Cost-Effective Evaluation of Asymmetric Sensorineural Hearing Loss with Focused Magnetic Resonance Imaging

Diagnostic Validity of Auditory Brainstem Response for the Initial Screening of Vestibular Schwannoma

Background and Objectives

: To investigate the diagnostic validity of auditory brainstem response (ABR) in the screening of vestibular schwannoma (VS).

Subjects and Methods

: Forty patients diagnosed with VS using magnetic resonance imaging who had undergone ABR before treatment between 2005 and 2015 were included. ABR results were considered positive when findings met at least one of the following criteria: 1) absent evoked response, 2) desynchronization of waves other than wave I, 3) interpeak latency (IPL) between waves I and III >2.5 ms, 4) IPL between waves I and V >4.4 ms, 5) wave V interaural latency difference >0.2 ms, and 6) interaural difference in IPL between waves I and V >0.2 ms.

Results

: The overall sensitivity of ABR was 85.0%. For tumors measuring <10 mm, the sensitivity of ABR was 66.7%, whereas it increased to 90.3% for tumors measuring >10 mm. The sensitivity of tumors confined to the internal acoustic canal was 73.3% compared with 100.0% for tumors confined to the cerebellopontine angle. In patients with serviceable hearing, the mean tumor size was 7.8±2.9 mm in patients with a normal ABR and 15.1±9.4 mm in patients with an abnormal ABR, indicating a significant difference (p<0.05).

Conclusions

: ABR alone is insufficient for the screening of VS, bearing the risk of false-negative outcomes when examining small, intracanalicular tumors. However, ABR can be inexpensively applied for the screening of VS measuring >10 mm in patients with serviceable hearing, supporting the need for further active diagnostic and treatment modalities in clinical practice.

Sudden sensorineural hearing loss - A contemporary review of management issues

Sudden sensorineural hearing loss (SSNHL) is an enigmatic entity, with obscure pathophysiology and debatable efficacy of the treatment agents used. An underlying cause is identified in only 10-15% of cases. The management of the remaining patients, classified as 'idiopathic', is empirical, and is conventionally with systemic steroids, vasodilator therapy, rheological agents, and antioxidants, to list a few amongst the host of the agents employed for the treatment. The availability of conflicting outcomes and lack of conclusive evidence has resulted in the propagation of consensus-based treatment protocols. In the present review, we discuss the various controversial issues and newer developments in the management of idiopathic SSNHL. The current review aims to present a narrative outlook of the updated evidence base available from PUBMED, augmented with relevant designated publications.

Radiographic findings in young adults with asymmetric sensorineural hearing loss

PURPOSE

To evaluate radiographic findings in US Navy recruits found to have asymmetric sensorineural hearing loss (ASNHL) during routine medical screening.

MATERIALS AND METHODS

Retrospective analysis of US Navy recruits receiving screening audiometry and medical suitability evaluation from January 2011 to October 2016. Single-institution, institutional review board-approved study of US Navy recruits screened for hearing loss over a six-year period. All recruits with ASNHL were evaluated by an otolaryngologist and received diagnostic radiographic evaluation. Audiometric and imaging results were retrospectively reviewed for this population and compared to common screening criteria.

RESULTS

ASNHL was identified in 674 of 228,504 total recruits screened. This population was 91% male and between 17 and 29 years old (mean age 21.1). Six-hundred fifty-three (97%) met criteria for further ASNHL evaluation. Subjective hearing loss was reported in only 6% of patients. Six-hundred sixty-one (99%) received magnetic resonance imaging of the internal auditory canals. Intracranial pathology was identified in 43 (6.3%) patients and 2 (0.3%) had a causative intracranial lesion corresponding to ASNHL. No patients were found to have a vestibular schwannoma.

CONCLUSIONS

In a population of healthy young adults with audiometric proven ASNHL, 0.3% had radiographic proven intracranial pathology explaining the hearing loss. Intracranial masses may be less likely to cause ASNHL in this population; further research is needed to determine appropriate MRI screening methods for young adults with ASNHL.

Diagnostic yield of MRI of the brain and IAC in patients with neurotologic complaints

OBJECTIVES

Quantify number of MRI scans obtained in a tertiary neurotology practice and identify likelihood of pathologic findings.

