otosclerosis

source: dept. of otolaryngology, utmb, grand rounds
date: may 22, 1996
resident physician: gregory young, m.d.
faculty: jeffrey vrabec, m.d.

i, brian taylor, have had 5 right ear surgeries, 4 of them stapedectomies - all of which have failed. i have been functionally deaf in my right ear for years, and wear an oticon digital hearing aid in my left ear - without it, my hearing is worthless. i have otosclerosis and tinnitus (ear ringing) in both ears, but the ear ringing in my operated ear is 10 times louder, and never stops.

series editor: francis b. quinn, jr., m.d. "this material was prepared by resident physicians in partial fulfillment of educational requirements established for the postgraduate training program of the utmb department of otolaryngology/head and neck surgery and was not intended for clinical use in its present form. it was prepared for the purpose of stimulating group discussion in a conference setting. no warranties, either express or implied, are made with respect to its accuracy, completeness, or timeliness. the material does not necessarily reflect the current or past opinions of members of the utmb faculty and should not be used for purposes of diagnosis or treatment without consulting appropriate literature sources and informed professional opinion."

introduction

otosclerosis is a primary disease of the ossicles and otic capsule, in which endochondral bone is replaced with periosteal bone over a period of several years. this process results in a more porous and less dense bone, which has led many to prefer the term "otospongiosis". the most common site involved, or "site of predilection" is just anterior to the oval window niche. a focus of disease in this area may result in a conductive hearing loss due to stapes fixation. a sensorineural component of hearing loss is not uncommon, and is thought to be due to ototoxic enzymes released into the cochlea. the disease is usually subclinical, with only 10% of patients with microscopic evidence of the disease ever developing symptoms.¹ the inherence pattern is autosomal dominant, with variable penetrance.

historical aspects

1735 -valsalva- found a stapes fixed to an oval window niche during autopsy of a deaf patient
1857 - toynbee- stated after 1659 ear dissections that "osseous ankylosis of the stapes to the fenestra ovalis was one of the common causes of deafness."
1873 - schwartze- described the reddish discoloration of the tympanic membrane, later found to be increased vascularity of the cochlear promontary during the active stage of otosclerosis. this later became known as schwartze's sign, and occurs in 10% of otosclerosis ears.
1881 - von troltsch- used the term "sclerosis" for stapes fixation. he thought that sclerosis of the tympanic cavity mucosa caused stapes fixation.
1890 - katz- first to find microscopic evidence of otosclerosis resulting in stapes fixation
1893 - politzer- studied the temporal bones of 16 patients whom he had followed while alive with stapes fixation, and determined that stapes fixation was a primary disease of the otic capsule, rather than a result of repeated inflammation or infection.
1908 - bezold - described the typical history and physical findings, as well as audiometric findings of otosclerosis.
1912 - siebenmann- found that the diseased bone of otosclerosis is more porous and less dense than the normal otic capsule, and suggested that the disease be more accurately termed "otospongiosis." he also postulated that this disease may cause sensorineural hearing loss.

epidemiology

inheritance:

the inheritance of otosclerosis is usually described as autosomal dominant with incomplete penetrance of around 40%. however, other types of inheritance have been described for the disease, including monohybrid autosomal inheritance with 25-45% penetrance, polygenic multifactorial inheritance, and autosomal dominant with incomplete penetrance and variable expressivity.^2,3 these studies of inheritance of otosclerosis were conducted on hundreds and in some cases thousands of patients with clinical otosclerosis. the limitation of all inheritance studies to date is that they are calculated based on clinical otosclerosis. only about 10% of otosclerosis becomes clinically apparent, so 90% of all otosclerosis remains unaccounted for in these studies. the true inheritance pattern may not be known until epidemiological studies incorporate microscopic evaluation, so that subclinical cases of otosclerosis are included in the data.²

family incidence:

around half of patients with clinical otosclerosis report a family member with the disease. failure of penetrance of other family members and new mutations account for the majority of patients without a known family history.

race:

several studies have shown that otosclerosis is most common in caucasians, about half as common in the oriental population, and very rare among blacks and american indians. multiracial populations that include caucasians have an increased incidence of otosclerosis.

