Occult schwannomas of the vestibular nerve

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.

Intralabyrinthine schwannomas: a two-case series and literature review with a focus on hearing rehabilitation

PURPOSE

Intralabyrinthine schwannomas (ILSs) are an uncommon finding. Diagnosis is challenging and no gold standard treatment exists yet. In this article, we present a two-cases series and review the latest available literature to assess the best diagnostic and therapeutic scheme.

METHODS

We reviewed the latest available literature assessing most frequent and relevant sets of symptoms, clinical features of the disease, diagnostic tests and imaging, possible treatments and after-surgery hearing rehabilitation techniques. We then compared literature data to our own series ones.

RESULTS

ILSs clinical presentation and development may overlap with other, more common otological conditions. Full audiometric battery test, electrophysiological study of VEMPS and MRI with contrast enhancement all appear to be critical to correctly diagnose these tumors. Several treatments exist: radiological follow-up, radiation therapy, full or partial surgical excision. Hearing rehabilitation is mostly accomplished through simultaneous cochlear implantation.

CONCLUSIONS

Our case-series data matches the available literature. ILSs are a rare type of vestibular schwannomas. Diagnosis in challenging and delayed in time as all the diagnostic tests, yet sensitive, are not specific for ILSs. The most suitable treatment seems to be surgical excision of these tumors followed by simultaneous cochlear implantation to restore hearing.

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.

Tumor-Related and Patient-Related Variables Affecting Length of Hospital Stay Following Vestibular Schwannoma Microsurgery

OBJECTIVE

Review a single institution's vestibular schwannoma (VS) microsurgery experience to determine (1) correlations between demographics, comorbidities, and/or surgical approach on hospital length of stay (LOS) and discharge disposition and (2) trends in surgical approach over time.

METHODS

Retrospective case series from a multidisciplinary skull base program at a tertiary care, academic hospital. All adult (>18 years) patients undergoing primary microsurgery for VS between 2008 and 2018 were included.

RESULTS

A total of 147 subjects were identified. Surgical approach was split between middle fossa (MF) (16%), retrosigmoid (RS) (35%), and translabyrinthine (TL) (49%) craniotomies. For the 8% of patients had other than routine (OTR) discharge. Mean LOS was significantly longer for patients undergoing RS than either MF or TL. Brainstem compression by the tumor was associated with longer LOS as were diagnoses of chronic obstructive pulmonary disease (COPD) and peripheral vascular disease (PVD). For all discharges, the 40 to 50- and 50 to 60-year-old subgroups had significantly shorter LOS than the 70-years-and-older patients. For the 92% of patients routinely discharged, there was a significantly shorter LOS in the 40 to 50-year-olds compared to the 70-years-and-older patients. There was a significant shift in surgical approach from RS to TL over the study period.

CONCLUSION

Over 90% of VS microsurgery patients were routinely discharged with a median hospital LOS of 3.2 days, both of which are consistent with published data. There is an inverse relationship between age and LOS with patients older than 70 years having significantly longer LOS. Brainstem compression, COPD, PVD, and the RS approach negatively affect LOS.

LEVEL OF EVIDENCE

4.

Tracking Spontaneous Vestibular Schwannoma Regression with Volumetric Measurements

OBJECTIVE

To characterize a series of patients with MRI evidence of spontaneous vestibular schwannoma (VS) regression.

STUDY DESIGN

Retrospective case series.

METHODS

Retrospective review between 2012 and 2020 from a single, tertiary-care center of all patients with an untreated, sporadic VS and spontaneous regression in volumetric tumor size over the course of observation. The main outcome measures included VS size and location, presenting symptoms, medication use, changes in pure-tone averages and word recognition scores.

RESULTS

The 13 treatment-naïve patients (62% female, mean age 67.1 years) with spontaneous VS regression represented 3.9% of all patients undergoing observation with serial imaging during the study period. Median tumor size from initial MRI was 529.0 mm³ (range: 108 mm³ -13,180 mm³ ). The mean interval between MRI measurements was 5.5 years (SD 4.4 years). The average percent decrease in tumor size was 36.1% (SD 21.9%) and the average rate of volume decrease was 15.8 mm³ /yr (SD 25.4 mm³ /yr). Five patients were classified as having major regression, defined by a relative decrease in volume of >40%, while eight patients had minor regression (<40% relative volume reduction). No significant differences in initial tumor size, rate of regression, or audiometric changes were observed between the major and minor regression cohorts.

