Neurosurg Focus 33 (3):E4, 2012

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

Richard F. Schmidt, B.A.,1 Zain Boghani, B.S.,1 Osamah J. Choudhry, M.D.,1 Jean Anderson Eloy, M.D.,1–3 Robert W. Jyung, M.D.,2,3 and James K. Liu, M.D.1–3 Departments of 1Neurological Surgery and 2Otolaryngology–Head and Neck Surgery; and 3Center for Skull Base and Pituitary Surgery, Neurological Institute of New Jersey, University of Medicine and Dentistry of New Jersey–New Jersey Medical School, Newark, New Jersey

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 manage- ment of these lesions poses a significant challenge for practitioners. Most incidental VSs tend to be small and as- sociated 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 screen- ing 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 pa- tients with progressive disease. Patients with incidental VSs will probably qualify for a course of conservative man- agement 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. (http://thejns.org/doi/abs/10.3171/2012.7.FOCUS12186)

Key Words • incidental lesion • vestibular • • acoustic neuroma • tumor growth • conservative management • hearing preservation • quality of life

estibular schwannomas account for up to 10% undertaken to try to characterize the prevalence of VSs in of all primary brain neoplasms39 and represent patients who are asymptomatic and whose VSs are diag- a largely heterogeneous group of tumors with a nosed due to an incidental finding.1,10–14,26,33,37 Vwide variety of clinical manifestations, growth patterns, Defining the prevalence of incidental VSs as well as and patient outcomes. Typically, patients with these le- managing them has become a challenge for neurosurgical sions present with unilateral high-frequency sensorineu- and neurootological practice. An increasing percentage ral , although they can also present with head- of patients with these lesions are presenting to these prac- ache, , vertigo, and balance problems.20 With the tice settings without asymmetrical hearing loss or any increased use of advanced radiographic imaging, particu- other suggestive symptoms. In fact, among patients seen larly contrast-enhanced MRI, a greater number of VSs for a VS on MRI, the tumor was an incidental finding in are diagnosed in patients without any of the symptoms 5%–12% of those patients.15,26 Furthermore, the wide va- typically associated with these tumors, and they are often riety of tumor growth rates and interventional outcomes detected incidentally after MRI for other suspected in- associated with incidental VSs make the long-term man- tracranial lesions. Recently, numerous studies have been agement of these lesions an issue that is much debated. In this paper, only sporadic VSs not associated with neurofi- Abbreviation used in this paper: VS = vestibular schwannoma. bromatosis Type 2 will be discussed.

