Asymptomatic acoustic neurilemoma

Epidemiology and Risk Factors for Development of Sporadic Vestibular Schwannoma

Vestibular schwannomas (VSs) are benign, slow-growing tumors of the eighth cranial nerve. Sporadic unilateral VSs constitute approximately 95% of all newly diagnosed tumors. There is little known about risk factors for developing sporadic unilateral VS. Potential risk factors that have been reported are familial or genetic risk, noise exposure, cell phone use, and ionizing radiation, whereas protective factors may include smoking and aspirin use. More research is needed to elucidate the risk factors for development of these rare tumors.

Global Incidence of Sporadic Vestibular Schwannoma: A Systematic Review

OBJECTIVE

Ubiquitous throughout the literature and during patient counseling, vestibular schwannoma is often quoted to affect about 1 per 100,000 people. Yet, reports from distinct international populations suggest that the incidence is likely much higher. The objective of the current work was to systematically characterize the global incidence of sporadic vestibular schwannoma.

DATA SOURCES

Scopus, Embase, and PubMed.

REVIEW METHODS

Population-based studies reporting incidence rates of sporadic vestibular schwannoma between January 2010 and August 2020 were searched with language restrictions requiring reports to be published in Chinese, English, German, Italian, or Spanish. The protocol was registered with PROSPERO (CRD42021228208) prior to commencement of data collection. PRISMA guidelines for transparent reporting of systematic reviews were followed.

RESULTS

Among 424 citations, 6 publications covering 4 distinct populations from Denmark, the Netherlands, Taiwan, and the United States met inclusion criteria. Most recent incidence rates of among all ages ranged between 3.0 and 5.2 per 100,000 person-years. Highest incidence rates were reported among patients aged ≥70 years, peaking at 20.6 per 100,000 person-years. One study from the United States reported the incidence of asymptomatic, incidentally diagnosed tumors at a rate of 1.3 per 100,000 person-years from 2012 to 2016.

CONCLUSIONS

Recent international incidence rates of sporadic vestibular schwannoma exceed the commonly quoted "1 per 100,000" figure by up to 5-fold among all ages and by up to 20-fold among age groups at highest risk. Based on modern incidence rates, the lifetime prevalence of developing sporadic vestibular schwannoma likely exceeds 1 per 500 persons.

Prevalence of Sporadic Vestibular Schwannoma: Reconciling Temporal Bone, Radiologic, and Population-based Studies

OBJECTIVE

Reported epidemiologic data surrounding vestibular schwannoma (VS) are controversial. Temporal bone prevalence studies have suggested that VS affects up to 2.4% of the population, whereas magnetic resonance imaging (MRI) studies have reported VS to affect 0.017%. Moreover, existing population-based data seem to underestimate the commonness of VS. In an attempt to reconcile temporal bone, radiologic, and population-based reports regarding VS, the current study was conceived to determine the modern prevalence of VS using a unique epidemiological database.

PATIENTS

All persons living in Olmsted County, Minnesota on January 1, 2017 with a confirmed diagnosis of sporadic VS identified using the Rochester Epidemiology Project (REP) medical records-linkage system.

MAIN OUTCOME MEASURES

Prevalence of all VS and asymptomatic, incidentally diagnosed VS.

RESULTS

Sixty-seven persons from a population of nearly 160,000 were living with VS on January 1, 2017, resulting in a point prevalence of 42.0 per 100,000 persons. The prevalence increased with older age, reaching 212.4 per 100,000 in those ≥ 70 years. Including only persons who have undergone head MRI, the prevalence of asymptomatic, incidentally diagnosed VS was 69.9 per 100,000 among adults age 20 years and older.

CONCLUSIONS

Using the unique infrastructure of the REP, the current study suggests that the clinical prevalence of sporadic VS approximates 1 in 2,000 adults and 1 in every 500 persons aged 70 years and older, with the prevalence of incidentally diagnosed tumors closely paralleling past MRI studies. These data characterize a shift in the modern patient demographic of sporadic VS, as now many people bearing a diagnosis of VS would have previously died without knowledge of their disease. Moreover, they typify an unfolding transition from an era of microsurgery and radiosurgery to the beginnings of an era that will be largely comprised of "chronic disease management."