CONCLUSIONS

Patients with evidence of a spontaneously shrinking VS have a heterogeneous presentation. Due to the scarcity of this phenomenon, predicting which tumors will eventually undergo regression remains unclear. Employing volumetric measurements to compare serial MRI scans may improve the accuracy of detecting shrinking tumors.

LEVEL OF EVIDENCE

4 Laryngoscope, 131:E1647-E1652, 2021.

Contextualizing the Modern Epidemiology of Neurofibromatosis Type 2 in an Era of Heightened Detection of Sporadic Vestibular Schwannoma

OBJECTIVE

Closely paralleling previous radiologic studies, recent population-based prevalence data suggest sporadic vestibular schwannoma (VS) affects over one in 2,000 adults and up to one in 500 in those aged 70 years or older. Attributable to increased utilization of magnetic resonance imaging and screening protocols for asymmetrical sensorineural hearing loss, the increasing detection rate of sporadic VS fundamentally changes the perception of VS as a whole. The primary objective of the current study was to contextualize modern epidemiological trends in neurofibromatosis type 2 (NF2) in light of these recent advancements in the understanding of sporadic VS.

STUDY DESIGN

Population-based study.

SETTING

Olmsted County, Minnesota. Population size on January 1, 2017: 159,689 people.

PATIENTS

All patients with NF2 diagnosed between Jan 1, 1966 and Dec 31, 2016, identified using the Rochester Epidemiology Project.

MAIN OUTCOME MEASURES

Incidence, prevalence.

RESULTS

Six incident cases were identified over the past 50 years. From 1966 to 2016, the age- and sex-adjusted incidence rate was 0.10 per 100,000 person-years. The incidence rate remained at 0.12 over the most recent decade. Five cases met disease prevalence criteria, and the age- and sex-adjusted prevalence of NF2 on Jan 1, 2017 was 3.1 per 100,000 persons. All prevalent cases were women, and the resultant prevalence among women only was 6.0 per 100,000 persons.

CONCLUSIONS

The modern age- and sex-adjusted incidence rate and prevalence of NF2 is 0.10 per 100,000 person-years and 3.1 per 100,000 persons, respectively. In contrast to trends in incidence rates of sporadic VS over the last half-century, this study demonstrates that the incidence of NF2 has remained relatively stable since 1966. This divergence in epidemiological trends is likely attributed to the nature of NF2, with early clinical manifestations resulting in diagnosis regardless of modern advances, whereas the increased incidence of sporadic VS is heavily influenced by improved detection in a greater population of patients with minimally symptomatic or asymptomatic tumors.

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."

Location of Small Intracanalicular Vestibular Schwannomas Based on Magnetic Resonance Imaging

Vestibular schwannomas (VSs) were proposed to arise from the glial-Schwann cell junction within the internal auditory canal (IAC). However, otopathology studies indicate that VS may arise anywhere along the course of the vestibular nerve. Recent studies suggested that the majority of tumors are located centrally within the IAC with an equal distribution near the porus acusticus and the fundus. However, these studies analyzed tumors of all sizes, obscuring their precise origin. Herein, we aim to quantify the position of small intracanalicular tumors (<5 mm), assessing hearing outcomes and growth patterns in relation to tumor position. Of the 38 small intracanalicular tumors analyzed, 61% originated closest to the fundus, 34% at the midpoint, and only 5% closest to the porus acusticus. Tumors were observed with serial magnetic resonance imaging for 3.37 ± 2.65 years (mean ± SD) without intervention. Our findings indicate a lateral predominance of small VS within the IAC, an independence between tumor location and hearing outcomes, and further support the slow natural progression of VS.

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.

Associations of Video Head Impulse Test and Caloric Testing among Patients with Vestibular Schwannoma

OBJECTIVE

To determine relationships between caloric testing (CT) and video head impulse testing (vHIT) among patients with unilateral vestibular schwannoma (VS). To describe the distribution of CT and vHIT measurements and assess associations with tumor size and self-perceived handicapping effects.

STUDY DESIGN

Retrospective review.

SETTING

Tertiary referral hospital.

