COL1A1 gene variants were the first to be associated with otosclerosis by McKenna et al.31 COL1A1 is involved in bone metabolism and is known to be associated with osteogenesis imperfecta and osteoporosis.31 Chen et al. identified five variants in COL1A1, as well as two haplotypes associated with otosclerosis.33 Other genes involved in the metabolism and chondrogenesis of the otic capsule were also investigated, such as FGF2, RARA, OTOR, and PTH, but most of them did not show an association with otosclerosis. Thus, although studies have been conducted with different populations, the results are not very reproducible, and there is limited consistent evidence supporting the association between these genes and otosclerosis.19

The TNFRSF11B gene encodes Osteoprotegerin (OPG), a decoy receptor to activate the Receptor Activator of Nuclear Factor Kappa B Ligand (RANKL). RANKL binds to both RANK, leading to osteoclast maturation and bone resorption, and OPG, which regulates this process.34 Functional studies on OPG have shown that it plays a role in otosclerosis. Compared with normal stapes tissue samples, the mRNA expression of OPG is reduced in patients with otosclerosis.35,36 In addition, homozygous mutations in TNFRSF11B play a role in Paget’s disease, which may also lead to hearing loss,37 making it an interesting candidate gene for otosclerosis.

The TGFB1 gene plays an important role in the development and regulation of bones and cartilage38 and is related to otic capsule metabolism. It has been associated with otosclerosis in two different populations.27 An amino acid variant at position 263 of TGFB1 (I263) was shown to be protective, suggesting that it decreases otosclerosis susceptibility. An increase in nonsynonymous variants in the TGFB1 gene was identified in patients with otosclerosis.27 Bone morphogenetic proteins 2 and 4 (BMP2 and BMP4), which are members of the TGFB superfamily and play important roles in several stages of bone metabolism, have also been associated with otosclerosis susceptibility.39 A study investigating rare and common variations in BMP2 and BMP4 did not identify an association between common variants and otosclerosis. However, 4 rare variations were identified, and the functional analysis showed a reduction in phosphorylation of the receptor Smad.40 These results suggest that BMP2 and BMP4 play a role in the pathophysiology of otosclerosis.19

The ossicular chain and otic capsule undergo endochondral ossification during their development and, after this process, minimal bone remodeling occurs throughout life. Bone remodeling has reduced activity in the petrous portion of the temporal bone and is almost null near the perilymphatic space.42 This is explained by the presence of OPG, a mediator produced in large quantities by the spiral ligament that inhibits the recruitment, formation, and activation of osteoclasts. Therefore, low levels of OPG may be related to pathological new bone formation and resorption.42 Several cytokines are likely to be active in otosclerotic lesions, and the disinhibition of one or more of these cytokines may trigger the development of otosclerosis. Although other cells, such as osteocytes and bone lining cells, may contribute to calcium flux on bone surfaces, bone remodeling only occurs through the action of osteoblasts and osteoclasts.42

The otic capsule contains regions of immature cartilage called globuli interossei, which may correspond to the earliest loci of otosclerosis.42 The otosclerotic focus is identified on histologic sections of the temporal bone by its distinct appearance in the otic capsule after undergoing a remodeling process in which normal bone is replaced by otosclerotic bone. The otosclerosis focus may appear as dense mineralized bone (sclerosis) or active, well-vascularized bone (spongiotic).42 One of the first histologic manifestations of otosclerosis is known as blue mantles, which are basophilic staining regions visualized after application of Hematoxylin and Eosin (H&E). They are found near regions of otosclerosis and probably represent bone that has been recently remodeled, also known as basophilic bone.42

Another remarkable characteristic of the initial process of otosclerosis are the vascular channels, which result from an enlargement of the perivascular spaces. Bone is resorbed around a vessel and replaced by a fibrous connective tissue. These areas of active disease are characterized by the presence of osteoclastic giant cells and vascular proliferation. Within this space, reticular cells and fibroblasts assume the form of osteoblasts. At the same time, calcification begins in the matrix and a new, immature bone is formed with a bluish stain on H&E.70 Depending on whether the disease is active or inactive, it is termed otospongiosis (active) or otosclerosis (inactive).

Osteoblasts and osteoclasts precursors, histiocytes, and macrophages are commonly observed on electron microscopy. The otosclerotic process does not respect the normal limits and contours of the labyrinth or ossicles and may become exophytic and extend into the middle ear and perilymphatic space.42

Otosclerosis is limited to the temporal bone, and involvement of other regions has never been described.42 In approximately 70%–80% of patients, both temporal bones are affected by otosclerosis.70Foci of otosclerosis consist of bone formation by osteoblasts, bone destruction by osteoclasts, vascular proliferation, and a stroma of fibroblasts and histiocytes. The main focus of otosclerosis (96%) is located anterior to the stapes footplate (fissula ante fenestram),42 but only 10%–15% of patients present stapes ankylosis.5,70 Another commonly affected region is the round window niche (in 30%–50% of cases), but complete obliteration of the niche is rare.5,70

Foci of otosclerosis can also be found posterior to the oval window, on the posterior wall of the Internal Auditory Canal (IAC), around the cochlear aqueduct, and involving the semicircular canals and leading to the thickening of the stapes footplate.71 Extensive involvement of the oval window and footplate may be present in 7%–11% of cases, whereas round window obliteration is found in 1%.69 Cases without involvement of the ossicular chain are rare.42 Schuknecht and Kirchner68 showed that when otosclerosis is severe enough to extend into the cochlear endosteum, the onset of Sensorineural Hearing Loss (SNHL) symptoms is typically associated with stapes fixation. Ankylosis results from an enlargement of the otosclerotic focus that affects the stapes footplate and then involves the cartilage at the margin of the oval window, replacing it with immature and fibrotic bone tissue that is thicker and involves the annular ligament.70

After the otosclerotic focus reaches the cochlear endosteum, atrophy of the stria vascularis and formation of hyalinization in the spiral ligament occur.5,68 This process has been associated with impairment of ionic homeostasis, causing hearing impairment by reducing the cochlear potential, with subsequent HC dysfunction and leading to SNHL.68 Immunohistochemical staining has demonstrated that the hyalin material is composed of type I collagen, chondroitin sulfate, and keratin sulfate. In very advanced cases of otosclerosis, there may be intracochlear deposition of bone.5

Another characteristic of advanced otosclerosis is deformation around the cochlea, leading to an irregular appearance and narrowing of the helicotrema, as well as blockage of the cochlear and vestibular aqueducts.5 Otosclerosis evolves from an “otospongiotic” phase in which the normal lamellar otic capsule bone around vessels is resorbed, creating perivascular (or pseudovascular) spaces. These areas are highly cellular, with an increased number of osteoclasts. On H&E staining, these areas are often highly acidophilic, with a clear distinction between normal bone and the otosclerotic focus. Ultimately, new woven bone is deposited, which may be larger in volume than the bone that was resorbed, sometimes resulting in thickening of the involved area (e.g., the stapes footplate).

The new bone is presumably converted into lamellar bone, which is dense, and results in a highly eosinophilic and relatively acellular “sclerotic” focus.5 Less active otosclerotic lesions display new, woven bone formation with hypercellularity, often with more than two cells situated within a single lacunae.42 They represent the end stage of the disease, with bone transformation characterized by solid, lammellar, mosaic-like osseous tissue, which contains few and tiny marrow spaces as well as few and thin blood vessels. Not rarely, both inactive and active lesions can be found in a single temporal bone.70

Based on histologic findings that include the identification of foci of disordered bone resorption, new bone deposition, vascular proliferation, and/or connective tissue, 3 clinically relevant zones were defined to simplify the description of the extent of otosclerosis (Fig. 1) (Box 2).72

Figure 1.

