Otosclerosis is a disorder of the middle ear that causes progressive deafness.The condition usually develops in both ears.

Causes and incidence 

Otosclerosis occurs when overgrowth of bone immobilizes the stapes (the innermost one of the three tiny bones in the middle ear). As a result, sound vibrations are prevented from passing along the bone to the inner ear. Otosclerosis frequently runs in families, and symptoms usually start to appear in early adulthood. The condition affects more women than men, and often develops during pregnancy.

Symptoms and signs

To an affected person, sounds are muffled but can be distinguished more easily if there is background noise. Hearing loss progresses slowly over 10 to 15 years and is often accompanied by tinnitus (ringing in the ears) and, more rarely, vertigo (a spinning sensation). A degree of sensorineural deafness may develop, making high tones difficult to hear and causing the sufferer to speak loudly.

Diagnosis and treatment 

The condition is diagnosed by hearing tests. It can be cured by stapedectomy, a surgical procedure in which the stapes is replaced by a tiny piston, which moves through a hole created in the inner ear. Because the piston can move freely, it can transmit sound vibrations to the inner ear. Alternatively, a hearing aid can markedly improve hearing.

Picture of auditory ossicles 

Anatomy

Otosclerosis is a hereditary localized disease of the bone derived from the embryonic otic capsule in which lamellar bone is replaced by woven bone of greater thickness and vascularity. The position of the focus of new bone formation determines its effect on the function of the ear. When new bone develops around the footplate of the stapes it may fix the footplate to the margin of the fenestra vestibuli and prevent it from moving. This impedes the passage of vibrations of the tympanic membrane passing through the ossicular chain to the inner ear, producing a conductive hearing loss. Complete deafness does not result, because vibrations can still pass directly to the cochlea via the bones of the skull, albeit in a markedly less efficient manner.

Picture of ossicles showing abnormal bone growth of stapes

Stapedectomy

Stapedectomy is a surgical procedure designed to bypass the fixation of the stapes footplate caused by otosclerosis. The tympanic membrane is temporarily elevated for access to the middle ear and, under microscopic control, the incudostapedial joint is disarticulated using microinstruments. The limbs of the stapes and stapedius are then both divided, usually with microscissors or a laser, and the superstructure of the stapes removed.

A small hole (stapedotomy) is then made in the fixed footplate of the stapes using a microdrill, reamer or laser to expose the fluids of the inner ear. In some, the whole footplate becomes detached (stapedectomy). A small graft of connective tissue derived from local fascia or perichondrium is used to seal the hole with a flexible membrane. A small piston, usually made of Teflon or titanium incorporating a wire made of stainless steel, platinum or titanium, is crimped onto the long process of the incus and placed in the perforation in the stapes footplate. The tympanic membrane is then returned. The connection between the tympanic membrane and the inner ear is thus reconstituted and hearing restored. 

Otosclerosis in detail - technical

Otosclerosis (also known as otospongiosis) is a localized disease of the bone, derived from the otic capsule and characterized by alternating phases of bone resorption and formation.

The term “otosclerosis” was introduced by Politzer in 1894 and refers to the final stage of a disease where the bone has become sclerotic and hardened. The term “otospongiosis” is more accurate from a pathological point of view and pertains to the active and vascular stages of the disease. It was first adopted by Siebenman in 1912 and was widely used in Europe. By that time the term otosclerosis was extensively applied and accepted.

Epidemiology

The prevalence of the disease in a general Caucasian population is 0.3–0.4%. In 10% of those patients, the focus is localized near the oval window niche leading to a fixation of the stapes with a consecutive conductive or mixed hearing loss. The disease is bilateral in 70–80% and usually symmetrical in extension and distribution of the otosclerotic foci. Clinical otosclerosis should be distinguished from histological otosclerosis, where changes are present without clinical signs. Histological otosclerosis is present in about 10% of a Caucasian population. The prevalence is much lower in other races; it is encountered in only 1% of blacks. Several studies report a female to male ratio of about 2:1; however histological studies of temporal bones do not show any differences. The age of onset has risen in Caucasians in the last decades. Otosclerosis is the most predominant cause of hearing loss in Europe and the USA, whereas it appears to be uncommon in developing countries and among the Japanese population.

