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Facial nerve injury in cochlear implantation.

We present eight cases of FN dysfunction after cochlear implantation. Four mechanisms of injury are proposed. The most common injury occurs from the heat of a bur shaft rotating over the FN in the facial recess. Several suggestions are made to help prevent the type of injuries we have seen. Preoperative imaging and intraoperative FN monitoring may be of general assistance in avoiding injuries to the FN, especially in cases of revision surgery and congenital malformations.

Adolescent↗

Cortical reorganization after acute unilateral hearing loss traced by fMRI.

Unilateral acoustic stimulation produces a functional MRI (fMRI)-blood-oxygenation-level-dependent (BOLD) response mainly in the contralateral auditory cortex. In unilateral deaf patients, the BOLD response is bilateral. We studied a subject with sudden hearing loss after cochlear nerve resection before and repeatedly after surgery. During normal bilateral hearing, contralateral cortical BOLD responses were found. Progressing compensatory reorganization with bilateral representation of unilateral stimulation was detected over a period of approximately 1 year.

Acute Disease↗

Improvement of hearing after microsurgical removal of acoustic neurinoma.

A case of a 3-cm acoustic neurinoma totally excised with preservation of the facial and cochlear nerves is reported. Hearing was not impaired by the operation, but dramatically improved within 2 months. The literature on operations of acoustic tumors with preservation of hearing is reviewed. In patients with some hearing ability, the operation should be conservative, whatever the size of the neurinoma, because there is a fair chance of success.

Adult↗

Surgical management of high jugular bulb in acoustic neurinoma via retrosigmoid approach.

Of 200 patients with acoustic neurinoma undergoing an operation via the retrosigmoid transmeatal approach in the semisitting position, 18 patients had a high jugular bulb on the tumor side. The frequency was 9%. From a neurosurgical point of view, a jugular fossa above the low border of the internal auditory canal (IAC) is classified as a high one. All 200 patients were evaluated by computed tomography with bone window reconstruction of high-resolution thin axial slices (1.5 mm). High jugular bulbs were classified into three grades as follows: Grade I, jugular bulb situated less than 1.5 mm above the low border of IAC; Grade II, jugular bulb between 1.5 and 3.0 mm above the low border of the IAC; Grade III, jugular bulb > 3 mm above the low border of IAC. There were eight patients with Grade I, six patients with Grade II, and four patients with Grade III. In these patients, in order to open the IAC without concomitant injury of the jugular bulb, the superior posterior portion of the porus was drilled away. Opening the jugular fossa was unavoidable in Grade III cases. No difference was noted in functional preservation of facial or cochlear nerve between HJB cases and normal jugular bulb cases, but HJB cases had a higher frequency of air embolism during tumor removal than did normal cases (16 versus 5%), especially Grade III cases (two of four). There was no mortality or morbidity in the cases of air embolism. Details of the surgical procedure in such cases are discussed.

Adolescent↗

Staging and management of primary cerebellopontine cholesteatoma.

Primary cerebellopontine angle (CPA) cholesteatoma grows slowly and silently in the subarachnoidal spaces. The diagnosis is often late, when the lesion has reached large dimensions. Surgical removal is the only available therapy. Fifteen consecutive cases of CPA cholesteatoma managed at a tertiary otoneurosurgical referral unit between September 1985 and April 1999 were reviewed. The study population, consisting of seven males and eight females, had a mean age of 44 years of age (range 21-69) at the time of surgery. The clinical, audiological and radiological presentations were examined. The tumours were classified according to the Moffat classification of CPA cholesteatomas. In 67 per cent of cases the presenting symptom was related to the vestibulo-cochlear nerve. The average duration of symptoms was 23 months (ranging from one month-10 years). The hearing preservation approaches were utilized the most (11 cases), while the translabyrinthine approach alone, or in association with a middle fossa craniotomy, was performed in four cases. Tumour removal was total in 12 cases and subtotal in three cases. In cases undergoing hearing preservation surgery the mean pre-operative pure tone average (PTA) for the frequencies 0.5, 1, 2, and 3 kHz was 19.3 dB HL (SD 13.84) and the mean pre-operative speech discrimination score (SDS) was 89.8 per cent (SD 5.97). In 44.4 per cent of patients the hearing was preserved and the mean post-operative PTA was 20.29 dB HL (SD 15.84). In five patients post-operative complications occurred. No peri- or post-operative death occurred in this series, one patient developed a recurrence 15 years after the initial surgery.

Adult↗

Investigation of acoustic trauma from the airbag.