Axial section of temporal bones of patients with different stages of otosclerosis. (A) Fenestral otosclerosis. (B) Cochlear otosclerosis.; O, Otosclerotic focus on the ante fenestram fissula; V, Vestibule; (*), Reissner’s membrane distention compatible with endolymphatic hydrops; Arrowhead, Otosclerotic focus involving the cochlea.

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Several histopathologic findings are sufficient to explain and corroborate the conductive hearing loss seen in otosclerosis. However, cases with mixed or purely SNHL are not uncommon. To explain such findings, many theories have been proposed and many histopathologic studies have been conducted. In 1987, a study including 6 temporal bones with otosclerosis and purely sensorineural auditory symptoms showed a moderate reduction in ganglion cell counts within the Rosenthal’s canal, in addition to impairment of inner and outer HCs.73 However, the authors associated these findings with an age-related process called presbycusis and were not convinced that cochlear otosclerosis existed.73

Two years after the publication, other researchers analyzed a larger number of temporal bones and measured the volume of inner and outer HCs. They found that, in temporal bones with otosclerosis, there was no significant difference in counts of outer HCs and density of spiral ganglion cells between regions with and without endosteal involvement by otosclerosis. However, total outer HC counts were lower in cochleae with 2 or more sites of endosteal involvement by otosclerosis than in cochleae with 1 site of endosteal involvement.74 Furthermore, other studies found different degrees of degeneration of inner and outer HCs in temporal bones with otosclerosis but failed to correlate this reduction in organ of Corti cells and spiral ganglion neurons with the extent of endosteal involvement by otosclerosis.5

In addition to these findings, IAC diverticulum has also been found in patients with otosclerosis. In a retrospective study analyzing Computed Tomography (CT) scans and audiometry results of 807 patients, patients with otosclerosis alone were more likely to present conductive hearing loss, whereas those with otosclerosis and IAC diverticulum were more likely to present mixed hearing loss. In most patients, IAC diverticulum is an isolated finding. The authors suggested that this finding may represent a manifestation of otosclerosis in patients with SNHL alone.75 Another study involving 97 temporal bones demonstrated that IAC diverticula were more common in the temporal bones of patients with otosclerosis than in patients without the disease (37.5% vs. 16%; p = 0.019).76

The presence of vestibular symptoms was elucidated by a study that found a reduction in the mean density of type I HCs in the saccule of patients with otosclerosis, but only when endosteal involvement was present. (Hızlı, 2016, Quantitative assessment of vestibular otopathology in otosclerosis: A temporal bone study) In an attempt to explain the associated vestibular symptoms, it has been hypothesized that toxic metabolites may be liberated by otosclerotic foci into the inner ear fluids, damaging the neuroepithelium.77 In addition, Endolymphatic Hydrops (EH) have been observed in some patients and may also explain the presence of vestibular symptoms. EH occurs when otosclerosis involves the spiral ligament, resulting in changes in intracochlear ionic homeostasis and obstruction of the endolymphatic duct and sac.69 Magnetic Resonance Studies (MRI) studies have shown varying degrees of cochlear and vestibular EH often in association with symptoms of concomitant vertigo, including in patients undergoing stapedotomy.78 Patients with otosclerosis may present clear signs of EH, but its degree is not related to symptom intensity. By being aware of this information, surgeons might be able to predict whether patients undergoing surgery may experience symptoms similar to Ménière’s disease postoperatively, but further studies are still needed to support this hypothesis (Fig. 1).79

Temporal bone CT scans in patients with otosclerosis who will need a CI most often show significant changes in the otic capsule and round window. It is often impossible to detect the lumen of the scala tympani (Figs. 14A and B) secondary to labyrinthitis ossificans. Therefore, MRI in these cases is essential to detect a visible space in the scala tympani (Fig. 15A). Partial stenosis (Fig. 15B) of the Scala tympani may occur, characterized by ossification/calcification on CT and low signal on MRI, which may result from fibrosis and/or ossification in the basal turn of the cochlea.

Figure 14.

(A) Advanced otosclerosis with double ring/halo sign. (B) MRI ‒ T2-weighted sequence of the same patient showing stenosis of the scala tympani in the basal turn. BT, Basal Turn; SV, Scala Vestibuli; PCSC, Posterior Semicircular Canal.

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Figure 15.

(A) MRI ‒ T2-weighted sequence A. Normal. (B) Advanced otosclerosis with showing stenosis of the scala tympani in the basal turn. BT, Basal Turn; SV, Scala Vestibuli; ST, Scala Tympani; PCSC, Posterior Semicircular Canal.

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Another image that should be observed is calcification of the round window, which is the preferred entry route for insertion of the CI electrode bundle (Fig. 16), especially in cases where there is the possibility of preserving hearing.101

Figure 16.

(A) Obliteration of the round window and part of basal turn.A ‒ Temporal bone high-resolution computed tomography; (B) MRI ‒ T2-weighted sequence.

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Therefore, mastoid CT and MRI complement each other in CI cases, and it is important to request both tests to improve diagnosis and assess possible difficulties during surgery.101

MRI is not indicated for the imaging diagnosis of otospongiosis, but it may demonstrate signal alteration (hyperintensity on T2-weighted images with gadolinium enhancement) in some cases, which denotes disease activity.

Stapes surgery for otosclerosis can result in vestibular symptoms in approximately 70% of patients during the first postoperative week. Late vertigo as a complication of stapes surgery is relatively rare (5%–8% of cases).108 Persistent vertigo associated with a poor audiologic outcome is one of the indications for revision stapes surgery for otosclerosis. The revision surgery rate ranges from 2.5% to 13.2%.109

Prostheses up to 0.4‒0.6 mm in diameter can be safely applied during stapedotomy at a depth of up to 0.5 mm within the vestibule. The safest location for stapes footplate fenestration during stapedotomy is the center of the footplate. The shortest distance from the center of the stapes footplate to the utricle and saccule is 1.2 and 1.4 mm, respectively. The shortest distance to the cochlear duct was observed at the inferior edge of the stapes footplate (0.2 mm). The cochlear duct is always located below the inferior edge of the stapes footplate. Therefore, the risk of persistent vestibular damage during a correctly performed stapedotomy in the center of the footplate is virtually nonexistent.110

Early vertigo is usually caused by damage to the inner ear during surgery. It is mainly caused by contact between the utricle (which is located very close to the oval window) and surgical instruments or the prosthesis or as a result of perilymph aspiration. In these cases, treatment includes bed rest and adequate pharmacotherapy.