Surgery of the lateral skull base: a 50-year endeavour

Disregarding the widely used division of skull base into anterior and lateral, since the skull base should be conceived as a single anatomic structure, it was to our convenience to group all those approaches that run from the antero-lateral, pure lateral and postero-lateral side of the skull base as “Surgery of the lateral skull base”. “50 years of endeavour” points to the great effort which has been made over the last decades, when more and more difficult surgeries were performed by reducing morbidity. The principle of lateral skull base surgery, “remove skull base bone to approach the base itself and the adjacent sites of the endo-esocranium”, was then combined with function preservation and with tailoring surgery to the pathology. The concept that histology dictates the extent of resection, balancing the intrinsic morbidity of each approach was the object of the first section of the present report. The main surgical approaches were described in the second section and were conceived not as a step-by-step description of technique, but as the highlighthening of the surgical principles. The third section was centered on open issues related to the tumor and its treatment. The topic of vestibular schwannoma was investigated with the current debate on observation, hearing preservation surgery, hearing rehabilitation, radiotherapy and the recent efforts to detect biological markers able to predict tumor growth. Jugular foramen paragangliomas were treated in the frame of radical or partial surgery, radiotherapy, partial “tailored” surgery and observation. Surgery on meningioma was debated from the point of view of the neurosurgeon and of the otologist. Endolymphatic sac tumors and malignant tumors of the external auditory canal were also treated, as well as chordomas, chondrosarcomas and petrous bone cholesteatomas. Finally, the fourth section focused on free-choice topics which were assigned to aknowledged experts. The aim of this work was attempting to report the state of the art of the lateral skull base surgery after 50 years of hard work and, above all, to raise questions on those issues which still need an answer, as to allow progress in knowledge through sharing of various experiences. At the end of the reading, if more doubts remain rather than certainties, the aim of this work will probably be achieved.

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.

Intralabyrinthine Acoustic Neurinomas

Two temporal bones are presented that contain acoustic neurinomas unsuspected during life and anatomically limited to the perilymphatic labyrinth. One tumor occupies the modiolus and scala tympani of the cochlea without involving the internal auditory canal. The other tumor originates in the fibers below the utricular macula and spares both the macula and the lamina cribrosa. Neither case demonstrates bone destruction. Even if these tumors had been suspected during life, tomograms would have been normal and the posterior fossa myelogram would have shown complete filling of the internal auditory canal.

Intralabyrinthine schwannomas: a case series with discussion of the diagnosis and management

OBJECTIVE

By extracting cases of intralabyrinthine schwannomas (ILS) from the sum of all vestibular schwannomas, we aim to identify and analyze unique features of its presentation. This allows us to refine the management protocol of this rare condition.

DESIGN

This is a retrospective study of all patients seen in the Department of Otorhinolaryngology-Head and Neck Surgery, Rouen University Hospital, with either ILS or ILS with intracanalicular extension (ILS-IAC) between 2001 and 2011. A literature search was performed and results combined to draw conclusions on management strategies.

METHOD

Three patients with ILS and 6 patients with ILS-IAC were identified. We retrieved data on age, sex, symptoms, audiometry, imaging, and management. Pure tone audiometry and speech discrimination score were assessed and hearing classification recorded. Facial nerve function and vestibular function were documented throughout. The diagnostic and surveillance imaging (MRI with or without CT) were reviewed.

RESULTS

The average age at presentation was 62.8 years and the sex ratio was (male: female) 4:5. An ipsilateral hearing loss was observed in all patients. Eight of 9 patients had tinnitus at presentation, 2 had rotatory vertigo, and 1 patient had a facial palsy and hemifacial spasm. In 2 cases, the labyrinthine extension was initially missed. The patient presenting with a large tumor and facial palsy was operated on without delay. The others underwent MRI surveillance, with 4 requiring surgery at a later stage. No postoperative facial palsies were encountered other than the one that had been present preoperatively.

CONCLUSION

Frequency of ILS is underestimated because of poor diagnostic criteria. These tumors have often been described as having features, which resemble Ménière's disease, which is not found in our series. In the absence of tumor progression or disabling symptoms, their management is surveillance/medical, and when surgery is considered, facial paralysis and recurrence rates seem low. The treatment of IAC-ILS differs from that of ILS.