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We reviewed the latest research with regard to the eric studies (Table 2). It has been shown that VSs account prevalence and presentations of incidental VSs. In this for approximately 0.2% of incidental MRI findings.38 Two paper, we discuss how tumor growth rates and clinical studies in particular have provided the best illustration outcomes relate to the management of these lesions, in- of the prevalence of incidental VSs in patients not sus- cluding the benefits and pitfalls of conservative manage- pected of having the disease. In the first of these stud- ment techniques. Our goal is to elucidate how the latest ies, Anderson et al.1 found 17 patients with unsuspected research can help to guide the clinician to effectively VSs after reviewing 24,246 MRI studies obtained for manage the increasing number of patients likely to pres- reasons other than ruling out a VS or evaluating patients ent with incidental VSs. with tinnitus, sensorineural hearing loss, or vertigo. This yielded a VS prevalence of 0.07% in patients in whom no Epidemiological Data VS was suspected. More recently, Lin et al.14 analyzed 46,414 MR images obtained for reasons other than au- Early attempts to define the prevalence of VSs in diovestibular signs, revealing a much lower prevalence of the general population were made in cadaveric studies in 0.02%, or only 8 patients with a positive reading. These both the pre- and post-MRI era. These studies involved latter authors determined that the difference between the the serial dissection of numerous temporal bones from two studies was statistically significant, ultimately attrib- deceased patients and ultimately suggested a prevalence 13,14,33 uting the discrepancy to numerous factors. They cited the of around 0.8%–2.4% (Table 1). Since VSs had not increase in the number of MRI studies, the shorter time been diagnosed in these patients’ lifetimes and the pa- period analyzed by Anderson et al., and differences in tients may not have undergone a workup for symptoms the criteria of accepted MRI studies as possible reasons related to VSs, in theory these early study results could for this discrepancy. Moreover, Lin and colleagues spe- correlate well with the actual prevalence of asymptom- cifically excluded studies on the internal auditory canal, atic incidental VSs. However, the numerous limitations whereas Anderson and associates did not. Imaging stud- in studying only cadavers make it difficult to generalize ies of the internal auditory canal are usually conducted to these results to the entire population. Primarily, the fact rule out a VS, even though it may not have been specified that these studies were conducted in patients who were in the imaging database. Thus, the prevalence of 0.02% no longer living results in an obvious selection bias for proposed by Lin et al. probably represents the best esti- older patients with other significant comorbidities. Fur- mation of incidental VSs to date. thermore, cultural differences, changes in the practice Interestingly, the study by Lin et al.14 also revealed a of medicine, and changes in our understanding of VSs number of other patient variables associated with finding throughout the time periods in which these studies were a VS on MRI. The number of patients presenting with conducted probably meant that a number of these tumors VSs, whether symptomatic or not, was not statistically were undiagnosed in life, adding further bias to the re- significant for a sex difference; however, when the study sults. As a consequence, these values probably represent was limited to just those patients with an incidental find- a gross overestimation of the actual prevalence of inci- ing, men represented a significantly larger proportion of dental VSs within the current population. Regardless, the the study group. The authors postulated that this could relative consistency of these findings suggests that the re- be the result of behavioral differences; that is, men may sults are not entirely baseless and may represent a close be less likely to seek treatment or consult a physician for estimate of the prevalence of VSs in older populations at audiovestibular concerns. This point was illustrated by the time that these studies were conducted. a male patient who presented with an incidental finding In contrast to those early cadaveric studies, more but later reported profound unilateral deafness on further recent attempts to elucidate the prevalence of VSs in questioning after receiving the MRI results. Actually, 5 of patients not suspected of having the disease have taken 1,14 the 8 patients determined to have incidental findings later advantage of modern advances in imaging technology. reported significant audiovestibular symptoms that were With the advent of MRI, researchers can retrospectively not initially related when their histories were taken. This analyze large imaging databases, enabling them to in- finding implies that while the Lin et al. study shows a clude a wider variety of patients and yield sample sizes lower prevalence of incidental VSs as compared with that significantly greater than what was possible with cadav- in the Anderson et al.1 study, the actual number of truly TABLE 1: Prevalence of incidental VSs in studies of temporal asymptomatic patients with positive findings could be bones at autopsy even lower than suggested if one assumes that all patients with symptoms can be ruled out by taking a thorough VS history. Regardless, both of these studies were within a Authors & Year No. of Bones No. of VSs Prevalence (%) TABLE 2: Prevalence of VSs in studies using MRI for diagnosis Hardy & Crowe, 1936 250 6 2.4 Leonard & Talbot, 1970 490 4 0.8 Authors & Year No. of Cases No. of VSs Prevalence (%) Stewart et al., 1975 893 5 0.9 Selesnick et al., 1993 161* 0 0 Karjalainen et al., 1984 298 0 0 Anderson et al., 2000 24,246 17 0.07 Lin et al., 2005 746 5 (4)* 1.0 Lin et al., 2005 46,414 9 0.02

* One cadaver had bilateral VSs. * Study performed prospectively.