STUDY DESIGN

Retrospective cohort study.

SETTING

Tertiary neurotology center.

SUBJECTS AND METHODS

A retrospective analysis of all adult patients over 20 months (3/2012-10/2013) where MRI was deemed necessary for evaluation of neurotologic complaints. Demographics, clinical history, physical examination, and audiometric findings were used to categorize new patients into 7 groups: definite Meniere's disease (MD), probable MD, possible MD, vague dizziness, tinnitus only, asymmetric hearing loss (HL), and other symptoms to stratify risk for retrocochlear tumor and other relevant pathology.

RESULTS

1537 MRI scans were performed, 932 of these were for a new diagnosis. Discovering retrocochlear tumors was rare (1.4%). Patients with HL had a 0.3% (1/314) chance of retrocochlear tumor and 3.2% (10/314) chance of relevant pathology. Patients with only unilateral tinnitus had no evidence of retrocochlear tumors, and 3.8% chance of finding relevant pathology. Patients with "definite" or "probable" MD had no evidence of retrocochlear tumor or other relevant findings. All discovered acoustic neuromas were in the "possible MD" category, which had a 9.3% chance of finding all relevant pathology.

CONCLUSIONS

In a tertiary neurotology center, the likelihood of finding a retrocochlear tumor on MRI is rare. In the current study, unilateral tinnitus exclusively, "definite MD," and "probable MD" failed to yield a single example of retrocochlear tumor. Patients with "possible MD" had the highest probability of finding retrocochlear tumors and other relevant pathology.

High resolution T2 MRI in the diagnosis of cerebellopontine angle and internal auditory canal lesions

High resolution T2 magnetic resonance imaging (MRI) can provide exquisite detail of internal auditory canal (IAC) and cerebellopontine angle (CPA) lesions. In this retrospective case series, blinded imaging sequences were delivered to three radiologists and compared with previously archived clinical reads that were non-blinded and incorporated both T1+C and T2 sequences together. This article demonstrates high sensitivity and specificity for high resolution T2 MRI particularly with lesions >5mm. This suggests a role for high resolution T2 MRI as an initial screening sequence or as a surveillance sequence.

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.

ABR in the diagnosis of vestibular schwannomas: a meta-analysis

PURPOSE

The aim of this study is to rigorously evaluate the role of auditory brainstem response (ABR) testing in the diagnosis of vestibular schwannomas (VS).

MATERIALS AND METHODS

Searches were conducted in multiple online databases, supplemented by hand searches. From the studies chosen for final inclusion, relevant data were extracted and meta-analysis of pooled data was performed.

RESULTS

623 studies were identified from which 43 met inclusion criteria for analysis (1978 to 2009) including 3314 patients. Pooled sensitivity for ABR detection of vestibular schwannomas was 93.4% (95% CI 92.6-94.3, P=0.0000). For tumors less than 1cm (8 studies, 176 patients) sensitivity was 85.8% (95% CI 80.6-90.1, P=0.0116). For tumors greater than 1cm (6 studies, 251 patients) pooled sensitivity was 95.6% (95% CI 93.1-98.2, P=0.0660). Sensitivity of ABR to detect extracanalicular tumors was higher than for intracanalicular tumors, though pooled data were not statistically valid. Pooled specificity (8 studies, 2432 patients) was 82.0% (95% CI 80.5-83.6, P=0.0000).

CONCLUSIONS

Although MRI remains the gold standard, emerging trends towards more conservative management coupled with limited financial resources may prompt many clinicians to review the role of ABR testing in screening for retrocochlear pathology. In light of the high sensitivity and specificity of ABR testing for VS, we strongly urge its reconsideration as a useful diagnostic tool for patients with clinically suspected VS.

Sudden sensorineural hearing loss: a review of diagnosis, treatment, and prognosis

Sudden sensorineural hearing loss (SSNHL) is commonly encountered in audiologic and otolaryngologic practice. SSNHL is most commonly defined as sensorineural hearing loss of 30 dB or greater over at least three contiguous audiometric frequencies occurring within a 72-hr period. Although the differential for SSNHL is vast, for the majority of patients an etiologic factor is not identified. Treatment for SSNHL of known etiology is directed toward that agent, with poor hearing outcomes characteristic for discoverable etiologies that cause inner ear hair cell loss. Steroid therapy is the current mainstay of treatment of idiopathic SSNHL in the United States. The prognosis for hearing recovery for idiopathic SSNHL is dependent on a number of factors including the severity of hearing loss, age, presence of vertigo, and shape of the audiogram.