race	percent with microscopic evidence of otosclerosis
caucasian	10%
oriental/south american	5%
black	1%
american indian	0%

only 10% of those with microscopic disease ever develop clinical disease.²

gender:

otosclerosis is often reported as twice as common in females as males. however, more recent estimates have been closer to a 1:1 ratio. the disease is most likely inherited without sex-linked influences, so a 1:1 ratio would be expected. there is some evidence that hormonal changes of pregnancy may stimulate the active phase of the disease, resulting in an increase in clinically apparent otosclerosis among females. clinical onset during pregnancy has been reported to be between 10% and 17%. shambough estimated the risk of increased hearing loss from a pregnancy or oral contraceptives in a woman with otosclerosis to be 25%. another possible explanation for the reported increased prevalence in females is that bilateral otosclerosis seems to be more common in females than males (89% and 65%, respectively). having both ears affected will likely prompt a clinic visit.²

age:

the incidence of clinical otosclerosis increases with age. microscopic evidence of otospongiosis are found in 0.6% of autopsies of individuals less than 5 years old. by late middle age, the incidence of microscopic disease is 10% in white men and nearly 20% in white women. both active and inactive disease occurs at all ages, but higher activity is more prevalent to those less than 50 years old, and very low activity is common after 70 years of age. clinical onset is usually between 15 and 35 years of age, but the disease may manifest itself as early as age 6 or 7, and as late as the mid 50's.2

pathology

gross pathology:

gross examination of the immature, active focus of otosclerosis shows a region of bone covered by thickened vascular mucosa. when viewed through a translucent tympanic membrane, a pinkish hue is sometimes seen on the promontary ("schwartze's sign").¹

a mature disease focus is white, in contrast to the slightly yellow appearance of the normal otic capsule. there may also be distortion of the normal anatomy of the oval window niche. the size of the focus varies from a few millimeters to a large area involving most or all of the promontory, and sometimes even the round window niche.¹

the usual site of onset, or site of predilection is just anterior to the oval window niche. the area is known as the fissula ante fenestrum. a focus of disease occurs here in 80-90% of temporal bones with microscopic evidence of otosclerosis. the next most commonly involved region is the border of the round window niche, where a focus is found in 30-50% of diseased ears. although involvement near the round window is common, complete obliteration of the niche is quite rare(1-3%). in order of decreasing frequency, foci are also found in the apical medial wall of the cochlea, posterior to the oval window, the posterior internal auditory canal, the primary footplate, and the semicircular canals. involvement of the incus and malleus is rare. half of diseased ears contain more than one focus, which may occur in various stages of activity.²

microscopic pathology:

microscopic examination of the immature, active focus of otosclerosis reveals a porous spongy structure of irregular bony lamellae separated by wide vascular spaces containing an abundance of histiocytes, osteoblasts, and some osteoclasts. conspiciously missing are the islands of calcified cartilage characteristic of endochondral bone.²

the mature disease focus is relatively acellular, with narrower vascular spaces and smaller blood vessels. various levels of activity may be seen among foci in the same ear. however, there tends to be a prevailing level of disease activity within a given individual.

the borders of the focus are irregular and tend to project into normal bone along blood vessels. these finger-like projections of disease impart a blue-staining border (or mantle) around the involved blood vessels, known as "blue mantles of manasse."^1,2,4

otosclerosis has been shown by schuknecht to conform to the original endochondral bone which it replaces.⁵ for example, the fallopian canal wall is frequently involved, but the canal lumen is never compromised, and facial weakness is not seen.

etiology

the etiology of otosclerosis is still unclear, but a commonly held theory is that the disease originates from cartilagenous remnents of the otic capsule. the cartilagenous otic capsule matures to full size by midterm in utero. ossification then occurs from 14 centers, and is completed by the 23 gestation week. however, 3 small cartilagenous centers persist, and otosclerotic foci have been shown to originate from each of these areas. the fissula ante fenestrum is one of these cartilagenous centers.¹

the endosteum lining the labyrinth forms a thin layer of endosteal bone, while the thicker layer of periosteal bone is formed outside the endochondral capsule. the periosteal bone undergoes active bone remodeling with formation of haversian canals, marrow spaces, and pneumatization. with the exceptions of the ossicles and the endochondral labyrinthine capsule, endochondral bone initially formed by cartilage is later replaced by periosteal bone.