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Unauthenticated | Downloaded 09/26/21 07:21 AM UTC Incidental vestibular schwannomas similar order of magnitude compared with the cadaveric ability among studies, with 15%–85% of tumors showing studies and probably represent a closer assumption of the growth. This author also demonstrated an overall growth real prevalence of incidental VSs. rate of 1.2 mm/year. Taking into consideration all stud- Despite the prevalence of incidental VSs within the ies in the meta-analysis, he established that an average of general population, in neurosurgical practice these le- 46% of tumors showed growth. However, he also indicat- sions represent a significant fraction of the patients pre- ed that the percentage of tumors that were determined to senting with positive MRI findings. In a study conducted grow was greatly affected by the type of study conducted. by Jeyakumar et al.,11 among 121 patients with diag- The average percentage of growing tumors was 39% in nosed VSs, the lesions were incidentally discovered in 15 the studies in which MRI alone was used and only 29% (12.3%) of them. In direct contrast to the findings of Lin when considering only prospective studies. This finding et al.,14 Jeyakumar and colleagues showed that inciden- suggests that the number of tumors that grow may actu- tal VSs were diagnosed in 4 times as many women than ally be lower than initially predicted, as higher-quality men, although the authors did not offer an explanation for studies are likely to be more representative of real growth this finding. Additionally, they showed that there was no characteristics. Interestingly, both of these reviews also age difference between those presenting with symptom- showed that a significant portion of tumors actually re- atic VSs and those with incidental VSs. By putting all of gress, which occurred in 8%–22% of tumors.22,41 these studies in the context of neurosurgical practice, it Studies have shown that “tumor growth” is a broad can be determined that patients with incidental VSs rep- descriptive term used to identify what is actually a large- resent a significant portion of the neurosurgery patient ly heterogeneous group of tumor growth patterns. Three base and that a diagnosis of VS will probably result from studies in particular have attempted to characterize VSs an incidental finding in a notable percentage of patients into specific groups based on their growth patterns (Table with VS. Therefore, neurosurgeons must have an intimate 3).22,24,28 What these studies have shown is that there is understanding of the tumor characteristics and treatment not a one-size-fits-all description that characterizes tumor choices for incidental VSs, as they are likely to encounter growth patterns. Furthermore, how the growth rate at one this disease entity in their practice. interval fits into the entire natural history of the tumor is largely unpredictable.22,41 Thus, it is crucial that practitio- Growth Patterns and Natural History ners appreciate the variability in individual tumors and Recently, an extensive body of literature has emerged do not use a growth rate from one interval to define the discussing the natural history and growth patterns of rate for future intervals. For example, just because a pa- VSs in both symptomatic and asymptomatic patients. A tient presents with a small incidental tumor that reduced thorough understanding of the variety of characteristics in size on the first follow-up scan does not mean that fu- associated with tumor progression is crucial in determin- ture scans are unnecessary. At any moment the growth ing the proper care of patients who are asymptomatic rate of that tumor can change. with incidental findings. We are not aware of any studies There have also been attempts to define independent patient and tumor characteristics that can predict tumor specifically focused on the growth rates of incidental or 41 asymptomatic tumors by themselves; however, numerous growth. For example, Yoshimoto proposed that larger tumors represent a lower risk for future VS enlargement. studies have been conducted to characterize the natural 30 history and growth patterns of VSs that were not subject- Solares et al. also suggested that tumor size plays a role ed to any initial intervention. An understanding of growth in defining tumor growth, showing that 5-year no-growth patterns in these tumors is paramount to guiding long- rates vary significantly among intracanalicular, Grade I term treatment and follow-up decisions.30 In general, VSs tend to be a relatively slow-growing TABLE 3: Literature survey of studies examining tumor growth lesion as compared with other more malignant intracra- patterns on follow-up imaging in patients who underwent nial tumors, with many showing little to no growth after conservative management* diagnosis. A recent meta-analysis conducted by Nikolo- poulos et al.22 showed that the rate of tumor growth varies Shin et Nikolopoulos Rosenberg, significantly among patients who undergo conservative Growth Pattern al., 2000 et al., 2010 2000 management. In 41 of the studies included in that review, reduction only 5 7 8 the number of tumors demonstrating growth varied from reduction followed by growth 20 NA NA 6% to 73%, with the rate of individual tumor growth varying significantly as well, from 0.3 to 4.8 mm/year. stability only 20 50 35 While the mean growth rate varied between 1 and 2 mm/ stability followed by growth NA 16 13 year for all tumors, the growth rate was between 2 and 4 growth only 15 25 21 mm/year when only tumors that grew were considered. growth followed by stability NA 3 13 Moreover, some studies in the meta-analysis documented growth then reduction 40 NA 10 exceptional growth rates in excess of 15 mm/year. Niko- lopoulos and colleagues also demonstrated that tumors * Values expressed in %. Note that the specific radiological definitions showing only continuous growth represented a minor- used for growth varied slightly among the studies. Moreover, the exact ity of the lesions, accounting for only 15%–25% of the names for growth patterns were altered for simplification, and not all tumors across the studies. Another meta-analysis con- patterns were accounted for in every study. Abbreviation: NA = not ap- ducted by Yoshimoto41 also reported a wide range of vari- plicable.