History

Otosclerosis was described for the first time by Antonio Maria Valsalva in 1735 as a disease of the human temporal bone. More than a century later, Toynbee recognized it as a cause of hearing loss. In the middle of the nineteenth century, Kessel treated a patient with otosclerosis who had fallen off a wagon and was then able to hear. During the autopsy after the patient’s death, Kessel discovered a fracture through the horizontal semicircular canal. Using a hammer and gauge, he later tried to reproduce this fracture in other patients. In 1876 he also removed stapes and covered an oval window with scar membrane. These early efforts to improve hearing in otosclerosis patients failed. In 1942 Meniere first reported stapes mobilization to improve hearing, and toward the end of the nineteenth century, stapes surgery in Europe was performed by Kessel, Boucheron, Miot, Moure, Passow, and Faraci. Early surgeons in the USA were Jack, Burnett, Alderton, and Blake.

Most of those previous attempts at stapes mobilization or stapedectomy were unsuccessful, and at the end of the nineteenth century, Siebenmann, together with Moure, “closed the door” on further stapes surgery. It was now considered to be useless and dangerous.

Holmgren from Stockholm, Sweden, created a fistula in the horizontal semicircular canal, covering it with mucoperiosteum in 1923, reporting his results in 1937. Nylen, his associate, developed a binocular microscope and was the first to use it for that operation. Sourdille, a French student of Holmgren, employed a three-stage operation. The first stage was mastoidectomy, the second was the creation of an external ear canal skin flap, and the third the creation of a fistula in the horizontal canal, covered with the canal skin. After having visited Sourdille and Holmgren, Julius Lempert cultivated his own one-stage fenestration operation and was able to achieve an improvement of hearing in most patients. He performed mastoidectomy through an endaural incision, created a fenestra over the ampullated end of the horizontal canal and covered it with the previously prepared skin flap from the posterior portion of the ear canal. He published his new procedure in 1938.

In 1953, Samuel Rosen from New York evolved a technique for mobilizing the stapes. The results were immediate and an air-bone gap could be closed completely, which never occurred in fenestration surgery. However, hearing would often regress later due to a refixation of the stapes.

John Shea Jr. performed the first successful stapedectomy in 1956. After removing the stapes, he covered the oval window with a vein and attached an artificial nylon stapes prosthesis from the incus to the oval window vein graft. Shea originally recommended covering the oval window with a vein graft; others have used fascia, perichondrium, and Gelfoam. The polyethylene strut introduced by Shea was abandoned after slippage into the vestibule or erosion of the incus occurred, and it was replaced in 1960 by a wire prosthesis introduced by Schuknecht and Oleksiuk. The first stapedotomies were performed in 1970. David Myers inserted a 0.2 mm piston, but surgeons turned to 0.4 or 0.6 mm pistons, which gave better results (House 1993).

In the 1980s, the era of lasers in stapes surgery began. For stapedotomy, argon (Gherini et al. 1993), KTP and CO2 were and still are widely used. Also, a new piston design was developed which enables easier crimping of the piston on the long process of the incus.

Clinical Features

Histopathologically, the otosclerotic process is characterized by an abnormal bone remodeling, involving the replacement of the otic capsule bone with a hypercellular woven bone, which may undergo further remodeling to finally reach a mosaic sclerotic appearance. The site of predilection is the fissula ante fenestram, which lies anterior to the stapes footplate. Otosclerotic foci may also appear in other sites, even in the region of the round window and cochlea (Linthicum 1993). If the otosclerotic process begins to develop anterior to the footplate, the footplate becomes displaced posteriorly, resulting in a low frequency conductive hearing loss. If the whole footplate is fixated, a conductive hearing loss takes place in all frequencies. Rarely, the otosclerotic process may overgrow the footplate and cause obliterative otosclerosis; this occurs in about 2% of the cases. Otosclerotic lesions may also involve the cochlear capsule and penetrate the cochlear endosteum with progressive sensorineural hearing loss (SNHL). It was found that the spiral ligament is hyalinized and the circulation of potassium ions within the cochlea is disturbed.

