Faculty Bibliography

OBJECTIVE:The goal of this study was to describe the clinical presentation associated with atypical schwannoma of the cerebellopontine angle, characterize the pathologic findings and describe the long-term outcome. MATERIALS AND METHODS/METHODS:The study design was retrospective case review of patients with the histopathologic diagnosis of atypical and benign schwannoma of the cerebellopontine angle diagnosed at the study institution over a 10-year period. SETTING/METHODS:Tertiary referral center. MAIN OUTCOMES MEASURE/METHODS:Demographic data of the cohort were recorded. Findings on pathology were evaluated. Initial treatment and post-operative course was recorded. Main outcome measures were clinical presentation, including cranial nerve deficits at the time of presentation, complication and recurrence rates. RESULTS:At presentation, a somewhat accelerated course of cranial nerve deficit was noted among patients with atypical schwannoma as compared to benign schwannoma. In the immediate post-operative period, there were no differences noted in the complication rate. Atypical schwannomas appear to have higher recurrence rate compared to benign schwannomas. CONCLUSIONS:Atypical schwannoma is an intermediate disease process with an accelerated clinical course and higher recurrence rate as compared to vestibular schwannoma. Traditional operative approaches may be employed without increased concern for post-operative complications. Thorough counseling and close follow-up should be offered to these patients given the higher recurrence rate. Larger studies are required to determine if these patients need more frequent MRIs for long-term surveillance.

BACKGROUND:Intraosseous petrous apex schwannomas are an exceedingly rare entity; little is known about their epidemiology, natural history, and post-operative outcomes. CASE DESCRIPTION/METHODS:Here, we present the fourth known case of a primary intraosseous schwannoma of the petrous apex: a 68-year-old woman presenting with diplopia, facial numbness, progressive intermittent vertigo, tinnitus, diminished hearing, and ataxia. She underwent a transtemporal approach for subtotal resection of the tumor with subsequent stereotactic radiosurgery. CONCLUSIONS:Our two-year follow-up demonstrates slow growth and success of multimodal management in the treatment of these tumors. We review the three prior reports of petrous apex schwannomas, and identify unifying radiographic and clinical characteristics in order to aid in future diagnostic considerations of lesions of the petrous apex.

OBJECTIVE:There remains a large discrepancy among surgeons in expectations of vestibular schwannoma (VS) growth. The anticipated growth rate of a VS and its potential clinical impact are important factors when deciding whether to observe the lesion over time or to intervene. Previous studies of VS natural growth remain limited, mostly confined to linear measurements, often without high-resolution, thin-sequence imaging. The present study comprehensively assessed natural tumor growth rates using volumetric measurements. METHODS:Between 2012 and 2018, 212 treatment-naïve patients diagnosed with a unilateral VS were evaluated. A total of 699 MR images were assessed, with a range of 2-11 MR images per patient. All MR images preceded any intervention, with patients subsequently being observed through completion of data analysis (36%) or treated with stereotactic radiosurgery (32%) or microsurgical resection (32%). To determine precise tumor volumes, the tumor area was outlined on every slice, and the products of the area and slice thickness were summed (99% of scans were ≤ 1-mm slice thickness). A multilevel model with random effects was used to assess the mean volume change over time. Each tumor was categorized as one of the following: growing (volume increase by more than 20% per year), fast growing (volume increase by more than 100% per year), stable (volume change between 20% decrease and 20% increase per year), and shrinking (volume decrease by more than 20% per year). RESULTS:The mean VS volumetric growth rate was 33.5% per year (95% CI 26.9%-40.5%, p < 0.001). When assessing the frequencies of individual tumor annual growth rates, 66% demonstrated growth (30% fast growing), 33% were stable, and 1% exhibited shrinking over an average interval of 25 months. Larger tumors were associated with increased absolute growth, but there was no relationship between tumor size and proportional growth rate. There was also no relationship between patient age and tumor growth rate. CONCLUSIONS:This study comprehensively assessed VS volumetric growth rates using high-resolution images and was conducted in a large and diverse patient sample. The majority of the tumors exhibited growth, with about one-third growing at a rate of 100% per year. These findings may contribute to a consensus understanding of tumor behavior and inform clinical decisions regarding whether to intervene or observe.