in the middle of the second decade of life, the osteocytes begin to die, leaving empty lacunae. these empty lacunae have been observed just prior to foci of otosclerosis. it is suggested that these otosclerotic foci may be a response to an area of devitalized bone, such that the empty lacunae are filled with vascular periosteal bone. this active periosteal bone contains hydrolytic enzymes which dissolve collagen and injure adjacent osteocytes. the result is a slowly expanding focus of periosteal bone surrounded by relatively inactive endosteal bone.¹

in most cases, the focus of otosclerosis begins in the fissula ante fenestrum (80- 90%), just anterior to the stapes footplate. with time, the superficial and deep edges of the anterior footplate are invaded by otosclerotic bone, producing a "lobster-claw" fixation. occasionally, the disease is confined to the footplate ("biscuit" footplate), without extension to the walls of the oval window. the entire oval window may become obliterated with disease (obliterative otosclerosis). involvement of the round window is common (30-50%), but unlike the oval window, the round window must be completely obliterated to induce hearing loss. this occurs in less than 1% of cases.

the conductive component of otosclerosis is due to the reduced mobility of the ossicles. the etiology of the sensorineural component is less clear but probably is due to a release of toxic enzymes or metobolites into the cochlear fluid. vascular compomise to the cochlea may also contribute to the sensorineural loss.

diagnosis

history:

patients with otosclerosis usually present with a slowly progressive hearing loss without prior trauma or infection. tinnitus is present in 75% of cases, a positive family history in 60%, and imbalance in 25% of cases. women may notice onset or exacerbation during pregnancy.¹

physical exam:

the tympanic membrane is normal appearing in most cases, with only 10% having a pinkish hue behind the tympanic membrane (schwartze's sign). although uncommon, schwartze's sign is almost pathognomonic for otosclerosis. nystagmus is rare. the tuning fork exam may indicate a conductive hearing loss, with bone conduction greater than air conduction first at 256 hz, then 512hz, and finally 1024 hz.³

laboratory:

the audiogram typically shows a slowly worsening conductive hearing loss that progresses from low to high frequencies. most patients also have a sensorineural loss that is disproportionate to the patient's age. carhart's notch is a 10-30db drop in the bone line at 2000hz, induced by stapes fixation. when present, carhart's notch is virtually diagnostic of otosclerosis.³ maximal conductive hearing loss is 50db for otosclerosis, unless combined with ossicular chain discontinuity. speech discrimination is better than normally expected, except when associated with severe sensorineural loss or endolymphatic hydrops.

tympanic membrane mobility and stapedial reflexes are normal early in the disease course, and may become reduced as the stiffness of the ossicular chain increases. in pre- clinical otosclerosis, tympanometry may show an "on-off" effect, in which there is an abnormal decrease in impedance at the beginning and ending of the eliciting signal. with disease progression, this "on-off" effect usually gives way to an absent stapedial reflex.³

vestibular testing and radiography is usually non-diagnostic. however, fine-cut computed tomography is occasionally helpful in determining the cause of sensorineural hearing loss. radiolucent areas near the cochlea provide evidence for cochlear otosclerosis.³

sensorineural otosclerosis:

the vast majority of cases of otosclerosis are associated with conductive or mixed hearing loss. occasionally, a case of pure sensorineural otosclerosis will be described, but its existence is controversial. the first case of pure sensorineural otosclerosis was described by shambaugh sr. in 1903.¹ in 1967, shambaugh jr. developed seven criteria for diagnosing pure sensorineural otosclerosis.⁶

1) a positive schwartze's sign

2) family history of surgically confirmed stapedial otosclerosis

3) symmetric progressive sensorineural loss, with stapes fixation in one ear

4) unusually good speech discrimination for a pure sensorineural loss

5) onset of hearing loss at usual age for stapes fixation and progressing without other known etiology

6) ct scan in patient with one or more of above criteria that shows cochlear capsule demineralization (a negative scan does not preclude diagnosis because mature disease resembles normal bone on ct)

