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OTOSCLEROSIS

Figure 12.1 Axial computed tomography scan of the left middle ear through the stapes footplate

showing lucency anterior to the stapes footplate (1) and around the cochlear (2).

Medical Management

Whilst oral uoride has been proposed to prevent further deterioration in otosclerosis, the evidence for its use is debated and currently it is not used in the United Kingdom.

e use of bisphosphonates to prevent deterioration is in its infancy and studies show conicting evidence on benet. Future studies may show ecacy, but they are currently not used widely.

Hearing Aids

As most patients with otosclerosis have predominantly a conductive hearing loss, conventional hearing aids oer an excellent management option and should always be discussed with the patient. In patients with bilateral hearing loss opting for surgery a hearing aid should be oered for the non-operated ear.

Bone-Anchored Hearing Aids

Bone-anchored hearing aids are a useful method of hearing rehabilitation in patients who are unsuitable for conventional aids and who do not wish to have surgery.

Far Advanced Otosclerosis

Far advanced otosclerosis is dened as average hearing thresholds of over 85 dB with unmeasurable bone conduction. is can occur in patients with conductive hearing loss from otosclerosis combined with sensory hearing loss from ageing, cochlear otosclerosis, or any other cause of sensory loss. ese patients are treated either with surgery and a hearing aid or by cochlear implantation. Most clinicians oer surgery and hearing aids in the rst instance with cochlear implantation reserved for those who fail the rst treatment option. Cochlear implantation in patients with otosclerosis may be challenging due

68 e Ear

OTOSCLEROSIS

to the presence of otosclerotic plaques obstructing the round window or narrowing of the basal turn of the scala tympani. In addition, facial nerve stimulation from the cochlear implant is more common due to abnormal current spread in the diseased otic capsule.

Controversies in Stapes Surgery

Age: ere is no age limit for stapes surgery and, as described above, in patients with

•

severe mixed hearing loss stapedotomy may allow patients to use a hearing aid. Flying aer stapes surgery: Whilst there are no absolute rules, most surgeons recom-

•

mend not ying aer stapes surgery for at least 2 weeks. Scuba diving: Most surgeons recommend at least a delay to returning to diving with

•

50% of surgeons recommending a lifelong ban on scuba diving. Unilateral otosclerosis: When considering surgery for patients with unilateral

•

otosclerosis it is important to consider the chance of achieving symmetry of hearing aer surgery. is means looking carefully at the bone conduction thresholds of the proposed ear. Patients need careful counselling on the likely outcomes of surgery for real-world binaural hearing. Second-sided surgery: Most stapes surgeons will happily operate on the second ear

•

provided the rst-side surgery was successful and the appropriate audiometric criteria for the second ear are met. It is prudent to delay the second-side surgery for at least 6 months. Air-bone gap: Traditionally a minimum average air-bone gap of 20 dB is felt to be

•

a sensible threshold to justify surgery, although in some circumstances experienced surgeons may reduce this required level.

Consent for Surgery

As hearing aids give an excellent outcome for otosclerosis patients they should be oered to all patents. ose contemplating surgery should be aware of the risks. e risks are operator dependent and ideally surgeons should quote their own gures. Total sensory hearing loss is reported to be in the region of 0.4–2%. ese dead ears can rarely occur immediately following surgery but more typically are reported as occurring within a week postoperatively and are frequently accompanied by severe rotational vertigo. e cause of such sensory loss is unclear but clearly represents a major insult to the inner ear. Intracochlear bleeding, infection, or perilymph stulae are all possible causes. Unfortunately there is little evidence that revision surgery is helpful in these unfortunate cases. Most surgeons will give oral steroids and antibiotics. Reparative granuloma where granulation tissue forms around the stapes prosthesis and extends into the inner ear is a potential cause of sensory hearing loss, which was common when total stapedectomy was performed but fortunately is now extremely rare. Closure of the air-bone gap to within 10 dB is achievable in the range of 80% to the high 90%. Some distortion of hearing and discomfort with loud sounds may be reported but typically settles in the rst few weeks aer surgery. Alteration in taste due to damage to the chorda tympani occurs in up to 30% but in most cases lasts only a few months. Vertigo has become much less common with the move to small fenestra stapedotomy. When vertigo occurs it is usually in the immediate post-operative period and typically settles quickly. Benign positional vertigo presumably from the trauma of surgery is reported in the literature and can be treated with particle repositioning. Facial nerve injury is very rare; however, direct trauma is possible. A delayed facial paresis can occur as with any case of middle ear surgery. Whilst the aetiology of such delayed palsies is debated, they usually recover within 6 weeks.

