Nonoperated Ear Research Articles

Hearing preservation after acoustic tumor removal: Long‐term results

This report examines the durability of preserved postoperative hearing in 25 middle fossa acoustic tumor patients with a minimum follow-up of 3 years. The mean follow-up time for this group was more than 8 years, with a maximum of almost 20 years. The initial postoperative audiogram was compared to the most recent audiogram for each patient, with change in the nonoperated ear serving as the control. Fourteen of the patients (56%) had a significant loss of the preserved hearing in the operated ear over time. The mean loss of speech discrimination was 25%, and the mean loss of speech reception threshold was 12 dB. Only one of the 14 patients had a similar loss in the contralateral ear. No recurrent tumors were identified. Good preoperative hearing is an obvious criterion for selection of candidates for hearing preservation surgery. Results of this study emphasize that a good initial postoperative hearing level is necessary to offset the potential deterioration of hearing that may occur over time.

Endolymphatic sac surgery in congenital malformations of the inner ear.

A retrospective analysis of 40 patients (49 ears) with congenital progressive sensorineural hearing loss who underwent endolymphatic sac surgery was performed. The inner ears were radiographically abnormal in 57% of operated ears. In the remaining cases, subtle malformations beyond the resolving power of radiographic studies were suspected. Early postsurgical hearing loss (defined as a loss greater than 10 dB in three-tone average or greater than 15% in speech discrimination score) was found in 29% of operated ears (14/49). However, only two of these patients lost all of their residual hearing postoperatively (2/49 or 4%). An enlarged endolymphatic sac was noted at surgery in 50% of those with significant postoperative hearing losses. Longer-term stability of hearing was assessed in 22 patients with bilateral inner-ear pathology who underwent surgery on one side only. A comparison of the hearing fate of the operated and nonoperated ears suggested no benefit from the surgical intervention when compared to the natural history of the disease. Based upon this experience, endolymphatic sac surgery for the purpose of hearing stabilization in patients with congenital malformations of the inner ear is no longer recommended.

Cochlear potentials and their modulation by low-frequency sound in early endolymphatic hydrops

Seventeen guinea pigs were unilaterally operated to produce endolymphatic hydrops. After 2 wk (9 animals) or 4 wk (8 animals), extracochlear electrophysiological responses to tone bursts of several frequencies were recorded in both the operated and non-operated ears. In addition, modulation by low-frequency (29 Hz sinusoidal bias) sound of the responses to 8 kHz tonebursts was measured. After the electrophysiological measurements, the animals were killed and examined histologically. Four weeks after the operation, cochlear microphonics in response to a 500 Hz tone burst and to the 29 Hz bias were significantly smaller in the operated ears. The summating potential showed a tendency to be larger in the operated ears. The compound action potential input-output curves for 2 kHz probes showed a small threshold shift accompanied by steep slopes, reminiscent of recruitment. Modulation of summating potentials by the low-frequency bias was smaller on the operated side. In most cochleae an endolymphatic hydrops was observed. Three cochleae showed a collapse of Reissner's membrane.

Maps of auditory cortex in cats reared after unilateral cochlear ablation in the neonatal period

The responses of many neurons recorded in the high best-frequency region of primary auditory cortical field, AI, of the normal adult cat depend upon intensity differences of the sounds arriving at the two ears. These binaural interactions are exhibited early in postnatal life, well before structural maturation of the auditory pathways from the ear to the cortex is complete. The aim of the present work was to study certain aspects of the functional development of the auditory cortex in adult cats unilaterally deaf from birth. In adult animals reared with a neonatal cochlear ablation, field AI ipsilateral to the non-operated ear showed a normal tonotopic map, which was derived from single neurons and neuron clusters driven securely by best-frequency tonal stimulation in virtually every electrode penetration. The acoustic thresholds at many recording sites were as low as those obtained in AI contralateral to the non-operated ear. These findings are in marked contrast to those from control experiments on normal adult cats where only about 65% of AI neurons were excited by a sound delivered to the ipsilateral ear and where thresholds to ipsilateral ear stimulation were significantly higher than contralateral thresholds. The spatial distribution of cortical neurons based on acoustic thresholds also appeared to be different in cats unilaterally deaf from birth when compared to control cats. Closely spaced electrode penetrations in AI ipsilateral to the non-operated ear suggested that neurons were separated into low-threshold regions and high-threshold regions. There was no evidence for this type of non-random segregation in control experiments.