Incidental vestibular schwannomas: a review of prevalence, growth rate, and management challenges

With the relatively recent increase in the use of MRI techniques, there has been a concurrent rise in the number of vestibular schwannomas (VSs) detected as incidental findings. These incidental VSs may be prevalent in up to 0.02%–0.07% of individuals undergoing MRI and represent a significant portion of all diagnosed VSs. The management of these lesions poses a significant challenge for practitioners. Most incidental VSs tend to be small and associated with minimal symptoms, permitting them to be managed conservatively at the time of diagnosis. However, relatively few indicators consistently predict tumor growth and patient outcomes. Furthermore, growth rates have been shown to vary significantly over time with a large variety of long-term growth patterns. Thus, early MRI screening for continued tumor growth followed by repeated MRI studies and clinical assessments throughout the patient's life is an essential component in a conservative management strategy. Note that tumor growth is typically associated with a worsening of symptoms in patients who undergo conservative management, and many of these symptoms have been shown to significantly impact the patient's quality of life. Specific indications for the termination of conservative management vary across studies, but secondary intervention has been shown to be a relatively safe option in most patients with progressive disease. Patients with incidental VSs will probably qualify for a course of conservative management at diagnosis, and regular imaging combined with the expectation that the tumor and symptoms may change at any interval is crucial to ensuring positive long-term outcomes in these patients. In this report, the authors discuss the current literature pertaining to the prevalence of incidental VSs and various considerations in the management of these lesions. It is hoped that by incorporating an understanding of tumor growth, patient outcomes, and management strategies, practitioners will be able to effectively address this challenging disease entity.

Three-Year Ear, Nose, and Throat Cross-sectional Analysis of Audiometric Protocols for Magnetic Resonance Imaging Screening of Acoustic Tumors

Objectives. (1) Evaluate audiometric protocols and recommend protocols with best sensitivity and specificity for magnetic resonance imaging (MRI) screening of acoustic tumors; (2) determine clinical risks (false negative) of missing acoustic tumors and potential wastes in screening (false positive) nonacoustic tumors or radiologically “normal” cases; and (3) identify the decibel difference and range of frequencies compared by the best-performing protocols.

Study Design. Cross-sectional study with chart review.

Setting. Ear, nose, and throat (ENT); audiology; and radiology departments in a tertiary-care hospital.

Subjects and Methods. Three-year cohort (2006-2009) of 1751 ENT patients underwent MRI screening and pure-tone audiometry indicating sensorineural hearing loss. Audiometric protocols were ranked by highest sensitivity to acoustic tumors, specificity A to nonacoustic tumors, and specificity B to “radiologically normal” cases.

Results. No audiometric protocols achieved 100% sensitivity or specificity rates. Only 2 protocols achieved ≥90% sensitivity: the AMCLASS-A-Urben protocol (93.16%) and the Mangham protocol (91.58%). Eleven of 15 protocols for specificity A and 12 of 15 protocols for specificity B achieved ≥50%. Clinical risks ranged from 6.84% to 18.95%, whereas potential wastes ranged from 33.56% to 68.37% for specificity A and 31.76% to 66.86% for specificity B. Interaural difference parameters indicating highest mean sensitivity were on the order of ≥10 dB, ≥15 dB, and ≥20 dB. For frequency comparison parameters, “2 or more adjacent frequency” and “single-frequency” comparison indicated higher mean sensitivity than the “averaged multifrequency” comparison. Mean specificity showed an opposite pattern.

Conclusions. For optimum sensitivity, the Mangham protocol is preferred (sensitivity, 91.58%; specificity A, 44.23%; specificity B, 44.91%), which proposes a ≥10-dB interaural difference, averaging 1 to 8 kHz. For optimum specificity, the American Academy of Otolaryngology–Head and Neck Surgery protocol is preferred (sensitivity, 87.37%; specificity A, 65.38%; specificity B, 66.04%), which proposes ≥15 dB between ears, averaging 0.5 to 3 kHz.

Medicolegal significance of asymmetrical hearing loss in cases of industrial noise exposure

OBJECTIVE

In Australia, the current guidelines for evaluation of noise-induced hearing loss suggest that, in cases of asymmetrical loss, 'the worse ear be equated to the better ear' for purposes of compensation. This study aimed to establish that such a method was prejudicial to the worker (i.e. the plaintiff). In consideration of the legal duty 'to co-construct the ideas of truth and the ideas of justice in the context of legal proceedings', our study objectives were (1) to document the incidence of asymmetrical hearing loss in compensation cases seen in our practice, and (2) to provide a reasoned argument for inclusion of the same for compensation considerations.

STUDY DESIGN

Open, retrospective, clinical study.

SETTING

Australian plaintiffs with asymmetrical hearing loss (who comprise a significant percentage of industrial hearing loss legal cases) may be excluded from full consideration of their hearing loss as a result of the current guidelines. In contrast to the process of medical diagnosis and treatment, it appeared that the application of accepted probability standards within the legal process may permit inclusion of such clients' hearing loss in compensation considerations.