Picture of ear showing otosclerosis with abnormal bone growth affecting stapes

Portman (1979) divided otosclerotic fixations into five stages:

Type 1: The appearance of the stapes and annular ligament are strictly normal as seen through a microscope. The stapes is fixed because the annular ligament is slightly hardened or stiff anteriorly. In Type 1-A, the same occurs around the entire circumference, resulting in fixation.

Type 2: The stapes is fixed anteriorly by an otosclerotic focus in the footplate, involving no more than the anterior quarter of the oval window. In Type 2-A, the entire annular ligament is also stiff and the stapes is fixed around the entire circumference.

Type 3: The stapes is fixed because of the anterior focus that extends posteriorly, comprising half of the footplate and the oval window niche. In Type 3-A, the stapes is totally fixed around the annular ligament.

Type 4: The entire footplate is affected but the interface with the oval window niche is visible, even though the niche itself is caught up in the otosclerotic process.

Type 5: The disease is usually too far advanced and too active for normal stapes surgery. The focus around the oval window has completely obliterated the niche, which is only represented by a slight depression between the superior and inferior foci.

Tests

Weber and Rinne tuning fork tests are performed at 512 and 1,024 Hz and compared to the audiogram.

In stapedial reflex, the offset increment is found only in early stapes fixation. Some 40% of patients with normal ears may also show a brief compliance increase at the onset of the response. In the early stages of the disease, acoustic reflex abnormalities may be present only when the probe is placed in the affected ear.

Advancing stapedial fixation affects bilateral acoustic reflexes, even in unilateral involvement. The ipsilateral reflex with the probe and activator sound in the same ear is the first to show reductions in amplitude, followed by elevated thresholds. As the degree of hearing loss increases, contralateral reflexes become abnormal, yielding the “inverted–L pattern” in which only the ipsilateral reflex in the unaffected ear (in the case of unilateral disease) remains observable. The probability of observing a contralateral reflex is reduced up to 50% with an air-bone gap averaging 27 dB between 500 and 4,000 Hz; when reflexes are measured ipsilaterally, acoustic reflex abnormalities may be present when the air-bone gap is only 10 dB.

A tympanogram in early- and mid-stage otosclerosis shows the presence of a normal, type A tympanogram. A type As tympanogram, in the presence of a normal appearing tympanic membrane, should raise suspicion of a fixation at the malleus rather than a stapes. As the disease progresses and the otosclerotic focus involves more extensive areas of the stapes footplate, the height of the tympanic peak decreases.

Acoustic immittance studies provide no frequencyspecific information about the hearing status, and they do not specify the severity of the impairment. A pure tone audiogram is always a part of the audiologic assessment procedure. Early in the development of otosclerosis, patients may have a low-frequency conductive loss that narrows in high frequencies. This is due to the posterior displacement of the footplate as the result of an anterior otosclerotic lesion. The jammed footplate first maintains the capacity for transmission in the higher frequencies. Patients may be unaware at first of the low-frequency conductive hearing loss until it exceeds 25 dB, but may complain that speech sounds “hollow.” The loss may be limited to frequencies below 1,000 Hz. This characteristic rising audiogram configuration has been referred to as a “stiffness tilt.” When the footplate becomes completely fixed, a mass effect is added to the audiogram. This results in a stabilization of low-frequency thresholds with a progression of loss in high frequencies and a gradual widening of the air-bone gap. The audiogram configuration changes from upward sloping to flat. In the absence of cochlear involvement, the pure conductive hearing loss produced by complete stapes fixation is limited between 60 and 65 dB with a maximum airbone gap across the frequency range.

Another typical finding in otosclerosis is the Carhart’s notch, which means a depression in bone conduction at 2,000 Hz. This is thought to be an audiologic artifact, possibly from the effect of stapes fixation upon middle ear resonance. A successful operation may eliminate a Carhart’s notch.

With the development of cochlear otosclerosis, air conduction thresholds continue to worsen and the loss becomes mixed or sensorineural in cases of pure cochlear otosclerosis. High frequencies are more severely affected. Tinnitus is present in a large percentage of patients. It may interfere with their ability to respond reliably to pure tone testing in frequency ranges that correspond to those of the tinnitus. The use of pulsed or warbled tones may help the patient to separate tinnitus from test stimuli in these cases. Also a meticulous masking technique is necessary to avoid errors in overestimating and underestimating cochlear reserve during surgical planning.