Surgery

Stapedectomy was rst described by John Shea in 1956. is involves removing the xed stapes and placing a piston from the incus to the vestibule. e basic technique Shea described remains in place. However, renements have taken place over the last 60 years,

e Ear 69

BONE CONDUCTION AND MIDDLE EAR IMPLANTS

and the main modication of the technique is to perform a small stapedotomy rather than removing the whole stapes footplate. is has reduced the risk of total sensory hearing loss and probably improved high-frequency hearing results. ere are many piston designs but with little to choose between them. A larger piston diameter should theoretically give better hearing, but the dierences are small. Most surgeons use a piston with a diameter between

0.4 and 0.6 mm. ere are a variety of methods of removing the stapes superstructure and

performing the stapedotomy. Cutting the stapes crura with a laser reduces the risk of stapes dislocation when removing the superstructure. Many surgeons use a laser when performing the stapedotomy, but there is no good evidence to favour laser over microdrill or hand trephine. If the incus is eroded the piston can be secured using bone cement. If the residual incus long process is very short or dislocated a malleostapediopexy can be performed in which a piston is placed from the malleus handle to the stapedotomy. Whilst not as good as standard stapedotomy, excellent results can still be achieved with this technique.

Revision Stapes Surgery

is is usually performed when there is a signicant post-operative conductive hearing loss, which may be immediate or come on at a later stage. e most common reasons are erosion of the long process of the incus, displaced prosthesis, too short prosthesis, dislocated incus, or incorrect diagnosis such as malleus head xation. is surgery should only be performed by experienced stapes surgeons. A laser is very useful in revision surgery to divide so tissue at the footplate.

KEY POINTS

• Otosclerosis is the presumptive diagnosis in an adult patient with a slow-onset conductive

hearing impairment with the presence of a normal mobile tympanic membrane.

• Pre-operative CT scanning is useful in conrming the diagnosis and predicting possible

surgical difculties.

• Conventional hearing aids are effective in managing the hearing loss of otosclerosis.

• Stapedotomy is an effective treatment for the hearing loss and tinnitus of otosclerosis.

Further Reading

1. Browning GG, Gatehouse S. e prevalence of middle ear disease in the adult British population Clin Otol 1992; 17: 317–21).

13. BONE CONDUCTION AND MIDDLE EAR IMPLANTS

Some patients are unable to wear, cannot tolerate, or do not gain sucient benet from conventional air-conducting hearing aids (ACHAs). Depending on the severity of their hearing loss there are a number of other options. ere are non-implantable solutions and implantable options that require surgery. Suitability for a hearing implant requires specialist assessment in one of the United Kingdom’s designated hearing implant centres by a multidisciplinary team.

Bone-Conducting Hearing Devices

Due to the eciency of transcranial transmission, bone-conducting hearing devices (BCHDs) deliver sound energy to both inner ears. Middle ear implants in contrast are ear specic,

70 e Ear

BONE CONDUCTION AND MIDDLE EAR IMPLANTS

delivering sound only to the implanted side. ere are three main pathways of transmission of bone-conducted sound:

Outer: Down the ear canal transmitting energy to the tympanic membrane.

•

Middle: Due to the relative inertia of the ossicles and skull, they decouple and cause

•

relative movement. Inner: Directly through bone exerting inertial or compressive forces on the inner ear

•

uid.

