13 Auditory Implantation in Otosclerosis Patients Otosclerosis is a process of bone resorption of the petrous bone (otospongiosis) followed by replacement with thick, irregular, sclerotic bone (otosclerosis) often leading to hearing loss. The most commonly affected location is around the oval window, which can result in conductive hearing loss due to stapes foot-plate fixation (fenestral otosclerosis). In ~10% of patients, otosclerotic foci will also affect the otic capsule (retrofenestral otosclerosis), resulting in cochlear otosclerosis accompanied by sensori-neural hearing loss.1 Next to the radiologic diagnosis, there exists a functional diagnosis for otosclerosis with severe mixed hearing loss called far advanced otosclerosis (FAO). FAO was first described by House and Sheehy2 as an air conduction threshold of at least 85 dB and an unmeasurable bone conduction threshold (due to the limitations of audiometers at that time). Nowadays, in the era of cochlear implantation, it is more likely that speech discrimination scores will be used instead of pure tone thresholds. Hence, the term FAO is no longer applicable and in this chapter we use the term advanced otosclerosis when referring to patients with sensorineural hearing loss and diminished (<100%) speech discrimination scores. Advanced otosclerosis is a purely audiologically based term in contrast to fenestral and retrofenestral oto-sclerosis (explained below). High-resolution computed tomography (HRCT) scanning can reveal subtle bone formations and demineralization of the cochlea. It is therefore considered to be the imaging technique of choice for the diagnosis of otosclerosis. HRCT may predict additional difficulties during surgery, as it can detect subtle otosclerotic foci in and around the cochlea. For instance, the necessity for extra drilling to achieve successful electrode insertion is related to the extent of fenestral involvement and/or narrowing of the basal turn,3–5 both visible on HRCT. In radiologic terms, otosclerosis can be divided into fenestral otosclerosis (demineralization of the bone adjacent to the oval window) and retrofenestral otosclerosis (demineralization of the bone around the cochlea). Different grading systems (Rotteveel1 and Symons and Fanning5) are available for the classification of otosclerosis (Fig. 13.1). In general, they are based on the location of the otosclerotic lesions: purely fenestral (grade 1), patchy retrofenestral (grade 2), and diffuse confluent retrofenestral involvement (grade 3).1,5–7 Difficulties in electrode insertion tend to be associated with cochlear involvement on CT (grades 2 and 3), even though no statistical significance was found.1,6 The severity of otosclerosis on CT is also associated with the risk of postoperative facial nerve stimulation: patients with a higher CT classification are significantly more likely to develop facial nerve stimulation.1,5,6 Unfortunately, there are no standard guidelines regarding the rehabilitation of advanced otosclerosis. In advanced otosclerosis three treatment options can be proposed to the patient: (1) no intervention and continuation of the use of hearing aids; (2) stapedotomy and hearing aid use; or (3) the placement of a cochlear implant (CI). In some patients with advanced otosclerosis the decision can be difficult because of two factors: first, with mixed hearing loss it is hard to predict the success rate of stapedotomy, especially if compared with cochlear implantation as an alternative intervention. Second, extensive imminent otosclerotic foci around the otic capsule can lead to surgical complications during implantation.1,8,9 As well as the role of the success rate in the decision, each intervention has specific advantages and disadvantages. Stapedotomy is a relatively simple, safe, and low-cost procedure that can accomplish very good results. However, the results of stapedotomy in severe mixed hearing loss are unpredictable and variable because stapedotomy is not applicable for treatment of the sensorineural component of hearing loss.10,11 The Weber test can be of help in deciding the best side for stapedotomy, as it will indicate the ear with the better bone conduction and the more severe air–bone gap. One has to be aware that in case of a calcified round window the success of the stapedotomy might be disappointing. Moreover, a feared complication of stapedotomy is an increase of sensorineural hearing loss, which in advanced oto-sclerosis could result in a functionally deaf ear. Cochlear implantation has yielded excellent results and seems to be a good treatment for patients with advanced otosclerosis, provided that the electrode can be inserted.3,12,13 On the debit side, it is an