METHODS

This study included 208 consecutive clients referred by legal practitioners for assessment of hearing loss for compensation purposes.

RESULTS AND CONCLUSION

A total of 22.6 per cent of clients (47 of 208) had asymmetrical hearing loss, with the left side having the greater loss in 60 per cent of cases. We believe that asymmetrical hearing loss should be included in compensation considerations, both on medical and legal grounds.

Herpes and acoustic neuromas: is there a cause and effect to observe?

Acoustic neuromas are a result of damage to the affected nerve function and can potentially press surrounding tissues. Although some sources suggest that observation is the treatment of choice for only those over 65 years of age and those unable to tolerate undergoing surgery or radiosurgery, most affected individuals should strongly consider not doing any aggressive therapies. Herpes has already been shown to mimic acoustic neuroma clinically, but growing evidence suggests that it is likely the cause of most cases of this entity.

Gamma knife radiosurgery for intracanalicular acoustic neuromas

In the present study we reviewed our long-term experience with radiosurgery for intracanalicular acoustic neuromas. The study involved 25 patients with unilateral intracanalicular acoustic neuromas. The treatment volume was 0.07 to 0.8 cm(3) (median: 0.27 cm(3)). The marginal radiation dose used for treatment was 12 Gy for all patients. The follow-up period ranged from 36 to 132 months (mean: 89 months). The actuarial rate of tumour growth control at 5 and 10 years after radiosurgery was 96%. Hearing preservation was achieved in 16 patients (64%) and improvement (>20 dB relative to presurgical values) was noted in one patient (4%). No patients experienced post-radiosurgery facial palsy or other cranial nerve deficits. Based on our study and long-term follow-up, radiosurgery can produce high rates of tumour growth control and hearing preservation for intracanalicular acoustic neuromas, and is an alternative to surgical resection given its low level of invasiveness. When determining treatment for intracanalicular acoustic neuromas, the condition's benign natural course and the likelihood of hearing preservation must be taken into account.

Origin of endolymphatic sac tumor

Autopsy temporal bone sections showing a one mm papillary glandular neoplasm, confined to the left endolymphatic duct, are described. This is the second literature report confirming the post-mortem site of origin of the "endolymphatic sac tumor". The patient died after surgery for right vestibular schwannoma, but no features of von Hippel Lindau disease or neurofibromatosis 2 had been displayed clinically or at autopsy. A study of the epithelium of normal human mature endolymphatic ducts and sacs (EDSs) in archival temporal bone sections showed hyperplastic tubular outgrowths, usually situated in the intraosseous portion of the endolymphatic sac, in most cases. Such appearances imply that the epithelium of the EDS has the potential of producing a malignant papillary glandular neoplasm. Papillary ingrowths, some forming collagenous polypoid projections, and cysts were frequent among the epithelial cells. Psammoma bodies were present in the ducts and sacs of older patients. Appearances suggesting erosion of the bony interface of vestibular aqueduct with EDS could be ascribed to the entry and exit of blood vessels into and from the vestibular aqueduct. Care should be taken in the evaluation of surgical or autopsy material from EDSs not to overcall any of these normal features as malignant.

Atypical clinical presentations of vestibular schwannomas

A significant number of patients with vestibular schwannomas present atypically, with none of the classical symptoms of unilateral sensorineural hearing loss, tinnitus, and/or dysequilibrium. The aim of this study is to highlight those patients with unusual clinical symptoms.

STUDY DESIGN

The clinical data of all patients who presented to the vestibular schwannoma clinic at Beaumont Hospital over the past 12 years was prospectively recorded in a computerized database. This paper reviews the atypical presenting symptoms.

RESULTS

Three hundred ninety-eight patients were included in this study. A total of 3.7% of patients presented with atypical symptoms only.

CONCLUSION

A significant subgroup, 3.7% in our study, did not present with the audiovestibular symptoms classically associated with vestibular schwannoma. Clinician awareness of the atypical clinical symptoms may lead to earlier detection of these lesions.