SUBJECTS AND METHODS

Subjects were adults with presumed unilateral VS between 2014 and 2017. Interventions were CT and vHIT. Primary outcomes were vHIT value (abnormal <0.8) and CT value (abnormal >25%). Secondary outcomes were tumor size and Dizziness Handicap Inventory scores.

RESULTS

Fifty-one individuals had complete data for CT and vHIT. The odds of abnormal gain increases by 2.18 for every 10% increase in unilateral weakness on CT (range, 1.44-3.34; P < .001). A significant negative correlation between CT and gain exists (r_s = -0.64, P < .001). Odds of observing saccades increased by 2.68 for every 10% increase in unilateral weakness (range, 1.48-4.85; P = .001). This association was larger in magnitude for overt than covert saccades (odds ratios, 2.48 and 1.59, respectively). Tumor size was significantly associated with an increase in caloric weakness (β = 0.135, P < .001). With every 10-mm increase of tumor size, odds of abnormal gain on vHIT increased 4.13 (range, 1.46-11.66; P = .007). Mean Dizziness Handicap Inventory score was 19.7 (σ = 22), without association to caloric weakness, gain, or tumor size.

CONCLUSION

CT and vHIT both effectively assess vestibular function for patients with VS and correlate to tumor size. These findings are important as vHIT has a lower overall cost, improved patient tolerance, and demonstrated reliability.

Magnetic Resonance Imaging-Based Screening for Asymptomatic Brain Tumors: A Review

Brain tumors comprise 2% of all cancers but are disproportionately responsible for cancer-related deaths. The 5-year survival rate of glioblastoma, the most common form of malignant brain tumor, is only 4.7%, and the overall 5-year survival rate for any brain tumor is 34.4%. In light of the generally poor clinical outcomes associated with these malignancies, there has been interest in the concept of brain tumor screening through magnetic resonance imaging. Here, we will provide a general overview of the screening principles and brain tumor epidemiology, then highlight the major studies examining brain tumor prevalence in asymptomatic populations in order to assess the potential benefits and drawbacks of screening for brain tumors. IMPLICATIONS FOR PRACTICE: Magnetic resonance imaging (MRI) screening in healthy asymptomatic adults can detect both early gliomas and other benign central nervous system abnormalities. Further research is needed to determine whether MRI will improve overall morbidity and mortality for the screened populations and make screening a worthwhile endeavor.

Common Histologically Benign Tumors of the Brain

PURPOSE OF REVIEW

As a group, benign tumors account for the majority of primary neoplasms affecting the central nervous system (CNS). This article reviews the epidemiology, clinical presentation, neuroimaging features, and management of the most common of these tumors: meningiomas, schwannomas, and pituitary adenomas.

RECENT FINDINGS

Awareness of the most common nonmalignant tumors of the CNS and their management guidelines is important as many of these tumors are managed conservatively, with neurologists playing a primary role in both surveillance and symptom management. Knowledge of the varied neurologic consequences of these tumors allows optimizing interventions that improve quality of life in people living with these tumors without incurring treatment-related complications. Awareness of the clinical features that require surgery, radiation therapy, or chemotherapy is imperative. Finally, important discoveries in both germline and somatic mutations underlying some of these lesions have contributed to the launch of several novel drug trials for these tumors.

SUMMARY

As a group, nonmalignant neoplasms are the most common neoplasms affecting the CNS in adults. Because of their unique neuroanatomic location or containment within the bony skull, these histologically benign lesions can cause significant neurologic morbidity. Management with a multidisciplinary team that includes neurologists, neuro-oncologists, radiologists, neurosurgeons, radiation oncologists, otolaryngologists, pathologists, neuropsychologists, physiatrists, and others is necessary for the optimal management of these lesions.