7) on-off effect of impedance tympanometry

differential diagnosis

otosclerosis is sometimes difficult to distinguish from other diseases that affect ossicular chain or tympanic membrane mobility. indeed, final diagnosis is often delayed until surgical exploration.3

ossicular discontinuity- may cause a conductive loss of up to 60db, and the tympanic membrane shows increased compliance on tympanometry.³

malleus head fixation- causes a similar conductive hearing loss, and may occur in conjunction with stapes fixation. this may be caused by otosclerosis, tympanosclerosis, or infection. careful inspection of all ossicles is essential in stapes surgery to avoid missing such lesions.¹

congenital fixation of the stapes- may occur as a isolated abnormality of the middle ear, and should be considered in cases of stable hearing loss since early childhood. congenital stapes fixation may also occur in conjunction with an abnormally small tympanic membrane, partial meatal atresia, or a shortened manubrium. a high degree of suspicion must be maintained in these patients. the sometimes abnormal course of the facial nerve in these patients makes operative repair a greater challenge.¹

chronic secretory otitis media- may otoscopically resemble otosclerosis, but tympanometry should indicate the presence of middle ear fluid in otitis media.

tympanosclerosis- may fix one or more of the ossicles. the conductive hearing loss may be similar to that seen in otosclerosis. a history of prior infections, the finding of associated myringosclerosis, and a stable rather than progressive hearing loss are typical of tympanosclerosis. however, the correct diagnosis may only become apparent at surgery.¹

paget's disease (osteitis deformans) of the temporal bone- begins in the periosteal bone outside the capsule instead of in the endochondral capsule like otosclerosis. it causes sensorineural loss similar to that sometimes seen in otosclerosis, probably due to hydrolytic enzymes entering the cochlear fluid. conductive hearing loss is rare in paget's disease.^1,3

osteogenesis imperfecta (van der hoeve-de kleyn syndrome)- is an autosomal dominant condition in which a defect in osteoblast activity results in fragile bones and blue sclera. in addition to multiple long bone fractures, around half of these patients develop stapes fixation. the short term surgical response to stapes surgery in these patients is similar to that seen in otosclerosis, but progressive postoperative sensorineural hearing loss is more common.^1,3,7

management of otosclerosis

natural history of otosclerosis:

roughly 90% of cases of otosclerosis are never clinically apparent. the foci originate in childhood, remain immature for several years but never reach the cochlea or oval window, and then mature into the inactive form before ever causing hearing loss. in those patients who do develop symptoms, the average age of onset of subjective hearing loss is 20 years. over the next 20 - 40 years, these patients may develop conductive, sensorineural, or mixed hearing loss. typically, the disease progresses in a stepwise fashion, with periods of quiescence alternating with periods of deterioration. in addition to worsening hearing, periods of disease progression are characterized by worsening tinnitus, a positive schwartze's sign, and sometimes a mild imbalance. the foci usually mature by age 50 to 70, leaving patients with as much as 50db of conductive hearing loss, and varying degrees of sensorineural hearing loss.^1,3

nonsurgical management:

non-surgical treatment should be offered to poor surgical candidates and to those who decide against surgery for any reason. in addition, those patients with a pure sensorineural hearing loss or vestibular symptoms should be considered for non-surgical management.

amplification- is offered to patients with hearing loss due to otosclerosis. these patients typically have good speech discrimination and do not have the recruitment problems common to most types of sensorineural hearing loss.³

sodium fluoride- taken orally has been shown to stabilize the hearing loss associated with otosclerosis in 80% of patients.¹ the fluoride ion replaces the usual hydroxyl ion in periosteal bone, forming fluorapatite, instead of the usual hydroxyapatite. in addition, bone resorption is reduced, and calcification of new bone is enhanced. actively expanding foci of otosclerosis are inactivated, as has been documented by computed tomography. in addition, tinnitus and imbalance are reduced, and schwartze's sign frequently becomes negative. the most frequent side effects are rash, arthritis, and gastric distress. permanent serious side effects are very rare. it is available over the counter as florical (sodium fluoride and calcium carbonate), and the usual dose is about 20-40 mg of fluoride a day.^1,8 this dosage is decreased for children and pregnant women. after two years, the efficacy of the treatment is evaluated. schwartze's sign, and the degree of tinnitus and imbalance are reassessed, and a ct scan is repeated. if overall stabilization of the disease has occurred, the patients is placed on a life-long maintanence dose of about 25mg of fluoride a day.1,8 stopping the treatment in those patients whose disease process stabilized while on therapy may result in a reactivation of the disease in 2-3 years.^1,8

surgical treatment:

historical

1878-1899- kessel, boucheron, miot, blake and jack, faraci- in all, more than 300 stapes mobilizations were performed. the incudostapedial joint was seperated, then the stapes was mobilized by applying pressure in various directions. there were many reported improvements in conductive hearing loss.