Funktion des N.�facialis nach operativer Therapie des Akustikusneurinoms

The aim of this study was to evaluate the influence of intraoperative monitoring on the function of the facial nerve after surgical treatment of acoustic neurinomas, classified according to the grading system of Stennert. One hundred thirty patients were divided into two groups. The first group underwent surgery without intraoperative facial monitoring; the second group included intraoperative facial monitoring. Concerning degree of paresis, preoperatively there was no statistically significant difference between the two groups (group 1: 0.77+/-1.5; group 2: 0.4+/-1.2). Despite structural preservation of the facial nerve, postoperative deterioration of its function was observed which consecutively improved postoperatively. Postoperatively, the mean degree of paresis increased to 4.4+/-3.0 in group 1 and 2.4+/-2.3 in group 2. For better understanding of the role of intraoperative monitoring, we investigated the outcome of patients with acoustic neurinomas who underwent surgery over the following 6 months postoperatively. At that time, function improved by 4.1+/-3.2 (group 1) and 2.0+/-2.3 (group 2). We could show that intraoperative monitoring of the facial nerve was a significant factor for better postoperative function in patients undergoing microsurgical excision of neurinomas (P=0.001) .

MR findings in intralabyrinthine schwannomas

AIM

Intralabyrinthine schwannomas (ILS) are rare benign tumours. They are not always recognized on routine magnetic resonance imaging (MRI). We aimed to study the clinical presentation and MRI findings in our patients with ILS.

MATERIALS AND METHODS

Retrospective analysis of patients with vestibular schwannomas treated at this center.

RESULTS

Of 144 vestibular schwannomas studied at this centre, three patients had an ILS. The most common presenting symptoms were unilateral hearing loss, tinnitus and vertigo. Two patients demonstrated a progressive sensorineural hearing loss (SNHL). The third patient had a severe SNHL at presentation. MRI enhanced with contrast medium was positive in the two patients with progressive SNHL and negative in the patient with the severe SNHL.

CONCLUSION

This series demonstrates the ability of MRI to identify schwannomas filling the labyrinth, and also its inability to identify extremely small ILS. It underlines the importance of sending the cristae of patients undergoing labyrinthectomy for presumed Ménière's disease for histological examination.

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.

Normal audiologic presentations in patients with acoustic neuroma: An evaluation using strict audiologic parameters

Although several studies have previously reported on patients presenting with "normal" audiologic parameters in acoustic neuroma, the present study is, to our knowledge, the first to exclusively examine in detail cases involving exceptionally stringent objective audiometric features. Of 369 patients with acoustic neuroma who were operated on between April 1980 and April 1997 by our group, 10 had strictly normal hearing, defined as follows: (1) pure-tone average < 20 dB; (2) speech discrimination score > 90%; and (3) interaural differences </= 10 dB at every hertz level. A high level of audiologic functioning was found to significantly lower the sensitivity of auditory brainstem response in the detection of acoustic neuroma. Magnetic resonance imaging was the only preoperative test exhibiting 100% sensitivity in this setting. Thus, a high level of clinical suspicion appears warranted in any case involving unexplained unilateral audiovestibular symptoms-including those instances in which strictly normal hearing parameters exist and are associated with negative auditory brainstem response findings.

The role of conservative management of vestibular schwannomas

Although microsurgery is generally regarded as the conventional treatment of choice for most vestibular schwannomas, there remains a group of patients in whom a conservative management approach may be a desirable alternative. The aim of this study was to determine the natural history and outcome following the conservative management of 72 patients with unilateral vestibular schwannomas. The reasons for conservative management included poor general health, age, patient preference, small tumour size, minimal or no symptoms, and tumour in the only/better hearing ear. The mean duration of follow-up was 39.8 months (range 12-194 months). All patients underwent serial magnetic resonance imaging (MRI) for assessment of tumour growth. Patients were deemed to have failed conservative management if there was evidence of continuous or rapid radiological tumour growth and/or increasing symptoms or signs. The mean tumour growth rate, according to the 1995 guidelines of the American Academy of Otolaryngology/Head and Neck Surgery, was 1.16 mm/year (range: 0.75 9.65 mm/year). Approximately 83% of tumours grew at < 2 mm/year. Significant tumour growth was seen in 36.4%, no or insignificant growth in 50%, and negative growth in 13.6% of tumours. The growth rate of CPA tumours (1.4 mm/year) was significantly greater than that of IAC tumours (0.2 mm/year) (P = 0.001). Failure of conservative management, in which active treatment was required, occurred in 15.3%. The outcome of these patients appeared to be as favourable to a comparable group who underwent primary treatment, without a period of conservative management. The mean growth rate of tumours in patients who failed conservative management (4.2 mm/year) was significantly greater than that in patients who did not fail (0.5 mm/year) (P < 0.01). No factors predictive of tumour growth or failure of conservative management were identified. Deterioration of mean pure tone average (0.5, 1, 2, 3 kHz) and speech discrimination scores occurred regardless of whether radiological tumour growth was demonstrated or not. This study suggests that in a select number of cases of vestibular schwannoma, a conservative management approach may be appropriate. Regular follow-up with serial MRI is mandatory. Deterioration of auditory function occurs even in the absence of tumour growth.