Incidence of Vestibular Schwannoma over the Past Half-Century: A Population-Based Study of Olmsted County, Minnesota

Objective The absence of a centralized health system has limited epidemiologic research surrounding vestibular schwannoma (VS) in the United States. The Rochester Epidemiology Project (REP) comprises a unique medical consortium that covers a complete population of all ages in a well-defined geographic region over the past half-century. The objective of this study was to characterize the incidence of sporadic VS over this extended period. Study Design Population-based study. Setting Olmsted County, Minnesota. Subjects and Methods Review of all VSs diagnosed between January 1, 1966, and December 31, 2016, was conducted with the REP medical records linkage system. Results A total of 153 incident cases of VS were identified. The incidence of VS significantly increased over the past half-century from 1.5 per 100,000 person-years during the first decade to 4.2 in the last decade ( P < .001). Incidence increased with age ( P < .001): those aged ≥70 years exhibited the highest incidence rate at 18.3 per 100,000 person-years in the last decade. Age at diagnosis significantly increased from a median of 52 years in the first decade to 62 years in the last ( P < .001). Despite presenting with fewer symptoms and smaller tumors, the time delay between symptom onset and diagnosis significantly decreased over the past 5 decades (all P < .05). Almost 1 in 4 patients was diagnosed incidentally in the last decade. Conclusion The incidence of VS increased significantly over the past half-century to a rate greater than previously reported. Patients' ease of access to medical care in Olmsted County and the comprehensive REP system likely contributed to this elevated detection rate of VS.

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.

Vestibular schwannoma and pituitary adenoma in the same patient: coincidence or novel clinical association?

Over the years the authors have evaluated a number of patients with vestibular schwannomas (VS) who have also been diagnosed with a pituitary adenoma (PA). No associations between these tumors have been established to date. The objective of the current study is to investigate the epidemiological association between VS and PA via a population-based study and to supplement these data with a retrospective case series of 12 patients who were evaluated at the authors' center over the past 15 years. An analysis of the Surveillance, Epidemiology, and End Results database including all patients identified with a diagnosis of VS and/or PA was performed. A comparison between the observed and expected annual incidence was calculated and population differences between those with VS + PA were compared with single tumor populations. 9888 patients with VS and 26,577 patients with PA were identified among 822.9 million person-years. Within these populations, 31 patients were diagnosed with both tumor types. Overall, 1 in every 319 patients with VS was also diagnosed with a PA. The average annual incidence for VS was 1.2 per 100,000 persons per year while the average PA rate was 3.2 per 100,000 persons per year. The observed rate of co-incident VS and PA was greater than what is expected by chance alone assuming independence. The cohort of patients with coexisting VS and PA were older and more commonly male compared to VS-only or PA-only groups. These data strongly suggest that a common environmental or genetic predisposition exists for VS and PA development. Further study of this population may help elucidate the cause of tumorigenesis in a subset of patients with seemingly sporadic tumors.

Incidence of vestibular schwannomas in the United States

There is a paucity of population-based data evaluating the incidence of vestibular schwannomas according to age, gender, race, and ethnicity. Such data are necessary to assess the burden of vestibular schwannomas on varying populations and to inform future research and healthcare planning. The Central Brain Tumor Registry of the United States, which contains the largest aggregation of population-based data on the incidence of primary central nervous system tumors in the US, was used. Age-adjusted incidence rates and incidence rate ratios (IRR) of vestibular schwannomas from 2004 to 2010 were calculated by age at diagnosis, gender, race, and ethnicity. Annual percent change (APC) was calculated using Joinpoint to characterize temporal trends. From 2004 to 2010, there were 23,729 newly diagnosed vestibular schwannomas in the US; overall incidence was 1.09 per 100,000 population. Incidence was stable over time (APC -0.41 %, 95 % confidence interval -3.4, 2.7). Incidence increased with age to a peak of 2.93 per 100,000 in the 65-74 year old age group. Overall, there was no difference in incidence by gender. Compared to Whites, incidence was highest in Asian Pacific Islanders (IRR 1.37, p < 0.001) and lowest in African Americans (IRR 0.36, p < 0.001). Incidence was lower in Hispanics than non-Hispanics (IRR 0.69, p < 0.001). Over 3300 vestibular schwannomas are diagnosed per year in the US and incidence is 1.09 per 100,000 population. Incidence increases with age up to the 65-74 year old age group. Incidence is higher in Asian Pacific Islanders and lower in African Americans and Hispanics.

Lack of Association between Human Herpesvirus and Vestibular Schwannoma

Objective

To assess for the presence of human herpesvirus (HHV) using immunohistochemical and polymerase chain reaction (PCR) assay in surgically excised vestibular schwannoma (VS) samples.

Study Design

Cross-sectional study.

Setting

A retrospective laboratory-based study of tumors from patients with vestibular schwannoma.

