a 4-mm fixture if there is bone still present
  at the bottom after using a 4-mm drill guide
• Patients with thin, brittle bone should have a
  two stage surgery

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Other complications

• Penetration of sigmoid sinus Insert bone wax or
  muscle plug
• Brain abscess

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Critical review of literature

• Wide age range
• Altered technique mid-series from inferiorly
  based skin flap to superiorly based flap
• Unknown surgeons involved
• Why were there more complications early on?
  Was there a learning curve for the surgeons?
• Low power

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Additional Discussion