The effects of unilamellar perichondrial dissection on the growth of rabbit ear cartilage.

The effects of elevation of the perichondrium from a surface of growing ear cartilage were investigated in immature rabbits. Eight 21-day-old rabbits completed the study in which perichondrium was elevated from one cartilaginous surface of one ear and the nonoperated ear served as a control. By maturity, both ears had developed symmetrically and no statistically significant difference could be demonstrated in length and surface area. Although several ears demonstrated subtle shape changes, the overall growth and development of the surgically manipulated ear cartilages did not appear to be affected. These findings appear to contradict a widely held view that perichondrial dissection of developing cartilage has a high potential for subsequent growth disturbances. The corollary has been that cartilage manipulation, such as that required in the surgical repair of the cleft lip nose deformity, should be delayed until the growth of cartilage is complete. These data would support the findings of long-term clinical studies which demonstrate the efficacy of early limited perichondrial dissection in the correction of the cleft lip nose deformity.

Single-unit responses in the inferior colliculus: effects of neonatal unilateral cochlear ablation.

Monaural responses of single units isolated in the inferior colliculus of adult gerbils that have developed postnatally with one cochlea were compared with monaural responses recorded in animals that have developed with both cochleas. One cochlea of 2-day-old gerbils was ablated, and at approximately 6 mo of age, excitatory responses to stimulation of the nonoperated ear were recorded in the ipsilateral inferior colliculus. These responses were compared quantitatively with responses evoked by ipsilateral and contralateral monaural stimulation in normal gerbils. Responses to ipsilateral stimulation in adult gerbils subjected at 2 days of age to ablation of the contralateral cochlea are significantly different from ipsilateral responses in nonoperated gerbils. In several respects they are very similar to contralateral responses in nonoperated gerbils. (Differences between monaural contralateral and ipsilateral responses in control animals are documented in the companion paper, Ref. 24.) These conclusions are based on analyses of response threshold, peak discharge rate, response pattern, and minimum response latency. The mean dynamic range of ipsilateral rate/intensity functions obtained in neonatally ablated gerbils is significantly larger than the mean ipsilateral and contralateral dynamic ranges in control animals. Analyses of threshold tuning curves indicate that the frequency tuning of units in the inferior colliculus of neonatally ablated animals does not differ significantly from the tuning of units in control animals in response to either ipsilateral or contralateral stimulation. These data reveal that in normal gerbils responses of single units in the inferior colliculus to stimulation of the ipsilateral ear result in part from interactions during postnatal development between pathways that convey information from the contralateral ear. The results are discussed in terms of the known anatomic consequences of a neonatal cochlear ablation and the competition for available synaptic space in the development of the retinotectal system.

Pathology as it relates to ear surgery. IV. Surgery of Menière's disease.

Conservative shunting procedures, i.e. ESS, ultrasonic irradiation and cryosurgery, are based on the assumption that there is increased volume and/or pressure of endolymph in Menière's disease. Since there is no reliable clinical test to detect endolymphatic hydrops, shunting procedures on cases without hydrops are doomed to failure. Surgery on the endolymphatic sac was not associated with fibrosis or obliteration of its lumen. Silastic shunt tubes were well tolerated by the body, and the shunt between the sac and the subarachnoid space seemed to remain open. The results of experimental surgery on the endolymphatic sac and its applicability to humans should be revised. Temporary improvement of Menière's symptom-complex may be expected from any surgical procedure on the membranous labyrinth, even in cases without endolymphatic hydrops. Post-operative serous labyrinthitis with associated biochemical changes is the cause of this improvement. The success of shunting procedures cannot be judged histologically by the position of Reissner's membrane. This membrane acts like varicose veins: once dilated, always dilated. Ultrasonic irradiation and cryosurgery of the labyrinth result in limited degenerative changes close to the site of probe application. Degenerated intact membranous walls may act as an internal otic-perotic shunt and may result in symptomatic improvement in Menière's disease. The idea of selective vestibular neurectomy and internal shunting procedures, i.e. without drainage of endolymph to the outside (mastoid) or to the inside (CSF), should be developed further. Recurrence of symptoms following shunting procedures may be due to failure of the shunt, or to the presence of endolymphatic hydrops in the non-operated ear. MF vestibular neurectomy results in complete denervation of the vestibular end-organs, without effect on the cochlea or facial nerve. Excision of Scarpa's ganglion causes retrograde degeneration in the proximal stump of the vestibular nerve, most probably to the level of the brain-stem. Recurrence of dizziness following TC labyrinthectomy is most commonly due to inadequate removal of the vestibular end-organs. The high regenerative capacity of the vestibular nerve is evidenced by the formation of traumatic neuromas in the vestibule following TC labyrinthectomy. Whether these neuromas produce symptoms is unknown. Persistent cochlear hydrops occurs following TC labyrinthectomy and TL vestibular neurectomy owing to obstruction in the hook region of the cochlea and in the ductus reuniens. This may result in persistent tinnitus and feeling of pressure in the ear.

