Douglas C. Bigelow

Prevalence of unsuspected acoustic neuroma found by magnetic resonance imaging.

OBJECTIVES: Acoustic neuromas (ANs) comprise 6% of intracranial tumors. Population and autopsy studies have widely divergent estimates of AN incidence. With widespread use of MRI, asymptomatic ANs will be identified, which should improve estimates of the prevalence of this tumor. METHODS: The reports of all brain MRI scans during a 5-year period were retrospectively searched for the diagnosis of AN. MRIs obtained because of a suspicion of AN were discarded, leaving only the unsuspected ANs. RESULTS: A total of 24,246 MRI studies were performed during this time period. Seventeen patients had unsuspected ANs. Eight tumors were smaller than 1 cm, 6 were between 1 and 2 cm, and 3 were 2 cm or larger. For all MRI scans, we found 7.0 unsuspected ANs per 10,000 brain MRI studies (0.07%). CONCLUSION: The true prevalence of AN is likely greater than the 10 per million per year previously reported. This implies that there may be a larger number of asymptomatic ANs than previously suspected.

Tinnitus suppression in patients with cochlear implants.

Objective To determine the degree of tinnitus suppression provided by currently available multichannel cochlear implants and to determine factors that can influence this process. Study Design Prospective cohort. Setting Tertiary-care referral center. Patients Thirty-eight adult patients (18 years of age or older) with severe-to-profound hearing loss and tinnitus who met criteria for cochlear implantation. Intervention Cochlear implantation with a multichannel cochlear implant device. Main Outcome Measures Patients rated the intensity of their tinnitus using a semiquantitative scale before and after cochlear implantation. These data were analyzed to determine the significance of the reduction of tinnitus after implantation. Tinnitus levels after implantation were also analyzed to determine whether the level of speech recognition, patient gender, or the implant type influenced the degree of tinnitus reduction. Results Statistical analysis revealed a significant reduction in tinnitus intensity in patients using cochlear implants, with 35 of 38 patients (92%) experiencing a reduction in tinnitus intensity. All multichannel implants studied afforded similar degrees of tinnitus suppression. The degree of tinnitus reduction was not correlated with speech recognition, as measured by CID Everyday Sentence scores. Female patients had significantly greater degrees of tinnitus before implantation, but both male and female patients demonstrated similar levels of tinnitus after implantation. No patient experienced greater levels of tinnitus after implantation. Conclusion All currently available multichannel cochlear implant devices provide effective and similar levels of tinnitus suppression when activated. Exacerbation of tinnitus as a result of cochlear implantation does not represent a significant risk. The mechanisms by which cochlear implants exert tinnitus suppression are, as yet, unclear.

Lipomas of the internal auditory canal and cerebellopontine angle

Objective: To evaluate lipomas of the internal auditory canal (IAC) and cerebellopontine angle (CPA). Study Design: Retrospective review. Methods: Review of a multi‐institutional series of 17 lipomas of the IAC/CPA, combined with a Medline review of the 67 cases reported in the world literature. Results: This series of 17 IAC/CPA lipomas is the largest reported series to date, bringing the total number of documented cases to 84. There appears to be a nearly 2:1 male to female predominance. Sixty percent were leftsided lesions, and three were bilateral. Hearing loss, dizziness, and tinnitus were the most common presenting symptoms. Surgical resection was performed in 52 (62%) of these lesions; however, total tumor removal was accomplished in only 17 (33%), which is most likely because of the fact that these tumors tend to have a poorly defined matrix and a dense adherence to neurovascular structures. Sixty‐eight percent of patients experienced a new deficit postoperatively, 11% were unchanged, and only 19% improved with no new deficit. Only one documented case of tumor growth was identified; however, the reported follow‐up was short (average, less than 3 years). Conclusion: With the magnetic resonance imaging techniques now available, lipomas can be reliably differentiated from other masses within the CPA and IAC, so histopathologic diagnosis is rarely necessary. Because of the potential for significant morbidity with resection of these lesions, we believe that conservative follow‐up is the best treatment option for patients with these rare lesions. Surgery is indicated only when significant progressive or disabling symptoms are present. Laryngoscope, 108:1459–1469, 1998