Vertigo that persists for months after surgery may have been caused by an excessively long stapes prosthesis, which extends too far into the vestibule and compresses the utriculosaccular structure. Persistent vertigo may also be caused by a perilymphatic fistula in the oval window. Therefore, choosing the appropriate prosthesis length for insertion into the vestibule is extremely important.111

Persistent vertigo as an indication for revision surgery in otosclerosis accounts for 2.9% of cases. Incorrect prosthesis length in primary surgery affects 5.8% of all patients undergoing revision surgery. Persistent late vertigo may result from bone fragments left in the inner ear during primary surgery, directly compressing the saccule. Other causes of late vertigo include blood penetration into the labyrinth, acute postoperative labyrinthitis, incorrect prosthesis position, and adhesions and scarring around the prosthesis.112

In a study comparing the occurrence of vertigo after stapedectomy vs. stapedotomy, Sakamoto et al. showed that postoperative vertigo duration was 1.0 ± 2.0 days after stapedotomy and 3.3 ± 4.0 days after stapedectomy, with a significant difference between them (p = 0.003). Therefore, the duration of postoperative vertigo is shorter in patients undergoing stapedotomy.113

Two tests have been proposed for preoperative and postoperative vestibular assessment in stapedectomy/stapedotomy: video Head Impulse Test (vHIT) and Vestibular Evoked Myogenic Potentials (VEMP). These tests also aim to detect other disorders of the inner ear that may have repercussions on surgical indication, such as Ménière’s disease.

Catalano et al.114 published the preliminary findings of a study investigating the role of vHIT in the evaluation of otosclerosis. There was no difference between preoperative and postoperative vHIT gains. They suggested that semicircular canal function is not modified by otosclerosis itself and does not change after stapes surgery.

However, Satar et al.115 investigated the effects of otosclerosis and stapedotomy on vHIT and concluded that otosclerosis and stapedotomy may affect the functions of the semicircular canals evaluated by vHIT. The lowest gain was obtained from operated ears, followed by unoperated and control ears, respectively. In terms of incidence of covert saccade, operated and unoperated ears differed significantly from control ears for lateral and posterior semicircular canals. Therefore, the results are still conflicting regarding the role of vHIT in the evaluation of patients with otosclerosis.

In VEMP testing, airway stimulation allows evoking myogenic potentials to be recorded in the contracted neck muscles, called cervical VEMP (cVEMP), and in extraocular muscles, called ocular VEMP (oVEMP). The battery of tests has been recently expanded to assess dynamic otolith function. Manzari et al.116 proposed that cVEMP represents predominantly saccular function and oVEMP primarily reflects utricular function, although the relative contribution of utricular vs saccular afferents to VEMP is still hotly debated.117 Stimuli transmitted through the middle ear conduction system have failed to elicit cVEMPs in ears with conductive hearing loss, i.e., chronic otitis media or otosclerosis.118 To overcome the attenuation of stimulation caused by middle ear disease, bone conduction stimulation has been used to induce cVEMPs. However, the stimuli are not consistent, and the method limits their clinical use.119 In the early stage, localized fibrous fixation of the footplate may not hinder sound transmission. As the disease progresses to an advanced stage, either diffuse fixation of the footplate or ankylosis of the entire ligament can lead to an absence of cVEMPs even with the use of bone conduction stimulation.

Therefore, the use of electrophysiologic tests for preoperative and postoperative evaluation of patients who will undergo stapes surgery is still controversial.

Regarding prognostic evaluation, studies indicate that previous surgery in the contralateral ear is the main poor prognostic factor for persistent spontaneous nystagmus and prolonged vertigo after stapedotomy in the opposite ear.120

Otosclerosis surgery is commonly indicated in patients with other vestibular disorders, such as Ménière’s disease. According to the study by Shiosansi et al.,121 stapes surgery provides excellent outcomes for most patients with Ménière’s disease, even though fluctuating hearing and progressive cochlear degeneration may occur. Thus, concomitant Ménière’s disease would not be a contraindication. The study included 15 patients with a clinical diagnosis of Ménière’s disease, being only indicated after Ménière’s disease was considered clinically stable for at least 6 months without fluctuating hearing. However, as the sample was small, this indication should be done with caution.122

Likewise, according to Shiosansi et al.,90 the coexistence of otosclerosis with superior semicircular canal dehiscence syndrome would not be a contraindication to surgery. However, residual conductive hearing loss can be expected after surgical treatment, while the onset of new symptoms of the syndrome after otosclerosis surgery is rare.123

Therefore, concomitant vestibular disorders, such as Ménière’s disease and superior semicircular canal dehiscence, may not be a contraindication to surgery, but patients should be informed of the possible different audiologic outcomes in these scenarios.

Stapes fixation was first described as a cause of hearing loss by Antonio Maria Valsalva in 1704 after dissection of a deaf patient. In 1841, Toynbee dissected 1659 temporal bones and found stapes fixation in 39 of them, concluding that “osseous ankylosis of the stapes to the fenestra ovalis was one of the common causes of deafness”. However, chronic inflammatory processes in the middle ear were believed to be responsible for secondary ankylosis of the stapes. In 1893, Adam Politzer described the histologic findings of 16 cases of stapes fixation, which indicated that the deafness was due to a primary disorder of the labyrinthine capsule. He referred to this disease as otosclerosis.124

In 1842, Prospere Ménière reported the case of a patient who temporarily improved his own hearing by tapping the stapes directly with a small gold rod. Johannes Kessel was the first to describe stapes surgery in 1876. He believed that the hearing loss associated with otosclerosis was caused by increased pressure on the inner ear fluids. Based on experimental research in pigeons, he performed stapes mobilization and removal in humans. He would first separate the incus from the stapes and then attempt to mobilize the stapes by applying pressure to its head in various directions. When this was not successful, he would remove the stapes. Kessel reported some improvement in hearing and no serious complications. However, his findings differed from other physicians. In many cases, the hearing improvement only lasted for days or weeks and with the risk of labyrinthitis and meningitis.125 In 1899, Kessel was harshly criticized by some of the leading surgeons of the time, such as Politzer, Siebenmann, and Moure, at the 6th International Otology Congress in London. During this meeting, stapes surgery was declared “useless, often mutilating, and dangerous”. In 1900, Johannes Kessel was publicly censured for unscrupulousness.124

Because stapes surgery was considered too dangerous, surgeons started using “third-window” fenestration techniques. At the end of the 19th century, Passov and Floderus proposed the idea of a fenestration on the promontory or vestibular labyrinth, but it did not become fully established until 1913, when Jenkins described fenestration of the lateral semicircular canal. Several surgeons developed fenestration techniques – Holmgren, Sourdille, and Julius Lempert. Lempert’s contribution was to simplify the fenestration technique that was previously performed in three stages to only one stage. The single-stage endaural approach to fenestration was a significant improvement of Sordille’s three-stage approach.12,126 The hearing results were consistent: more than 50% of patients reported hearing gains of 20–25 dB. Lempert’s technique became the main technique for otosclerosis in the 1930s and 1940s.124,127

Samuel Rosen was the first to describe stapes mobilization in the mid-twentieth century. Rosen used Lempert’s technique; however, before performing the fenestration, he would check for the mobility of the stapes to ensure it was fixed. In 1952, almost by accident, Rosen developed the operation that would make him famous. During a routine procedure, Rosen accidentally mobilized the stapes while tapping on it to check for fixation. The patient, who was awake during the procedure, started noticing sound coming from the operating room next door.128 Rosen’s procedure was performed under local anesthesia via a transcanal approach. Patients had immediate results on the operating room table, and the recovery period was short. The surgery was relatively simple when compared with Lempert’s fenestration operation and was easy to teach. The shortcoming of the mobilization procedure was that many patients would refixate shortly after the operation. Rosen would often have to perform revision surgery. After more than half a century, stapes surgery was finally reestablished.127,129

John Shea, by reading the literature on stapes surgery from the end of the 19th century, realized the significance of the procedure described by Frederick Jack about a patient who maintained good hearing for 10 years after stapes surgery, and that it must be possible to remove and replace a stapes fixed by a prosthesis. In a female patient with otosclerosis, after removing the stapes and sealing the oval window with a subcutaneous tissue, Shea used a Teflon prosthesis to replace the stapes for the first time on May 1, 1956, with complete success.126 At the time of Shea’s discovery, complete stapes removal was still considered too dangerous and was forbidden. Within a decade, Shea’s stapedectomy procedure became the standard operation for the treatment of otosclerosis. In the 1960s, thousands of patients with impaired hearing due to otosclerosis were treated with great success. In 1960, Schuknecht developed a steel-wire prosthesis to address both the need to seal the vestibule and to reconstruct the ossicular chain.130 As the stapedectomy procedure evolved, several methods to remove just a part of the footplate emerged. The procedure was modified so that only a small fenestra was created.