Auditory Brainstem Response versus Magnetic Resonance Imaging for the Evaluation of Asymmetric Sensorineural Hearing Loss

OBJECTIVES/HYPOTHESIS

Auditory brainstem response (ABR) testing and magnetic resonance imaging (MRI) are compared for the evaluation of patients with asymmetric sensorineural hearing loss (SNHL). MRI with gadolinium administration is the current gold standard for identifying retrocochlear lesions causing asymmetric SNHL. The study seeks to determine the sensitivity and specificity of ABR in screening for possible retrocochlear pathology. Most important among SNHL etiologies are neoplastic lesions such as vestibular schwannomas, cerebellopontine angle (CPA) tumors, as well as multiple sclerosis, stroke, or other rare nonneoplastic causes. The study results will allow the author to recommend a screening algorithm for patients with asymmetric SNHL.

STUDY DESIGN

The study is a multi-institutional, institutional review board approved, prospective, nonrandomized comparison of ABR and MRI for the evaluation of patients with asymmetric SNHL.

METHODS

Three hundred twelve patients (between the ages of 18 and 87) with asymmetric SNHL completed the study. Asymmetric SNHL was defined as 15 dB or greater asymmetry in two or more frequencies or 15% or more asymmetry in speech discrimination scores (SDS). These patients prospectively underwent both ABR and MRI. The ABR and MRI were interpreted independently in a blinded fashion. In addition to the ABR and MRI results, a variety of clinical and demographic data were collected.

RESULTS

Thirty-one (9.94%) patients of the study population of 312 were found on MRI to have lesions causing their SNHL. Of the 31 patients with causative lesions on MRI there were 24 vestibular schwannomas, 2 glomus jugulare tumors, 2 ectatic basilar arteries with brainstem compression, 1 petrous apex cholesterol granuloma, 1 case of possible demyelinating disease, and 1 parietal lobe mass. Twenty-two of the 31 patients had abnormal ABRs, whereas 9 patients (7 with small vestibular schwannomas) had normal ABRs. This gives an overall false-negative rate for ABR of 29%. The false-positive rate was found to be 76.84%. Sensitivity of ABR as a screening test was 71%, and specificity was 74%.

CONCLUSIONS

Ten percent of patients with asymmetric SNHL (by this study's criteria) are likely to have causative lesions found on MRI. Although the recently reported annual incidence of vestibular schwannoma in the general population is 0.00124%, for patients with asymmetric SNHL in this study, the incidence was 7.7% (nearly 4 orders of magnitude higher). ABR has been demonstrated to have low sensitivity and specificity in the evaluation of these patients and cannot be relied on as a screening test for patients with asymmetric SNHL. Keeping the use of MRI conditional on the results of ABR will annually result in missed or delayed diagnosis of causative lesions in 29 patients per 1,000 screened. The author recommends abandoning ABR as a screening test for asymmetric SNHL and adoption of a focused MRI protocol as the screening test of choice (within certain guidelines).

Asymmetric sensorineural hearing loss evaluation with T2 FSE-MRI in a public hospital

CONCLUSIONS

T2-weighted fast-spin echo magnetic resonance imaging (MRI) can be an economically beneficial protocol for screening patients with asymmetric sensorineural hearing loss without other neurologic findings in a public hospital population.

OBJECTIVE

The goal of this study was to determine if fast spin echo T2 MRI is similar to gadolinium-enhanced MRI in evaluating asymmetric sensorineural hearing loss in a county hospital population.

PATIENTS AND METHODS

This was a retrospective chart review of all outpatients seen at a public hospital, comprising patients with no other cranial nerve findings who underwent gadolinium-enhanced MRI of the internal auditory canal and brain between January 2002 and September 2003. Patients with >15 dB difference in hearing at one frequency or 10 dB hearing difference at two frequencies underwent gadolinium-enhanced MRI scan with FSE T2 sequence as part of the examination protocol.