Evaluation of auditory function after stapedectomy in the absence of the other ossicles.

96 stapedectomies (92 primary and 4 re-operations) were performed on 92 ears of 85 patients (on 7 patients bilaterally) between 1965 and February 1980. In addition to fixation of the stapes or footplate, a variety of different lesions of the sound-conducting apparatus required the use of a ‘drum to oval window’ columella. In each case, the body of the incus or an autogenous cortical bone columella connected the tympanic membrane with a fascia graft covering the oval window. Of the possible check-ups, the following have been performed so far: within 1 year, 95/96; longer than 1 year, 83/90; longer than 2 years, 65/73; longer than 5 years, 40/44; the longest possible 67/96. Comparison between the best results achieved and the data obtained at the latest follow-up shows that the results tend to deteriorate with time. An improvement in air conduction of 30 dB or more occurred in 48% of the cases, of more than 20 dB in 73%, no change was observed in 12%, and a deterioration in 1%. At the latest follow–up these figures had changed to 33, 52, 18 and 7%, respectively. In terms of the best results there is a 30-dB interval between the peaks of the curves indicating the distribution of the pre-operative and the post-operative air-bone gaps. According to the latest data this interval has decreased to 20 dB. In the majority of ‘unsuccessful’ cases, deterioration of the hearing improvement once achieved or the absence of post-operative improvement is associated with a wide air-bone gap. The cause of the conductive component in the hearing loss lies in factors other than the columella. No extrusion of the columella has been observed so far. Although pre-operative bone conduction deteriorated over the speech frequencies in 11 patients and at 4 000 Hz in 6, this process could also be observed in the non-operated ear. There was only 1 patient in whom a considerable deterioration occurred at 4 000 Hz, and in another at 500–4000 Hz only on the operated side. No immediate post-operative drop and no total deafness have occurred so far. The necessity of long-term follow-ups for judging any surgical technique of improving hearing is stressed.

Serous otitis media and type 1 tympanoplasties in children. A retrospective study.

The prevalence of serous otitis media has caused a philosophical difference as to when a tympanoplasty should be performed in children. This retrospective study of 74 children (aged 3-17) who underwent 80 operations was undertaken to investigate this problem. The overall success rate for type 1 tympanoplasty was 66%. Age was not a reliable factor in predicting successful results. A history of recurrent serous otitis media was not an important indicator. Adenoidectomy did not influence the surgical outcome. The status of the nonoperated ear was probably a significant factor. Type 1 tympanoplasty has a reasonably good chance of success in children regardless of age and/or previous middle ear ventilation problems. However, a good clinical test of eustachian tube function is still needed to improve further the predictability of timpanoplasty in children.

Long-term results after stapedectomy.

296 cases of stapedectomy accomplished by vein grafting plus polyethylene tubing with a primary (one-year) result of a greater than 10 dB improvement in Air Conduction (AC) threshold in speech frequencies have been tested with pure tone audiometry 1-12 years postoperatively. The AC threshold of the operated ear increased by about 1 dB per year for both low and high frequencies. In the high frequency range this increment can be ascribed to normal aging; in the low range the reason is probably progressive conductive loss. There is no evidence to support the assumption that the operation impairs the sensorineural function of the operated ear. The AC threshold of the unoperated ear also increased--by more than that of the operated ear, for both low and high frequencies. In the low range this was ascribed to progressive stapes fixation; in the high range to stapes fixation plus normal aging. The progression for the non-operated ear is relatively slow, about 2 dB per year.