Stapedotomy is currently the most accepted surgical treatment for fenestral otosclerosis with good cochlear reserve. Some surgeons prefer local anesthesia or local anesthesia with sedation to assess intraoperative auditory and vestibular response, whereas others prefer general anesthesia for the patient’s comfort. In 2008, Vital et al.146 compared the incidence of profound hearing loss among 160 patients undergoing stapedectomy under general anesthesia vs. 108 under local anesthesia and found a higher incidence of profound hearing loss in the general anesthesia group (1.8%) compared with the local anesthesia group (0%). A systematic review compared local vs general anesthesia in 417 procedures and found no statistical difference in postoperative ABG, worsening SNHL, or postoperative vertigo.147

Although any method of anesthesia may be equally acceptable in primary surgery, local anesthesia or local anesthesia with sedation has an advantage in revision surgery. If a patient experiences vertigo while the surgeon is manipulating or removing the previously placed prosthesis, this may indicate the presence of adhesions between the prosthesis and the saccule. Without patient feedback, the surgeon may continue to manipulate or remove the prosthesis, putting the patient’s hearing at risk.

An effective way of delivering topical anesthesia is using 1%–2% lidocaine hydrochloride with 1/100,000 adrenaline. Although lidocaine has a short half-life (between 1.5 and 2 h after intravenous bolus injection), it is indicated for typically being a quick procedure. The total dose administered in the various injection sites is approximately 10 mL and should not exceed 7 mg/kg.148 Infiltration starts in the retroauricular region to block branches of the cervical plexus (lesser occipital nerve and greater auricular nerve) and the vagus nerve (Cranial Nerve [CN] X) innervating the posterior surface of the outer ear and continues between the tragus and the helix. The needle must be advanced until contact with the bone to block the tympanic branch of the auriculotemporal nerve. Finally, the posterior part of the External Auditory Canal (EAC) is infiltrated to block branches of the facial nerve (VII CN) innervating the concha.

Total intravenous anesthesia reduced bleeding in studies with endoscopic surgery.149 Because total intravenous anesthesia causes less vasodilation than inhalational anesthesia, it reduces both mean arterial pressure and heart rate in patients, decreasing cardiac output and bleeding. Injectable local anesthetics are beneficial for achieving hemostasis during general anesthesia. Infiltration of 1 mL of 1% lidocaine with 1/100,000 adrenaline can be performed in the EAC laterally to the osteocartilaginous junction. As an adjuvant to obtain local vasoconstriction, cotton pledgets soaked in 1:1000 epinephrine can be used and positioned inside the EAC for approximately 5 min while the trichotomy is performed, if necessary.

The approach to stapes surgery has evolved over the years. Some surgeons prefer the classic transcanal approach, while others advocate using an endaural approach to increase exposure. More recently, endoscopic surgery has been used for stapedotomy. Those who advocate using endoscopes cite improved visualization, reduced need for scutum curettage, and decreased chorda tympani manipulation.150,151 Proponents of traditional endaural and transcanal approaches point to limitations of the endoscopic approach such as loss of depth perception, potential for thermal injury to the chorda tympani, difficulty using the microdrill, and having to place the prosthesis with one hand. Despite these concerns, audiologic outcomes are comparable according to recent reports.151

Analyzing the risks of thermal injury to middle ear structures, Dundar et al.152 measured changes in oval window temperature during endoscopic stapedotomy in a guinea pig model. The authors concluded that using a 4 mm endoscope with a xenon light source caused the highest temperature increase, whereas the lowest temperature increase occurred with a 3 mm endoscope with a LED light source.152

The classic technique involves removing the superstructure of the stapes, then performing the fenestration and placing the prosthesis. In 1994, Ugo Fisch proposed reversing these steps during stapedotomy, in an attempt to minimize the risk of floating footplate, inner ear injury, and ossicular chain dislocation.153,154 Instead of removing the superstructure of the stapes and then performing the fenestration, Fisch proposed first performing the fenestration and then replacing the prosthesis, still with both the incudostapedial joint and stapedius tendon intact. After the prosthesis is secured, the stapes and the lenticular process of the incus are separated, the stapes crura is fractured, the stapedius tendon is cut, and its superstructure is consequently removed. The inversion of surgical steps reduces the time of vestibule exposure, ensuring minimal blood entry into the vestibule and consequently reducing the need for manipulation and the chance of injury to the inner ear.153 An additional advantage of the so-called Fisch’s reversal steps stapedotomy is the increased stability of the ossicular chain, making it easier to place the piston in the long process of the incus.

According to Malafronte et al.,154 not all cases of otosclerosis benefit from the reversed technique. Fisch’s reversal steps stapedotomy is more indicated when the visible portion of the footplate is blue in all its points (known as “blue otosclerosis”), in which the footplate is strongly welded to the rim of the oval window, as the bone is healthy and elastic and quite resistant to trauma. In this case, Fisch’s original idea avoids incus and footplate complications. When the visible portion of the footplate, before removal of the stapes superstructure, is white in all or most of its points (“white otosclerosis”), Fisch’s reserved technique is not recommended because it does not prevent incus luxation/subluxation and floating footplate. In white otosclerosis, the footplate is well welded to the annular ligament by the otosclerotic focus that involves most of the footplate, which becomes white, fragile, and less resistant to trauma.153,154

While Shea originally removed the entire footplate, more limited removal is currently preferred by most surgeons performing stapedotomy.13 In some cases of fixation limited to the anterior footplate, the laser stapedotomy minus prosthesis technique is used. In this technique, the anterior crus is separated from the footplate using a laser, allowing complete mobility of the posterior footplate despite anterior fixation. Although in one study the laser technique resulted in improved high-frequency hearing compared with small fenestra stapedotomy, it was associated with a higher rate of revision surgery for refixation. Furthermore, this technique can only be used in selected cases of otosclerosis limited to the anterior footplate and favorable anatomy.155

The creation of a small fenestra is the most used approach. When comparing stapedectomy vs stapedotomy, Fisch156 concluded that stapedotomy is the procedure of choice because it achieves better hearing results and is less traumatic to the inner ear than stapedectomy. Despite the universal acceptance of stapedotomy, there are conflicting opinions on how to best create the fenestra and what size the fenestra should be. To create the fenestra, some surgeons advocate using a diamond microdrill, whereas others prefer using a laser due to the lack of mechanical trauma; some even prefer using a combination of both.