Since the automobile-airbag passive restraint system may be in general use in early 1976, and, the fact, is now an opinion on some automobiles, its potential biomedical hazards need to be examined. The objective of this study was to investigate the effects of local slap pressure of airbag deployment against the external ear and tympanic membrane and to measure its effects on subsequential hearing acuity. Adult and infant squirrel monkeys were used as experimental subjects. To create an adequate simulation of the airbag trauma, a small airbag was fabricated and mounted on a pneumatic impact facility. This device was designed to produce a specific velocity to determine the behavior of objects under impact conditions simulating accident kinematics. Cochlear nerve action potentials were measured in both ears of 10 subjects prior to blast, immediately post-blast and several weeks post-blast. High-speed photography recorded events of the blast as well as the technique of recording the electrical potential from the cochlea. No permanent hearing damage, eardrum perforation, disruption of ossicles, or loss of hair cells occurred at airbag velocities up to 100 mph and a sound intensity level of 150 db.

Age Factors↗

Auditory-evoked responses in benign intracranial hypertension syndrome.

In this study, auditory brainstem-evoked responses were conducted on 28 patients with otologic symptoms (pulsatile tinnitus, hearing loss, aural fullness) secondary to benign intracranial hypertension syndrome. Abnormalities consisting mainly of prolonged interpeak latencies were detected in one third of these patients. It is speculated that the pathophysiologic mechanisms responsible for these auditory brainstem-evoked abnormalities are stretching-compression of the cochlear nerve and brainstem caused by the intracranial hypertension and/or primary edema of the same structures due to the benign intracranial hypertension syndrome itself. Normalization or improvement was noticed in the majority of the patients after management. Since the number of patients in this study is small, it is felt that the diagnostic and prognostic value of this test needs further evaluation.

Adult↗

Donut-like topology of synaptic vesicles with a central cluster of mitochondria wrapped into membrane protrusions: a novel structure-function module of the adult calyx of Held.

Structural and functional properties of synapses are intricately and reciprocally coupled. To cope with the functional requirements in auditory processing, the calyx of Held developed distinct structural specializations such as a large number of active zones, large size, elaborate morphology, and defined distribution of ion channels. These specializations typically appear during postnatal maturation within the first 3 weeks of life and are accompanied by marked changes in the properties of synaptic transmission. We examined the arrangement of synaptic vesicles at different postnatal stages of maturation by genetically labeling vesicles with the fluorescent fusion protein synaptophysin-enhanced green fluorescent protein. Fluorescence and electron microscopy-based analyses revealed a new anatomical specialization in the mature calyx of Held. Within small, membrane-delimited compartments (swellings), synaptic vesicles formed donut-like assemblies around a central cluster of interconnected mitochondria. Adult calyces contained approximately 100 such structural units, each of them consisting of approximately 800 synaptic vesicles, six to nine mitochondria, and five to nine active zones. A donut of synaptic vesicles measured approximately 1 microm in diameter and was placed in a swelling with a volume of approximately 5 fl. Conspicuously, this structural specialization appears with the onset of hearing and may contribute to maturational changes in presynaptic function.

Age Factors↗

Circling mouse, a spontaneous mutant in the inner ear.

A spontaneous mutant was established in the ICR mouse strain. The affected mice became hyperactive at about 7 days of age, and then showed circling behavior. The body weight decreased significantly 2 weeks after birth, and developmental defects were revealed in the middle ear, cochlea, cochlear nerve, and semicircular canal areas. The mutation was inherited by an autosomal single recessive gene and is referred to as cir.

Animals↗

Acoustic neurinomas. Diagnosis and treatment.

We present our experience with 83 patients with acoustic neurinomas (January 1988 to November 1996); 81 patients underwent surgery and 2 patients with intracanalicular neurinomas received conservative therapy due to their advanced age (1 case) and patient's option (1 case). The surgical approach was retrosigmoid/transmeatal and the goal was total removal in one procedure with preservation of facial and cochlear nerves. Radical removal of lesion was attempted in 79 cases and it was possible in 77 patients. Subtotal tumor resection was planned in 2 cases. Facial nerve function (grades I to III, House and Brackman) was preserved in 90% and hearing in 58% of those with preoperative hearing. Three patients died due to postoperative complications. Early diagnosis of acoustic neurinomas is the most important factor in the prognosis and is one of the most important conquest of neurophysiology and modern neuroimaging. The management of these patients still present many controversial points. This article presents the diagnostic procedures used for acoustic neurinomas, the advantages and disadvantages of the different surgical approaches and the alternative management of these lesions.

Adolescent↗

Tinnitus in the older adult: epidemiology, pathophysiology and treatment options.

