Post Cochlear Implantation Vertigo: Ictal Nystagmus and Audiovestibular Test Characteristics

OBJECTIVE

To investigate ictal nystagmus and audiovestibular characteristics in episodic spontaneous vertigo after cochlear implantation (CI).

STUDY DESIGN

Retrospective and prospective case series.

PATIENTS

Twenty-one CI patients with episodic spontaneous vertigo after implantation were recruited.

INTERVENTIONS

Patient-initiated home video-oculography recordings were performed during one or more attacks of vertigo, using miniature portable home video-glasses. To assess canal and otolith function, video head-impulse tests (vHITs) and vestibular-evoked myogenic potential tests were conducted.

MAIN OUTCOME MEASURES

Nystagmus slow-phase velocities (SPVs), the presence of horizontal direction-changing nystagmus, and post-CI audiovestibular tests.

RESULTS

Main final diagnoses were post-CI secondary endolymphatic hydrops (48%) and exacerbation of existing Ménière's disease (29%). Symptomatic patients demonstrated high-velocity horizontal ictal-nystagmus (SPV, 44.2°/s and 68.2°/s in post-CI secondary endolymphatic hydrop and Ménière's disease). Direction-changing nystagmus was observed in 80 and 75%. Two were diagnosed with presumed autoimmune inner ear disease (SPV, 6.6°/s and 172.9°/s). One patient was diagnosed with probable vestibular migraine (15.1°/s).VHIT gains were 0.80 ± 0.20 (lateral), 0.70 ± 0.17 (anterior), and 0.62 ± 0.27 (posterior) in the implanted ear, with abnormal values in 33, 35, and 35% of each canal. Bone-conducted cervical and ocular vestibular-evoked myogenic potentials were asymmetric in 52 and 29% of patients (all lateralized to the implanted ear) with mean asymmetry ratios of 51.2 and 35.7%. Reversible reduction in vHIT gain was recorded in three acutely symptomatic patients.

CONCLUSION

High-velocity, direction-changing nystagmus time-locked with vertigo attacks may be observed in post-CI implant vertigo and may indicate endolymphatic hydrops. Fluctuating vHIT gain may be an additional marker of a recurrent peripheral vestibulopathy.

Clinical, oculographic and vestibular test characteristics of Ménière's disease

Seventy Ménière's disease (MD) patients with spontaneous vertigo (100%), unilateral aural fullness (57.1%), tinnitus (78.6%), and subjective hearing loss (75.7%) self-recorded nystagmus during their episodes of vertigo using portable video oculography goggles. All demonstrated ictal spontaneous nystagmus, horizontal in 94.3% (n = 66) and vertical in 5.7% (n = 4), with a mean slow-phase velocity (SPV) of 42.8 ± 31.1°/s (range 5.3-160.1). Direction reversal of spontaneous horizontal nystagmus was captured in 58.6%, within the same episode in 34.3%, and over different days in 24.3%. In 18.6%, we observed ipsiversive then contraversive nystagmus, and in 12.9% contraversive to ipsiversive direction reversal. Ictal nystagmus SPV (42.8 ± 31.1°/s) was significantly faster than interictal (1.4 ± 3.1°/s, p < 0.001, CI 34.277-48.776). Compared to age-matched healthy controls, interictal video head impulse test gains in MD ears were significantly lower, cumulative and first saccade (S1) amplitudes were significantly larger, and S1 peak velocities were significantly faster (p = 0.038/0.019/0.008/ < 0.001, CI 0.002-0.071/0.130-1.444/0.138-0.909/14.614-41.506). Audiometry showed asymmetrically increased thresholds in 100% of MD ears (n = 70). Significant caloric, air-conducted (AC) cervical vestibular-evoked myogenic potential (VEMP), and AC ocular VEMP asymmetries were found in 61.4, 37.9, and 44.4% of patients (MD ear reduced). Transtympanic electrocochleography tested in 36 ears (23 patients) showed 81.8% of MD ears had a positive result for hydrops (either a summating potential at 1/2 kHz < - 6 µV, or an SP/AP ratio > 40%). Using ictal nystagmus findings of SPV > 12°/s, and a caloric canal paresis > 25%, we correctly separated a diagnosis MD from Vestibular Migraine with a sensitivity and specificity of 95.7% and 85.1% (CI 0.89-0.97).

The Clinical Uses of Electrocochleography

The clinical uses of electrocochleography are reviewed with some technical notes on the apparatus needed to get clear recordings under different conditions. Electrocochleography can be used to estimate auditory thresholds in difficult to test children and a golf club electrode is described. The same electrode can be used to obtain electrical auditory brainstem responses (EABR). Diagnostic testing in the clinic can be performed with a transtympanic needle electrode, and a suitable disposable monopolar electrode is described. The use of tone bursts rather than click stimuli gives a better means of diagnosis of the presence of endolymphatic hydrops. Electrocochleography can be used to monitor the cochlear function during surgery and a long coaxial cable, which can be sterilized, is needed to avoid electrical artifacts. Recently electrocochleography has been used to monitor cochlear implant insertion and to record residual hearing using an electrode on the cochlear implant array as the non-inverting (active) electrode.