BCHDs are either percutaneous (an abutment sticks out through the skin) or transcutaneous (the skin is intact). e systems are ‘passive’ if the vibration occurs within the external processor or ‘active’ if there is a vibrating component within the implant itself, for example, an internal vibrating actuator or amplication device. Passive transcutaneous devices are aected by skin/ scalp attenuation of approximately 10–15 dB of sound energy. Transcranial attenuation is close to 0 dB for frequencies up to 700 Hz and increases with higher frequencies. Higher transcranial transmission is benecial for patients with single-sided deafness (SSD) where the contralateral cochlea is being stimulated. Lower transcranial transmission is better for binaural cues.

Patient Selection

Candidates

NHS England published commissioning guidelines in 2016.1 Funding would be considered for the following:

1a Patients with unilateral or bilateral conductive or mixed hearing loss within the manufacturer’s tting criteria

AND

Stable bone conduction (BC) thresholds (<15-dB deterioration in >2 frequencies in a 2-year period)

1b Unilateral sensorineural hearing impairment (including SSD) where the better ear

has BC hearing thresholds within the manufacturer’s tting criteria

AND

2 e patient has trialed an ACHA or wireless contralateral routing of sound (CROS)/

BiCROS hearing aid for a minimum of 4 weeks, or is anatomically or physiologically unable to undertake a trial of an ACHA

AND

3 Has trialed a BCHD on a headband for a minimum of 14 days and shown benet in

speech tests.

Bone-conducting implants will not be commissioned for patients with:

Bone that is unable to support an implant, e.g. osteoradionecrosis

•

Sensitivity or allergy to the materials used (silicone or titanium)

•

Physical, emotional, or psychological disorders that, despite suitable treatment

•

and support, would mean signicant benet would be unlikely

Clinical Indications

Conductive and mixed losses are caused by the following:

Congenital causes such as microtia or atresia

•

Acquired causes such as chronic suppurative otitis media, recurrent otitis externa, or

•

ossicular pathology

e Ear 71

BONE CONDUCTION AND MIDDLE EAR IMPLANTS

SSD – sensorineural or severe to profound mixed loss – can be caused by the following:

Congenital

•

Trauma or surgery resulting in hearing loss

•

Unsuitable ear canal for a conventional hearing aid and insucient ipsilateral BC, e.g.

•

radical mastoid cavity, narrow ear canal, or ‘blind sac’ ear canal closure

Devices

Non-Implantable Solutions

Non-implantable solutions may be indicated for children that are too young for an implant (insucient skull thickness), as trial devices for patients to gain an understanding of how they would benet from an implantable solution, and for patients that are not willing to commit to surgical intervention. Devices include the Contact Mini on a Soband, Cochlear Baha 5 Processor or Oticon Ponto 4 Processor on a Soband, MED-EL ADHEAR, Cochlear SoundArc (with Baha 5 processor).

Implantable Solutions

Percutaneous solutions can deliver more power and are therefore suitable for patients with worse hearing levels. Transcutaneous active solutions have more power than transcutaneous passive devices and deliver more gain in the higher frequencies (Table 13.1).

In 2005 an international consensus recommended that BCHD surgery not be undertaken prior to age 2–3 years. is was to allow the skull to reach a sucient thickness and allow osseointegration. A skin thickness of at least 3 mm is required for Baha Attract to minimise problems with pressure sensitivity from the magnetic attachment. It is, however, important to stimulate hearing as early as possible; therefore in children too young for implantation the use of a BCHD via a Soband is advocated as soon as possible aer birth in bilateral cases and around 3 months for unilateral patients.

Percutaneous bone-anchored hearing implant surgery in children can be staged in an attempt to reduce the failure rate in patients with thinner skull bone or developmental/ behavioural issues that may predispose them to trauma to the abutment before the implant has osseointegrated.

Table 13.1 Implantable BCHD

Device Stimulation BC requirement SSD CL ear BC MRI strength

Cochlear Baha

Connect Baha 5 Baha 5 power Baha 5 Superpower Oticon Ponto Percutaneous Up to 45 dB ≤20 dB Up to 3.0 T Ponto 4 Pro Pro Power Up to 55 dB Superpower Up to 65 dB Cochlear Baha

Attract MED-EL

Bonebridge Cochlear Osia Transcutaneous

Note: BC, bone conduction; CL, contralateral; dB, decibel; MRI, magnetic resonance imaging; SSD,

single-sided deafness; T, tesla; TBC, to be conrmed once CE approved.