Subjects and Methods

Tissue microarrays (TMAs) representing sporadic and NF2-associated VS from 121 patients, as well as appropriate positive and negative controls, were studied. TMA sections were immunostained using antibodies directed against HHV-1, HHV-2, HHV-3, HHV-4, HHV-5, and HHV-8. PCR was used for the detection of all 8 known human herpesviruses.

Results

There was no detectable HHV (HHV-1, HHV-2, HHV-3, HHV-4, HHV-5, HHV-8) by immunohistochemistry in any of the 121 cases of sporadic and NF2 cases analyzed. These data were further validated by DNA sequence analyses using PCR in a subset of the VS samples, all of which were found to be negative for all HHV.

Conclusions

The data offer no support for an association between HHV and the development of sporadic or NF2-associated VS in humans.

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.

Vestibular schwannoma: 825 cases from a 25-year experience

INTRODUCTION

 Acoustic nerve tumors have been recognized as a clinico-pathologic entity for at least 200 years, and they represent 90% of cerebellopontine angle diseases. Histologically, the tumors are derived from Schwann cells of the myelin sheath, with smaller tumors consisting of elongated palisade cells, while in large tumors, cystic degeneration can be found in the central areas, possibly due to deficient vascularization. We retrospectively reviewed 825 cases of vestibular schwannomas, reported between January 1984 and August 2006, in which the patients underwent surgery to remove the tumor.

OBJECTIVE

 To evaluate signs, symptoms, aspects of clinical diagnosis, including the results of audiological and imaging studies, and surgical techniques and complications.

METHODS

 A retrospective chart review. The medical records of all patients undergoing surgical treatment for schwannoma during the period indicated were reviewed.

RESULTS AND CONCLUSION

 Hearing loss was the first symptom reported in almost all cases, and tumor size was not proportional to the impairment of the auditory threshold. The surgical techniques allowed safe preservation of facial function. In particular, the retrolabyrinthine route proved useful in small tumors, with 50% preservation of hearing.

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.

Epidemiology and natural history of vestibular schwannomas

This article describes various epidemiologic trends for vestibular schwannomas over the last 35 years, including a brief note on terminology. Additionally, it provides information on the natural history of tumor growth and hearing level following the diagnosis of a vestibular schwannoma. A treatment strategy based on the natural history of tumor growth and hearing also is discussed.

Is an Acoustic Neuroma an Epiarachnoid or Subarachnoid Tumor?

BACKGROUND:

There are arguments about whether acoustic neuromas are epiarachnoid or subarachnoid tumors.

OBJECTIVE:

To retrospectively examine 118 consecutively operated-on patients with acoustic neuromas to clarify this point.

METHODS:

Epiarachnoid tumors are defined by the absence of an arachnoid membrane on the tumor surface after moving the arachnoid fold (double layers of the arachnoid membrane) toward the brainstem. In contrast, subarachnoid tumors are characterized by the arachnoid membrane remaining on the tumor surface after moving the arachnoid fold. Based on this hypothesis, we used intraoperative views and light and electron microscopy to confirm the existence of an arachnoid membrane after the arachnoid fold had been moved.

RESULTS:

The tumors were clearly judged to be subarachnoid tumors in 86 of 118 patients (73%), an epiarachnoid tumor in 2 patients (2%), whereas a clear judgment was difficult to make in the remaining 30 patients (25%).

CONCLUSION:

The majority of acoustic neuromas are subarachnoid tumors, with epiarachnoid tumors being considerably less common.

True incidence of vestibular schwannoma?

BACKGROUND

The incidence of diagnosed sporadic unilateral vestibular schwannomas (VS) has increased, due primarily to more widespread access to magnetic resonance imaging.

OBJECTIVE

To present updated epidemiological data on VS incidence, as well as patient age, hearing acuity, tumor size, and localization at diagnosis for the last 4 decades in an unselected population, with emphasis on developments in recent years.

METHODS

From 1976 to 2008, 2283 new cases of VS were diagnosed and registered in a national database covering 5.0 to 5.5 million inhabitants. Incidence during the period, patient sex and age, data on hearing (pure tone average and speech discrimination), and tumor size at diagnosis were retrieved from the database.

RESULTS

The incidence increased from 3.1 diagnosed VS per million per year in 1976 to a peak of 22.8 VS per million per year in 2004, which was followed by a decrease to 19.4 VS per million per year in 2008. Mean tumor size at diagnosis decreased from 30 mm in 1979 to 10 mm in 2008, whereas hearing acuity at diagnosis has improved over the years.