1900- international congress- siebenmann, politzer, and other leaders in otology condemned stapes mobilizations and other surgery for otosclerosis as both dangerous and ineffective.

1930s- lempert- performed horizontal canal fenestrations, with some improvement in hearing. this procedure did not correct all of the conductive hearing loss.

1952- rosen- while exposing an ossicular chain in preparation for horizontal canal fenestration, a stapes became mobilized with dramatic improvement in hearing. he then began attempting mobilizations on several patients, evidently unaware of similar treatments used more than 50 years earlier.

1954- shambaugh - first used a microscope for stapes operations.

1956- shea- with an operating microscope, he removed the stapes, then reconstructed the ossicular chain and sealed the oval window. modifications of his original technique are still used today.

patient selection:

potential stapedectomy candidates have a socially restrictive hearing loss, which is confirmed by tuning fork exam and audiometry to be a conductive or mixed loss. speech discrimination should be good. generally, patients with a hearing loss of more than 40db, and bone conduction better than air conduction on tuning fork exam will benefit from surgery. the patients should have a good anesthetic risk, and none of the contraindications discussed below.1,3,10

contraindications:

in the past, stapedectomy was not performed on those who experience frequent changes in barometric pressure, such as pilots and divers. when gelfoam and wire prostheses were commonly used, postoperative fistula and prosthesis displacement were more common in these patients.3 however, with small fenestra stapedotomy and piston reconstruction, displacement is uncommon and perilymph fistula is very rare, even with flying and scuba diving. according to a recent communication on otology online, john house, m.d. allows his patients to fly after five days, resume physical exercise after 10 days, and play football or scuba dive after three weeks.11 a conservative approach would be to discuss the patient's hobbies and job requirements, and encourage the patient to make the final decision.

since postoperative dysequilibrium sometimes occurs, elderly patients with a baseline imbalance, or those whose jobs demand excellent balance (e.g. ironworkers) may want to consider non-surgical treatment.³ however, with small fenestra surgery, the risk of prolonged postoperative dizziness is very low.

known endolymphatic hydrops is an absolute contraindication. stapedectomy in these patients will often lead to a permanent profound sensorineural loss. patients with vertigo and poor speech discrimination may have endolymphatic hydrops, and therefore are not surgical candidates.1

tympanic membrane perforation with middle ear infection is a contraindication to stapedectomy due to the increased risk of suppurative labyrithitis. stapedectomy in these patients is delayed until the infection is treated, and the tympanic membrane has been repaired.3

recent stapes operation (within 6-12 months) usually precludes operating on the opposite ear, due to the risk of delayed sudden profound hearing loss in the operated ear. similarly, operating on an only hearing ear is generally contraindicated.

patients with a substantial downsloping sensorineural loss as part of a mixed loss usually have a poor speech discrimation, which does not improve after surgery. in addition, these patients are considered to have a "compromised cochlea" with sensorineural loss often worsening after any degree of intraoperative trauma.

preoperative counseling:

potential stapedectomy candidates should be advised that stapedectomy is an elective procedure, and that many times amplification is a viable alternative to surgery. patient currently experiencing an active phase of otosclerosis, as evidenced by worsening imbalance or a positive schwartze's sign, may benefit from 6-12 months of sodium fluoride therapy prior to treatment. preoperative fluoride may induce maturation of the focus, reducing chances of postoperative disease progression. the risks of imbalance, tinnitus, changes in taste, dry mouth, tympanic membrane perforation, facial nerve injury, and permanent cochlear deafness should be fully explained to the patient. the risk of cochlear deafness should be a reflection of the operating surgeon's own experience, not merely published data (about 1%). patients may expect to return to work about a week after surgery.^1,10

anesthesia:

both local and general anesthesia have been used successfully for stapes surgery. proponents of local anesthesia state that the awake patient would be able to report vertigo or nausea, which could indicate impending cochleovestibular damage. however, general anesthesia is now often thought to be safer than awake sedation. the anesthesia of choice is usually that which affords the most comfort to both the individual surgeon and patient.

