A stapedectomy is a surgical procedure of the middle ear performed to improve hearing. The world's first stapedectomy is credited to Dr. John J. Shea, Jr., performed in May, 1956, the first patient being a 54 year-old housewife who could no longer hear even with a hearing aid.
If the stapes footplate is fixed in position, rather than being normally mobile, then a conductive hearing loss results. There are two major causes of stapes fixation. The first is a disease process of abnormal mineralization of the temporal bone called otosclerosis. The second is a congenital malformation of the stapes.
In both of these situations, it is possible to improve hearing by removing the stapes bone and replacing it with a micro prosthesis - a stapedectomy, or creating a small hole in the fixed stapes footplace and inserting a tiny, piston-like prothesis - a stapedotomy. The results of this surgery are generally most reliable in patients whose stapes has lost mobility because of otosclerosis. Nine out of ten patients who undergo the procedure will come out with significantly improved hearing while less than 1% will experience worsened hearing ability or deafness. Successful surgery usually provides an increase in hearing ability of about 20 dB. That is as much difference as having your hands over both ears, or not. The relative success rate for this surgery varies considerably between surgeons. As for any surgical procedure, all other variables fixed, the more experience the surgeon has with the surgery, the better the outcome. Since stapes surgery is fairly rare, significantly better success rates are found at facilities that specialize in this procedure.
Indications of stapedectomy:
- Conductive deafness due to fixation of stapes.
- Air bone gap of at least 40 dB.
- Presence of Carhart's notch in the audiogram of a patient with conductive deafness.
- Good cochlear reserve as assessed by the presence of good speech discrimination.
Contraindications for stapedectomy:
- Poor general condition of the patient.
- Only hearing ear.
- Poor cochlear reserve as shown by poor speech discrimination scores
- Patient with tinnitus and vertigo
- Presence of active otosclerotic foci (otospongiosis) as evidenced by a positive flemmingo sign.
Complictions of stapedectomy:
- Facial palsy
- Vertigo in the immediate post op period
- Perilymph gush
- Floating foot plate
- Tympanic membrane tear
- Dead labyrinth
- Perilymph fistula
When a stapedectomy is done in a middle ear with a congenitally fixed footplate, the results may be excellent but the risk of hearing damage is greater than when the stapes bone is removed and replaced (for otosclerosis). This is primarily due to the risk of additional anomalies being present in the congenitally abnormal ear. If high pressure within the fluid compartment that lies just below the stapes footplate exists, then a perilymphatic gusher may occur when the stapes is removed. Even without immediate complications during surgery, there is always concern of a perilymph fistula forming postoperatively.
A modified stapes operation, called a stapedotomy, is thought by many otologic surgeons to be safer and reduce the chances of postoperative complications. In stapedotomy, instead of removing the whole stapes footplace, a tiny hole is made in the footplate - either with a microdrill or with a laser, and a prosthesis is placed to touch this area with movement of the tympanic membrane. This procedure greatly reduces the chance of a perilymph fistula (leakage of cochlear fluid) and can be further improved by the use of a tissue graft seal of the fenestra
Otosclerosis is a progressive degenerative condition of the temporal bone which can result in hearing loss.
Chronic conductive hearing loss (CHL) is the finding in almost all cases of otosclerosis (in fact should a person present with sensorineural hearing loss they would likely never be diagnosed with otosclerosis). This usually will begin in one ear but will eventually affect both ears with a variable course. On audiometry, the hearing loss is characteristically low-frequency, with higher frequencies being affected later. Sensorineural hearing loss (SNHL) has also been noted in patients with otosclerosis; this is usually a high-frequency loss, and usually manifests late in the disease.
Approximately 0.5% of the population will eventually be diagnosed with otosclerosis. Post mortem studies show that as many as 10% of people may have otosclerotic lesions of their temporal bone, but apparently never had symptoms warranting a diagnosis. Whites are the most affected race, with the prevalence in the Black and Asian populations being much lower. Females are twice as likely as males to be affected. Usually noticeable hearing loss begins at middle-age, but can start much sooner. The hearing loss often grows worse during pregnancy.
The disease can be considered to be heritable, but its penetrance and the degree of expression is so highly variable that it may be difficult to detect an inheritance pattern. Most of the implicated genes are transmitted in an autosomal dominant fashion.
The pathophysiology of otosclerosis is complex. The key lesions of otosclerosis are multifocal areas of sclerosis within the endochondral temporal bone. These lesions share some characteristics with Paget’s Disease, but they are not thought to be otherwise related. Histopathologic studies have all been done on cadaveric temporal bones, so only inferences can be made about progression of the disease histologically. This being said, it seems that the lesions go through an active “spongiotic” / hypervascular phase before developing into “sclerotic” phase lesions. There have been many genes and proteins identified that, when mutated, may lead to these lesions. Also there is mounting evidence that measles virus is present within the otosclerotic foci, implicating an infectious etiology (this has also been noted in Paget’s Disease).
CHL in otosclerosis is caused by two main sites of involvement of the sclerotic (or scar-like) lesions. The best understood mechanism is fixation of the stapes footplate to the oval window of the cochlea. This greatly impairs movement of the stapes and therefore transmission of sound into the inner ear (“ossicular coupling”). Additionally the cochlea’s round window can also become sclerotic, and in a similar way impair movement of sound pressure waves through the inner ear (“acoustic coupling”).
SNHL in otosclerosis is controversial. Over the past century, leading otologists and neurotologic researchers have argued whether the finding of SNHL late in the course of otosclerosis is due to otosclerosis or simply to typical presbycusis. There are certainly a few well documented instances of sclerotic lesions directly obliterating sensory structures within the cochlea and spiral ligament, which have been photographed and reported post-mortem. Other supporting data includes a consistent loss of cochlear hair cells in patients with otosclerosis; these cells being the chief sensory organs of sound reception. A suggested mechanism for this is the release of hydrolytic enzymes into the inner ear structures by the spongiotic lesions.
Treatment of otosclerosis relies on two primary options: hearing aids and a surgery called a stapedectomy. Hearing aids are usually very effective early in the course of the disease, but eventually a stapedectomy may be required for definitive treatment. Early attempts at hearing restoration via the simple freeing the stapes from its sclerotic attachments to the oval window were met with temporary improvement in hearing, but the conductive hearing loss would almost always recur. A stapedectomy consists of removing a portion of the sclerotic stapes footplate and replacing it with an implant that is secured to the incus. This procedure restores continuity of ossicular movement and allows transmission of sound waves from the eardrum to the inner ear. A modern variant of this surgery called a stapedotomy, is performed by drilling a small hole in the stapes footplate with a micro-drill or a laser, and the insertion of a piston-like prothesis. The success rate of either a stapedotomy or a stapedectomy depends greatly on the skill and the familiarity with the procedure of the surgeon.
Other less successful treatment includes fluoride administration, which theoretically becomes incorporated into bone and inhibits otosclerotic progression. This treatment cannot reverse conductive hearing loss, but may slow the progression of both the conductive and sensorineural components of the disease process. Recently, some success has been reported with bisphosphonate medications, which stimulate bone-deposition without stimulating bony destruction.