RESULTS

A total of 146 patients were identified who met all the inclusion criteria for the study. Of the 146 MRI scans performed, abnormalities were seen on 71 of them, the majority of which were inconsequential. No acoustic neuromas were identified in our study population. Cost savings of over 100,000 dollars would have been realized if only T2 FSE protocols had been used.

The stacked ABR: a sensitive and specific screening tool for detecting small acoustic tumors

The failure of standard ABR measures to detect small (< or =1 cm) acoustic tumors has led to the use of enhanced magnetic resonance imaging (MRI) as the standard to screen for small tumors. This study investigates the suitability of the stacked ABR as a sensitive screening alternative to MRI for small acoustic tumors (SATs). The objective of the study was to determine the sensitivity and specificity of the stacked ABR technique for detecting SATs. A total of 54 patients with acoustic tumors identified by MRI that were either < or =1 cm in size or undetected by standard ABR methods, irrespective of size, were studied. A control population of 78 nontumor normal-hearing subjects was also tested. For comparison, two standard ABR measures (IT5 and I-V delay) were also analyzed. The stacked ABR demonstrated 95% sensitivity and 88% specificity; 100% sensitivity was obtained at 50% specificity. Standard ABR measures were much poorer in detecting these tumors. In conclusion, the stacked ABR can be used as a sensitive, widely-available, cost-effective, and comfortable tool for screening SATs.

Schwanoma vestibular como causa de surdez súbita

A Surdez Súbita (SS) é um sintoma causado por mais de 60 doenças diferentes, dentre elas, o Schwanoma Vestibular (SV). Shaia & Sheehy (1976) apresentaram uma incidência de 1% de SV em 1220 casos de SS. Não há características específicas para o diagnóstico do SV, sendo a ressonância magnética (RM) o exame de escolha. OBJETIVO: Verificar a real incidência de SV em casuísticas de SS com a realização de RM. FORMA DE ESTUDO: Coorte transversal. MATERIAL E MÉTODO: Estudo prospectivo com a realização de RM com contraste de gadolínio em todos os pacientes com SS do serviço de urgência em Otorrinolaringologia do Hospital São Paulo no período de abril de 2001 a maio de 2003. RESULTADOS: Foram realizados exames de RM em 49 pacientes que apresentaram SS, sendo diagnosticados 3 (6,1%) casos de SV. CONCLUSÃO: A incidência real de SV em casuísticas de SS pode ser maior do que o classicamente descrito na literatura, devido ao subdiagnóstico pela não-utilização da RM de rotina nestes casos.

Chronic Pachymeningitis Presenting as Asymmetric Sensorineural Hearing Loss

OBJECTIVE

The objective of this study was to characterize the auditory dysfunction associated with chronic pachymeningitis (inflammation of the dura mater).

STUDY DESIGN AND SETTING

We conducted a university-based retrospective review.

RESULTS

Three patients were identified who were diagnosed with chronic pachymeningitis after being referred for asymmetric sensorineural hearing loss. All patients were found to have other neurologic symptoms and signs during careful neurotologic evaluation. Two varieties of chronic pachymeningitis exist: a hypertrophic mass lesion and a linear dural thickening. Although the hypertrophic variety could be easily detectable by noncontrast magnetic resonance imaging (MRI), the linear form is only visible with the use of gadolinium enhancement.

CONCLUSION

Chronic pachymeningitis is a rare form of sensorineural hearing loss that could portend an underlying disease of greater concern. Extensive evaluation is needed to exclude identifiable causes of chronic pachymeningitis, including infectious, neoplastic, and autoimmune diseases.

SIGNIFICANCE

The clinician should be aware that the evaluation of a patient with asymmetric sensorineural hearing loss involves more than simply ruling out an acoustic neuroma. Fast-spin echo MRI techniques without the use of gadolinium contrast could miss a number of potentially treatable diseases such as chronic pachymeningitis. Patients with asymmetric sensorineural hearing loss should be carefully evaluated for other neurologic findings, and imaging with enhanced MRI is recommended.