intra-aural preparation:

the ear is prepped and draped in the usual sterile fashion. the ear canal is injected with 1% lidocaine with 1:100,000 epinephrine using the quadratic technique. complete vasoconstriction of the tympanomeatal flap region is needed.1

tissue graft harvest:

a variety of autograft tissues have been used successfully to seal the oval window after placement of the stapes prosthesis. temporalis fascia and dorsal hand vein are most often used. in either case, the graft is harvested, and the incision is closed.

oval window exposure:

with the operating microscope and ear speculum in position, a u-shaped lempert type incision is made in the posterior canal wall with a round knife. the incision begins at 6 o'clock just lateral to the annulus, extends posteriorly and laterally , and then courses medially again to end just lateral to pars flaccida at 12 o'clock. the flap is elevated to the sulcus tympanicus with a round knife, and the tympanic cavity mucosa is then perforated with a curved blunted needle. the tympanomeatal flap is folded anteriorly, taking care to preserve the chorda tympani nerve.¹

if the case is being performed under local anesthesia, a small amount of 2% lidocaine with 1:20,000 epinephrine is infused into the middle ear, and immediately suctioned. this provides excellent middle ear anesthesia. more prolonged bathing of the round window with lidocaine may induce vestibular paresis and cause vertigo.¹

a 2-4 mm rim of posterior-superior canal (scutum) must usually be removed in order to provide adequate exposure of the stapes and oval window. initially, a lateral furrow is made in the scutum with a curette. once the furrow is made, the medial bone adjacent to the incus is curettaged more easily, with less risk of damage to the ossicles. sufficient curettage is performed when the pyramidal process is visualized.¹

the chorda tympani is then sometimes separated from its attachments to the medial surface of the malleus in order to allow any stretching of the nerve to occur along the entire intratympanic course of the nerve. the horizontal portion of the facial nerve is evaluated for bony dehiscence, which occurs in about 50% of all ears.¹⁰

the malleus is then probed to assess the mobility of the malleus and incus. this is done to exclude fixation of the these ossicles as a cause of conductive hearing loss. the stapes is then palpated to confirm fixation, and the oval and round windows are evaluated for extent of disease.³

the distance between the footplate and the medial surface of the lower aspect of the long process of the incus is then measured. about 0.25 to 0.50mm is added to the measured distance to accommodate entrance of the prosthesis slightly into the vestibule. measurement before disarticulation of the i-s joint may be more accurate, since movement of the incus is possible with joint disarticulation.¹

stapes manipulation:

several methods of stapes manipulation have been developed to release the stapes fixation and allow transmission of sound along the ossicles and into the oval window.

1) stapes mobilization- when only a very small focus of otosclerosis exists, the stapes footplate is sometimes mobilized with a curved blunted needle. this often leads to a temporary improvement in hearing. because re-fixation is common, this procedure is rarely performed.¹⁰

2) anterior crurotomy- when disease is limited to the fissula ante fenestram, removal of the anterior crus and anterior half of the footplate is sometimes performed. the exposed portion of the oval window niche is covered with a connective tissue graft. the incudostapedial joint is left in place, so no prosthesis is required. the stapedial tendon is also left in place, which may be helpful to those who work in noisy environments.

3) stapedectomy - more extensive disease often requires removal of the entire stapes footplate. here, the stapedial tendon is divided, and then control holes are placed in the footplate for stabilization during i-s joint division. after division of the i-s joint with a joint knife, the stapes suprastructure is fractured or drilled and removed. the entire footplate is removed with small hooks, taking care to avoid entry or suctioning into the vestibule. a stapes prosthesis is placed, and the oval window is sealed with an autogenous tissue graft.1,10

4) drill-out stapedotomy- in some patients with an extensive thickened otosclerotic focus covering the oval window (obliterative otosclerosis), stapedectomy cannot be performed. in these cases, the stapes suprastructure is removed, then the bone overlying the oval window is thinned with a small drill. a 0.8 to 1.0 mm opening is then made in the footplate, and the prosthesis surrounded by autogenous tissue graft is placed in the opening.

