Ronen Perez

Vestibular and cochlear ototoxicity of topical antiseptics assessed by evoked potentials.

Objectives/Hypothesis To evaluate and compare the effect of chlorhexidine gluconate, povidone‐iodine, and alcohol—three antiseptics used before ear surgery—on the function of the vestibular and cochlear parts of the sand rats inner ear. The assessment of damage is based on the recording of vestibular evoked potentials (VsEPs) and auditory brainstem response (ABR).

Intratemporal facial nerve schwannoma: a management dilemma.

Objective: To report the findings in patients with facial nerve schwannoma in whom surgery was elected at onset versus patients treated expectantly. Study Design: Retrospective case review. Setting: Tertiary referral center. Patients: Twenty-four patients with a mean age of 44 years (range, 18-65 yr) were followed for an average of 6 years (range, 1-19 yr). Intervention: Eleven patients underwent complete tumor excision and 13 patients were enrolled in ongoing monitoring only. Main Outcome Measures: Facial nerve function and hearing acuity were noted at the time of initial and last visits. Magnetic resonance imaging was used to determine tumor growth in those individuals treated expectantly and as a means of excluding tumor recurrence/persistence in those treated surgically. Results: Of the 11 patients who underwent tumor removal, the facial nerve was spared in 7. Eight had varying degrees of facial nerve dysfunction initially. In this group (mean follow-up, 8 yr), six patients had unchanged nerve function, four had improved nerve function, and one had worsened. No long-term recurrence was noted. Of the 13 patients followed expectantly, three had facial weakness initially. During the follow-up interval (mean, 5 yr), facial function remained unchanged for eight and worsened in five. During this interval, 4 of the 13 patients demonstrated tumor growth and 3 have recently undergone tumor removal. Conclusion: Facial nerve schwannomas are extremely slow growing and frequently present without facial dysfunction. It is possible to surgically remove these tumors while sparing the nerve; as a result, postoperative function is correspondingly better. Finally, the decision on how to treat these patients should be individualized and based on initial facial function, growth rate, surgical experience, and informed patient consent.

Semicircular canal fenestration – improvement of bone- but not air-conducted auditory thresholds

Auditory stimulation can, under certain circumstances, activate the vestibular end organs and this is facilitated by fenestration of a semicircular canal (SCC). Several fenestrated profoundly deaf patients reported improvements in their bone- (BC) but not air-conducted (AC) thresholds. Bone conduction auditory thresholds have been reported to be better than normal in several patients with thinning or absence of bone over a SCC (dehiscence). This phenomenon was carefully studied in the fat sand rat (Psammomys obesus) by recording auditory brainstem evoked responses to BC and AC auditory stimulation, before and after SCC fenestration. Fenestration would be expected to decrease the pressure difference across the cochlear partition, causing a reduction in the amplitude of the classical base to apex input traveling wave, and should therefore lead to an elevation in AC and BC thresholds. Instead, BC thresholds decreased (i.e. improved) following fenestration (by 7.0+/-4.2 dB; P<0.005), while AC thresholds did not change. Thus the cochlea becomes more sensitive to BC, but not AC, stimulation in the presence of a SCC fenestration. This may be due to the removal by the fenestration of a factor impeding BC cochlear responses, or by the addition of a facilitating factor. The result that the SCC fenestration did not affect AC threshold provides support for the concept that at low intensities the outer hair cells are directly activated by components of the fluid pressures surrounding them, which alternate at audio-frequencies. These cochlear fluid audio-frequency pressures are induced by stapes footplate movement and not by a base to apex input traveling wave. The audio-frequency pressures would not be affected by SCC fenestration. The outer hair cell motility thus induced somehow excites the inner hair cells and the auditory nerve fibers. At low intensities the outer hair cell motility causes localized displacement at the appropriate position on the basilar membrane.

Vestibular end-organ impairment in an animal model of type 2 diabetes mellitus.

Objectives/Hypothesis To define and assess the functional impairment of the vestibular part of the inner ear in a diabetic state, using a direct and objective test for evaluating the vestibular end‐organ and an animal model for diet‐induced type 2 diabetes mellitus.

The Pathway Enabling External Sounds to Reach and Excite the Fetal Inner Ear

The human fetus in utero is able to respond to sounds in the amniotic fluid enveloping the fetus after about 20 weeks gestation. The pathway by which sound reaches and activates the fetal inner ear is not entirely known. It has been suggested that in this total fluid environment, the tympanic membrane and the round window membrane become ‘transparent’ to the sound field, enabling the sounds to reach the inner ear directly through the tympanic membrane and the round window membrane. It is also possible that sounds reach the inner ear by means of tympanic membrane – ossicular chain – stapes footplate conduction (as in normal air conduction). There is also evidence that sounds reach the fetal inner ear by bone conduction. Several animal and human models of the fetus in utero were studied here in order to investigate the pathway enabling sounds to reach and activate the fetal inner ear. This included studying the auditory responses to sound stimuli of animals and humans under water. It was clearly shown in all the models that the dominant mechanism was bone conduction, with little if any contribution from the external and middle ears. Based on earlier experiments on the mechanism and pathway of bone conduction, the results of this study lead to the suggestion that the skull bone vibrations induced by the sound field in the amniotic fluid enveloping the fetus probably give rise to a sound field within the fetal cranial cavity (brain and CSF) which reaches the fetal inner ear through fluid communication channels connecting the cranial cavity and the inner ear.