Magnetic Resonance Imaging Findings in the Auditory Pathway of Patients With Sudden Deafness

OBJECTIVES

The objectives of this study were to evaluate magnetic resonance imaging (MRI) findings of patients with sudden sensorineural hearing loss (SSNHL) and to grade the findings based on their clinical importance.

STUDY DESIGN

A prospective clinical study.

SETTING

A tertiary referral center (university hospital).

PATIENTS

MRI findings of 82 consecutive patients with SSNHL fulfilling the inclusion criteria.

MAIN OUTCOME MEASURES

We studied 1.0-T MR images that were analyzed by one experienced neuroradiologist.

RESULTS

Of the six cases (7%) in which clearly hearing loss was obviously associated with the observed pathology, four patients had an acoustic neuroma in the internal auditory canal or cerebellopontine angle, one patient had changes at the level of pons, and one patient had an obliterated internal carotid artery. Of the six other patients (7%) in which MRI revealed changes that suggest a possible etiology to hearing loss, two patients showed a demyelinating process and four patients showed blood vessel abnormalities such as caroticocavernous fistula, abnormally locating vertebral or basilar artery, and a venous angioma.

CONCLUSIONS

Enhanced MR imaging seems to be a useful examination in patients with SSNHL. The aim should not be only to exclude specific retrocochlear etiologies, but by appropriate techniques, MRI could reveal both peripheral and central abnormalities.

Cost-effective diagnosis of acoustic neuromas: a philosophical, macroeconomic, and technological decision

OBJECTIVE

Our goals were to define the most sensitive techniques of acoustic neuroma diagnosis, to examine their relative costs, and to propose diagnostic modality selection given the rarity of acoustic neuroma incidence and given the other costs that society faces in more commonly encountered diseases.

METHODS

We conducted a MEDLINE search of the English language from 1966 to 2001 using the following keywords: acoustic neuroma, acoustic tumor, vestibular schwannoma, diagnosis, cost effectiveness, MRI, auditory brainstem response, brainstem audiometric evoked response, incidence, and prevalence.

RESULTS

Although magnetic resonance imaging with gadolinium remains the most sensitive diagnostic modality in the discovery of acoustic neuromas, its cost may be prohibitive for some societies.

CONCLUSION

Which modality to use in acoustic neuroma diagnosis is just as much a philosophical and macroeconomic question as a technological one.

CLINICAL SIGNIFICANCE

The cost of a timely diagnosis of acoustic neuromas must be weighed against using resources for other, more pressing, health concerns.

Magnetic resonance imaging in patients with sudden hearing loss, tinnitus and vertigo

OBJECTIVE

The etiopathogenesis in audiovestibular symptoms can be elusive, despite extensive differential diagnosis. This article addresses the value of magnetic resonance imaging (MRI) in analysis of the complete audiovestibular pathway.

STUDY DESIGN

Retrospective evaluation.

SETTING

Tertiary referral center.

PATIENTS

Consecutive sample of 354 patients (mean age 49 years, range 8 to 86 years) with audiovestibular disorders.

INTERVENTION

Contrast-enhanced MRI of the head with thin-slice investigation of the inner ear, internal auditory meatus, and cerebellopontine angle.

MAIN OUTCOME MEASURE

All MRIs were evaluated by experienced independent investigators. Statistical analysis was performed using the Statistical Package of Social Sciences data analysis 9.0.

RESULTS

MRI abnormalities were seen in 122 of 354 patients (34.5%). The MRIs revealed the following: 4 pathologic conditions (1.1%) of the cochlea/labyrinth, 23 abnormalities (6.5%) at the internal auditory meatus/cerebellopontine angle, 12 pathologic lesions (3.4%) that involved the central audiovestibular tract at the brainstem, 78 microangiopathic changes of the brain (22%), 3 focal hyperintensities of the brain that turned out to be the first evidence of multiple sclerosis in 2 patients and sarcoidosis in 1 patient, and 1 temporal metastasis. Other pathologic conditions, such as parotid gland or petrous bone apex tumors, were unrelated to the audiovestibular symptoms.

CONCLUSIONS

This study indicates that contrast-enhanced MRI can be used to assess a significant number of different pathologic conditions in patients with audiovestibular disorders.

