CHAPTER 144 Otosclerosis
Otosclerosis is a disease of bone that is unique to the otic capsule. It may cause a conductive hearing loss, a mixed conductive-sensorineural hearing loss, or occasionally a purely sensorineural hearing loss. In 1860, Toynbee1 first described the condition causing a hearing loss by fixation of the stapes. In 1893, Politzer2 referred to the fixation of the stapes as otosclerosis. Siebenmann3 revealed on microscopic examination that the lesion seemed to begin as spongification of the bone and termed the process otospongiosis.
Otosclerosis is an autosomal-dominant hereditary disease with variable penetrance and expression. Two thirds of patients are women. The hearing loss usually begins in the late teens or early 20s, but may not occur until the 30s or early 40s. At the House Ear Clinic, the youngest patient with surgically confirmed otosclerosis was 6 years old.4 It may be accelerated by pregnancy. Many female patients first report hearing loss during or shortly after their first pregnancy.
The prevalence of otosclerosis varies with race and its expression (Table 144-1). In whites, the disease is found in 7.3% and 10.3% of temporal bones for men and women. The stapes appears fixed in only 12.3% of patients with histopathologic evidence of otosclerosis. Clinical otosclerosis is rare in blacks, Asians, and Native Americans.5–11
Table 144-1 Occurrence of Clinical Otosclerosis
| Reference | Prevalence |
|---|---|
| Fowler and Fay, 1961, U.S.44 | 5% of patients with hearing loss* |
| Morrison and Bundey, 1970, England45 | 0.3% of East London’s population |
| Surján et al, 1973, Hungary (two sites)46 | 5.1% of patients with hearing loss; 2.4% of patients with hearing loss |
| Hall, 1974, Norway47 | 0.3% of Norway’s population |
| Pearson et al, 1974, U.S.48 | 239 : 100,000 in Rochester, MN, in 1970 |
| Moscicki et al, 1985, U.S.49 | 0.52% of a cohort study begun 29 years earlier |
| Huang and Lee, 1988, Taiwan50 | 1.13% of patients with hearing loss |
| Reference | Incidence |
|---|---|
| Hall, 1974, Norway47 | 56 : 100,000 for Norway’s population (1960-1969) |
| Pearson et al, 1974, U.S.48 | 13 : 700,000 in Rochester, MN, from 1950-1969; 8.9 : 100,000, from 1950-1959 |
| Stahle et al, 1978, Sweden51 | 12 : 100,000 yearly |
| Levin et al, 1988, Sweden8 | 6.1 : 100,000 for 1981 |
* Discounted patients with cerumen impaction.
From Cummings CW, Fredrickson JM, Harker LA, Krause CT, Schuller DE, eds. Otolaryngology–Head and Neck Surgery. 2nd ed. St. Louis: Mosby; 1993.
Histopathology
Early lesions appear adjacent to the fissula ante fenestram as sheets of connective tissue replacing bone. Bone is absorbed by osteoclastic activity, and new bone is deposited by osteocytes. The osteocytes are found at the advancing edge of the lesion, which extends into the otic capsule in finger-like projections. These lesions contain vascular spaces in the center. The result is disorganized bone rich in osteocytes with enlarged marrow spaces rich with blood vessels and connective tissue. These lesions have an affinity for hematoxylin, which makes the bone appear darker. Healthy surrounding bone has few viable osteocytes and chondrocytes, and is relatively avascular. The osteoclasts are multinucleated and appear in the center of the lesion, absorbing the already disorganized bone.
The extent and location of these lesions vary. Some are small and do not involve the stapes. Lesions that have ceased all activity appear sclerotic. As the disease advances, the lesions spread across the stapedial annular ligament, causing stapedial fixation. If the lesion progresses medially to involve the endosteum of the cochlea, sensorineural hearing loss results (Fig. 144-1). It may spread in both directions, resulting in a mixed sensorineural conductive hearing loss (Fig. 144-2).