Sensitivity of the cochlear nerve to acoustic and electrical stimulation months after a vestibular labyrinthectomy in guinea pigs

Single-sided deafness patients are now being considered candidates to receive a cochlear implant. With this, many people who have undergone a unilateral vestibular labyrinthectomy for the treatment of chronic vertigo are now being considered for cochlear implantation. There is still some concern regarding the potential efficacy of cochlear implants in these patients, where factors such as cochlear fibrosis or nerve degeneration following unilateral vestibular labyrinthectomy may preclude their use. Here, we have performed a unilateral vestibular labyrinthectomy in normally hearing guinea pigs, and allowed them to recover for either 6 weeks, or 10 months, before assessing morphological and functional changes related to cochlear implantation. Light sheet fluorescence microscopy was used to assess gross morphology throughout the entire ear. Whole nerve responses to acoustic, vibrational, or electrical stimuli were used as functional measures. Mild cellular infiltration was observed at 6 weeks, and to a lesser extent at 10 months after labyrinthectomy. Following labyrinthectomy, cochlear sensitivity to high-frequency acoustic tone-bursts was reduced by 16 ± 4 dB, vestibular sensitivity was almost entirely abolished, and electrical sensitivity was only mildly reduced. These results support recent clinical findings that patients who have received a vestibular labyrinthectomy may still benefit from a cochlear implant.

Variation in speech perception scores among children with cochlear implants

OBJECTIVE

The objective of this study was to identify common factors affecting speech perception scores in children with cochlear implants.

DESIGN

Speech perception data for 167 implanted children were collected at two cochlear implant centres in Melbourne and Sydney. The data comprised audition-alone scores on open-set word and sentence tests. Children were selected on the basis that they had a Nucleus 22-electrode cochlear implant. The average age of the children was 5 yr. Information was also collected about 12 factors that may have influenced speech perception scores for each child. Analysis of covariance was used to identify factors that significantly affected speech perception scores. Pearson pairwise correlation coefficients were also calculated for all factors analyzed.

RESULTS

The analyses in this study identified factors that accounted for 51%, 34%, and 45% of the variance in phoneme, word and sentence perception scores. Scores decreased by 1.4 to 2.4% per year of profound deafness prior to implantation. Children who normally use oral communication scored significantly higher than children normally using sign or simultaneous oral and sign communication. Children implanted in Sydney scored higher on average than children implanted in Melbourne.

CONCLUSIONS

The results show that a significant part of the variation in speech perception scores is systematically related to audiological and environmental factors for each child. The reasons for significant differences between children using different communication modes or from different clinics were not identified.

Abnormal positive potentials in round window electrocochleography

OBJECTIVE

To describe an atypical waveform, termed an abnormal positive potential (APP), on round window electrocochleograms (RW ECochG) of children and to relate its occurrence to clinical history.

STUDY DESIGN

APPs were identified prospectively, and a retrospective analysis was made of these patients' clinical histories, audiograms, and auditory outcomes (hearing aid, cochlear implant, or nonauditory communication)

SETTING

Tertiary referral teaching hospital, day surgery and clinics.

PATIENTS

All 431 children <110 months of age suspected of a severe to profound hearing loss who underwent RW ECochG from January 1993 to August 1997.

INTERVENTION

Diagnostic RW ECochG for auditory threshold estimation.

MAIN OUTCOME MEASURE

The presence on the RW ECochG of the APP: an early positive potential in the absence of a compound action potential (CAP).

RESULTS

An APP was observed in 34 children. The APP was most marked in response to clicks and 8-kHz tones. The APP click threshold averaged 70 dB hearing loss. The brainstem evoked potential of these children showed an absence of waves, or a broad positive wave with no subsequent waves. Twenty-nine of 30 behavioral audiograms obtained were indicative of severe to profound hearing loss. Auditory outcomes were available from 26 children; 45% of them derived no help from a hearing aid, and 8 children received a cochlear implant. Clinical factors frequently associated with APP were prematurity in combination with kemicterus or hypoxia.

CONCLUSIONS

APP thresholds were lower than neural thresholds or behavioral thresholds. Children with APP need close follow-up, because half of those studied needed nonauditory strategies to develop effective communication.

The influence of residual high-frequency hearing on the outcome in congenitally deaf cochlear implant recipients

OBJECTIVE

To show that congenitally deaf children who receive a cochlear implant between 10 and 15 years of age find it significantly more difficult to learn the new signal, and that a history of sound detection at high frequencies with hearing aids is predictive of better outcomes in these children.