expensive and more complex procedure that requires experienced surgeons especially because otospongiosis and otosclerosis can cause difficulties during implantation. Furthermore, programming of the CI can be challenging since the progression of otosclerosis can cause postoperative impairment in performance of the CI.14 A treatment algorithm is presented in Fig. 13.2. Patients are divided into three main groups using standard speech audiometry, as explained below. Fig. 13.1a–d Grading of otosclerosis on computed tomography images (according to Rotteveel et al1). Axial CT scan of the petrous bone in patients with otosclerosis. Fig. 13.2 Treatment algorithm in otosclerosis patients with less than 70% speech discrimination. (Adapted from Merkus et al 201115 with permission of Laryngoscope.) New evidence has shown benefit of stapedotomy also if the air-bone gap is unknown.16 The presented algorithm15,16 divides patients into two main groups based on maximum speech discrimination scores: 0–50% and 50–70% (Fig. 13.2). Based on the radiologic findings and the extent of the air–bone gap (ABG), patients will be treated with a CI, with a stapedotomy, or with a hearing aid and follow-up. Patients with speech discrimination between 0 and 50% (open-set monosyllables16,17) may be treated with either cochlear implantation or stapedotomy. In case of severe retrofenestral oto-sclerosis on HRCT (grade 2C or 3), CI is the better option because of the very good results for hearing and the likely progression of cochlear pathology that could make CI very difficult if postponed. If the CT scan shows less cochlear involvement (radiologic grade 1, 2A, or 2B), ABG will guide the surgeon to either stapedotomy or cochlear implantation. If the ABG is 30 dB or more, a stapedotomy seems to be a cost-effective option with good chances of improvement of hearing. If hearing remains insufficient or decreases with time after stapedotomy, patients can still be treated with CI. If the ABG is 30 dB or less, patients should be treated with CI rather than stapedotomy because in this patient group stapedotomy yields insufficient improvement of hearing. Patients with a speech discrimination of 50 to 70% can be candidates for stapedotomy, rehabilitation with hearing aids, or in some cases even CI placement. Patients with limited cochlear involvement on HRCT (grade 1, 2A, or 2B) and an ABG of 30 dB or more should be treated with stapedotomy. When the ABG is 30 dB or less and HRCT shows limited cochlear involvement, patients will generally benefit from hearing aids and follow-up. If, on the other hand, HRCT shows extensive retrofenestral otosclerosis (grade 2C or 3), CI seems a viable option in this patient group. To date, SD scores of 50 to 70% are not universally accepted as an indication for CI and in some countries reimbursement may be a problem. However, extensive cochlear involvement on HRCT with impending cochlear obliteration may constitute an indication for CI because speech perception as well as the chances of successful cochlear implantation will diminish further with time. There seems to be a window of opportunity for successful implantation, and CI should be considered as a treatment option in this category of patients.1,6,15 Many authors have described surgical difficulties during cochlear implantation in otosclerosis patients such as fenestral and basal turn ossification, the necessity for extra drilling, partial electrode insertion, and scala vestibuli insertion (Table 13.1). Table 13.2 shows the incidence of these difficulties and the occurrence of postoperative facial nerve stimulation as reported in the literature. Fenestral ossification frequently requires extra drilling to identify the lumen of the scala tympani to achieve successful electrode insertion in this scala.1,3,4,10,12,15
13.1 Otosclerosis
13.2 CT Classification in Otosclerosis
13.3 Decision Making in Otosclerosis
a Grade 1: Fenestral involvement, otospongiotic lesion on the anterior border of the vestibulum (fissura ante fenestram) (red arrow).
b Grade 2A: Retrofenestral otosclerosis: the double ring effect. Also described as “halo sign” or the “ring of Valvasori”.
c Grade 2B: The basal turn is calcified within the scala tympani (red arrow), which makes it grade 2B.
d Grade 2C: The ossification of the basal turn is visible (green arrow), but also the double ring around the cochlea (red arrow). This situation has an increased risk of a false route of insertion. The narrow and mostly white round window membrane, next to a new (but false) lumen in the same direction as the basal turn. See Case 13.6 at the end of this chapter.
e Grade 3: Diffuse confluent cochlear involvement with an unrecognizable cochlea.