Different types of lasers have been used in stapes surgery, including argon, Erbium-doped Yttrium Aluminium Garnet (Er:YAG), potassium-titanyl-phosphate (KTP), 532 nm diode, and CO2 laser systems. Advocates of the CO2 laser highlight increased energy absorption by the perilymph, which reduces the penetration of energy into the vestibule. However, the CO2 laser beam is invisible to the human eye and originally required a micromanipulator. Advances in optical fiber technology have led to a fiber-optic delivery system with a separate beam for CO2 lasers. Despite the theoretical advantages of using the Er:YAG or CO2 laser, based on the maximum absorption of their beams by the perilymph, a recent study by Kamalski et al.157 showed no difference in hearing outcomes or complications when comparing KTP, Er-YAG, and CO2 lasers.

Reviewing optimal fenestra diameter, fenestra sealing technique, type of prosthesis used, and technique to determine appropriate prosthesis length, a temporal bone study conducted by Wegner et al.158 showed that the use of 0.6 mm- and 0.8 mm-diameter pistons resulted in better hearing results compared with smaller diameter pistons. The use of a 0.6 mm piston was predicted to cause an ABG of 8–12 dB, whereas the use of a 0.4 mm piston was predicted to cause an ABG of 15–20 dB. (egner, 2016, The Effect of Piston Diameter in Stapedotomy for Otosclerosis: A Temporal Bone Model) Sennaroglu et al. (Sennaroğlu, 2001, Effect of teflon piston diameter on hearing result after stapedotomy) reported that using a 0.8 mm prosthesis over a 0.6 mm prosthesis leads to better hearing outcomes. Despite these results, clinical studies by Fisch156 analyzing long-term hearing outcomes with 0.4 mm vs. 0.6 mm pistons showed similar results at long-term follow-up for both diameters. However, Fisch reported that using the 0.4 mm piston is relatively easier, particularly for the reversed stapedotomy technique used by him (the piston is placed after the fenestra is created, before the superstructure is removed).

After fenestration, the surgeon must decide whether to seal the fenestra or not. Some surgeons advocate sealing the fenestra with a connective tissue or venous graft before placing the prosthesis to prevent perilymph loss, whereas others prefer to place connective tissue around the prosthesis after it was placed in the fenestra. Some surgeons do not place any soft tissue around the fenestra and instead allow blood to pool around the prosthesis in the fenestra. Although, in theory, the surgeon should use a tissue seal to try to limit perilymph loss, there is no evidence corroborating an increased incidence of SNHL or perilymphatic fistula when a tissue seal is not used.

A plethora of stapes prostheses are currently available, with some requiring manual crimping, some that dent with heat activation, and others that require no friction. Regardless of prosthesis type, it is important that minimal pressure be exerted on the long process of the incus and that the connection to the incus is tight enough to prevent vibration. To date, no type of prosthesis has proven to be clearly superior to another, and the decision depends primarily on the surgeon.

In addition to the debate over optimal piston diameter, the method for measuring the prosthesis length may also vary. Some surgeons measure from the top of the long process of the incus and subtract 0.25 mm, whereas others measure from the undersurface of the incus and add 0.25 mm. Only a few surgeons do not measure the prosthesis and use a standard-length prosthesis for all procedures. Ideally, the selected prosthesis should extend into the vestibule by only 0.25 mm to 0.5 mm,159 which allows sufficient distance between the piston and the underlying saccule. If the surgeon does not measure the prosthesis, it may extend too deep into the vestibule and cause vertigo and hearing loss.

The microscope has been widely used in middle ear surgery over the decades. Binocular vision and the possibility of operating using both hands are very beneficial during surgery. However, depending on the region, the microscope has limited visualization, often requiring the performance of additional procedures to clear the surgical field, such as endaural incision and drilling of the auditory canal or the scutum, as well as frequently repositioning the surgeon and patient during the surgery.132,160

The main advantage of endoscopic surgery for otosclerosis is the wide angle of view of the surgical field, which, in addition to reducing the need for scutum removal, provides better exposure when teaching and training new surgeons.150,161,162 The wide-angle view provided by the endoscope allows a closer and more accurate visualization of the footplate while reducing the extent of bone removal from the scutum, in addition to reducing the need for manipulation of the chorda tympani nerve.160,163,164 Although these advantages have been described by almost all authors, a precise or minimally objective method for assessing improved visibility is currently lacking, meaning that one of the main advantages of endoscopic surgery is based on the individual experience of each surgeon.165 It should also be noted that the endoscope reduces depth perception by only allowing a two-dimensional view, in addition to requiring the use of only one hand to operate, which may hamper the management of the procedure and possible intraoperative complications.160,164,166 The association of these factors leads to a greater learning curve, which is why surgeons who commonly use the microscope prefer to continue using it.

Another issue related to endoscopic surgery is the diameter of the endoscope. Endoscopes were initially used in Otorhinolaryngology for nasal surgeries and thereby 4 mm nasal endoscopes were more common. They were only later introduced in the field of Otology, which led to the widespread use of 3 mm endoscopes. However, no study has been able to prove the superiority of narrower endoscopes, as both hearing outcomes and complication rates were similar in patients operated on with either diameter,167,168 despite reports of improved visibility with a smaller endoscope.

The introduction of the endoscope in the operating room did not change the surgical technique commonly used by surgeons, but rather provided an alternative access route. Therefore, it would be logical to assume that hearing outcomes remained similar to those of microscopic surgery. This assumption was confirmed by two recent systematic reviews that revealed a very similar ABG closure in all reported frequencies, with no statistically significant difference. According to Koukkoullis et al.,169 there would be a trend toward greater success in ABG closure with the endoscope if the study by Sproat et al.,170 one of the studies with the largest population and the only to use an instrument specifically designed for otologic procedures for data collection, had not been included in the systematic review.17 The length of experience of the surgeon should also be considered, as it may constitute an important bias. In accordance with these findings, Molinari et al.171 published a retrospective study in which the same surgical team was evaluated regarding to operating time for endoscopic surgery at two different time points, with a 3 year different between each assessment. The authors found that as the surgical team gained experience, the operating time for the same surgery decreased.

As for complications involving injury to the chorda tympani nerve and consequent dysgeusia as well as residual perforation, no study has found a significant difference between endoscopic and microscopic procedures.160,161,168,171,172 Some studies have even associated the use of the endoscope with a lower rate of chorda tympani nerve injury due to the reduced need for scutum removal to improve visualization.20,167 However, a direct relationship between the extent of necessary bone curettage and the occurrence of neural injury or dysgeusia in the immediate or late postoperative period cannot be established.171 Furthermore, a recent systematic review comparing microscopic and endoscopic stapes surgery found that these complications occurred more frequently in patients undergoing endoscopic surgery.169 As possible causes, the authors suggested the loss of three-dimensional (3D) view, which would facilitate the inadvertent use of sharp instruments, and the longer learning curve.

Postoperative dizziness is a very common symptom and varies greatly from patient to patient in terms of intensity and duration. Although expected and frequent, it causes significant discomfort and, when prolonged, substantially affects quality of life. Loss of 3D view and loss of depth perception have been suggested to cause increased dizziness in the postoperative period of endoscopic surgery due to inaccurate measurement of prosthesis length or window overheating due to direct incidence of endoscope light sources.150,160 However, published meta-analyses have not been able to prove this. On the contrary, they found that dizziness outcomes were similar in groups undergoing microscopic and endoscopic surgery, and that dizziness is more related to prosthesis length and trauma at the time of fenestration than to surgical approach.168,173,174

Finally, although some studies report the advantages of using one approach over the other, there is consensus that one cannot be actually considered superior to the other. Importantly, the choice of surgical approach should be based on the surgeon’s experience, training, and availability of adequate tools for the safe performance of stapedotomy or stapedectomy.