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Unauthenticated | Downloaded 09/26/21 07:21 AM UTC R. F. Schmidt et al. tumors, and tumors above Grade I (89.8%, 73.9%, and that there is extensive variability in tumor behaviors across 45.2% respectively). These latter authors also suggested patient populations and that there are few indicators that that when analyzed separately based on tumor size, wom- can accurately predict tumor growth. Given the dearth en had a significant difference in growth rates, showing of consistent evidence, it is difficult to provide specific growth in 90.9% of VSs smaller than 10 mm, as com- recommendations on who should undergo conservative pared with 62.3% of VSs larger than 10 mm. However, management and how they should be monitored. How- as illustrated in the extensive meta-analysis conducted by ever, a few protocols have been suggested to determine Nikolopoulos et al.,22 there is marked variability in the which patients should be conservatively monitored.3,29,30,32 significance and outcomes associated with independent One of the most cited studies used the following criteria predictive variables across studies. While some indicated to select patients for conservative management: advanced that the growth pattern within the 1st year was a signifi- patient age (> 60 years), poor health or significant medical cant indicator of tumor behavior, other studies directly risks for surgery, risk of further hearing loss (American contradicted this assertion.5,24 The same was true when Academy of Otolaryngology–Head and Neck Surgery initial tumor size was used to predict growth, that is, with Level A or Level B), small tumor size (Koos Grade I or contradictory evidence suggested across studies.7,18,22,23,25 2), minimal or no incapacitating symptoms, and patient However, Nikolopoulos and colleagues did assert that preference.3 Other protocols have generally used similar cystic tumors tend to have a higher growth rate (approxi- selection criteria, including symptoms, patient age, and mately 3.7 mm/year) as compared with solid tumors. Re- size of the tumor. gardless, no other consistent indicators of growth were By definition, incidental VSs tend to be associated revealed across the multiple studies: not age, initial lesion with few if any symptoms, with rare exceptions.1,14 Ad- size, duration of symptoms, tumor laterality, or patient ditionally, these lesions tend to be smaller than symptom- sex. However, the authors did admit that there were sever- atic VSs, with one study showing a significant size differ- al limitations to their review, including variability in fol- ence of 1.09 versus 1.50 cm between asymptomatic and low-up, different use of imaging studies, multiple publica- symptomatic lesions, respectively.11 Furthermore, it has tions from different institutions, and even the inclusion of been suggested that small and medium-sized incidental patients with Type 2 in some studies in VSs tend to have a more benign course and ultimately which a clear distinction was not specified. Thus, further require less intervention (47% vs 76%, small and medium large-scale prospective studies are needed to effectively versus larger lesions).11 Therefore, the majority of inciden- elucidate possible predictors of growth as well as poten- tal VSs will likely qualify for conservative management tial mechanisms leading to growth or regression. according to the above criteria. As mentioned, a few ex- ceptions do exist, including instances in which symptoms Management Selection Strategies are elucidated with further history taking after a positive Currently, 3 basic options exist for managing newly imaging study14 or a large high-risk tumor is discovered. diagnosed VSs: 1) microsurgical removal; 2) radiation Asymptomatic VSs have been reported to be as large as therapy, including stereotactic radiosurgery and stereotac- 5 cm.11 tic radiotherapy; and 3) conservative management. Specific Specific strategies for follow-up have also been rec- treatment decisions at the time of VS diagnosis are poorly ommended. Martin et al.16 suggested an initial rescan standardized at this point, with extensive variation in pro- with MRI at 6 months posttreatment followed by scans tocols among practice settings, but in general they have annually for 2 years and then every 5 years for the re- been determined based on tumor size, associated symp- mainder of the patient’s life. They recommended re- toms, and specific patient indicators. Details on the effi- assessment if growth > 2 mm occurs at any interval. cacy of and outcomes for primary interventional therapies, The rationale behind their protocol was based on their namely the use of microsurgery and radiation therapy at findings that 90% of the patients demonstrating tumor the time of diagnosis, have been well characterized in the growth did so before 3 years elapsed and the remaining literature.19,20,34,36 Recently, however, conservative manage- 10% manifested growth within 6 years. Furthermore, the ment via serial radiological studies has become increasing- necessity of MRI as opposed to other screening options ly popular in patients with smaller tumors, especially when was emphasized. Such screening options included hear- they are minimally or completely asymptomatic.22,34,41 The ing tests, which were reported to be equivocal between reasoning behind adopting a “wait-and-scan” approach is lesions that grew and those that did not.9,17,31 Interestingly, based on two fundamental ideas. First, a high proportion in line with the findings of Nikolopoulos et al.,22 Martin of the tumors do not grow following diagnosis. Second, and colleagues16 also suggested that cystic tumors should there is sparse evidence to indicate that the treatment of be followed more closely, as they represented a dispropor- a nongrowing lesion is beneficial. In contrast, surgery or tionate percentage of the tumors that grew, especially in radiotherapy can result in significant complications and is cases in which a solid tumor converted into a cystic one. best avoided when unnecessary.20 Therefore, conservative The protocol established by Martin et al.16 contrasts treatment in patients with smaller tumors ultimately en- with the one proposed by Strangerup et al.,32 who sug- ables them to avoid the possible complications of primary gested annual scans for 5 years after treatment and then intervention while allowing practitioners to closely moni- follow-up scans at 7, 9, and 14 years after treatment. tor their status over time. Smouha et al.29 proposed a different strategy, suggesting As discussed above, existing data on tumor growth that those selected for conservative management should rates, growth patterns, and predictors of growth suggest undergo MRI studies at 6 months after treatment and ev-