CONCLUSION

After a steady increase over the last 4 decades, the incidence of vestibular schwannomas appears to have peaked and decreased in recent years, stabilizing at about 19 tumors per million per year. Whereas the sex ratio and age at diagnosis have remained grossly unchanged over the years, hearing has improved, and tumor size has decreased considerably.

Magnetic resonance imaging screening in acoustic neuroma

OBJECTIVES

Magnetic resonance imaging (MRI) is the definitive investigation for detection of an acoustic neuroma. It is however an expensive resource, and pick-up rate of a tumor can be as low as 1% of all patients scanned. This study aims to examine referral patterns for MRI screening for patients presenting with asymmetrical sensorineural hearing loss (ASHL). A second aim was to suggest appropriate screening criteria.

METHOD

All 132 MRI scans performed for ASHL in the year 2005 were reviewed retrospectively along with their case records and audiograms. In addition, MRI scans and case records were reviewed for the last 30 patients diagnosed with acoustic neuromas. Information was analyzed using 2 published protocols and additional frequency-specific defined criteria.

RESULTS

Two acoustic neuromas were picked up out of 132 scans performed. Of the scans performed for ASHL, a third did not fit with any of the published criteria. Of the 30 positive scans for a tumor, the patients/audiograms revealed that 10% did not fit the published criteria despite the patients having no other audiovestibular symptoms.

CONCLUSIONS

There appears to be no universally accepted guidelines on screening in ASHL with clinical acumen being used by most ENT consultants in this region. Applying protocols may reduce the amount of scans performed, but up to 10% of tumors may be missed by this approach.

Imaging of intralabyrinthine schwannomas: a retrospective study of 52 cases with emphasis on lesion growth

BACKGROUND AND PURPOSE

Only a few case reports and small series of intralabyrinthine schwannomas (ILSs) have been reported. The purpose of this study was to assess prevalence, MR characteristics, location, clinical management, and growth potential/patterns of ILSs in the largest series reported.

MATERIALS AND METHODS

Lesion localization, MR characteristics, lesion growth, and clinical management were reviewed in 52 patients diagnosed with an ILS between February 1991 and August 2007 in 2 referral centers. The number of ILSs and vestibulocochlear schwannomas in the cerebellopontine angle/internal auditory canal was compared to assess the prevalence.

RESULTS

ILSs most frequently originate intracochlearly, are hyperintense on unenhanced T1-weighted images, enhance strongly after gadolinium administration, and are sharply circumscribed and hypointense on thin heavily T2-weighted 3D images. The scala tympani is more frequently or more extensively involved than the scala vestibuli. Follow-up MR imaging, available in 27 patients, showed growth in 59% of subjects. Growth was seen from the scala tympani into the scala vestibuli and from the scala vestibuli to the saccule and vice versa. Twelve lesions were resected, and the diagnosis of ILS histopathologically confirmed.

CONCLUSION

ILSs can account for up to 10% of all vestibulocochlear schwannomas in centers specializing in temporal bone imaging, grow in more than 50%, and are most frequently found intracochlearly, often anteriorly between the basal and second turn. Cochlear ILSs most often originate in the scala tympani and only later grow into the scala vestibuli. Growth can occur from the cochlea into the vestibule or vice versa through the anatomic open connection between the perilymphatic spaces in the scala vestibuli and around the saccule.

Intralabyrinthine schwannomas: Symptoms and managements

OBJECTIVE

To describe the characteristic presentations, radiologic findings and managements of the intralabyrinthine schwannomas.

METHOD

Retrospective review of patient records, their managements, and review of the literature.

RESULT

Four patients with a variety of otologic symptoms including hearing loss, vertigo, and tinnitus were found to have a schwannomas involving the labyrinth. In all cases, the inner ear lesions were preoperatively identified on magnetic resonance imaging, and the surgical removals were performed in all patients without serviceable hearing. The patients experienced improvement in their vertigo and tinnitus after surgery. Two patients were implanted the Bone-Anchored Hearing Aid (BAHA) to reconstruct the pseudo-stereophonic hearing.