An auditory brainstem implant (ABI) is a surgically implanted central neural auditory prosthesis for the treatment of profound sensorineural hearing loss in children and adults who are not cochlear implant candidates due to a lack of anatomically intact cochlear nerves or implantable cochleae. The device consists of a multielectrode surface array which is placed within the lateral recess of the fourth ventricle along the brainstem and directly stimulates the cochlear nucleus, thereby bypassing the peripheral auditory system. In the United States, candidacy criteria for ABI include deaf patients with neurofibromatosis type 2 (NF2) who are 12 years or older undergoing first- or second-side vestibular schwannoma resection. In recent years, several non-NF2 indications for ABI have been explored, including bilateral cochlear nerve avulsion from trauma, complete ossification of the cochlea due to meningitis, or a severe cochlear malformation not amenable to cochlear implantation. In addition, growing experience with ABI in infants and children has been documented with encouraging outcomes. While cochlear implantation generally remains the first-line option for hearing rehabilitation in NF2 patients with stable tumors or post hearing preservation surgery where hearing is lost but a cochlear nerve remains accessible for stimulation, an ABI is the next alternative in cases where the cochlear nerve is absent and/or if the cochlea cannot be implanted. Herein, we review ABI device design, clinical evaluation, indications, operative technique, and outcomes as it relates to lateral skull base pathology.

BACKGROUND:Measurement of the angular depth of insertion (aDOI) of cochlear implant electrode arrays has numerous clinical and research applications. Plain-film radiographs are easily obtained intraoperatively and have been described as a means to calculate aDOI. CT imaging with 3D reformatting can also be used for this measurement, but is less conveniently obtained and requires higher radiation doses, a particular concern in pediatrics. The extent to which plain-film and 3D CT image-based measurements are representative of the true position of the electrode within the cochlea is unknown. METHODS:Cochlear implantation was performed on 10 cadaveric temporal bones. Five bones were implanted with perimodiolar electrodes (Contour Advance TM, Cochlear, Sydney, Australia) and five were implanted with lateral wall electrodes (Slim Straight, Cochlear). The insertion depths of the electrodes were varied. Each bone was imaged with a radiograph and CT. aDOI was measured for each bone in each imaging modality by a neurotologist and a neuroradiologist. To obtain a 'gold standard' estimate of aDOI, the implanted temporal bones were embedded in an epoxy resin and methodically sectioned at 100 μm intervals; histologic images were captured at each interval. A 3D stack of the images was compounded, and a MATLAB script used to calculate aDOI of the most apical electrode. Measurements in the three modalities (radiograph, CT, and histology) were then compared. RESULTS:The average aDOI across all bones was similar for all modalities: 423° for radiographs, 425° for CT scans, and 427° for histology, indicating that neither imaging modality resulted in large systematic errors. Using the histology-measured angles as a reference, the average error for CT-based measures (regardless of whether the error was in the positive or negative direction) was 12°, and that for radiograph-based measures was 15°. This small difference (12 vs 15° error) was not statistically significant. CONCLUSION/CONCLUSIONS:Based on this cadaveric temporal bone model, both radiographs and CTs can provide reasonably accurate aDOI measurements. In this small sample, and as expected, the CT-based estimates were more accurate than the radiograph-based measurements. However, the difference was small and not statistically significant. Thus, the use of plain radiographs to calculate aDOI seems judicious whenever it is desired to prevent unnecessary radiation exposure and expense.

Introduction The aims of this study are to investigate a possible correlation between the time point at which peak hydraulic pressure and peak force on the cochlear wall appears during insertion of a cochlear implant electrode and to investigate whether a difference exists in maximum hydraulic pressure and maximum force on the cochlear wall during a fast and slow insertion, a manual and automatic insertion and an electrode insertion into a narrow or wide round window (RW) opening. Material and methods Twenty fresh frozen human temporal bones were used. Intracochlear hydraulic pressure and force on the cochlear wall were recorded during round window insertions of a straight electrode array with different insertion speeds, different insertion methods and with different widths of the opening of the RW. Results A statistical signifcant correlation between the time point at which peak hydraulic pressure and peak force on the cochlear wall appears was found (r=0.91, p<0.001). Furthermore, a slow insertion speed showed a higher hydraulic pressure and a higher force on the cochlear wall compared to a fast insertion speed (p<0.001). No statistically signifcant effect of insertion method or the width of the opening of the RW was found on hydraulic pressure and on force on the cochlear wall. Conclusions Peak hydraulic pressure and peak force on the cochlear wall during electrode insertion seems to appear at approximately the same time. Furthermore, a slow insertion speed seems to result in a higher intracochlear hydraulic pressure and a higher force on the cochlear wall