5) small fenestra surgery- this method of stapes surgery is now the technique of choice for otosclerosis, although some surgeons still prefer total footplate removal. the suprastructure is removed, then a small opening in the footplate is made with a drill or laser. the prosthesis used is typically the piston-bucket handle type. postoperatively, hearing results are the same for stapedectomy and fenestra surgery, and dizziness is less with fenestra surgery. in addition, the incidence of postoperative prosthesis displacement and perilymph fistula is less in fenestra surgery.¹⁰

tissue seal of the oval window:

the autogenous graft is draped over the oval window, and overlaps the oval window margin by 1-2 mm. several materials, including vein grafts and temporalis fascia have been successfully to create an oval window seal and thereby prevent fistula formation. small fenestra stapedotomy and piston reconstruction are often performed successfully without an autogenous graft, instead allowing blood or a piece of gelfoam to stabilize the piston.

prosthesis placement:

several stapes protheses have been developed over the past 30 years. the sharp or beveled polyethylene strut developed by shea is associated with a higher incidence of postoperative fistula, so is rarely used today. similarly, the wire prosthesis attached to compressed gelfoam has been associated with a higher incidence of postoperative fistula, due to reparative granuloma formation.¹⁰

most stapedectomies today are repaired with a wire prosthesis attached to a connective tissue graft that covers the oval window. stapedotomies are usually repaired with a piston type prosthesis of 0.6 mm or 0.8 mm diameter, which again rests on a connective tissue graft. the prosthesis usually attaches to the long process of the incus, either with a wire that is crimped into place, or a bucket handle that lifts over the long process. the exception is the robinson-type prosthesis, which is a metal stem that fits under the lenticular process of the incus. after placement of the prosthesis, the malleus is palpated to insure appropriate movement of the repaired ossicular chain.¹⁰

closure:

the tympanomeatal flap is placed back into its anatomic position. the external canal is packed with gelfoam or similar material, and a mastoid dressing is applied. postoperative antibiotics are sometimes given, but their usefulness in routine postoperative stapedectomy care has not been established.

postoperative course:

the patient is usually admitted for overnight observation, with head of bed elevated, and given instructions about no straining or nose blowing. any sneezing should occur through the mouth. the ear canal should remain dry until patency of the tympanic membrane can be established at follow-up. a mild imbalance that lasts a few days is fairly common and is thought to be due to serous labyrinthitis. postoperative audiograms are obtained 4-6 weeks after the procedure. closure of the air-bone gap to within 10db occurs in about 90% of patients. permanent sensorineural hearing loss occurs in 1-3% of patients.

problems in stapedectomy:

floating footplate: during the course of stapedectomy, the footplate sometimes dislodges from the surrounding niche (floating footplate). attempts at removal tend to push the footplate towards the vestibule. a safety hole drilled into the footplate at the beginning of the procedure helps in the removal of the footplate should it become floating. alternatively, a small hole may be drilled in the edge of the promontory to aid in removal of a floating footplate.1 small fragments that fall into the vestibule should not be retrieved.3 laser obliteration of the floating footplate is preferred by many surgeons today, because removal is accomplished without manipulation.12 alternatively, the floating footplate may be left in place, and the prosthesis placed directly on the footplate.

biscuit footplate: when an otosclerotic focus is limited to the footplate itself, the footplate appears thickened and is known as a biscuit footplate. manipulation in these cases may lead to a floating footplate. for this reason, laser obliteration of biscuit footplates is often performed.12

dehiscent facial nerve: in previously unoperated ears, dehiscent facial nerves are relatively easy to identify and avoid. in revision cases, the nerve is often embedded in fibrous tissue on the oval window niche. permanent facial nerve paralysis may result from even the most careful removal of this fibrous tissue.1 delayed facial palsy occurring after stapedectomy is usually due to edema, and is often treated with steroids. recovery from edema begins in 1 to several weeks, and is usually complete.

postoperative granuloma: the formation of a reparative granuloma after stapedectomy is rare. whether the use of gelfoam or gelatin to seal the oval window increases the risk of postoperative granuloma is contraversial. sensorineural hearing loss or vertigo that occurs within 6 weeks after stapedectomy should alert the surgeon to this possibility.3 a grayish mass in the posterior-superior quadrant is suggestive. hearing may possibly be stabilized with immediate surgical exploration and removal of the granulama, followed by placement of a connective tissue graft to seal the oval window. however, surgery in these cases is contraversial, since further manipulation of the oval window may increase trauma in this region, thereby risking additional hearing loss or dizziness.