Fenestration techniques in stapedotomy have been modified over time with the use of microinstruments, microdrills, and eventually lasers. Conventional techniques using manual drills are widely used and surgeons are familiar with them. The footplate can be easily and safely drilled, especially if thin, by hand drills.

The basic principle of prostheses used in otosclerosis surgery is to achieve a secure connection between the long process of the incus, which has preserved mobility, and the perilymph in the oval window.225 More than 100 types of stapes prostheses have been developed since Shea and Treace first carved a stapes replica in Teflon.225

Evolutions in surgical technique over the years required prostheses to evolve as well. Initially, the prosthesis had a wider base for sealing the oval window after removal of the stapes footplate. This base was later narrowed into a piston-like shape, which was designed to seal only the fenestra over the stapes footplate, and could be used in combination with different grafts or not.225 Changes in surgical materials and the emergence of materials with greater biocompatibility were also important factors in the development of new stapes prostheses over the years, as these new materials allowed to reduce the force required to adequately place the prosthesis on the target site. Shape-memory prostheses have also been developed.225,226

Although the success rate of stapedectomy in 1960 was in the 90% range, some challenges persisted, such as necrosis of the long process of the incus (particularly with the polyethylene strut), postoperative dizziness, loosening of the wire loop, fistula, and granuloma formation with Gelfoam prostheses.225 Other issues related to patient rehabilitation such as previous erosion of the long process of the incus or absence of incus, where the stapes prosthesis should connect the fenestra to the malleus, prompted the development of alternatives to treat each case individually.225 There are several models currently available on the market, which vary in shape, weight, diameter size, site, anchorage, and material.

Just as there are variations in stapes surgery technique, there are also variations in postoperative management. Once considered an inpatient procedure, stapedotomy in the US has evolved into an outpatient, or a 23-h inpatient procedure. Outside the US, many centers believe that it is important to admit the patient after surgery. Although stapes surgery is considered a clean otologic surgery, a Cochrane report found no evidence to support the perioperative use of antibiotic therapy.237 Most centers continue to treat patients with antibiotic prophylaxis because the risks associated with postoperative infection include deafness and labyrinthitis.238 In addition, intraoperative and postoperative corticosteroids can be used to minimize the chance of serous labyrinthitis. However, clinical studies to support this are lacking.

Stapedotomy is usually a safe procedure, with good results, few complications, and a failure rate of approximately 6%.132 Surgical complications are uncommon, may occur intraoperatively or postoperatively, and can include the following (Table 7).

Surgical failure usually results from poor positioning or inadequate length of the prosthesis. Due to the progressive nature of the disease, 20% of patients will need revision surgery.239,240

Disease progression or cochlear involvement cannot be predicted. After stapedotomy, hearing loss can progress at variable and unpredictable rates.241 A study evaluating patients 30 years after stapedectomy found that 88% had bilateral otosclerosis and 66% had moderate to profound loss secondary to the progressive development of SNHL.242

According to Strömbäck et al.,243 90% of patients were satisfied with the hearing improvement 1 year after the surgery. However, the complications associated with stapedotomy, although uncommon due to advances in the technology of PSAPs, require that surgical indication and the chance of failure be thoroughly discussed with the patient during preoperative evaluation.

Some reasons for surgical failure may be observed or suspected during the diagnostic investigation, before the surgical procedure. History of progressive hearing loss since childhood may suggest malformations such as an enlarged vestibular aqueduct, whereas aural fullness and pressure-induced vertigo may be indicative of superior semicircular canal dehiscence.244

Revision surgery is indicated in up to 20% of cases of primary otosclerosis surgery when there is persistent or recurrent ABG ≥ 20 dB, intractable vertigo, or SNHL with suspected perilymphatic fistula or granulation tissue.247–250 Symptom onset may occur early, such as persistent hypoacusis, vertigo, or SNHL typically associated with intense tinnitus, or they may appear later in a sudden, fluctuating, or progressive manner, such as recurrent ABG. Except in cases of suspected perilymphatic fistula or granulation tissue, which according to some authors should be treated early,251 an observational period of 6 weeks252 to 3 months253 is recommended. Because the outcomes of revision surgery in the literature are inferior to those of primary surgery, its indication should be carefully evaluated.112,252

The success rate of ABG closure ≤10 dB is 35%–80%, whereas recent studies have reported lower rates of SNHL (>15 dB), ranging from 0% to 2.7%. Blijleven et al.248 and Schwam et al.240 found SNHL rates of 5% and 13.1%, respectively, but used a threshold increase of 10 dB instead of 15 dB as a criterion. In Sweden, Lundman et al.254 obtained inferior results compared with results from large centers, which the authors believe may be associated with the smaller number of procedures performed at their center. They suggested that patients should be referred to more experienced centers and that results from large centers should not be extrapolated to the local reality of small centers when advising patients. Jervis-Bardy et al.255 investigated 15 patients aged <20 years to evaluate revision surgery in the pediatric population. The results were similar to those obtained in the general population, with no cases of significant SNHL. Lippy et al.239 evaluated 120 patients aged ≥65 years and obtained results similar to those of a control group consisting of patients aged <65 years, also indicating that age is not an isolated factor for higher risks or contraindication to revision surgery.

Although commonly performed with the microscope, Fernandez et al.249 conducted an uncontrolled retrospective study of endoscopic revision surgery and found similar results. Iannella et al.256 evaluated a series of 6 patients undergoing malleostapedotomy as revision surgery with the use of an endoscope and found comparable results to studies using a microscope. Bernardeschi et al.247 found that rhinologic disease was significantly more frequent in patients undergoing revision stapes surgery compared with primary surgery, and this difference was not addressed by other authors. Recent publications mention the indication of revision surgery for persistent or recurrent persistent ABG ≥ 20 dB and intractable vertigo,112 but not for SNHL.7,8,112,252 However, only a few studies investigated intractable vertigo as an indication for revision surgery; those that did found complaints of vertigo in 2%–3% of cases, mostly due to the prosthesis being too long. Patients responded well to replacement with an appropriately sized prosthesis.239,248,252

Persistent ABG ≥ 20 dB may indicate incorrect technique in the primary surgery, lateral fixation of the malleus or incus to the attic, or the presence of a previously undetected third window, usually leading to worse results in revision surgery.112,252,253 Recurrent or increasing ABG may indicate erosion of the long process of the incus, prosthesis displacement, inadequately sized prosthesis, scar adhesions, ossification of the fenestra, or granuloma.247,251,253 In up to 82% of cases, there is necrosis of the long process of the incus and/or prosthesis displacement.253 Massimilla et al.257 investigated 21 patients with incus erosion who either received a new prosthesis placed proximally to the long process or underwent incus reconstruction with bone cement. ABG was reduced to ≤10 dB in 59% of cases and to ≤20 dB in 86.4% cases, with no cases of SNHL. In cases of erosion of the long process of the incus, incus reconstruction with bone cement, positioning a new prosthesis proximally to the long process when possible, or attaching the prosthesis directly to the malleus are good options for achieving satisfactory results with the different surgical techniques. Adhesions and granulation tissue should be removed, and an appropriately sized prosthesis should be used.252,253 Fat, vein, and blood grafts are used around the prosthesis to prevent the occurrence of fistula.257