Figure 144-1. Stapes footplate and anterior crus adjacent to an anterior oval window otosclerotic process seen on the left. There is a small extension of otosclerosis in the annular ligament extending to the stapedial footplate and causing minimal fixation.
Figure 144-2. Three otosclerotic lesions involving the cochlear capsule. The largest one in the anterior oval window area also is fixing the stapedial footplate. This patient had sensorineural hearing loss and conductive loss caused by stapedial fixation.
The type of stapedial fixation varies depending on the site of the lesion. If the lesion begins in the posterior oval window and spreads to the stapes through the anterior and posterior annular ligament, it causes bipolar stapes fixation. When the lesion flows across the ligament onto the footplate, it totally obliterates any remnant of the original annular ligament. If the center of the footplate remains uninvolved, it retains its characteristic cartilaginous vestibular and bony tympanic surface. The lesion may replace the entire footplate, causing a solid footplate (Fig. 144-3).
Figure 144-3. A solid stapedial footplate wherein the annular ligament has been totally replaced with otosclerosis.
Occasionally, the lesion may involve only the cochlea, causing an isolated sensorineural hearing loss (Fig. 144-4). Sometimes the entire cochlea is surrounded by otosclerosis, causing total deafness. In the United States, 20 of the first 57 patients to have a cochlear implant were made deaf by otosclerosis.12
Evaluation
History
History is one of the most important aspects of the evaluation. Typically, with otosclerosis, hearing loss is of gradual onset and progresses slowly over several years. Approximately 70% of otosclerosis cases are bilateral and become apparent in individuals in their late teens or 20s. Hearing loss may not become apparent to the patient until age 30 or 40 years. Because most patients with otosclerosis have a conductive hearing loss, the patients report difficulty hearing conversation while chewing and may hear better in noisy rooms because of a phenomenon known as paracusis of Willis. This phenomenon is characteristic of conductive hearing loss and occurs because people speak louder in noisy surroundings. Unilateral hearing loss is less noticeable to the patient. With unilateral hearing loss, patients tend to have difficulty with direction of sound and in noisy rooms.
There is usually a positive family history of hearing loss and often of surgical correction of hearing loss. The patient usually has a negative history for infections or trauma as a possible cause of the conductive hearing loss.
Physical Examination
Physical examination includes careful otoscopy, often with the operating microscope. Pneumo-otoscopy is important to rule out middle ear serous fluid or a small perforation that could be the cause of a conductive hearing loss. There may be a red blush over the promontory or the area anterior to the oval window, known as the Schwartze sign. Tuning forks are essential for evaluation of any patient with a hearing loss13 because they may confirm or dispute the finding of a conductive hearing loss on audiometry.
Audiometry
The audiometric evaluation includes air conduction, bone conduction, and speech audiometry, and is usually performed by a trained audiologist. Because otosclerosis may cause unilateral conductive hearing loss, masking is important and may present problems for the tester.
The immittance audiometry battery consists of tympanometry, static compliance, and acoustic reflex testing. Immittance audiometry can be helpful in some cases of otosclerosis, confirming lack of mobility of the stapes with absent acoustic reflexes. The middle ear pressure is not affected by otosclerosis, and the tympanogram is normal with a distinct peak that occurs within the normal range. Many conditions affect the tympanogram, such as scarring of the tympanic membrane or tympanosclerosis. These conditions may coexist with otosclerosis. The peak may be lower than normal in the presence of a healthy-appearing tympanic membrane, alerting the examiner to the possible diagnosis.
Acoustic reflexes are a sensitive measure of the movement of the stapes. In the presence of otosclerosis, the reflex is absent. With early stapes fixation, the reflex may be abnormal in that there is a negative on-off effect or diphasic reflex (Fig. 144-5). With more advanced disease, the reflex is absent when the probe is in the involved ear. As the disease and hearing loss worsen, the contralateral reflex is affected as a result of the degree of conductive hearing loss in the otosclerotic ear. Hannley14 wrote an excellent article about audiologic evaluation of a patient with otosclerosis.