fixed malleus: the malleus should be palpated prior to stapedectomy to rule out malleus fixation. ankylosis of the malleus may occur by itself or in combination with stapes fixation. mobility of the malleus should be acheived prior to placement of the prosthesis so that vibrations along the ossicular chain are not transmitted to the cochlea.1

round window closure: otosclerosis involves the round window in 30-50% of patients, but hearing is rarely affected. unlike the oval window, the round window must be entirely obliterated to cause a decrease in hearing. when this occurs, a severe mixed hearing loss results. treatment is these cases is stapedectomy, which may give a moderate hearing improvement. surgically opening the round window has not been successful.1

fracture of the long process of the incus: a fracture of the long process may occur during crimping the wire prosthesis. if the fracture is near the body of the incus, a malleus to oval window prosthesis is used. if the fracture is near the tip of the long process, a platinum band is used to repair the fracture.1

postoperative infection: postoperative otitis media often results in total hearing loss, and meningitis. early treatment with myringotomy and intravenous antibiotics is essential.³

perilymph gusher: occasionally, a dehiscence of the lateral internal auditory canal may result in a profuse flow of perilymph when the footplate is removed. in these cases, the head is elevated, and the oval window niche is sealed with a tissue graft and prosthesis. otorrhea usually stops in 2-6 days, but permanent hearing loss is likely.^1,3 further surgery on the ear is contraindicated. the incidence of perilymph gusher is less than 1:1000.

postoperative perilymph fistula: postoperative perilymph fistula should be suspected in patients with persistent vertigo, or worsening hearing loss. surgical exploration should be considered, but entry in the vestibule should only be performed if a fistula is strongly suspected or certain. the fibrous tissue overlying the oval window is carefully removed, and a larger than usual connective tissue graft is placed over the oval window, and secured with a prosthesis. vertigo usually improves after repair of a fistula, but hearing rarely improves. postoperative fistulas are less common following stapedotomy than stapedectomy.¹

revision stapedectomy

there are several causes of post stapedectomy conductive hearing loss, all of which may be indications for revision stapedectomy. these include displacement of the prosthesis, loosening of the wire attachment to the incus, refixation of a mobilized footplate, adherence of the prosthesis to the oval window edge, advancement of disease into the oval window, pressure necrosis of the long process tip, or anklylosis of the malleus or incus.

revision stapedectomy is performed similar to initial stapedectomy, except that injury to the chorda tympani and facial nerves is more common due to soft tissue adhesions.1 in addition, successful air-bone gap closure is significantly reduced. glasscock reported on 828 operated ears from 1970-1994.¹³ air-bone gap closure to within 5 db was achieved in 91% of primary operations, and in 66% of revisions.

bibliography

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2. goycoolea mv. otosclerosis. in: paparella mm, shumrick da, gluckman jl, and meyerhoff wl, eds. otolaryngology, vol 2. philadelphia: w.b. saunders, 1991: 1489- 1512.

3. meyerhoff wl. otosclerosis. in: bailey bj, ed. head and neck surgery- otolaryngology, vol 2. philadelphia: jb lippincott, 1993: 1688-1701.

4. linthicum fh. histopathology of otosclerosis. otolaryngology clinics 1993; 26(3):335-352.

5. schuknecht hf. stapedectomy. boston: little, brown & co., 1971.

6. shambaugh ge, jr. surgery of the ear, 2nd ed. philadelphia: w.b. saunders, 1967.

7. garretson tj, cremers cw. stapes surgery in osteogenesis imperfecta: analysis of postoperative hearing loss. annals orl 1991;100(2):120-130.

8. causse jr et al. sodium fluoride therapy. am j otology 1993;14(5): 482-490.

9. house hp. the evolution of otosclerosis surgery. otolaryngology clinics 1993; 26(3):323-333.

10. meyerhoff wl, paparella mm. management of otosclerosis. in paparella mm, shumrick da, gluckman jl, and meyerhoff wl, eds. otolaryngology, vol 2. philadelphia: w.b. saunders, 1991: 1513-1528.

11. house j. personal communication. otology online. 12/30/95.

12. perkins r. otosclerosis. in gates ga, ed. current therapy in otolaryngology-head and neck surgery, 5th ed. st. louis: mosby, 1994: 32-43.

13. glasscock iii me, et al. twenty-five years of experience with stapedectomy. laryngoscope 1995;105:899-904.