CONCLUSION

Intralabyrinthine schwannomas are the rare tumours in the otology. The tumour can be removed by surgical approach, but we do not propose surgical excision for the patients with serviceable hearing. BAHA can give patients a post-operative monaural pseudo-stereophonic hearing.

Treatment of vestibular schwannomas. Why, when and how?

Sporadic vestibular schwannoma (VS) causes unilateral hearing loss, tinnitus, vertigo and unsteadiness. In many cases, the tumour size may remain unchanged for many years following diagnosis, which is typically made by MRI. In the majority of cases the tumour is small, leaving the clinician and patient with the options of either serial scanning or active treatment by gamma knife radiosurgery (GKR) or microneurosurgery. Despite the vast number of published treatment reports, comparative studies are few, and evidence is no better than class III (May, 2006). The predominant clinical endpoints of VS treatment include tumour control, facial nerve function and hearing preservation. Less focus has been put on symptom relief and health-related quality of life (QOL). It is uncertain if treating a small tumour leaves the patient with a better chance of obtaining relief from future hearing loss, vertigo or tinnitus than by observing it without treatment. Recent data indicate that QOL is reduced in untreated VS patients, and may differ between patients who have been operated and patients treated with GKR. In the present paper we review the natural course and complaints of untreated VS patients, and the treatment alternatives and results. Furthermore, we review the literature concerning quality of life in patients with VS. Finally, we present our experience with a management strategy applied to more than 300 cases since 2001.

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.

Systematic review of the natural history of vestibular schwannoma

OBJECT

Magnetic resonance (MR) imaging now permits diagnosis of increasing numbers of small, minimally symptomatic vestibular schwannomas (VSs). Because VS growth patterns over time are very important in refining treatment strategies, these matters were systematically reviewed.

METHODS

An extensive MEDLINE search was performed to cull studies on VS growth according to sequential imaging. The percentages of growing and regressing tumors and lesions requiring treatment during follow-up periods were calculated. Factors associated with differences among studies were identified. Twenty-six studies including 1340 patients met all inclusion criteria. The overall frequency of VS growth during a mean follow-up period of 38 months was 46% (95% confidence interval [CI] 43-48%) and that of regression was 8% (95% CI 6-10%). The mean annual tumor growth rate was 1.2 mm/year. Furthermore, the percentage of cases requiring treatment during follow up was 18% (95% CI 16-21%). According to results of a sensitivity analysis, evaluation by serial MR imaging (39%, 95% CI 35-43%) and a prospective study design (29%, 95% CI 21-37%) were associated with less frequent reported tumor growth.

CONCLUSIONS

Although their applicability may be limited to relatively elderly patients with small tumors, data revealing a limited frequency of VS enlargement and an infrequent necessity for eventual therapy should assist decision-making in the treatment of small VSs causing minimal symptoms.

Intralabyrinthine Schwannomas: Diagnosis, Management, and a New Classification System

OBJECTIVE

To outline the diagnosis and management of intralabyrinthine schwannomas and to propose a new classification system to further define them.

STUDY DESIGN

Retrospective case review.

SETTING

Tertiary referral center at a university hospital.

PATIENTS

Twenty-eight patients seen at the institution with intralabyrinthine schwannomas between 1996 and 2002 were included in the study.

INTERVENTIONS

Diagnosis was made with magnetic resonance imaging in all but one case. Our ability to detect these tumors has been greatly enhanced by the introduction of high-resolution T2-weighted magnetic resonance imaging. Treatment options were observation with serial magnetic resonance imaging versus complete surgical removal via a translabyrinthine or transotic approach. Surgery was indicated for dizziness caused by the tumor or extralabyrinthine growth.

MAIN OUTCOME MEASURES

Clinical features, audiology, radiology, and management outcomes were evaluated.

RESULTS

Eight patients have undergone successful surgery with removal of their tumors and resolution of symptoms. One patient chose to have stereotactic radiotherapy. Of the 20 patients who were managed with observation and serial magnetic resonance imaging, only 1 has shown significant growth requiring surgical removal.

CONCLUSION

Intralabyrinthine schwannomas are uncommon tumors that mimic the clinical features of many other neurotologic conditions. A high index of suspicion and precise imaging are often required to detect these tumors. Surgical treatment is indicated for specific indications and will be needed in the minority of patients with this disorder. The classification system that we propose is helpful in both the diagnosis and the management of these tumors.