Tinnitus is the perception of sound in the absence of an apparent acoustic stimulus. More than 35 million Americans experience tinnitus, with 2-3 million severely debilitated by this distressing symptom. The prevalence increases with age and there is a high incidence associated with both noise-induced and age-related hearing loss. Although there are several theories regarding the pathophysiology of tinnitus, the precise mechanism remains to be elucidated. The most compelling of these is the hypothesis that tinnitus occurs as a result of spontaneous and aberrant neural activity at any level along the auditory axis, even after cochlear nerve transection or labyrinthine ablation. There are numerous aetiologies associated with tinnitus. Tinnitus, in clinical practice, is characterised as either objective or subjective. The distinction is relevant in terms of both aetiology and treatment. Despite a large number of therapeutic interventions and studies claiming success in treating tinnitus, a cure remains elusive. However, there are several potential treatment options that offer patients varying degrees of symptomatic improvement and enhanced quality of life. It is imperative to formulate a rational and systematic approach in evaluating an older adult with tinnitus. An individualised treatment regimen and the creation of a strong therapeutic relationship are the hallmarks of successful management of the patient with tinnitus.

Aged↗

Prevention of cerebrospinal fluid leakage and delayed loss of preserved hearing after vestibular schwannoma removal: reconstruction of the internal auditory canal in the suboccipital transmeatal approach--technical note.

The suboccipital transmeatal approach uses packing of a muscle or fat graft into the internal auditory canal (IAC) to prevent postoperative cerebrospinal fluid (CSF) leakage. However, preserved hearing after removal of vestibular schwannomas may decline over time because of the progressive constriction of cochlear vascular supply due to scarring of the IAC. We propose a surgical technique for IAC reconstruction, which separates the preserved cochlear nerve and vasculature from the graft, and regains the CSF space in the IAC. Prior to the drilling of the posterior wall of the IAC, the dura mater of the petrous bone forming the posterior wall of the IAC is harvested for IAC reconstruction. After completion of tumor removal, a "roof" of the IAC is reconstructed using the dura mater, and a muscle or fat graft soaked with fibrin glue is placed on the "roof" of the IAC. The IAC was reconstructed using this technique in 26 consecutive patients with vestibular schwannomas who underwent tumor removal via the suboccipital transmeatal approach. Postoperative magnetic resonance imaging confirmed the regained CSF space in the IAC. No delayed hearing loss occurred in four patients with preserved hearing. No CSF leakage occurred after surgery. This new technique of IAC reconstruction may prevent delayed hearing loss as well as postoperative CSF leakage after removal of vestibular schwannomas via the suboccipital transmeatal approach.

Aged↗

Disappearance of hemifacial spasm after ventriculoperitoneal shunting in a patient with achondroplasia--case report.

A 15-year-old boy with achondroplasia developed right hemifacial spasm associated with headache, vomiting, and hearing disturbance. Computed tomography showed hydrocephalus. A ventriculoperitoneal shunt was placed. His hydrocephalus subsequently resolved, the hemifacial spasm and headache disappeared, and his hearing disturbance improved. The episodes of hemifacial spasm were probably related to a small posterior cranial fossa volume, the so-called crowding of the posterior fossa. Increased intracranial pressure due to hydrocephalus apparently contributed to further reduction in the posterior cranial fossa volume and led to the hemifacial spasms. In addition, his hearing disturbance may have been the result of dysfunction of the cochlear nerve due to the increase in intracranial pressure caused by hydrocephalus.

Achondroplasia↗

Postnatal development of the mammalian central auditory system and the neural consequences of auditory deprivation.

The auditory system of many mammalian species is immature at the time of birth. Peripheral elements, particularly the middle ear and cochlea, account for much of the physiological immaturity observed in central auditory structures. However, there is now considerable evidence that the central pathway undergoes developmental changes that, at least partially, occur in parallel with peripheral development. Auditory nerve fibres and their terminals have been shown to be of smaller diameter and less extensively arborized in neonatal than in adult cats. These factors almost certainly contribute to many of the sluggish physiological properties of neurones in the kitten auditory nerve and cochlear nucleus. At higher levels of the cat auditory system (inferior colliculus, auditory cortex) mechanisms subserving binaural interaction also undergo a period of postnatal development. Recent studies of sound deprivation produced by either deafferentation or a conductive hearing loss have demonstrated that alteration of cochlear output during the immediate postnatal period may change the normal development of the central auditory system.

Animals↗

Origin of auditory brainstem responses in cats: whole brainstem mapping, and a lesion and HRP study of the inferior colliculus.

In order to identify the origin of five waves of auditory brainstem responses (ABRs) in cats, we designed three experiments. In particular, we focused on the inferior colliculus (IC). Experiment 1: Evoked potential maps of the frontal sections of the brainstem from the level of the cochlear nuclei to the level of the ICs were constructed from the results of whole brainstem field-potential analysis comparing ABR peaks. Experiment 2: Both ICs were aspirated and the brainstem and midbrian were transected along the midline. Experiment 3: HRP was injected to the central nucleus of the IC to cause phase reversal of field potentials, and localization of brainstem auditory neurons projecting to the IC was studied. The results of these experiments suggest that each wave of the ABR is elicited from multiple sources of auditory brainstem nuclei and tracts only.

Animals↗