The Neonate Has a Temporary Conductive Hearing Loss due to Fluid in the Middle Ear

Postnatal functional changes in the activity of the ear and auditory pathway in neonatal guinea pigs [from day of birth (postnatal day, PND = 0), PNDs 1–4, 7 and then weekly up to 7 weeks] were studied as a model of maturation of hearing in human neonates. On the day of birth there were signs of a conductive hearing loss: negative middle ear pressure, auditory nerve brainstem evoked response (ABR) threshold elevation, ABR wave 1 latency prolongation and low amplitude otoacoustic emissions. The conductive hearing loss is probably a result of the (amniotic) fluid found in the neonatal middle-ear cavity. Over the next PNDs, this conductive hearing loss was resolved. In order to confirm this neonatal conductive hearing loss and its resolution, saline was instilled into the middle ear of guinea pigs. This induced signs of a conductive hearing loss similar to those seen in the neonatal guinea pigs which disappeared with clearance of this fluid. Therefore it may be concluded that most of the changes in auditory function seen over the first PNDs are due to absorption of amniotic fluid from the middle-ear cavity.

Bone conduction activation through soft tissues following complete immobilization of the ossicular chain, stapes footplate and round window

Classically it has been thought that bone conduction activation at the mastoid leads to relative motion between the stapes footplate and the oval window due to inertial and to compression (distortion) mechanisms. However, several recent clinical findings and experimental manipulations may point to additional mechanisms. These manipulations were extended in the present study. In ten fat sand rats, following obliteration of one ear, auditory nerve brainstem evoked response (ABR) thresholds were recorded in response to broad band click stimuli, either air conducted (AC) through insert earphones or bone conducted (BC) delivered directly to the exposed skull bone. Following this, the entire ossicular chain, stapes footplate and round window were completely immobilized with super glue, leading to a mean AC threshold elevation of 44 dB, but to a mean BC threshold change (elevation) of only 3.5 dB. In this state of complete immobilization, the bone vibrator was applied to a pool of saline in the surgical area and ABR was elicited with a mean threshold which was not significantly different from that of the BC threshold. When the bone vibrator was then applied to the eye without touching the bone at the orbit, the resulting ABR threshold was about 20 dB greater than the BC threshold. In conclusion, BC stimulation can activate the cochlea without two mobile windows. Furthermore, the cochlea can be activated by a fluid pathway and by application of a bone vibrator to non-osseous sites (soft tissue conduction).

Stratification for Malignant External Otitis

OBJECTIVE: To propose a CT-based method for early identification of severe cases of malignant external otitis (MEO) by correlating between initial CT findings and clinical course. STUDY DESIGN AND SETTING: Eighteen MEO patients who underwent CT on admission were included in this retrospective study conducted at a tertiary center. The number and extent of anatomical areas involved according to CT were compared to clinical course severity. RESULTS: The patients were categorized into two groups according to clinical course. There were 13 patients in the “nonsevere” group and 5 in the “severe.” In six out of eight CT anatomical areas the “severe” group had significantly higher scores (P < 0.05 to P < 0.0005). The average number of areas involved in the “nonsevere” group was 2.9 and in the “severe” 5.4 (P < 0.0005). CONCLUSION: We found a clear correlation between clinical course and initial CT findings in MEO patients. Based on these findings it may be possible to predict clinical course severity according to initial CT.

Acute mastoiditis in children: is computed tomography always necessary?

Objectives Acute mastoiditis (AM) is the most common intratemporal complication of acute otitis media in children. In the past decade, reports have indicated a rise in the incidence of AM in the pediatric population. A parallel rise in the use of computed tomography (CT) imaging has occurred. The rise in the use of CT scanning in the pediatric population, entraining with it a rise in pediatric brain irradiation, has led us to question the necessity of using CT for pediatric patients with AM. Methods We reviewed the medical files of pediatric patients who had AM in the years 2005 through 2007. Results Fifty patients were identified. The gender distribution was equal, and the ages ranged from 4 months to 12 years. Of the 46 patients who were admitted to our institution “de novo,” only 2 underwent CT scanning on admission, and 4 other patients had CT performed during hospitalization. The majority of patients (92%) with AM did not have a CT scan performed and were treated conservatively with no complications. Conclusions In most pediatric patients, CT does not seem to be indispensable in the diagnosis of AM. Conservative therapy and close follow-up seem to suffice for most.

Shifting trends: mastoiditis from a surgical to a medical disease.

OBJECTIVE The aim of this study is to review the outcome of pediatric patients suffering from acute mastoiditis treated conservatively and to correlate this to the evolution of our understanding of the shift in which mastoiditis has been transformed from a surgical to a medial disease. METHODS We performed a retrospective review patient files hospitalized in our tertiary-care center between 2005-2008. We examined the data concerning the infection which included: presenting signs/symptoms, prior otologic history, treatment (including both surgical and conservative) prior to hospitalization and during hospitalization, computed tomography (CT), hospital duration, complications and overall outcome. This data was analyzed and compared between different patients who underwent different treatment strategies. RESULTS Fifty-one patients were included in this retrospective review. Initially, forty-nine patients admitted to our hospital were treated conservatively. This treatment included intra-venous antibiotics, myringtomy and if needed subperiosteal abscess incision and drainage. Only 2 patients underwent CT scanning on admission. Further on, during hospitalization 4 additional patients underwent CT scanning due to continued fever or progression of local disease. All four CT scans showed no intra-cerebral complications, and so all continued with conservative treatment. CONCLUSION Most cases of acute mastoidits may be treated with a conservative therapy regime. This regime, in our opinion, should include three branches: the first intravenous antibiotic therapy using a broad spectrum antibiotic. The second is myringotomy and the third branch is incision and drainage of subperiosteal abscess when needed.