Figure 144-5. Progressive changes in the configuration of the acoustic reflex with stapedial fixation. A, Healthy reflex with a sustained change in compliance as long as the stimulus is on. B, Diphasic reflex with an on-off pattern. This is seen in cases of early otosclerotic stapedial fixation. C, As the stapes becomes fixed, the diphasic reflex is replaced by an absent acoustic reflex.
Surgery
Small Fenestra Stapedotomy
Before surgery is considered, the risks, complications, and alternatives are thoroughly discussed with the patient. Although the risk of sensorineural hearing loss is low, the patient needs to be informed of this possibility. Total sensorineural hearing loss occurs in about 0.2% of cases, but the patient is told that there is a less than 2% chance of further hearing loss, and a less than 1% chance of losing all hearing in the operated ear. Because of the slight chance of further or total hearing loss. the poorer hearing ear is selected for surgery. We never operate on the only-hearing ear or better hearing ear.
There is a slight chance of dizziness postoperatively. This possible complication must also be discussed with the patient before surgery. Dizziness is usually transient and brief, but may persist, and in extremely rare cases could be permanent. The possibility of facial palsy is mentioned in written material, but is not discussed because of the extremely rare incidence of this complication. In a review of more than 700 stapedectomies at the House Ear Clinic, only 2 patients had transient facial weakness of delayed onset. Since the senior author has been performing small fenestra stapedectomy, he has not seen postoperative temporary facial palsy.
Surgery is usually performed as an outpatient procedure with the patient under local anesthesia. We prefer local anesthesia because (1) an awake patient can inform the surgeon if vertigo occurs, and (2) the surgery is usually of short duration with minimal discomfort and does not warrant the risks or costs of general anesthesia.
An intravenous line is placed, and the patient is given sedation with midazolam (0.5 to 2 mg) as needed; this is occasionally supplemented with intravenous morphine (2 to 4 mg). The ear is anesthetized with 1% or 2% lidocaine with epinephrine 1 : 100,000. To lessen the pain associated with the injection, 18 mL of lidocaine can be buffered with 2 mL of 7.5% bicarbonate.
The patient is placed supine on the operating table with the head turned away from the surgeon. The microscope is placed at the head of the table with the nurse standing across the table from the surgeon (Fig. 144-6). If general anesthesia is used, the anesthesiologist is seated at the foot of the table.
Figure 144-6. The operating room during stapes surgery. The nurse is on the opposite side of the patient, and the microscope is at the head of the table.
There are many variations in the basic stapedectomy technique. Any technique that produces comparably good results should be continued.
The four quadrants of the ear canal are injected at the level of the hair-bearing area. This injection works best if placed just under the skin. A fifth injection is placed in the vascular strip down to the bone. If a tissue graft is to be used, the superior postauricular area is prepared and injected. Some surgeons use a vein graft; in this case, the graft is harvested from the hand before beginning the stapes surgery.
Incisions are performed with a sickle knife (No. 1) at the lateral process of the malleus and inferiorly at about the lower one fourth of the canal extended laterally approximately 8 mm. These two incisions are connected laterally with a House canal knife (No. 2). This flap is elevated evenly from lateral to medial with a canal elevator or a round knife (Fig. 144-7). It is important to elevate all of the flap at the same time so as not to tear it. When the anulus is reached, it is carefully exposed and elevated out of its bony canal with an anulus elevator “gimmick”. Care is taken during elevation to identify the chorda tympani nerve so that it is not stretched or injured. The superior elevation is carried forward to the malleus. Care is taken not to dislocate the incus. Usually the stapes is not entirely visualized because of the bony posterior superior external auditory canal overhang. This overhang is removed with a curet; alternatively, some surgeons prefer a microdrill (Fig. 144-8). The exposure is adequate when the facial nerve can be visualized superiorly, and the pyramidal process can be visualized posteriorly.
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