STUDY DESIGN

A retrospective study using a within-subjects design.

SETTING

Children's Cochlear Implant Centre, Sydney (CCIC), Royal Prince Alfred Hospital, and the New Children's Hospital in Westmead are tertiary referral centers.

PATIENTS

Forty-five congenitally deaf patients were grouped according to their age (in years) at implantation into group 1 (aged 10-15), group 2 (aged <10), group 2a (aged 6-9), and group 2b (aged 3-5). Within each group, individuals with previous hearing between 2 and 4 kHz before receiving a cochlear implant were identified, and their mean results were compared with those in their respective age-matched groups.

INTERVENTIONS

Surgical implantation, intensive weekly habilitation at the CCIC.

MAIN OUTCOME MEASURES

Speech perception, speech production, and language measures were compared. Questionnaires and telephone interviews were conducted.

RESULTS

Group 2 (age <10 years) consistently outperformed group 1 (10-15 years) on all outcome measures, and most of them learned to converse without lipreading. In group 1, children with previous aided hearing at high frequencies displayed exceptional gains in speech perception and speech production, with reduced dependence on lipreading. Previous high-frequency hearing does not benefit group 2.

CONCLUSIONS

Implant recipients aged 10 to 15 years experience more difficulty than younger children during the initial periods of device use. A history of high-frequency hearing before implantation in these individuals correlates with more rapid improvement.

Electrocochleography in the diagnosis of Meniere's disease

This study prospectively analyses electrocochleography (ECoG) recordings obtained from ears demonstrating symptoms highly suggestive of Meniere's disease. Comparison is made with ECoG recording from ears in which the diagnosis of Meniere's is considered unlikely (control ears). Electrocochleograph recordings were made through a transtympanic recording needle, situated in the round window niche. Analysis was made of the 1 kHz tone burst summation potential (SP) and the summation potential:action potential (SP/AP) ratio response to a 90 dB click. All patients were prospectively awarded a Meniere's score based on a 10-point scale, and comparison was made between ears awarded a score of 7 or greater (Meniere's ears; n > 500), and ears awarded a score 3 or less (control ears; n > 900). Results demonstrate a significant difference in the 1 kHz SP response, and the SP/AP ratio, between "control" and "Meniere's" ears. Furthermore, we show that SP negativity is proportional to the amplitude of the AP click response, and in patients producing an AP click amplitude exceeding 10 V, sensitivity of the tone burst test approaches 85%. This study provides further evidence suggesting the useful role of electrocochleography in determining a diagnosis of endolymphatic hydrops. and demonstrates improved sensitivity of the 1 kHz SP response, compared with SP/AP click ratio, in the diagnosis of Meniere's disease.

Performance after cochlear implantation: a comparison of children deafened by meningitis and congenitally deaf children

The speech perception and speech production performance following cochlear implantation of congenitally deaf children and children deafened by meningitis were analysed. Three groups consisting of 70 congenitally deaf children, 22 children deafened by meningitis before two years of age and 14 children deafened by meningitis after two years of age were compared. The group deafened by meningitis after two years of age demonstrated significantly better speech perception than the other two groups. Their speech production appeared better but did not achieve statistical significance compared with the other two groups. There was no significant difference in either speech perception or speech production between the congenitally deaf group and the group deafened by meningitis before two years of age.

Hearing loss associated with large internal auditory meatus: a report of five paediatric cases

This paper describes the abnormality of a large internal auditory meatus (LIAM). Computed tomography (CT) scans show the otic capsule to be affected by a widened, bulbar internal auditory meatus with loss of or reduction of the bony wall dividing the lateral fundus of the meatus from the cochlea. The vestibule is abnormally dilated. We report five cases of children with LIAM and profound hearing loss. Three of these children are girls and two children were boys. Three had congenital progressive hearing loss, one of these had an accompanying large vestibular aqueduct and dysplasia of the cochlea. Two patients had had meningitis resulting in profound loss.

Meniere's disease: the incidence of hydrops in the contralateral asymptomatic ear

OBJECTIVE

This study analyzes the incidence of endolymphatic hydrops in the asymptomatic contralateral ear of patients with classic Meniere's disease.

STUDY DESIGN

A retrospective study of 3000 subjects who underwent electrocochleography (ECOG) from 1988 to 1998.

METHODS

The presence of endolymphatic hydrops was determined by use of ECOG recordings, which were made through a transtympanic recording needle situated in the round window niche. Analysis was made of the 1-kHz toneburst summation potential (SP), and comparison was made between asymptomatic contralateral "Meniere's ears" (n = 144) and asymptomatic normal "control ears" (n = 114).