In cases of significant erosion of the long process of the incus or incus/malleus fixation to the attic, the prosthesis may be attached from the malleus to the oval window (malleovestibular prosthesis). Gargula et al.258 used a nitinol prosthesis in 12 patients, of whom 10 were undergoing revision surgery. An ABG ≤ 10 dB was achieved in 75% of cases and an ABG ≤ 20 dB was achieved in 92%, with no cases of SNHL. Hudson et al. (Hudson, 2014, Revision stapedectomy with bone cement: are results comparable to those of standard techniques?) used hydroxyapatite bone cement to reconstruct the incus of 27 patients. ABGs of ≤10 dB and ≤20 dB were achieved in 77.8% and 96.3% of cases, respectively, with no cases of SNHL. The results were similar to those achieved with the malleovestibular prosthesis. The use of a laser to open the footplate and lyse adhesions and/or the use of a microdrill to open the footplate are recommended for reducing the risk of SNHL (Sakano, 2022, Revision Stapes Surgery; Hudson, 2014, Revision stapedectomy with bone cement: are results comparable to those of standard techniques?).

Granuloma may occur 7–15 days postoperatively after primary surgery, with SNHL and worsening imbalance occurring in 0.1% of stapedectomies and 0.07% of stapedotomies. There is no consensus on whether to perform revision surgery to remove the granuloma and replace the prosthesis, with concurrent antibiotic use, or whether to simply treat the patient with systemic corticosteroids instead of performing surgery.8,9 Granuloma has not been addressed by the most recent studies, except for the ones conducted by Schwam et al. (Schwam, 2021, Outcomes in Revision Stapes Surgery), who reviewed 170 revision surgeries and found granulomas in 2.4% of cases, and Ghazi et al. (Ghazi, 2021, Post-stapedotomy reparative granuloma following use of acellular porcine small intestinal submucosa),who reported granuloma formation with the use of a porcine acellular matrix. Care should be taken when choosing or using tissues around the prosthesis due to the risk of developing granuloma. (Sakano, 2022, Revision Stapes Surgery; Schwam, 2021, Outcomes in Revision Stapes Surgery) (Ramaswamy, 2018, Revision Surgery for Otosclerosis).

In revision surgery, the opening of the oval window, the position of the prosthesis in the oval window and on the incus, the size of the prosthesis, the mobility of the malleus and incus, and the presence of granulation tissue and adhesions should be routinely checked. (Ramaswamy, 2018, Revision Surgery for Otosclerosis) (Polony, 2022, Revision Stapedotomies: The Role of Periprosthetic Scar Tissue Formation in the Development of Unsatisfactory Hearing Results after Stapedotomy) (Wegner, 2018, An internally validated prognostic model for success in revision stapes surgery for otosclerosis).

Preoperative CT can help diagnose the cause of the alteration, although it should be noted that it can overestimate the penetration of the prosthesis into the vestibule. Bernardeschi et al.247 showed that CT has good sensitivity for detecting malleus fixation and prosthesis displacement, but low sensitivity for detecting changes in the incus.

Wegner et al. (Wegner, 2018, An internally validated prognostic model for success in revision stapes surgery for otosclerosis) analyzed 705 cases of otosclerosis through multivariate analysis and established an internal mathematical model to predict the chance of success in revision surgery. With 57.7% of cases with an ABG < 10 dB, they identified that the technique used in primary surgery (stapedotomy), the cause of failure (displaced prosthesis or ankylosis of the incudomalleolar joint), and the type of prosthesis used in revision surgery (incus-oval window) were predictive factors of success. Conversely, Bernardeschi et al.247 found no differences between patients undergoing stapedotomy or stapedectomy as primary surgery.

Key data from some of these studies are summarized in Table 8.

Hearing aids are a good alternative for patients who are not candidates, are unwilling, or have bone conduction thresholds that limit the hearing gain from stapes surgery. PSAPs allow good functional gain for most patients, mainly for those with normal bone conduction thresholds. However, they have limited indications for patients with outer ear disorders such as eczematous external otitis. Although technical evolution has mitigated the effects of occlusion and feedback, they can still make it difficult for patients to adapt to hearing aids. Hearing aids can be customized to amplify only the frequencies needed based on the patient's audiometry. As otosclerosis progresses, additional amplification adjustments may be required.

Although PSAPs are beneficial for patients with otosclerosis, maintaining (particularly batteries) and replacing devices that become obsolete over time leads to accumulating costs over the years. The cost of hearing aids varies greatly; they can be very expensive and are often not covered by health insurance. In addition, the disease can affect children, which significantly increases costs over time considering life expectancy, and patients should not engage in water activities while using the devices.

Cost-effectiveness models may be used to determine the lifetime costs and benefits of certain interventions and compare them against each other. They incorporate both initial costs and years, as well as health-related quality of life to determine the overall value of an intervention. Gillard et al.259 argue that, from the patient’s perspective, stapedectomy is a good, cost-effective strategy for the treatment of otosclerosis because it maximizes quality of life and minimizes costs. Probabilistic sensitivity analysis showed that stapedectomy was cost-effective compared with hearing AIDS 99.98% of the time, even when considering revision surgeries. Thus, stapedectomy is a great public health strategy.

Advances in the knowledge of metabolism in inflammatory bone diseases have overcome the well-established barriers of endocrine regulation between bone resorption/reposition and reached an understanding of a local system of regulation of osteoclasts/osteoblast activity mediated by well-described inflammatory cytokines for arthritis. There is evidence of an imbalance in this process in inflammatory bone diseases such as osteoporosis and arthritis, and by extension otosclerosis, which is studied according to new concepts in osteoimmunology.260

Modern concepts of the bone remodeling process established the crucial role of a balance between bone formation and resorption in this process, which result from a metabolic balance that is ultimately derived from the effector activity of osteoclasts and osteoblasts.260 The inflammatory process in otosclerosis promotes an imbalance in the affected ear and is linked to the production of cytokines that directly influence cell activity.261

Medications that target substances produced in the otosclerotic focus, which feed the inflammatory and bone remodeling processes, seem promising for future off-label use via intratympanic delivery in clinical research based on randomized and placebo-controlled clinical trials with a sufficient sample size to demonstrate or not the potential effects of this class of drugs, which directly interfere with the pathogenesis.