Patients with a conductive hearing loss may describe improved speech understanding in noisy situations, unlike those with a sensorineural hearing loss, who understand worse in noisy environments. This paradox is known as paracusis of Willis. Faced with speaking in a noisy environment, most speakers raise the level of their voices to be heard above the din by themselves and others. The listener’s conductive hearing loss attenuates the background noise, leaving the speaker’s voice more audible through an apparent improvement in the signal-to-noise ratio.

High-frequency sensitivity critically influences word identification scores; in a mixed or primarily sensorineural hearing loss resulting from cochlear otosclerosis, reductions in word identification are related to the degree of sensorineural involvement. Poor preoperative word identification scores contribute to a poor prognosis for hearing improvement following surgery (Hannley 1993).

As otoacoustic emissions are generated in the cochlea and must propagate out through the middle ear to be recorded by a probe, it is predictable that they would be reduced in cases of abnormal middle ear function. DPOAEs are not measurable preoperatively, and even postoperatively they register no significant increase. It remains unclear why DPOAEs are not detected, despite a subjective hearing improvement and a sufficiently closed air-bone gap, at least in middle and low frequencies. The results of our study show that DPOAEs cannot replace behavioral threshold tests; they may only be included in a battery of tests for a complete clinical follow-up to efficiently monitor postsurgical stapes (Filipo et al. 2007).

Symptoms of dizziness and imbalance are reported less frequently by patients with otosclerosis. Almost 60% of these patients showed abnormal responses to bithermal caloric stimulation.

In addition to audiologic tests, a CT evaluation can be performed to assess middle and inner ear structures. Congenital ossicular deformity can be excluded and a retrofenestral disease should not be overlooked. Obliterative otosclerosis can be diagnosed, and also obliterative round window involvement can be distinguished on the CT scan. In the inner ear membranous labyrinthine, ossification in the basilar cochlear turn may occur, which is an important finding if a cochlear implantation is contemplated. The facial nerve should be evaluated for dehiscence or protrusion in the tympanic segment as this may disturb surgery in the oval window area.

A wide cochlear aqueduct was believed to play a role in the incidence of the perilymphatic (stapes) gusher, but this concept has fallen into disrepute in recent years. Deformity of the internal auditory canal fundus is much more commonly associated with this aberration.

Otosclerotic fenestral foci are usually best diagnosed on axial CT sections owing to the anteroposterior orientation of the ovalwindowand stapes crura. These foci are of variable size and density and are most often seen in the anterior oval window region. CT findings compatible with fenestral otosclerosis have a limited differential diagnosis. Tympanosclerotic foci within the oval window niche are much more irregular, although smooth thickening of the stapes footplate/annular ligament complex may also occur and be indistinguishable from otosclerosis. Patients with tympanosclerosis almost invariably have an obvious middle ear disease that includes an underpneumatized mastoid, making the differentiation from otosclerosis relatively easy (Swartz and Mukerji 2008).

Differential Diagnosis

The correct diagnosis of otosclerosis is based upon the histologic analysis of the ankylotic stapes footplates removed during stapedectomy. Otosclerosis is characterized by a gradually progressive conductive or mixed hearing loss. Both ears are affected in about 70% of the cases. A progressive SNHL may occur as a result of cochlear otosclerosis. Otoscopic examination reveals normal appearing tympanic membranes. Diseases like tympanosclerosis that can give rise to ossicular chain fixation should be ruled out. Also, the retraction pocket should be excluded as a cause of conductive hearing loss. Circa 10–20% of the patients may complain about dizziness and vertigo. In rare cases, otosclerosis may also involve the endolymphatic sac causing symptoms like those of Meniere’s disease.

Etiology

Despite intensive research, the origin of otosclerosis still remains unclear. Otosclerosis is an active bone process that occurs within the endochondral layer of the temporal bone that, under normal conditions of development, undergoes virtually no remodeling. In that aspect, the otic capsule is unique and different from all other bones in the body. The inner ear may play a direct role in the inhibition of otic capsule remodeling by producing substances that diffuse into the surrounding bone and prevent remodeling. The spiral ligament produces a compound called osteoprotegerin (OPG), which is secreted to the perilymph and diffuses into the surrounding otic capsule bone. OPG inhibits the recruitment, formation, and activity of osteoclasts, which resorb bone (Stankovic and Mc Kenna 2006).