Effects of calorizations and repeated unidirectional angular accelerations on the nystagmus of unilaterally labyrinthectomized cats.

Right unilateral labyrinthectomy of cats resulted in a left-beating, spontaneous nystagmus that was still weakly present in most animals when recorded in darkness 2 months after surgery. Cats given cold calorizations of the non-operated ear during the month following surgery showed no differences in behavior, optokinetic nystagmus, spontaneous nystagmus, or rotation-induced nystagmus when compared with operated cats which received no caloric stimulation. All operated cats showed a reduction in optokinetic responses that was more marked to CCW stimulus and that persisted through the second month after surgery. Most nystagmic responses to angular accelerations were bidirectionally diminished by more than 50%, 1 month after surgery. A series of 15 unidirectional habituation trials was ineffective in producing a directional imbalance in the nystagmic responses of operated cats, but the series was effective with non-operated Control animals. It appears that an intact vestibular system may be necessary for directionally specific habituation effects to evidence themselves. One month after the habituation series, all operated cats showed improved nystagmic output while Control cats showed a trend toward equalization of responses for the two directions.

Interaction between the utricles and the vertical semicircular canals. VI. Unilateral selective sectioning of the horizontal and vertical ampullar nerves, followed by tilting around the longitudinal axis.

Unilateral, selective left-sided sectioning of the horizontal and vertical ampullar nerves was performed. After the operation, horizontal-rotatory nystagmus developed. When the cats were tilted around their longitudinal axis towards the operated ear, the horizontal nystagmus increased in intensity at the same time as the rotatory component disappeared. Tilling towards the non-operated ear increased the rotatory nystagmus and completely inhibited the horizontal component. The cause of this reaction is discussed.

Interaction between the utricles and the horizontal semicircular canals. II. Unilateral selective section of the horizontal ampullar and the utricular nerve, followed by tilting around the longitudinal axis.

Selective unilateral section of the horizontal ampullar nerve and the utricular nerve was performed. By tilting the animals around their longitudinal axis, the alterations in the horizontal nystagmus were studied. It was shown that these alterations were released from the intact utricle. An increase in utricular activity due to tilting toward the operated ear resulted in a positive triggering of the nystagmus from the ipsilateral horizontal semicircular canal. A decrease in its activity by tilting toward the nonoperated ear inhibited the nystagmus. The cause of these findings is discussed.

Effect of stapedectomy on the nonoperated ear.

Vestibular reactivity changes on the nonoperated side of the ear after all types of stapes surgery occurred in 89% to 92% of otosclerotic patients. Vestibular excitability contralateral changes in the form of hyperreflexia appeared immediately after operation and were characterized by 10-to 25-second reduction of the latent period, by 25- to 50-second lengthening of total nystagmus duration, by the increase of the total number of beats, and by the amplitude increasing by two to ten and more times. Contralateral changes of vestibular excitability persisted for one to ten days in the majority of patients (in 74% to 76% of patients; it persisted for a month in 18.5% to 21.0% of patients and for six months in 5.0% to 5.5%. In 34% of cases, vestibular excitability increase was accompanied by hearing improvement in the nonoperated ear.

Delayed speech feedback in normal hearing and conductive hearing loss, with and without a functioning stapedius muscle.

Normal ears, otosclerotic ears with normal hearing after stapedectomy, and ears with pure conductive hearing loss from otosclerosis and packing of the ear canal, were subjected to a delayed speech feedback test (DSF-test). The results showed no difference in the DSF-effect between the normal ears and the normal hearing operated otosclerotic ears. Neither was there any difference between the nonoperated otosclerotic and the normal hearing ears with an artificial hearing loss. The results suggest that activity in the stapedius muscle has no influence on the DSF-effect in normal hearing ears and in ears with conductive hearing impairment. The DSF-effect, however, was almost double in the non-operated otosclerotic ears and in ears with artificial hearing loss. This may be due to the acoustic energy from the earphones, in the pure conductive hearing losses of about 40 dB, reaching the cochlea both by air and bone conduction in almost equal amounts.