Should patients with asymmetrical noise-induced hearing loss be screened for vestibular schwannomas?

The Peterborough ENT department receives many referrals for MoD personnel who have suffered hearing loss from occupational noise exposure. Those patients with asymmetrical sensorineural hearing loss are routinely screened for vestibular schwannomas by MRI scanning. Scan reports from the past 5 years have been reviewed and out of 152 scans, four revealed vestibular schwannomas giving a pick-up rate of 2.5%, which compares favourably with other published pick-up rates. Review of the audiograms in these cases suggests that they can be misleading in this context. The conclusion is that patients with noise-induced asymmetrical hearing loss should be screened for acoustic neuromas.

Intralabyrinthine schwannomas

OBJECTIVE

To describe the patient presentation, radiographic findings, and treatment results in a series of eight patients with a diagnosis of intralabyrinthine schwannoma, and to review the presentation of other cases of intralabyrinthine schwannoma in the English otolaryngologic literature.

METHODS

Retrospective review of patient records, operative reports, and radiologic studies, and review of the literature.

RESULTS

Eight patients with a variety of otologic symptoms including progressive hearing loss, episodic vertigo, and tinnitus were found to have a schwannoma involving the vestibule or cochlea. Surgery was performed to remove the tumors from four patients with nonserviceable hearing. The patients experienced significant improvement in their vertigo and tinnitus after surgery. Observation and serial magnetic resonance imaging were adequate treatment of the four patients with serviceable hearing. In the literature review, 447 cases of intralabyrinthine schwannoma were identified, and the presentations were similar to those in the cases described here.

CONCLUSION

Intralabyrinthine schwannomas are rare tumors that arise from the distal portion of either the vestibular nerve or the cochlear nerve. Consequently, the cochlea, the semicircular canals, the vestibule, or a combination of these structures may become involved with these lesions. Transmastoid labyrinthectomy or a transotic approach can be used to remove intralabyrinthine tumors from patients with nonserviceable hearing and severe vertigo or tinnitus. In addition, these surgical approaches should be used if the tumor grows to involve the internal auditory canal. Observation is an appropriate option for patients who have serviceable hearing.

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.

Acoustic Neuromas in the Elderly

OBJECTIVE

To determine if an "observation" protocol with serial scanning is a safe and effective management paradigm for acoustic neuromas in the elderly.

STUDY DESIGN

A retrospective case review was performed.

SETTING

This study was performed in an academic, tertiary care center.

PATIENTS

Forty-one patients over the age of 65 years were identified with the primary diagnosis of unilateral acoustic neuroma, without prior treatment or observation.

INTERVENTION

The patients were followed with serial, gadolinium-enhanced magnetic resonance imaging (MRI) scans performed at 6 months and then yearly, if no significant growth occurred.

MAIN OUTCOME MEASURES

The patients were monitored for tumor growth, cranial nerve deficits, and hydrocephalus.

RESULTS

The patients were followed for an average of 3.5 years (range, 6 months to 9 years). The average tumor size at presentation was 1.14 cm, with a range of growth rates from 0 to 1.2 cm per year. Twenty-one patients demonstrated tumor growth at an average rate of 0.322 cm per year. Only five patients (12%) required further intervention. Three patients underwent translabyrinthine excision, and two patients were treated with radiation. No patients developed significant complications during the observation period.

CONCLUSIONS

Acoustic neuromas in the older population can be managed safely using serial MRI scanning. No correlation could be made between initial tumor size and subsequent growth rate.

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.

A comprehensive classification system of vestibular schwannomas

Because traditional classifications of vestibular schwannomas (according to relative size) cannot comprehensively describe lesions that grow in different patterns after arising in regions as diverse as the cerebellopontine (CP) angle, the internal auditory canal, and the region lateral to the fundus of the internal auditory canal (labyrinth), we developed a new system to classify vestibular schwannomas, a system that describes the anatomical structures involved by the tumour, rather than size alone. The vestibular schwannoma is classified first by location and then by extent. Our system provides surgeons information helpful in choosing the surgical approach, in estimating the difficulty of tumour excision, and in determining whether hearing might be preserved. Our system also avoids confusion and misunderstanding in discussions of treatment results because it reflects the diverse biological characteristics of vestibular schwannomas.

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.

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.