OBJECTIVE:Given rising scrutiny of healthcare expenditures, understanding intervention costs is increasingly important. This study aimed to compare and characterize costs for vestibular schwannoma (VS) management with microsurgery and radiosurgery to inform practice decisions and appraise cost reduction strategies. METHODS:In conjunction with medical records, internal hospital financial data were used to evaluate costs. Total cost was divided into index costs (costs from arrival through discharge for initial intervention) and follow-up costs (through 36 months) for 317 patients with unilateral VSs undergoing initial management between June 2011 and December 2015. A retrospective matched cohort based on tumor size with 176 patients (88 undergoing each intervention) was created to objectively compare costs between microsurgery and radiosurgery. The full sample of 203 patients treated with resection and 114 patients who underwent radiosurgery was used to evaluate a broad range of outcomes and identify cost contributors within each intervention group. RESULTS:Within the matched cohort, average index costs were significantly higher for microsurgery (100% by definition, because costs are presented as a percentage of the average index cost for the matched microsurgery group; 95% CI 93-107) compared to radiosurgery (38%, 95% CI 38-39). Microsurgery had higher average follow-up costs (1.6% per month, 95% CI 0.8%-2.4%) compared to radiosurgery (0.5% per month, 95% CI 0.4%-0.7%), largely due to costs incurred in the initial months after resection. A major contributor to total cost and cost variability for both resection and radiosurgery was the need for additional interventions in the follow-up period, which were necessary due to complications or persistent functional deficits. Although tumor size was not associated with increased total costs for radiosurgery, linear regression analysis demonstrated that, for patients who underwent microsurgery, each centimeter increase in tumor maximum diameter resulted in an estimated increase in total cost of 50.2% of the average index cost of microsurgery (95% CI 34.6%-65.7%) (p < 0.001, R2 = 0.17). There were no cost differences associated with the proportion of inpatient days in the ICU or with specific surgical approach for patients who underwent resection. CONCLUSIONS:This study is the largest assessment to date based on internal cost data comparing VS management with microsurgery and radiosurgery. Both index and follow-up costs are significantly higher when tumors were managed with resection compared to radiosurgery. Larger tumors were associated with increased resection costs, highlighting the incremental costs associated with observation as the initial management.

OBJECTIVE It is common for a medical disorder to be managed or researched by individuals who work within different specialties. It is known that both neurosurgeons and neurotologists manage vestibular schwannoma (VS) patients. While overlap in specialty focus has the potential to stimulate multidisciplinary collaboration and innovative thinking, there is a risk of specialties forming closed-communication loops, called knowledge silos, which may inhibit knowledge diffusion. This study quantitatively assessed knowledge sharing between neurosurgery and otolaryngology on the subject of VS. METHODS A broad Web of Science search was used to download details for 4439 articles related to VS through 2016. The publishing journal's specialty and the authors' specialties (based on author department) were determined for available articles. All 114,647 of the article references were categorized by journal specialty. The prevalence of several VS topics was assessed using keyword searches of titles. RESULTS For articles written by neurosurgeons, 44.0% of citations were from neurosurgery journal articles and 23.4% were from otolaryngology journals. The citations of otolaryngology authors included 11.6% neurosurgery journals and 56.5% otolaryngology journals. Both author specialty and journal specialty led to more citations of the same specialty, though author specialty had the largest effect. Comparing the specialties' literature, several VS topics had significantly different levels of coverage, including radiosurgery and hearing topics. Despite the availability of the Internet, there has been no change in the proportions of references for either specialty since 1997 (the year PubMed became publicly available). CONCLUSIONS Partial knowledge silos are observed between neurosurgery and otolaryngology on the topic of VS, based on the peer-reviewed literature. The increase in access provided by the Internet and searchable online databases has not decreased specialty reference bias. These findings offer lessons to improve cross-specialty collaboration, physician learning, and consensus building.