[Magnetic resonance: first choice test in the screening of internal auditory canal and cerebellopontine angle tumors]

Although internal auditory canal (IAC) and cerebellopontine angle (CPA) tumors are rare, their clinical suspicion is quite common in the otolaryngology office. MRI is the imaging modality of choice in diagnosing these tumors. Perceived high costs may prevent clinicians from using it as a screening tool. A protocol designed to improve cost-effectiveness in such diagnosis results in a more rationale clinical practice. Our aim was to evaluate the usefulness of MRI as screening tool in diagnosis of IAC and CPA tumors in our population. Between March 1998 and March 2000, a prospective series of 200 cases had a MRI screening requested. MRI were performed following Fast Spin Echo technique, providing T2-weighted images. Gadolinium enhanced MRI was reserved for selected cases. We report on 190 MRI done. We found 7 neuromas (3.5%), one CPA metastasis, one epidermoid cyst and 9 IAC vascular anomalies. Only 138 cases (69%) had normal MRI images. When used following a designed protocol, MRI is our procedure of choice while screening IAC and CPA tumors because it is a cost-effective tool.

Magnetic resonance imaging in the search for retrocochlear pathology

OBJECTIVES

The purpose of this study is to evaluate the incidence of retrocochlear pathologic conditions that may be seen with full, contrast-enhanced magnetic resonance imaging of the brain, relative to more limited studies of the internal auditory canals (IACs) in patients with unilateral hearing loss or tinnitus with or without dizziness.

METHODS

A retrospective study was performed on all patients who had a magnetic resonance imaging of the brain and otologic symptoms over a 7-year period.

RESULTS

Abnormalities were found in 11 of 128 patients with only auditory symptoms and in 63 of 282 patients with auditory symptoms and/or dizziness (P = 0.005). Treatable lesions may not have been identified with a limited IAC study in 3 of 128 patients with only unilateral auditory symptoms, and 21 of 282 patients with dizziness (P = 0.045).

CONCLUSIONS

Limited MRI of the IACs may serve as an adequate screening test for retrocochlear pathologic conditions in patients with unilateral auditory symptoms and no dizziness.

Accuracy of terminology and methodology in economic analyses in otolaryngology

OBJECTIVE

Economic studies increasingly guide health care resource allocation decisions. Because rigorous adherence to accepted definitions and research techniques is critical to ensure accuracy, we evaluated the terminology and methods of otolaryngology economic analyses.

STUDY DESIGN

A total of 71 articles published from 1990 to 1999 in 6 peer-reviewed otolaryngology journals with terms such as "cost-effective" in their title or representing economic analyses were reviewed for terminology and use of established methodology guidelines.

RESULTS

Over half (35 of 66) of terms such as "cost-effective" were used incorrectly, and 60% of articles (39 of 64) confused "charge" and "cost" data. Eleven percent (7 of 64) of papers specified the perspective of their analysis. About half (17 of 30) reported a summary measure such as a cost-effectiveness ratio. Only one third (23 of 63) performed sensitivity analyses.

CONCLUSION

Adherence to accepted definitions and research methods is inconsistent, although we did note moderate improvements in making the distinction between costs and charges, defining of study perspective, and performing sensitivity analysis.

SIGNIFICANCE

Greater attention to both terminology and methodology can enhance the quality of economic analyses and ultimately improve certain resource allocation decisions.

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.

Efficacy of serologic testing in asymmetric sensorineural hearing loss

PURPOSE

The goal of this study was to determine the efficacy of a detailed questionnaire, auditory brain stem response testing (ABR), MRI, and an extensive battery of serologic tests in diagnosing asymmetric sensorineural hearing loss (ASNHL).

METHODS AND MATERIAL

Patients with audiograms demonstrating ASNHL of 10 dB or greater in 2 consecutive frequencies or 15 dB in any 1 frequency between 250 and 6000 Hz were asked to participate. Patients underwent MRI scanning of the cerebellopontine angle, internal auditory canals, and posterior fossa with gadolinium contrast, ABR, and an extensive battery of tests. The causative diagnosis was made by the individual clinician based on each patient's history, physical examination, and test results.