RESULTS

Results demonstrated that more than 10% of the contralateral asymptomatic Meniere's ears have an ECOG recording that is highly suggestive of the presence of endolymphatic hydrops. In contrast, less than 2% of the control population demonstrate abnormal ECOG recordings. Furthermore, 15% of the population of contralateral Meniere's ears lie above the 95th percentile of the control population for 1-kHz tone-burst (100 dB) SP negativity.

CONCLUSIONS

This study suggests that a high percentage of patients who have what appears to be unilateral Meniere's disease have evidence of endolymphatic hydrops in the contralateral asymptomatic ear. This finding has important clinical relevance for the management of patients in whom destructive surgery is planned and further highlights the importance of electrocochleography in the diagnosis and management of this disease process.

Surviving cochlear function in the presence of auditory nerve agenesis

This case reports electrophysiological evidence for cochlear function in a child with radiological evidence of bilateral auditory nerve agenesis or severe hypoplasia. The diagnosis of auditory nerve agenesis was supported by a bilateral atresia of internal auditory canals on computed tomography (CT) scan and magnetic resonance imaging (MRI) absent auditory brainstem responses and absent behavioural responses to sound. Despite the apparent absence of an auditory nerve or spiral ganglion, electrocochleography revealed surviving cochlear function at 70-80 db HL and an abnormal electrocochleographic waveform. This case demonstrates that cochlear function may develop without afferent, or efferent innervation. It also emphasizes that cochlear function may occur in the presence of profound deafness.

Positioning of the receiver-stimulator for the CI-24M cochlear implant in infants

A new cochlear implant (CI-24M) has recently been released by Cochlear Ltd. The shape and size of the receiver-stimulator differs from that of the CI-22M. Infants as young as one year of age are now receiving cochlear implants. We have examined the likely effect of skull growth following the implantation of a CI-24M cochlear implant in an infant of this age.

Cochlear origin of hearing loss in MELAS syndrome

There have been few studies investigating the mechanism and nature of the hearing loss that occurs in the mitochondrial disorders. We studied 18 patients with the MELAS A3243G point mutation from four different kindreds. Pure tone audiometry, speech discrimination testing, acoustic reflexes, tympanometry, and brain stem auditory evoked responses were performed to localize the site of pathology in the auditory pathways. In 12 patients, we performed electrocochleography and otoacoustic emissions to assess cochlear involvement. Neuroimaging and promontory nerve stimulation were performed to exclude retrocochlear pathology. Audiological testing confirmed sensorineural hearing loss in 14 of the 18 patients studied; hearing loss was usually gradual in onset, was symmetrical, and initially affected the higher frequencies. In some patients, there were features that distinguished the hearing loss from presbyacusis, including a young age at onset, asymmetrical involvement, stepwise progression, and partial recovery. We treated one patient who had profound bilateral hearing loss with cochlear implantation; this restored good functional hearing. Hearing loss in MELAS syndrome appears to be due to dysfunction of the cochlea, probably resulting from metabolic failure of the stria vascularis and outer hair cells. Cochlear implantation is a therapeutic option worth considering in those patients who become deaf.

Pathophysiologic theories in the etiology of Meniere's disease

The etiology of the attacks of vertigo that occur in Meniere's disease is discussed in this article. None of the current theories remain tenable in view of recent findings concerning the physiology and pathophysiology of the cochlea and endolymphatic sac. A new theory suggests that a narrowed duct becomes obstructed by debris that is cleared by a combination of the secretion of hydrophillic proteins within the sac and a hormone, saccin, that increases the volume of endolymph within the cochlea. It is proposed that the sudden restoration of longitudinal flow initiates the attacks of vertigo.

Speech perception results for children with implants with different levels of preoperative residual hearing

OBJECTIVE

Many reports have established that hearing-impaired children using the Nucleus 22-channel cochlear implant may show both significant benefits to lipreading and significant scores on open-set words and sentences using electrical stimulation only. These findings have raised questions about whether severely or severely-to-profoundly deaf children should be candidates for cochlear implants. To study this question, postoperative results for implanted children with different levels of preoperative residual hearing were evaluated in terms of speech perception benefits.

STUDY DESIGN/SETTING

A retrospective study of the first 117 children, sequentially, to undergo implantation in the Melbourne and Sydney Cochlear Implant Clinics was undertaken. All children had been assessed by and received their implants in a tertiary referral centre.

MAIN OUTCOME MEASURES

To assess aided residual hearing, the children were grouped into four categories of hearing on the basis of their aided residual hearing thresholds measured preoperatively. To assess benefits, the scores of children on standard speech perception tests were reviewed. As different tests were used for children with different ages and language skills, children were grouped into categories according to the level of postoperative speech perception benefit.

RESULTS

The results showed that children in the higher categories of aided preoperative residual hearing showed significant scores on open-set word and sentence perception tests using the implant alone. For children in lower categories of aided residual hearing, results were variable within the groups. More than 90% of children with implants with aided residual hearing thresholds in the speech range above 1 kHz achieved open-set understanding of words and sentences.