Management of far advanced otosclerosis in the era of Cochlear implantation

Objective To evaluate issues pertaining to cochlear implantation in patients with far advanced cochlear otosclerosis. Study Design Prospective cohort. Setting Tertiary care referral center. Patients Eight adult patients (18 years of age or older) referred for management of profound hearing loss, the cause of which was determined to be otosclerosis. Intervention Cochlear implantation with multichannel cochlear implant device. Main Outcome Measures Benefit from cochlear implant as measured by CID sentence scores, incidence and management of facial nerve stimulation, and technical issues pertaining to cochlear implantation in this patient population. Results All patients demonstrated significant improvement in auditory function as measured by performance on CID sentence scores and ability to engage in telephone conversation. Facial nerve stimulation was present in two of eight patients and was managed with deactivation of the stimulating electrodes. Ossification in the basal turn of the cochlea, detected on preoperative computed tomography, necessitated placement of the electrode into the scala vestibuli in two patients and use of a thinner electrode (Nucleus 24) in a third patient. Conclusion Patients with profound hearing loss secondary to otosclerosis derive excellent benefits from cochlear implantation. Surgical implantation may be complicated by ossification of the cochlea, which can be detected on preoperative computed tomography. Electrode activation may be complicated by facial nerve stimulation, which can be addressed with programming strategies.

The Effect of Tympanic Membrane Perforation Size on Umbo Velocity in the Rat

The tympanic membrane (TM) in adult rats was surgically exposed and laser interferometry was used to measure TM velocity at the umbo for frequencies between 1.0 and 40.0 kHz. Velocity measures were obtained for five conditions: TM intact, and four progressively larger holes cut into the posterior region of the membrane. Photomicrographs of each condition were used to calculate the percentage of pars tensa lost to the perforation. The relation between TM velocity and stimulus sound pressure level (SPL) was also examined for each of the conditions. The results revealed a systematic loss in low‐frequency velocity as perforation size increased. These observations were consistent with clinical reports of low‐frequency hearing loss in the perforated human TM. The rat appears to be a successful model for studying this form a conductive pathology.

Immunologic and serologic testing in patients with Ménière's disease.

Objective To establish the value of immunologic and serologic testing in patients with Ménières disease. Study Design Prospective cohort. Setting University-based, tertiary care balance center. Intervention Patients with active unilateral or bilateral Ménières disease underwent testing, including antinuclear antibodies, anti-DNA antibodies, rheumatoid factor, complement levels, anti-Sjögren syndrome A and B antibodies, sedimentation rate, antiphospholipid antibodies, Western blot for anticochlear antibodies (anti-heat shock protein 70), microhemagglutination test for Treponema pallidum, and Lyme titers. Outcome Measures Results of laboratory tests. Results In patients with unilateral Ménières disease (n = 40), 27% demonstrated elevated antiphospholipid antibody titers (population norm, 6–9%). The majority of these patients manifested negative assays on the other tests listed above. In patients with bilateral Ménières disease (n = 18), elevations in antinuclear antibody titers (38%) were the most notable finding. As part of a broader study of patients with progressive hearing loss, four patients with positive syphilis titers were identified; however, none of these patients complained of vertigo. Conclusion In general, the results of this study do not support the hypothesis that immune or infectious pathologies are involved in the pathogenesis of unilateral Ménières disease. In particular, Lyme disease does not seem to cause labyrinthine disease. However, the potential role of the thrombogenic antiphospholipid antibodies must be further investigated. Patients with bilateral Ménières disease may be more likely to have a systemic autoimmune process.

Endolymphatic sac tumor in a 4-year-old boy.

Introduction: Endolymphatic sac tumors (ELST) are rare, low-grade, locally aggressive papillary neoplasms. We present a case of a 4-year-old boy with an ELST, the youngest described in the literature. Case: A boy presented with a right-sided serous otitis media and sudden-onset right facial nerve palsy. An audiogram revealed right-sided profound sensorineural hearing loss. Radiographic imaging demonstrated a 3-cm expansile lytic lesion along the posterior face of the petrous bone. Intervention/Results: The patient initially underwent a right transmastoid–infralabyrinthine biopsy. Pathologic examination revealed a papillary lesion suspicious for an ELST. Subsequently, a transtemporal–transcochlear approach with intra-and extradural resection of the tumor was performed. The facial nerve was dissected and transposed anteriorly and preserved. Histopathologic and immunohistochemical studies confirmed the ELST. At his 6-month follow up, there is no evidence of recurrence and the facial nerve function has returned to Grade II palsy. Conclusion: ELST are rare tumors of the temporal bone. This is the youngest case of ELST reported. Presentation, evaluation, and management of ELST is discussed.