13.4 Treatment Algorithm
13.5 Surgical Difficulties and Management in Cochlear Implantation in Advanced Otosclerosis
Surgical difficulties | Sclerotic obliteration of the round window |
In severe otospongiosis | CSF gusher/CSF leakage |
| Progression of the electrode into a false route (internal auditory canal, carotid canal, etc.) |
Postoperative difficulties | Partial insertion, shifting programming |
Basal turn ossification caused by osteoneogenesis is a serious pathology as almost all patients (80–100%) with a partial electrode insertion or misplacement during surgery have basal turn ossification.1,13,15 Obliteration of the scala tympani requires scala vestibuli electrode insertion in 2 to 25% of the cases.1,10,15,18 This method of insertion is described in Chapter 11.
Fig. 13.3 Facial nerve stimulation in severe retrofenestral otospongiotic lesions. Coronal scan of a patient prior to implantation. The otospongiotic bone lesions are seen all around the cochlea and are confluent with the bony facial nerve canal between the internal auditory canal and the geniculate ganglion (black arrows). When a cochlear implant is in position within this cochlea, the electrical current in the cranial part of the electrode will stimulate the spiral ganglia of the cochlear nerve as well as the facial nerve. The CI should then be reprogrammed and the middle electrodes should be turned off.
Some authors suggest that advanced otosclerosis could also be an indication for an auditory brainstem implant (ABI), but in our opinion this is not, as in all otosclerosis cases a CI can be implanted.19 This could be difficult, as explained above, and one should sometimes plan a subtotal petrosectomy for better access and visibility, but cochlear implantation is usually feasible (for auditory brainstem implantation indications see Chapter 8; for subtotal petrosectomy see Chapter 10).
In severe otospongiosis a cerebrospinal fluid (CSF) gusher can occur due to the otospongiotic bone and connection to the internal auditory canal (see the cases presented in this chapter). Three important steps are suggested to overcome difficulties in case of a cerebrospinal fluid (CSF) gusher:
Surgical difficulty/complication in literature | Range | Average |
Round window ossification | 0–89% | 38% |
Basal turn ossification | 3–60% | 31% |
Extra drilling | 0–60% | 28% |
Facial nerve stimulation | 0–75% | 25% |
Scala vestibuli insertion | 2–25% | 5% |
Partial insertion | 0–19% | 5% |
Source: Adapted from Merkus et al15 in a review of 13 studies.
1. Perform a subtotal petrosectomy. This will give you access, orientation, and most importantly a secure closure after surgery with minimal risks of meningitis.
2. Make a large enough cochleostomy that can firmly be packed with periosteum or fascia around the cochlear electrode.
3. Make sure the electrode is directed in the correct angle (superior-posterior to anterior-inferior). A false route is easily adopted. A perioperative CT scan can be an option.
Postoperatively, an electrical shunt between the implant and the facial nerve can cause facial nerve stimulation (FNS). FNS is a worrying complication of cochlear implantation occurring on average in 25% of patients with otosclerosis.15 The incidence of FNS was significantly higher in patients with otosclerosis compared with control patients in whom FNS was a rarely reported complication.5,8,12,13,20–22 This high occurrence of FNS can be explained by an increased conductivity of the otospongiotic bone, making it easier to stimulate the facial nerve.23 The management of facial nerve stimulation consists of a reduction in the stimulus levels of the cranially located electrodes, the total deactivation of the causative electrodes, or even reimplantation.1,13,20,22 Because the perigeniculate area is the facial nerve segment most frequently involved, the use of a precurved electrode will place the electrode endings farther away from the facial nerve and would therefore seem a more appropriate choice of electrode in otosclerosis patients. (See Fig. 13.3.)
Case 13.1 Stapedotomy in a Cochlear Implant Candidate with Otosclerosis (Fig. 13.1.1–Fig. 13.1.4)
Fig. 13.1.1 A 51-year-old woman presented with severe hearing loss, as shown on this audiogram. She was unaware that she probably had otosclerosis: she had been wearing hearing aids for years and had not had ear surgery in the past.
Fig. 13.1.2 On CT the extent of otosclerotic decalcification was entirely anterior of the oval window (grade 1: fenestral, yellow arrow). This case shows that the severity of the hearing loss is not directly related to the severity of the fenestral/retrofenestral decalcification.
Fig. 13.1.4 Three months postoperatively, the air–bone gap on the right side showed significant improvement as did the speech performance also. She is still wearing bilateral hearing aids, but with less fatigue. This patient is no longer a CI candidate. She is now considering a stapedotomy on her left ear.
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