72 e Ear

Percutaneous Up to 65 dB ≤20 dB Up to 3.0 T

Transcutaneous

– passive

Transcutaneous

– active

Greatest benet

up to 25 dB

Up to 45 dB ≤20 dB Up to 1.5 T

TBC ≤20 dB TBC

Up to 1.5 T (without

magnet removal)

BONE CONDUCTION AND MIDDLE EAR IMPLANTS

Traditionally in children a longer time period before loading the sound processor has been recommended to allow more time for osseointegration and to compensate for thinner bone. We load the processor anytime from 4 weeks aer the surgery depending on healing at the abutment site, patient factors that may predispose to trauma, and bone quality at the time of surgery. A number of studies in adults have shown that loading at 3 weeks is safe, well tolerated, and does not cause a reduction in stability of the implant/abutment with time.

Surgery

Percutaneous surgery can be carried out through a linear incision or a minimally invasive technique (Figure 13.1). Skin thickness is measured to enable the appropriate choice of abut- ment length. A hole is drilled in the skull and then widened/nished with a ‘countersink’ burr. e combined implant abutment is then screwed into the skull hole to a specied tightness (measured with a torque wrench). For Baha Attract surgery the technique is similar to open percutaneous surgery. e same implant/screw that osseointegrates into the skull is used, but the BIM400 implant magnet is attached to the screw rather than an abutment (Figure 13.2). In Bonebridge surgery the implant is embedded and screwed into the skull in an appropriate position behind the ear.

Complications

Skin problems including inammation, skin overgrowth, and infection occur in up to 10% of patients. Fixture loss can occur in up to 14% of children over 15 years. e linear incision technique and the minimally invasive Ponto surgery (MIPS) technique have signicantly reduced rates of localised skin problems with percutaneous devices.

Figure 13.1 Oticon Ponto. (A) Cannula and initial burr for minimally invasive Ponto surgery (MIPS).

(B) Ponto 4 processor, abutment. and implant. (Images courtesy Oticon Medical.)

e Ear 73

BONE CONDUCTION AND MIDDLE EAR IMPLANTS

Figure 13.2 Baha Attract. Implant and magnet, external magnet, and Baha 5 processor. (Image

Outcomes

Data from systematic reviews of bone-anchored hearing aids (BAHAs) have shown implant survival of 98% and that major complications are very rare. ere is improvement in quality of life when measured with the Glasgow Benet Inventory. Audiological benets are evident in quiet and in noise as well as for sound localisation.

A 2017 study showed no dierence in performance between CROS hearing aids and BAHAs when comparing speech-in-noise and localisation. When CROS aids were initially used by SSD patients, complaints of occlusion in the better ear, poor sound quality, and discomfort reduced uptake. Improvements in hearing aid processor technology mean that CROS aiding provides a more cost-eective, non-invasive solution that is satisfactory for some SSD patients.

Studies comparing unilateral with bilateral BAHAs suggested benets of bilateral BAHAs in many, but not all, situations.

KEY POINTS

• BCHDs are used for the rehabilitation of hearing loss when conventional acoustic aids

cannot be tted or have been trialed and have failed to improve the hearing.

• Numerous devices are now available, and tting criteria have expanded up to 65 dB BC

on the ipsilateral side for percutaneous devices.

• Non-implantable options enable a thorough trial and/or allow time for children to

develop sufcient skull and scalp thickness prior to an implantable solution.

When the hearing thresholds are too poor to enable sucient benet with a bone-anchored device or ear-specic stimulation is preferred, a middle ear implant may be possible.

74 e Ear

BONE CONDUCTION AND MIDDLE EAR IMPLANTS

Figure 13.3 Vibrant Sound Bridge System showing implant and different couplers. (Images cour-

tesy MED-EL.)