CONCLUSION

While the results of this preliminary study confirm previous findings of differential outcomes for children with different levels of preoperative residual hearing, they suggest that children with severe to profound hearing impairments should be considered for cochlear implantation.

Further experience with a straight, vertical incision for placement of cochlear implants

Experience with a straight, vertical incision for cochlear implantation in 168 patients of all ages is reported and comparison made with previous experience using a 'C' shaped incision in 173 patients with regard to complications encountered. With the straight incision the only complication was a wound infection which settled in one week; this is in contrast to the 'C' shaped incision, which was associated with a number of serious complications. The straight incision also compared favourably with the other incisions commonly used for cochlear implantation and appears to offer advantages over them.

Use of transtympanic round window electrocochleography for threshold estimations in children

OBJECTIVE

This study aimed to evaluate the efficacy of round window electrocochleography for the estimation of hearing thresholds in difficult-to-test children.

STUDY DESIGN

The study was a retrospective analysis.

SETTING

A standard day-stay operating room was used.

PATIENTS

Round window electrocochleography was performed on 198 children between January 1993 and January 1996.

INTERVENTION

The intervention was diagnostic.

MAIN OUTCOME MEASURE

Clinically reliable pure-tone audiograms were obtained in 101 patients (50.9%) for comparisons of electrocochleography and behavioral thresholds.

RESULTS

The mean differences between electrocochleography and behavioral thresholds at 0.5, 1, 2, and 4 kHz were less than 6 dB. Ninety-seven percent of the results were within +30 to -30 dB, and approximately 86% of the results were within +20 to -20 dB. Good correlation coefficients of 0.83, 0.84, 0.91 and 0.88 were found between electrocochleography and behavioral thresholds at 0.5, 1, 2, and 4 kHz, respectively. Only 2 of 395 ears were complicated postoperatively by suppurative otitis media. There were no anesthetic complications.

CONCLUSION

Round window electrocochleography can be used in conjunction with other audiometric methods for threshold estimations in the difficult-to-test children and as part of the preoperative assessment for cochlear implantation.

The effect of surgical removal of the extraosseous portion of the endolymphatic sac in patients suffering from Menière's disease

Between April 1990 and June 1996, the extraosseous portion of endolymphatic sac has been removed from the affected ear in 77 patients suffering from Menière's disease. Removal of the extraosseous part of the endolymphatic sac without any drainage procedure did not increase the frequency or severity of the attacks of vertigo in any patient. The results of 43 patients with unilateral disease who had a follow-up period of two years are presented. Only eight of the patients had more than two recurrent attacks of vertigo lasting over two minutes within the two years after the surgery, and in three of these patients the severity of the attacks was greatly reduced. In 56 per cent of the operated ears, the hearing deteriorated at least 10 dBHL across five audiometric frequencies (250 Hz, 500 Hz, 1 kHz, 2 kHz and 3 kHz). To the author, endolymphatic sac removal appeared to provide better relief from vertigo than a simple drainage procedure with less tendency for recurrence several months or years after the initial surgery. At present, the statistical analysis of the results shows no significant difference between removal of the extraosseous portion of the endolymphatic sac and the "so called' endolymphatic sac drainage procedures.

Racial considerations in acoustic neuroma removal with hearing preservation via the retrosigmoid approach

Racial differences in the size, shape and structure of the cranium exist. This paper evaluates the importance of race in influencing the required sizes of craniotomies for gaining access to the lateral end of the internal auditory meatus without breaching the labyrinth via the retrosigmoid approach. Fine-cut CT scans of the temporal bones (axial cuts) of 34 Chinese and 34 Europeans were studied. The relevant distances and angles of the posterior cranial fossa and temporal bone were measured and statistically significant differences between the two races were found. This led us to the conclusion that a larger craniotomy is required in Europeans than in Chinese. In recommending an optimal size for a retrosigmoid craniotomy to remove acoustic neuromas completely and preserve hearing, the racial factor must be considered.

A new incision for placement of cochlear implants

A straight, vertical post-aural incision for the 'Cochlear' multichannel cochlear implant has been evaluated in 52 patients (20 adults and 32 children). Nineteen of the children were under three years of age and five of these were under two years of age. The 7 cm long incision is placed approximately 3 mm behind the post-auricular crease and runs from the tip of the mastoid to a point 3 cm above the superior attachment of the pinna. The incision heals within several days. Because the incision is straight interruption of the blood supply to the flaps raised is the least possible. This also minimizes the possibility of scalp necrosis and implant extrusion. The likelihood of infection is reduced by the small size of the incision, minimal soft tissue dissection and small amount of dead space. Rapid healing has occurred in all cases despite infection in one.