It is considered an inflammatory disease of the human otic capsule caused by persistent measles virus infection. Genetic factors must also play a significant role in the etiopathogenesis of otosclerosis. The majority of epidemiological studies of families with stapes fixation has shown an autosomal dominant mode of inheritance with incomplete penetrance of approximately 40–45%. Genetic linkage studies have demonstrated the presence of eight loci (OTSC1, OTSC2, OTSC3, OTSC4, OTSC5, OTSC6, OTSC7, OTSC8) which are located on chromosomes 15q, 7q, 6p, 16q, 3q, 6q, and 9q. Until now, no causative genes and proteins have been identified (Ealy and Smith 2010).

Speculations in the literature point to stresses and strains in the temporal bone, consequences of an upright posture, as the cause of otosclerosis. Estrogens are also well-known stimulators of osteocytic activity and may play a role during the ossification of otosclerotic foci. The hypothesis that otosclerosis is a generalized disease brought about by abnormal parathyroid function could not be proved.

The first explanation of a sensorineural hearing loss in otosclerosis came from Politzer, who proposed that the sensorineural hearing loss would derive from a bony invasion of the scala tympani of the cochlea. The second theory suggested circulatory changes in the cochlea as the outcome of abnormal bony foci. The third theory held toxic metabolites released from the otosclerotic focus responsible for cochlear damage (Menger and Tange 2003). Histologic characteristics describe multinucleated osteoclasts, osteocyte-like cells, and proliferating endothelial cells in the pseudovascular spaces of an active otosclerosis. In the peripheral zone of active foci, CD8 positive, cytotoxic T lymphocytes and activated osteoclasts are found. In early stages of otosclerosis, cytotoxic enzymes (elastase, collagenase, cathepsin – D/B), inflammatory cytokine mediators (TNF-alfa, interlekin-1, interleukin-6), and complement fragments are suspected to release from the foci. These molecules could flow into the perilymph and interfere with the electromotility of outer hair cells, resulting in a sensorineural hearing loss (Sziklai et al. 2009).

Measles infection may also contribute to the development of otosclerosis. Researchers have found viral-like particles within osteoblasts in active otosclerotic lesions, measles antigens and measles virus products within active lesions. Otosclerosis appears only in humans and the measles virus also attacks only humans and closely related primates. Vaccination against measles should contribute to a decline in the incidence of otosclerosis as well.

Treatment

Surgery: Stapedectomy and stapedotomy

The first stapedectomy was performed in 1956 by John J. Shea, who removed a whole stapes and replaced it with an artificial prosthesis. A defect in the oval window was covered with a vein graft. This technique showed better results when compared with mobilization techniques and soon began to be widely used. Later, a stapedotomy technique was developed where a small fenestra was created in the footplate. Now broadly employed, the small fenestra technique provides a good closure of the air-bone gap with minimal risk of perilymphatic fistula or inner ear trauma and the resultant dizziness and hearing loss. Both techniques had very good hearing results; stapedotomy should have better results at 4,000 Hz (Fisch 1982).

Surgery is considered for patients with a conductive hearing loss of at least 15 dB in frequencies of 250– 1,000 Hz or higher. Also a Rinne test should be negative with 512 Hz fork. The presence of a sensorineural hearing loss is not a contraindication for surgery. It should be explained to the patient that a hearing aid may still be needed after surgery, but ear performance with amplification would be improved. If both sides are affected by otosclerosis, the poorer hearing ear should be operated on first. After a successful operation on the first ear, an operation on the other may follow after a period of about 1 year.

An operation should not be performed in an inflamed ear, whether in the middle ear or the external ear canal. Surgery is also contraindicated for patients with tympanic membrane perforation, as well as for those with Meniere’s disease, and it is questionable for patients with a contralateral ear problem which may decrease hearing over time.

A stapes operation in an only hearing ear is indicated just for those patients with a profound mixed hearing loss who cannot be helped by a conventional hearing aid. If the operation is not successful, the patient is a candidate for a cochlear implantation.