Middle Ear Implants

Active middle ear implants (AMEIs) are implantable hearing devices that have been developed with the aim of overcoming a number of shortcomings associated with ACHAs, such as distortion, feedback, occlusion eect, discomfort, and ear canal irritation. In some cases, they may also oer the potential for improved sound clarity. All AMEIs utilise a transducer that is coupled to the ossicular chain or inner ear uid compartment. ese devices utilise either an electromagnetic (a coil and magnet) or piezoelectric mode of transmission to drive the ossicles.

e most widely used AMEIs to date are the Vibrant Soundbridge (VSB; MED-EL, Innsbruck, Austria) (Figure 13.3) and the Carina system (Cochlear Ltd, Sydney, Australia), both of which are electromagnetic devices. e VSB is a semi-implantable AMEI (i.e. an implanted internal component and an external audio-processor), whilst the Carina system may be fully implantable (i.e. a subcutaneous microphone, battery, and an electronic receiver connected to a transducer) or used with an external audio-processor. e Carina device has, however, recently been withdrawn from the market.

Patient Selection

Candidates

AMEIs may be an option for adults and children aged 5 years and older with sensorineural, conductive, or mixed hearing loss who are not able to tolerate or benet from ACHAs or BCHDs. Candidates should not have any skin conditions that may prevent attachment of any external component of the device and should have realistic expectations of outcomes.

Audiological

Current devices are most suitable for mild to severe sensorineural hearing loss (SNHL). More recently, with the application of various couplers, indications have expanded to include patients with moderate-to-severe conductive or mixed hearing loss secondary to, for example, sequelae of chronic otitis media, advanced otosclerosis, and congenital external/middle

e Ear 75

BONE CONDUCTION AND MIDDLE EAR IMPLANTS

ear malformations. In cases of conductive or mixed hearing loss, the main objective of AMEI placement is to raise sound-eld thresholds above the residual sensorineural component. Hearing loss should ideally be stable, although very slowly progressive loss may still be considered in some cases.

Audiological assessment includes pure-tone audiometry, tympanometry, and speech perception (e.g. Arthur Boothroyd [AB] word lists) in the best-aided condition to evaluate any retrocochlear loss. In general, there should be no retrocochlear or central element in the hearing loss. e worse hearing ear is usually selected for implantation.

With the VSB, the maximum air-conduction thresholds stated by the manufacturer are 65–85 dB HL for candidates with SNHL, whilst those with mixed hearing loss should have BC thresholds better than 45–65 dB HL (frequency range 0.5–6 kHz). However, clinicians should proceed with caution when assessing candidates with hearing thresholds close to the upper limits of these tting ranges and counsel carefully with regard to potentially inadequate functional gain from the device.

Surgery

Active middle ear disease should be addressed prior to implantation. In some cases, blind sac closure may be necessary; whether or not AMEI surgery is performed simultaneously or as a staged procedure depends on the assessment by the surgeon of the potential risk of infection in each individual patient. Accurate clinical and radiological evaluation is crucial in determining the optimal site for transducer placement, which may be the incus, stapes superstructure/footplate, or round window.

e surgical approach for AMEI is similar to cochlear implantation (CI). In general, a postauricular transmastoid route is utilised to access the middle ear via the facial recess or attic. A combined transmastoid/transmeatal approach may be required to gain sucient access to the middle ear, depending on the device and transducer placement.

Complications

e potential complications of AMEI implantation are similar to that for mastoid surgery (see Chapter 10). Patients should also be warned about the possibility of transducer displace- ment, extrusion, device malfunction/failure, aural fullness, and insucient benet.

Outcomes

Overall and in experienced hands, AMEIs are considered a safe alternative when ACHAs or BCHDs are not suitable. Optimal coupling, be it to the incus, stapes, or round window, is of great importance for good audiological outcomes. Although currently available evidence is somewhat limited and sometimes contradicting, AMEIs appear to have a functional gain at least as good as, if not better than, ACHAs. In general, patients have reported a signicant benet with all current AMEIs in terms of sound quality, ease of communication, reverberation, and listening in background noise compared with the unaided situation.

KEY POINTS

• AMEIs are classically indicated for patients with mild-to-severe SNHL who are not able

to tolerate or benet from other hearing devices.

The indications have expanded to include moderate-to-severe conductive or mixed hearing loss through coupling of the transducer to one of the ossicles or cochlear windows.