Surgical technique for inserting the cochlear multielectrode array into ears with total neo-ossification

A method of inserting a multielectrode cochlear implant into a cochlea that has become totally ossified following meningitis is described. The method, called the inlay technique, involves drilling a cleft so that the electrode array can be inserted along the position of the basal coil. First, the technique involves drilling along the scala tympani. Second, by drilling out the scala vestibuli, space is created to follow the basal turn of the cochlea without removing the overlying promontory. Five children have had this surgery, and between 12 and 15 electrodes were inserted. Two of the children have developed some open-set listening ability, with open-set sentence recognition scores of over 10%. One child has obtained open-set listening scores of over 50%.

The influence of race on the position of the jugular bulb

The position of the jugular bulb (JB) is of great clinical significance to the otologist. A high and laterally situated jugular bulb may pose difficulties when dealing with the middle ear while a high and medially sited jugular bulb can create problems in neuro-otological surgery. This paper aims to study possible racial differences in the position of the jugular bulb. Fine-cut computed tomogram (CT) scans of temporal bones (in the axial plane) of 34 Caucasians and 34 Chinese were studied. The position of the jugular bulb was determined with reference to the midpoint of the lumen at the inferior limit of the cochlea (mpC). Of the 60 Caucasian and 58 Chinese temporal bones with identifiable jugular bulbs, 33 jugular bulbs of the Caucasian (55 per cent) and 34 jugular bulbs of the Chinese (58.6 per cent) were at the same height or higher than the mpC (p = 0.2; chi-squared test). The midpoint of the jugular bulb was 8.67 +/- 1.73 and 8.61 +/- 2.49 mm posterior to the mpC for the Caucasian and Chinese respectively (p = 0.2; t-test). However, the midpoint of the jugular bulb of eight Caucasian (24.2 per cent) and 22 Chinese (64.7 per cent) were medial to the mpC (p < 0.001; chi-squared test). Race does not influence the height of the jugular bulb nor its position in the sagittal plane but can influence whether a high jugular bulb is medially or laterally situated.

Cochlear implant extrusion in a young child--a preventive procedure

A Cochlear Mini System 22 Channel cochlear implant extruded through the skin of a young girl. The implant was saved by use of a transposition flap. Extrusion appeared to be due to pressure necrosis from the implant on the overlying tissues. It is believed that this problem can be prevented by angulation of the implant before insertion so that it conforms to the curvature of the skull, so avoiding pressure on the tissues. The method of angulation is described.

Surgical techniques for insertion of a multi-electrode implant into a postmeningitic ossified cochlea

Severe ossification within the cochlea occurs in more than 20% of children deafened by meningitis. A multi-electrode cochlear implant can dramatically restore useful hearing to such children, providing it can be inserted satisfactorily within the cochlea. Various surgical techniques for cochlear implantation into an ossifying cochlea are discussed. Partial ossification often can be negotiated by clearing the new bone from the scala tympani or by inserting the array through the scala vestibuli. Total ossification is not a contraindication to the use of a multi-electrode cochlear implant. A method of drilling out the basal cochlear turn without removal of the overlying promontory is proposed. The results of "inlay" insertion into a totally ossified cochlea are evaluated in five ears.

Electrocochleography in profoundly deaf children: comparison of promontory and round window techniques

It is important to be able to accurately assess residual cochlear function in profoundly deaf children. Profound hearing loss in children requires special consideration, because the choice between a cochlear implant and a hearing aid depends on accurate estimation of the residual hearing. Previous reports confirm that promontory (needle) electrocochleography (ECochG) is useful for evaluation of residual hearing in severely deaf children, but there were some limitations in assessing the lower audiometric frequencies and for assessing profound hearing loss. It is argued that accurate placement of a round window electrode (RW ECochG) provides better recordings. Round window ECochG testing is performed under general anesthesia in young children and gives an opportunity for inspection of the middle ear using an endoscope. This report describes a special "golf club" electrode that can be placed under direct vision into the round window niche, minimizing the risks of damaging an abnormal round window while providing the optimum extracochlear recordings. Round window ECochG gives better responses, especially in lower audiometric frequencies, than conventional promontory ECochG. In the Sydney children's cochlear implant program, RW ECochG has become an essential preoperative test.

Perilymphatic fistula with no visible leak of fluid into the middle ear: a new method of intraoperative diagnosis using electrocochleography

A new method for the intraoperative diagnosis of a perilymphatic fistula is presented. Two cases are reported in which the test clearly indicated the presence of a fistula even though no visible leak of fluid was noted by the surgeon. In each case, there was a clear history of vertigo and hearing loss. Preoperatively, the presence of a perilymphatic fistula was suggested using raised intrathoracic pressure test in electrocochleography (ECochG). During the surgery, there was no visible leak of fluid into the middle ear. Electrocochleography was undertaken intraoperatively by placing an electrode in the round window niche and suctioning the oval window area; in neither case was any ECochG change seen. Next the electrode was repositioned on the oval window and when the round window area was suctioned, obvious ECochG changes occurred. Action potential (AP) amplitude dramatically decreased in both cases and summating potential (SP) increased in one case.