A Cluster of Acoustic Neuromas in Fish Hatchery Workers

The National Institute for Occupational Safety and Health (NIOSH) received a request from the United States Fish and Wildlife Service (FWS) to determine if there is a relationship between acoustic neuroma and fish hatchery work. The request was triggered by a report from an FWS employee who suspected the possibility of such an association. Investigators used data provided by the personnel office of the FWS to calculate the incidence of acoustic neuroma among fish hatchery workers, and then to compare it with national rates.

Four confirmed cases of acoustic neuroma were found among former fish hatchery workers. The overall incidence was estimated to be 15.41 per 100,000 person-years. This rate is more than 15 times higher than the rate among the general population. Even so, the small number of cases, as well as other factors, preclude the NIOSH from concluding that there is a definite cause-and-effect relationship. Further study is warranted.

Incidental discovery of acoustic neuromas

Our objective is to report 4 cases of incidentally discovered acoustic neuromas (ANs) and to determine the incidence of asymptomatic ANs. A prospective study of 161 consecutive patients undergoing gadolinium-enhanced MRI (Gd-MRI) at a tertiary-care university-affiliated medical center was carried out from September 1994 to April 1995. The Gd-MRI scans were performed for tentative diagnoses other than AN or sensorineural hearing loss. In 161 consecutive patients examined, no ANs were found incidentally on Gd-MRI scans. Previous studies have suggested that the incidence of occult ANs is as high as 1%. On the basis of our results, we suggest that the actual incidence may be lower. However, our study is limited by its small size and the low incidence of ANs in the general population. Also reported are the clinical and MRI characteristics of 4 patients with incidentally diagnosed ANs.

Incidence of vestibular schwannomas

OBJECTIVE

To determine the incidence of vestibular schwannoma (VS) in Denmark in a period of 191/2 years.

STUDY DESIGN

Retrospective review of prospective registered data on all patients with VS operated on by the translabyrinthine, lateral suboccipital, or middle cranial fossa approach, as well as patients who were allocated to the "wait-and-scan" group.

METHODS

Charts were reviewed and tabulated for age, extrameatal tumor extension, and date of diagnosis. The available data were divided into three periods: June 1976 to June 1983, July 1983 to June 1990, and July 1990 to December 1995.

RESULTS

The number of newly diagnosed tumors in the first period was 278, corresponding to an incidence of 7.8 tumors/million population per year; in the second period 337, corresponding to an incidence of 9.4 tumors/million population per year; and in the third period 355, corresponding to an incidence of 12.4 tumors/million population per year. A significant increase in incidence of the newly diagnosed intracanalicular tumors in the second and third periods was observed.

CONCLUSION

The increase in incidence of VS can probably be explained by the awareness among otolaryngologists of the diagnosis of VS and better access to computed tomography and magnetic resonance imaging scans. The observed increase in the diagnosis of the small and intrameatal tumor creates a clinical dilemma, whether to operate on tumors in this early stage or to allocate patients to the wait-and-scan group. This problem will still be relevant in the upcoming years, since the incidence of intrameatal and small VS is expected to increase.

Magnetic resonance cisternography used to determine precise topography of the facial nerve and three components of the eighth cranial nerve in the internal auditory canal and cerebellopontine cistern

OBJECT

The detailed anatomy of intracranial structures has been studied mainly in cadavers, but the absence of cerebrospinal fluid and blood pressure in these models distorts normal spatial relationships. The authors investigated the rotation of the facial nerve (FN), superior vestibular nerve (SVN), inferior vestibular nerve (IVN), and cochlear nerve (CN) in the internal auditory canal (IAC) and cerebellopontine cistern in human volunteers and compared their results with those reported in cadaver studies.

METHODS

The IACs and cerebellopontine cisterns of 30 normal adults (34 sides) were examined using magnetic resonance (MR) cisternography with a heavily T2-weighted two-dimensional fast spin-echo technique. The positions of the four components were unaffected by the presence of the meatal loop of the anterior inferior cerebellar artery in the IAC. The spatial relationship between the FN and SVN was quite constant, but the spatial relationship between the CN and SVN was quite variable: the former changed position, mainly in the IAC, on nine (26.5%) of 34 sides, and in the cerebellopontine cistern on the other sides (73.5%), conflicting with findings in cadaver studies.