Predictors of hearing loss after gamma knife radiosurgery for vestibular schwannomas: age, cochlear dose, and tumor coverage.

BACKGROUND:Deterioration in hearing after Gamma Knife radiosurgery of vestibular schwannomas is a well-documented risk. Recent studies suggest a correlation between cochlear radiation dose and hearing preservation. OBJECTIVE:This study identifies additional variables that predict hearing loss after radiosurgery. METHODS:Retrospective analysis of 53 patients with audiogram follow-up. Median marginal tumor dose was 12.5 Gy. Mean tumor volume was 1.11 cm3. Statistical analysis included multivariate stepwise backward linear regression and multivariate logistic regression. Variables included age, prescription dose, tumor volume, intracanalicular length, and maximum and mean cochlear dose. Dose volume histograms were generated. The percentage of the cochlear volume that received 3.6 Gy or greater, 4.7 Gy or greater, and 5.3 Gy or greater was calculated. Plan conformality indicators were calculated. RESULTS:Forty-two patients had a less than 20-dB change in their pure tone average, with a hearing preservation rate of 79%. Two statistically significant predictors of hearing loss were identified using multivariate analysis: tumor coverage (odds ratio: 1.38 × 1018) and age (odds ratio: 1.1 per year). Multivariate linear regression was used to predict change in pure tone average. Age and percentage of the cochlear volume receiving 5.3 Gy or greater were found to be statistically significant predictor variables. CONCLUSION:Older patients are more vulnerable to detrimental effects of Gamma Knife radiosurgery on hearing. We propose that cochlear dose volume histograms be created and used to reduce the percentage of the cochlear volume exposed to radiation doses greater than 5.3 Gy. This is the first report to suggest that the conformity index tumor coverage may be an important predictor of hearing outcomes.

The efficacy of corticosteroids in restoring hearing in patients undergoing conservative management of acoustic neuromas.

Objective To evaluate the role of corticosteroids in restoring hearing in patients undergoing conservative management of acoustic neuromas. Study Design Prospective cohort. Setting Tertiary referral center. Patients Seven patients with acute hearing loss secondary to an acoustic neuroma. Intervention Oral prednisone (1 mg/kg for 1 to 2 weeks) within a week of onset of hearing loss. Main Outcome Measures Audiometric assessment at the time of presentation and after corticosteroid therapy. Results All seven patients had pure tone reception threshold improvements ranging from 10 to 50 dB in at least two frequencies or more. Speech discrimination thresholds improved after therapy in all seven patients, with gains of 4 to 38% points. Conclusions Patients with acoustic neuromas who are being treated with a “watchful waiting” approach should receive corticosteroid treatment at the first signs of hearing deterioration. An evaluation to rule out a retrocochlear lesion is mandated in patients with sudden hearing loss, regardless of whether the hearing loss responds to corticosteroid treatment. Older data documenting the efficacy of corticosteroids in the treatment of sudden hearing loss may need to be reevaluated, given that many of these studies were conducted before MRI was available.

Comparison of Endotrachial Tube and Hookwire Electrodes for Monitoring the Vagus Nerve

Monitoring the vagus nerve and the recurrent laryngeal nerve during surgical procedures may reduce the probability of significant nerve injury. As such, a number of methods to monitor these nerves have been devised including placing electrodes directly into the vocal cords or recording from surface electrodes. In direct comparison, monitoring the identical muscles, bipolar hookwire electrodes displayed approximately one order of magnitude greater amplitude, of both spontaneously occurring and evoked electrical activity than double wire endotracheal tube electrodes. The enhanced sensitivity of the hookwire electrodes, despite the technical difficulties with placement, suggests their use when maximum sensitivity is required.