Spontaneous perilymphatic fistula: electrophysiologic findings in animals and man

The case against the occurrence of spontaneous perilymphatic fistulas is presented. Electrophysiologic findings both in animals and in man suggest that small holes in either the round or oval window are not associated with any significant hearing loss. Removal of perilymph may cause some changes in the electrocochleogram that can be reversed when the perilymph is replaced. Tympanotomy surgery, especially when performed with the injection of local anesthetic solutions may result in transudates in the middle ear that are difficult to differentiate from perilymph leaking out from the inner ear. Perilymphatic fistulas were excluded by performing a posterior myringotomy under general anesthesia in 162 congenitally deaf ears. If fluid was present it was suctioned, and if no change occurred on the intraoperative electrocochleogram, it was concluded that no fistula existed. Based on the electrophysiologic findings and the clinical observations in over 240 ears, it was concluded that spontaneous perilymphatic fistulas do not exist. The author accepts that perilymphatic fistulas occur after surgery, especially after stapedectomy, and that they can occur after head injury or barotrauma. However, these should heal readily; persistent or intermittent fistulas are an otologic rarity.

Intraoperative electrocochleography of endolymphatic hydrops surgery using clicks and tone bursts

Seventy-seven ears of patients with Menière's disease (n = 69) and other ears with secondary endolymphatic hydrops (n = 8) underwent valved shunt surgery, and were monitored with intraoperative electrocochleography (ECoG) using clicks stimuli (n = 77), and both clicks and tone bursts (n = 37). Of the 41 ears in which the "baseline" measurement was > 35% summating potential to action potential (SP/AP) amplitude click ratio, 23 ears (56%) showed a significant ratio decrease (improvement). Twenty-six ears out of the 37 that were monitored by both clicks and tone bursts had abnormal absolute SP tone bursts amplitudes at "baseline" and 8 ears (31%) changed to normal at "closing". When tone burst ECoG information is combined with click stimuli, our basic understanding of click ECoG is enhanced and our ability to assess electrophysiologic changes intraoperatively is improved.

When the diagnosis of deafness is wrong

OBJECTIVE

To describe three children in whom there had been major errors in the diagnosis of hearing loss.

CLINICAL FEATURES

In three children (two developmentally delayed, one not developmentally delayed) hearing thresholds obtained by behavioural testing were later proven wrong. This resulted in significant family distress and inappropriate educational approaches.

INTERVENTION AND OUTCOME

Electrocochleography and brainstem audiometry were performed, demonstrating normal cochlear function. Simultaneous microinspection of the ears gave information about current or old middle ear disease and the likelihood of past conductive hearing loss. In each case hearing aids could be discarded, enabling parents and teachers to concentrate on one rather than multiple problems.

CONCLUSION

Electrocochleography and brainstem audiometry should be used more frequently to check the diagnosis of hearing loss in children who are developmentally delayed, hyperactive or autistic and who do not give consistent responses to behavioural testing. It should also be considered if parents are firmly convinced that the diagnosis of deafness is wrong.

Electrocochleography in the diagnosis of perilymphatic fistula: intraoperative observations and assessment of a new diagnostic office procedure

The intraoperative electrocochleogram (ECochG) was investigated during stapedectomy surgery and during cochleostomy surgery. This provided the justification for obtaining recordings with the oval window (OW) or round window (RW) intact and then when there was a definite fistula. It was noteworthy that no ECochG changes occurred on merely opening the OW or RW, but that marked changes occurred on removing perilymph, even by gentle suction. On raising the intrathoracic pressure and replacing the perilymph, the ECochG potentials usually recovered. Based on these intraoperative observations, an office procedure was designed. The subject was asked to raise the intrathoracic pressure on several occasions and changes in the amplitude of the ECochG potential were noted. An increase of over 15 percent in the action potential (AP), with or without a decrease in the negative summating potential (SP) during the period of raised intrathoracic pressure, was used as the diagnostic criteria for a perilymphatic fistula. A decrease in the AP with or without an increase in the negative SP immediately on relaxing after a period of raised intrathoracic pressure was also treated as a positive diagnostic criterion. Seventy-one normal ears were investigated and a positive result was recorded in two ears (false positive rate: 2.8%). Two hundred and six ears, strongly suspected as having a perilymph leak on the basis of the clinical history and vestibular signs have been investigated over the past 4 years. Ninety positive diagnoses have been reached and 46 of these ears have been surgically explored.(ABSTRACT TRUNCATED AT 250 WORDS)

Epithelial migration in the external auditory canal and the movement of the chondro-osseous junction