Before surgery, patients should be told about the risks of the operation, which include failure to improve hearing with residual conductive hearing loss, the possibility of a sensorineural hearing loss, deafness, vestibular dysfunction, perforation of the tympanic membrane, and disturbance in taste. As it occurs in most cases, it should be explained before surgery that there will be some disturbance in taste because of manipulations of the chorda tympani. It should also be explained to the patient that the possibility exists for hearing aid amplification, but that the quality of sound is usually not comparable to natural hearing.

Primary stapedectomy can be performed with either local or general anesthesia. General anesthesia provides control of head motion and prevention of pain. The results do not differ whether the patient was operated on under local or general anesthesia. The external ear canal is also injected in four quadrants with 1% xylocaine with 1: 100,000 epinephrine (Mc Kenna and de Venecia 2006).

A posterior tympanomeatal flap is raised and the bone is curetted from the posterosuperior portion of the tympanic annulus until the pyramidal process and tympanic segment of the facial nerve are easily visualized. The chorda tympani nerve should be preserved. The ossicular chain is palpated and the mobility of the ossicles is established.

The incudostapedial joint is separated and the stapedial tendon is sectioned.

The principle of stapedotomy is to form a calibrated hole in the footplate. This can be done with a microdrill, amicrohook, and a laser. Before stapedotomy, stapedial crura are separated and the stapes suprastructure removed.

Arguments favoring stapedotomy over stapedectomy are (Tos 2000a; Fisch 1982):

1. In stapedotomy only a limited part of the vestibule is exposed to possible trauma.
2. In stapedotomy the annular ligament is not disrupted.
3. After opening the footplate, a small air-liquid interface is created, and the concavity of the perilymph offers a barrier to penetration by foreign particles, such as pieces of footplate, mucoperiosteum, or bone dust. In stapedectomy, the concavity is larger and the small pieces will lie deeper toward the utricle.
4. Small microhooks cannot reach the utricle in stapedotomy.
5. The risk of elevation of the endosteum of the vestibule during removal of the entire footplate is eliminated in stapedotomy.
6. In large fenestra stapedectomy, there is an unavoidable risk of damage to the utricle when superior fibrous adhesions are present in the vestibule.
7. In large fenestra stapedectomy, there is a risk of migration of the wire prosthesis toward the border of the oval window, in contrast to stapedotomy where this cannot occur.
8. In large fenestra stapedectomy, lateral displacement of the oval windowmembrane may occur because of scala retraction, increased perilymphatic pressure, or by strong movements of the incus. In stapedotomy, the piston can be pulled out from the stapedotomy opening without damage to the inner ear.
9. The defect in the epithelial lining in stapedotomy is closed by an ingrowth from its edges underneath the tip of the piston. Mucosa covers the hole on the middle ear side in a similar way.

The advantages of performing a stapedotomy with a laser (argon, KTP, CO2) (Pictures 1, 2, 3 and 4) are: the hemostatic properties of the laser, “no touch” surgery that reduces the chance of a floating footplate, the ability to create a precise fenestra without entering the inner ear, thus minimizing the risk of acoustic trauma, and the possibility to fenestrate a floating footplate without the risk of depressing it into the vestibule. In cases of obliterative otosclerosis, where the oval window is filled with massive otosclerotic foci, a stapedotomy should be performed with a drill (Gherini et al. 1993).

Before stapedotomy, the length of the prosthesis is determined and the piston is trimmed to the right dimension. A large number of pistons are commercially available on the market. They are made from stainless steel, fluoroplastics, a combination of wire and fluoroplastic and titanium. The piston design has improved over the years. Soft-clip pistons enable easier fixation of the piston on the long process of the incus (Bast and Schrom 2009). Stapedotomy can also be performed before removing the stapes superstructure. After the piston is crimped on the incus, the stapes suprastructure is removed. Such an operation was introduced by Fisch. In the event of a narrow oval niche, the stapes suprastructure has to be removed first. The piston can be introduced safely 0.5 mm into the vestibule.

Some authors have also described a technique to preserve portions of the stapes and the stapes tendon during stapedotomy surgery. Although some findings indicate better hearing in noise and less intolerance to noise, there was no statistical significance between the groups with and without stapedius tendon preservation (Arnold et al. 2007).

Complications

Complications and failures in stapedectomy or stapedotomy can happen during an operation, immediately after the operation, in the intermediate period, and in the late period.