RESULTS

Forty-five patients completed the study. A review of the data confirmed the utility of a detailed history and physical examination, MRI, and fluorescent treponemal antibody test in all cases. Erythrocyte sedimentation rate, glycosylated hemoglobin, Lyme antibody titers, and total hemolytic component (CH50) were helpful in selected cases. Thyroid function testing, complete blood count, Sequential Multiple Analysis-7, prothrombin time/partial thromboplastin time, lipid profile, and ABR were of no value in these patients.

CONCLUSION

A careful history and physical examination, MRI, and fluorescent treponemal antibody test should be performed for the evaluation of all patients with ASNHL; however, more extensive serologic testing, including sedimentation rate, glycosylated hemoglobin, Lyme antibody titers, and CH50, should be selectively performed, based on a suggestive history or suspicious physical findings.

Magnetic resonance imaging of the internal auditory canal

Magnetic resonance imaging (MRI) is presently the study of choice for assessment of the internal auditory canal (IAC). MRI provides excellent assessment of the IAC and the bony changes occurring in the canal walls, and it provides excellent demonstration of the content of the canal. Pathological processes arising within the IAC are well visualized by various MR sequences. The possibility of demonstrating masses as small as 2 mm has propelled MRI into the leading role for diagnosis of vestibular schwannoma. Unfortunately, the high cost of MR has been a limiting factor in its use as a screening test for patients with sensorineural hearing loss (SNHL) of unknown origin. Auditory brain stem response has been widely used as a screening procedure, but this test fails to recognize small lesions and cannot be used whenever hearing loss is severe. In this article, we will discuss our approach to assessment of the IAC in patients with retrocochlear SNHL or vestibular symptoms of central origin, review the pathological processes involving the IAC walls or arising within the canal, emphasizing the appropriate MRI sequences used for diagnosis.

Outcome of using magnetic resonance imaging as an initial screen to exclude vestibular schwannoma in patients presenting with unilateral tinnitus

The improved cost-effectiveness of gadolinium-enhanced magnetic resonance imaging (MRIg) as a diagnostic tool for vestibular schwannoma has resulted in smaller tumours being diagnosed. There has been a change in the clinical presentation of these tumours and up to four per cent may present with unilateral tinnitus. The limitation of auditory brain stem response (ABR) as a screening tool that detects small tumours is recognized and there is a strong argument for using MRIg as the initial investigation. Various screening guidelines have been proposed, some include submitting patients with unilateral tinnitus for MRIg. This report describes the findings in a group of 174 patients presenting with unilateral tinnitus who underwent MRIg as part of a guideline-directed screen to exclude vestibular schwannoma. Five patients had a cause for their tinnitus diagnosed, one a vestibular schwannoma. Two had intracranial aneurysms and another three had pathology revealed that merited onward referral. A further nine patients had incidental findings that neither accounted for their symptoms nor needed further investigation or referral. The rationale for screening these patients with MRIg is discussed.

Asymmetric sensorineural hearing loss in a community-based population

Asymmetric sensorineural hearing loss (ASNHL) is fairly common, but it can be an indication of retrocochlear pathology. The incidence of acoustic neuroma (AN) has been estimated at 1/100,000; however, the incidence of AN in patients with ASNHL is unknown. The limitation of health care resources challenges otolaryngologists to develop reasonable cost-containment guidelines for the evaluation of patients with ASNHL for the presence of retrocochlear pathology. A 5-year (1990 to 1994) retrospective study of all patients with ASNHL who were evaluated in a community-based general otolaryngology practice was performed. Demographic, historic, and audiologic data and results from ABRs and radiologic studies were summarized. ASNHL was present in 325 patients. Auditory brain stem response tests were performed in 179 patients (55%), and 92% (164 of 179) were normal. Patients with abnormal or inconclusive auditory brain stem responses and patients with severe SNHL were evaluated with radiologic studies (46 patients). Among the 193 patients who had diagnostic studies, 4 were found to have ANs, for a prevalence of 2.1%. The charge of diagnosis per AN was more than $41,000. In summary, a small percentage of patients with ASNHL have retrocochlear pathology, and the charge of diagnosis per AN can be excessive. A cost-containment approach for the evaluation and management of patients with ASNHL is proposed.