Brånemark first demonstrated in 1965 that titanium implants form strong bonds with bone tissue through a process he called “osseointegration”. In 1977, Tjellström inserted titanium implants in the mastoid process in three adult patients with conductive hearing loss and attached a vibrator to the percutaneous implant, being the first to use a hearing aid anchored in the temporal bone. Sound energy is transmitted by skull bone vibrations directly to the cochlea, bypassing the middle ear.281

Surgically implanted BAHDs can be divided into percutaneous and transcutaneous. Percutaneous: stimulus occurs via a skin-penetrating abutment coupled to a sound processor – Baha Connect (Cochlear BAS, Gothenburg, Sweden) and the Ponto system (Oticon Medical AB, Askim, Sweden). Transcutaneous BAHDs transmit sound through intact skin, but they can function either actively or passively. Active transcutaneous: an active implant is placed under the skin and muscles of the temporal bone and communicates with the external sound processor wirelessly via radiofrequency – Bonebridge (MED-EL, Innsbruck, Austria) and Osia2 (Cochlear BAS, Gothenburg, Sweden). Passive transcutaneous: a titanium plate is implanted in the temporal bone and a processor is coupled to a magnet that transmits sound through intact skin – Baha Attract (Cochlear BAS, Gothenburg, Sweden) and Sophono (Medtronic, Jacksonville, FL).282,283

Patients with disorders that lead to occlusion of the EAC, such as congenital malformations, acquired stenosis of the EAC, and benign tumors, particularly benefit from the use of BAHDs due to the relatively large ABG associated with normal cochlear function.284 Because BAHD functioning depends only on bone conduction, these devices have been indicated in some cases of otosclerosis. However, it is not the best option due to the risk of deterioration of the cochlear reserve over the years. Also, stapedotomy complication rates are low with experienced otologists.132

Another point to consider when indicating BAHDs is the maximum hearing gain they can offer, considering bone conduction, which varies according to the model, as shown in the box below. In asymmetric hearing loss, BAHDs should be placed only on the side with better bone conduction (Table 9).

AMEIs emerged in the 1990s as a treatment option for patients who could not use a PSAP.285,286 They provide functional gain with speech recognition improvement superior to that of PSAPs, with no occlusion effect or feedback for most of them. AMEIs are widely indicated for sensorineural, conductive, or mixed hearing loss. They can be used in middle or outer ear malformations and in advanced otosclerosis. These devices can be fully or partially implantable, depending on the location of the power source and microphone.

AMEIs amplify hearing by mechanically vibrating the ossicles to which they are surgically attached. These devices require movements of the ossicular chain, which are often limited in patients with otosclerosis. They may be indicated in combination with stapedotomy in moderate-to-severe mixed hearing loss or in patients previously subjected to stapes surgery who have developed SNHL287 and do not benefit from hearing aids. In advanced otosclerosis, there are 2 implants that have been mostly indicated over time – Vibrant Soundbridge (VSB; Med-El, Innsbruck, Austria) and Codacs (Cochlear Ltd., Sydney, Australia) (Table 10). The latter has been discontinued. Other implantable systems are not indicated in patients with otosclerosis.

SNHL in patients with otosclerosis occurs when ionic homeostasis of the cochlea is disrupted due to atrophy and hyalinization in the stria vascularis and spiral ligament. Consequently, dysfunction or loss of HCs and loss of spiral ganglion can occur.311

Approximately 10% of patients with otosclerosis and conductive hearing loss also develop SNHL.312 Advanced otosclerosis is characterized by SNHL and decreased speech discrimination (<30% at 70 dB),280 associated with radiologic abnormalities.313

The severity of SNHL in otosclerosis is correlated with radiologic abnormalities on HRCT, which can detect oval window abnormalities in 80%–90% of cases.97,314 On CT, the finding of pericochlear lucencies is highly specific for otosclerosis. It presents as a double halo.96,315 T1-weighted MRI images may show a ring of intermediate signal in the pericochlear area with mild-to-moderate gadolinium enhancement.316 T2-weighted sequences are the best method to assess the patency of the cochlear duct.97,317

There is a consensus in the literature regarding the indication of cochlear implantation as a safe and beneficial treatment in cases of advanced otosclerosis.314,318,319 Recent systematic reviews on advanced otosclerosis reported that patients undergoing CI surgery experienced no major surgical complications.318,320,321 Despite technological advances in cochlear implantation in recent decades, otosclerosis presents unique challenges.

Intraoperative difficulties include ossification, partial obliteration of the basal turn and round window, and false tract insertion of electrode array into the cochlea.322 In a case series of advanced otosclerosis treated with CI surgery, the round window membrane was ossified in 60% of cases and the scala tympani in 30% of cases.323 Recently, software programs have been developed by CI manufacturers with the purpose of conducting a detailed planning of the surgery, identifying the best electrode array system, and choosing the best electrode insertion method based on CT data.324,325

Regardless of complications with electrode insertion, otosclerosis is an etiologic factor negatively correlated with the speech performance scores of CI users.326 Remodeling of the otic capsule alters the properties of electric current conduction in the cochlea, which may impair CI use over time. Increased electrode impedance327 and facial nerve stimulation, causing paresthesia, muscle spasms, and pain,96,312,315,327 require changes in the device programming and stimulation strategies.97,317 In view of such findings, more frequent mapping adjustments are recommended to adjust and optimize the stimulation parameters.314,320,322,328

Studies indicate increases, although not significant, in the minimum and maximum electrical stimulation levels (T and C levels) in patients with advanced otosclerosis compared with other etiologies.320,328 The progression of otosclerotic foci often occurs in the basal and medial regions of the cochlea and, due to decreased impedance of the otic capsule and flow of the electric current through the bone, the electric current required to stimulate the fibers of the auditory nerve is increased. Mapping adjustments are essential to manage this situation. With the increase in stimulation levels, if the perceived intensity is not adequate, there is a need to increase pulse duration, which can potentially result in a decrease in stimulation frequency and compromise the proper functioning of the chosen processing strategy. In certain situations, there may be a need to switch off the electrodes to avoid the negative effects generated by the significant increase in stimulation levels.314,329,330

Facial nerve stimulation resulting from a shunt of current from the otic capsule that reaches the labyrinthine segment of the facial nerve96,319,329 has been described as one of the most common postoperative complications in patients with advanced otosclerosis, with an average incidence of 20% in this population, reaching up to 75%.96,320,331 Authors have suggested that the high incidence of facial nerve stimulation is associated with the type of electrode array used (straight or perimodiolar), with the straight or more distal array showing a higher incidence.96,314,328,331

Facial nerve stimulation can occur both at the time of electrode activation and during subsequent device monitoring visits.318 To eliminate or at least minimize its effects, mapping adjustments must be done, such as decreasing the electric charges by changing the stimulation mode ‒ by reducing the amplitude of the maximum current levels, keeping them below the stimulation threshold for the facial nerve, or even by adjusting the biphasic pulse width.330 More recently, triphasic pulse patterns have also been successfully used to alleviate the symptoms of facial nerve stimulation.327,329

Switching off the problematic electrodes has been another procedure frequently described in studies as an alternative method to manage facial nerve stimulation.321 There is no consensus on which electrodes (basal, medial, or apical turn electrodes) are the most affected in facial nerve stimulation.96,331 The fact is that, depending on the number of deactivated electrodes, speech perception can be significantly affected. In these cases, reoperation using another CI model with characteristics suitable for targeted electrical stimulation (related to the positions of intracochlear electrode contacts, electrode geometry, and stimulation parameters) as well as sequential cochlear implantation may be viable alternatives to be considered.320,330,331

Most studies point to promising auditory perception outcomes in patients with advanced otosclerosis. Numerous studies have not found significant differences in word and speech recognition performance scores between implanted patients with advanced otosclerosis and those with other etiologies.318,320,330 In fact, it is assumed that this disease has little effect on the spiral ganglions of the auditory nerve.324 However, although not significant, some authors have reported a trend toward poorer performance in the group with advanced otosclerosis. The poorer results obtained in patients with advanced otosclerosis were associated with factors such as long deafness periods, older age, extensive ossification, presence of facial nerve stimulation, and a greater number of deactivated electrodes.318,319,328