Epithelial migration occurs in a lateral direction from the tympanic membrane to the external auditory canal. The underlying mechanism which determines the direction of this laterally directed movement has not been elucidated. This study attempts to analyze whether migration is stimulated at the chondro-osseous junction, the very place where squamous cells stop migrating and desquamate. Active movement of the junction is postulated as a stimulus for the migratory process. Such movement may be caused by contraction of the peri-auricular muscles which attach to the cartilaginous canal. In this study, eight guinea pigs underwent unilateral facial nerve section in order to paralyze the peri-auricular muscles and thus diminish active movement of the junction. Migration times were determined for both operated and unoperated ears. No significant difference was noted between the two groups. One may conclude that paralysis of the peri-auricular muscles does not alter the time taken for skin migration in the external auditory canal.

Intraoperative electrocochleographic monitoring of inner ear surgery for endolymphatic hydrops. A review of cases

The purpose of this review of cases was to determine whether or not the SP/AP amplitude ratio changes during unidirectional inner ear valved shunt surgery for the decompression of the hydropic labyrinth in Meniere's disease. A series of 62 patients underwent shunt surgery over a 20 month period. In 43 cases (43 ears), ECoG responses were successfully recorded throughout the duration of surgery. A pair of two-tailed paired t-tests were computed for SP/AP amplitude ratios acquired during intraoperative ECoG monitoring at the baseline and closing stage of surgery. The first t-test compared the mean SP/AP amplitude ratios at baseline and closing for those cases in which the SP/AP amplitude ratio at baseline was abnormal (baseline > 35%). The t was significant, t(19) = 4.63, p < 0.01). The second t-test compared the mean SP/AP amplitude ratios at baseline and closing for those cases in which the SP/AP amplitude ratio at baseline was WNL (baseline < or = 35%). The t was insignificant, t(20) = 0.31, p > 0.05. Variations between baseline and closing measurements were categorized as either a reduction, no change (very stable over time), or an increase in the SP/AP amplitude ratio. A change in the SP/AP amplitude ratio from baseline to closing of > or = 7% (x = 2%, SD = 2%) was considered statistically significant. Overall (43 cases), 49% of the variations fell into the no change category, with 42% and 9% of the cases placed in the reduction and increase categories, respectively. Of the cases (22) in which the baseline measurement was outside the limits of normal, 64% showed a reduction, 32% showed no change, and 4% showed an increase in the SP/AP amplitude ratio at closing. Changes in the SP/AP amplitude were observed at various stages of the surgical procedure. Reductions were found at each of the five surgical steps identified, with the majority of the changes almost evenly divided between the stages of mastoid drilling and opening sac. Increases in the SP/AP amplitude ratio were found in four cases. The increases were observed during drilling of the mastoid bone in two cases and sac decompression and opening the sac in the remaining cases.

The use of intraoperative electrocochleography in Meniére's surgery

Intra-operative electrocochleography was undertaken during surgery for Meniére's disease. It was found that the electrocochleogram (ECoG) provided a stable measure which accurately reflected changes within the inner ear during surgery. During salt osmosis of the round window, a rapid change in the summating potential versus action potential ratio (SP/AP) occurred which showed when the endolymphatic hydrops (ELH) had been altered. During a modified cochleostomy procedure, the ECoG showed when the cochlear duct had been ruptured. Forty ears were monitored during endolymphatic sac surgery. Twenty-five of these ears showed stable ECochG which did not alter at any time during the procedure; however, 8 of these ears showed normal SP/AP ratios during the surgery despite having been abnormal in the week prior to surgery. The SP/AP ratio was reduced in 8 ears, increased in 3 ears and showed other changes which were probably due to unstable electrode positioning in 4 ears. It was concluded that endolymphatic sac or duct surgery altered the inner ear physiology in a significant number of ears affected by endolymphatic hydrops.

Measurement of auditory brainstem responses evoked by electrical stimulation with a cochlear implant

Auditory brainstem responses evoked by electrical stimulation with a Nucleus/Cochlear implant can be measured if care is taken to prevent stimulus artefacts. A simple procedure is described which relies upon a passive LCR filter to prevent the radiofrequency carrier from entering the input of the recording amplifier. The filter simply prevents saturation of the amplifier by the carrier.

Polarity order of biphasic square pulse electric current stimulation of human cochlear nerve: observations with transtympanic electrodes

Eighteen totally deaf human cochleae were stimulated with biphasic square pulses of current through transtympanic needle electrodes. The thresholds of the 2 polarity orders, + - and - +, were compared for various pulse durations. For a pulse duration of 500 microseconds the polarity order - + had the lower threshold. For pulse durations of 2 ms and longer, the polarity order + - had the lower threshold. A discussion is given of the significance of the results for finding out the site of cochlear nerve excitation by the stimuli.