CONCLUSIONS

It is more accurate to describe the CN and IVN as coursing beneath the SVN in either the IAC or cerebellopontine cistern, rather than stating that the three components rotate, as reported in cadaver studies. The MR cisternography studies provided quite detailed information about the topography of the four components and the relationship between the blood vessels and cranial nerves in the IAC and the cerebellopontine cistern.

A Molecular, Clinical and Immunohistochemical Study of Vestibular Schwannoma

The molecular pathogenesis of vestibular schwannoma has been investigated by determining the extent of chromosome 22 loss of heterozygosity in 77 tumors and relating these findings to clinical and immunohistochemical indexes of tumor behavior. Loss of heterozygosity was looked for at eight chromosome 22q loci. Clinical details were obtained in all 77 cases, and a clinical growth index was calculated for each tumor. The proliferative index was estimated in all tumors by using a monoclonal antibody to the proliferating cell nuclear antigen and by calculating the labeling index. Forty percent (31 of 77) of the tumors showed allele loss, and in each case this loss involved the region of the neurofibromatosis type 2 gene. No evidence was found that the presence of chromosome 22 allele loss was associated with the clinical growth index. On the log scale, however, an association was seen between the clinical growth index and the proliferating cell nuclear antigen labeling index p = 0.001). These results suggest that chromsome 22 allele loss is a frequent event in vestibular schwannoma. Tumor behavior, however, appears to be independent of the chromosome 22 mutation. It is proposed that chromosome 22 allele loss and neurofibromatosis type 2 gene inactivation is an early event, possibly involved in the initiation of tumorigenesis in vestibular schwannoma. Tumor growth appears to be independent of this mutation and is likely to be determined by other as yet undefined factors.

Hearing preservation in the removal of intracanalicular acoustic neuromas via the retrosigmoid approach

In a series of 514 consecutive operations for complete excision of acoustic neuromas, 94 procedures were performed via a retrosigmoid approach to preserve the patient's hearing. Twenty-six of these procedures (5.1%) were performed in cases of intracanalicular tumor and 68 (13.2%) were for larger lesions in which most of the tumor was located medial to the porus acusticus within the cerebellopontine angle. Preservation of useful hearing was achieved in 13 (50%) of 26 patients with intracanalicular tumors and in 20 (29%) of 68 with larger tumors. A trend toward higher success rates in intracanalicular tumors appears to be present, although the difference is not statistically significant (p = 0.09). Normal or near normal facial function (House and Brackmann Grades I and II) was present postoperatively in 25 (96%) of 26 patients. Indications for treatment of intracanalicular acoustic neuromas are considered and treatment alternatives are reviewed. Results from other series reporting removal of intracanalicular acoustic neuromas are considered with respect to hearing conservation and postoperative facial nerve function. Surgical excision of intracanalicular acoustic neuromas in otherwise healthy patients appears to be warranted if preservation of useful binaural hearing is considered a worthwhile objective and if perioperative morbidity can be maintained at an acceptably low level. The retrosigmoid approach is familiar to all neurosurgeons and offers a comparable success rate for hearing conservation and probably a superior outcome in terms of facial nerve function when compared with the middle fossa approach.

Magnetic resonance imaging assessment of labyrinthine pathology

Membranous labyrinth pathologies are quite rare. They were until recently difficult to demonstrate by imaging technics, CT being the modality of choice. Our purpose was to stress the interest of MR examination for investigating patients complaining of vertigo, tinnitus, and profound sensorineural hearing loss. Normal anatomy as well as the main pathologically encountered changes are illustrated.

Accidentally detected brain tumors: clinical analysis of a series of 110 patients

The clinical records of 1,155 patients with 1,159 brain tumors who drained on Keio University Hospital between 1983 and 1994 were reviewed. Apparently asymptomatic patients and those whose complaints or neurological deficits were not caused by the brain tumors were defined as accidental cases. For example, patients with a headache which was considered to be unrelated to the presence of a tumor were included in this series. One hundred and ten (9.5%) of the 1,155 cases were found to be accidental. Since three accidental cases had multiple meningiomas, there were 113 accidental brain tumors which involved 63 meningiomas, 22 pituitary adenomas, 9 gliomas, 7 metastatic carcinomas. 5 acoustic neurinomas and 7 miscellaneous. Meningiomas occurred significantly more frequent than other types of accidentally identified tumors. Convexity meningiomas and falx meningiomas accounted for 53.9% of the accidental meningiomas, whereas parasagittal meningiomas were less frequent. It is of note that three out of four cases with multiple meningiomas were accidental. Comparison between the present results and the previously reported incidence of asymptomatic brain tumors in postmortem studies suggest that a substantial number of pituitary adenomas, acoustic neurinomas and small parasagittal meningiomas without suggestive symptoms are likely to be missed by routine neuroradiological examinations.