During the operation, an eardrum perforation may occur while the tympanic membrane is elevated, especially in atrophic eardrums. This complication happens in 2–5% of stapedectomies. The defect should be closed immediately by the adaptation of the perforation edges or by placing a fascia graft.

Facial nerve palsy is quite rare, varying between 0.2% and 0.05%, and it occurs most probably in dehiscent facial nerves. A temporary facial palsy appears more often and can be ascribed to local anesthesia.

The chorda tympani nerve should be preserved whenever possible, but sometimes the chordal eminence is very prominent and hampers visibility of the footplate. If the chorda is stretched, the patient feels a metallic taste. Usually the damage presents itself at the entrance into the bony canal.

Incus bone luxation and subluxation can occur while removing the bony annulus with a curette, in cases of partial or complete ossification of the incudostapedial joint, after removal of the stapedial crura and when fixing the prosthesis to the long process of the incus.

A floating footplate is a serious complication and energetic attempts to remove it may result in a sensorineural hearing loss. The stapes footplate becomes totally mobile and it can submerge into the vestibule. The best solution is to make a fenestra with the laser; the footplate can be removed by drilling a groove at the inferior border of the vestibule and placing a hook under the floating footplate. Removal of the submerged footplate could also be attempted by introducing a blood coagulum and aspirating the blood clot together with the submerged footplate.

An immediate postoperative sensorineural hearing loss can occur from a hydraulic effect following the removal of the mobilized footplate, rapid loss of perilymph, acoustic trauma from instrumentation, and the presence of blood in the inner ear vestibule with a consequent ionic disturbance. Treatment with hydrocortisone and sodium fluoride is recommended (Tos 2000b).

Reparative granuloma can be found around the prosthesis and in the oval niche. It is also possible for the granulation tissue to invade the inner ear. Reaction to a foreign body can trigger fibrous tissue growth. Symptoms of reparative granuloma include hearing loss, distortion of sounds, tinnitus, and vertigo a few days to 2 weeks after the operation. The granuloma should be removed from the oval window, a different graft material applied, and also a different prosthesis from that of the initial operation.

A perilymphatic fistula means the leakage of perilymph from the vestibule into the middle ear. It causes a fluctuating hearing loss and a disturbance in the labyrinth function. In an audiogram, the patient will have a sensorineural hearing loss, especially at low frequencies. This is much less common in stapedotomy than in stapedectomy, even without the sealing of the fenestra. A fistula test with the pneumatic otoscope is positive in two thirds of the cases, and a fistula test with electronystagmography and an impedance bridge are the procedures of choice. Tympanotomy, with sealing of the fistula, should be done if a perilymphatic fistula is suspected.

Conductive hearing loss after stapedectomy is caused by displacement of the prosthesis, an excessively short or long prosthesis, resorption of the incus, and adhesions around the prosthesis (Tos 2000c).

Sodium fluoride

Some 50 years ago, it was suggested that sodium fluoride might have a beneficial effect on the progression of otosclerosis. It reduces enzyme levels in the perilymph of patients with otosclerosis and inhibits trypsin. It could also increase mineralization and stabilization of otospongiotic lesions and halt the otosclerotic process. Some authors suggested that sodium fluoride treatment would be more effective if the initial sensorineural hearing loss was less than 50 dB. Others proposed preventive treatment once families at risk were detected. Sodium fluoride was also administered to otosclerotic patients with vestibular symptoms, effecting complete or partial relief from those symptoms.

Only one double-blind, placebo-controlled trial of sodium fluoride use in otosclerotic patients has been made, and this showed a reduced incidence of deterioration in hearing after 2 years in the treatment group. The wide diversity in treatment doses offers no evidence regarding the optimum duration of treatment.

Doses of sodium fluoride vary from 1.5 to 20 mg; patients in some countries may imbibe fluoride in drinking water in doses of 1 mg/l. Larger doses of sodium fluoride (25–60 mg) may slow resorption and occasionally cause gastrointestinal upset, sore tongue, hypersalivation, vomiting, diarrhea, and abdominal pain. It may even cause atrophic gastritis.

No trial has set out to determine how long treatment with sodium fluoride should continue (Cruise et al. 2010).

References

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