Management of acoustic neuroma

Images

MR imaging features of an intracochlear acoustic schwannoma

We present a very unusual case of an acoustic neuroma involving the left cochlea and internal auditory canal of a 24-year-old man. Clinical suspicion was aroused when the patient presented with a left total sensorineural hearing loss and continuing vertigo. The diagnosis was made pre-operatively with MRI after initial CT scanning was normal. The tumour was removed via a transotic approach. This case report demonstrates the MRI features of an intracochlear schwannoma and emphasizes the importance of MRI in patients with significant auditory and clinical abnormalities with normal CT scans of the relevant region.

Intracanalicular acoustic neuroma: early surgery for preservation of hearing

Diagnosis of very small acoustic neuromas has become much more common since the advent of magnetic resonance imaging. Many of the patients so diagnosed have minimal unilateral hearing loss as their only symptom. Because limited information is available on the natural history and prognosis of these lesions, the choice of treatment is controversial. The authors review their recent experience with the surgical treatment of intracanalicular acoustic neuroma. The records of 14 consecutive patients with intracanalicular acoustic neuroma were reviewed with respect to type of presentation, pre- and postoperative facial and auditory nerve function, surgical approach, and complications. Detailed results for patients operated on to preserve hearing are presented. Presenting symptoms were nearly equally divided among diminished hearing, vertigo, and tinnitus. Eleven of the 14 patients had serviceable hearing preoperatively and nine (82%) remained in this condition postoperatively. Facial nerve function was unchanged by operation in 12 patients. Seven operations were performed through the middle fossa, five through the posterior fossa, and two by the translabyrinthine approach. The probability of preserving hearing during surgical excision of intracanalicular acoustic neuroma in patients with serviceable hearing exceeds 80%. Given the relative infrequency of serious complications and the likelihood of progressive hearing loss in the untreated patient, excision of such small tumors shortly after diagnosis may offer the best chance of long-term hearing preservation.

Epidemiology and clinical features of vestibular schwannoma in Manitoba, Canada

The incidence of vestibular schwannoma (acoustic neuroma) in Manitoba, Canada was reviewed. From 1987 through 1991, 71 tumors were diagnosed in 69 patients. The overall annual incidence rate for both sexes was 1.27/100,000 with male and female annual incidences of 1.31/100,000 and 1.24/100,000 respectively. For males, there was an early peak in the age group 30-39 years (2.1/100,000). Following the fifth decade, the incidence for males plateaued (2.7-3.6/100,000). For females, the incidence increased with age up to age 60-69 years (4.1/100,000). This was followed by a progressive decline in the incidence. Although the incidence of vestibular schwannoma was relatively high, the clinical features were not unlike those previously reported in the literature.

Intralabyrinthine schwannoma

Intralabyrinthine schwannomas are rare tumours which present with symptoms similar to Menière's disease. Preoperative diagnosis is rarely possible and most are found incidentally during labyrinthectomy for persistent vertigo. A further case of this tumour is reported together with a review of the literature.

Acoustic neuromas. Diagnostic delay, growth rate and possible non-surgical treatment

In spite of an intensive campaign to achieve early diagnosis of acoustic neuromas, our attempts have not been successful, since we have even more tumours measuring more than 40 mm in diameter among our latest 100 patients than among the first one hundred. It is demonstrated that both patients and physicians (otologists) are to some extent still ignoring the possible significance of a unilateral, progressive, sensorineural hearing impairment. Guidelines for improving this condition are given. We have been able to follow 21 patients for an average of 4 years, with repeated CT scans, and only in 3 of these patients did the tumour appear to be progressing to a size requiring surgical intervention. In the remaining 18 patients the tumour has not increased in size, as judged by the CT. Because of our complete lack of knowledge about the causes of tumour growth in some patients and absence of growth in others, a more differentiated attitude towards indications for surgery is needed, and in some, mostly elderly, patients a period of 'watchful waiting' is appropriate.