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Unauthenticated | Downloaded 09/26/21 07:21 AM UTC Incidental vestibular schwannomas ery year thereafter. Regardless of the specific regimen, Multiple attempts have been made to elucidate the all of the studies agree that most tumors showing growth risks for hearing loss based on various tumor and pa- will do so early in the follow-up period. However, the tient characteristics. Sughrue et al.35 reported an overall lack of predictability for long-term growth or changes in hearing preservation rate of 54% in patients undergoing growth patterns throughout the natural history of indi- conservative management, showing that tumors with a vidual tumors requires extended follow-up of patients via slower growth rate (≤ 2.5 mm/year) were associated with serial imaging, and practitioners should anticipate growth a significantly higher rate of hearing preservation as com- at any interval. pared with lesions that grew faster (75% vs 32%, respec- While we do not specifically endorse one protocol tively). However, other studies have suggested that tumor over another or propose our own protocol for conserva- growth is not a reliable indicator of hearing loss.3,6,24 Fur- tive management, we do believe that patients should be thermore, Bakkouri et al.3 attempted to classify risk fac- monitored at regular intervals throughout the course of tors based on initial tumor size. These authors reported their lives. Additionally, we support the notions of Niko- that patients with preserved hearing tended to have larger lopoulos et al.,22 who emphasized the significance of initial tumor sizes (11.5 vs 9.3 mm). Taken together, these educating and counseling patients with incidental VSs studies suggest that the impact of specific tumor factors, about the lack of predictability in tumor growth and the such as initial size and growth rates, is highly variable. importance of patient compliance. A thorough discussion The relationship between hearing loss and qual- about the method and frequency of follow-up should take ity of life in the context of other complications is also place, and any barriers in the patient’s life that can lead an important parameter requiring discussion. Breivik et to poor compliance should be thoroughly explored. The al.4 showed that hearing deterioration actually had little insufficient follow-up of patients undergoing conservative impact on quality of life, except in terms of social func- management to monitor growth can result in catastrophic tioning in those with complete unilateral hearing loss. consequences and increase the risks associated with sec- In contrast, previous retrospective analyses suggested ondary intervention.8 that the negative impact of hearing loss was greater than all other complications, including weakness, numbness, Outcomes of Conservative Management spasm, pain, tinnitus, or even hydrocephalus.39 However, It is postulated that all symptomatic VSs probably these findings do not necessarily mean that the effect of have a silent asymptomatic period before presentation hearing loss on the quality of life was a significant change to a physician, providing the conceptual rationale for the from the baseline status of the patient since the study was existence of asymptomatic patients who present with in- conducted retrospectively. Again, these data show con- cidental findings.11 The evolution of symptoms and neu- clusions in this regard are highly variable. In general, we rological deficits in initially asymptomatic or minimally suggest taking a case-based approach to patients with symptomatic patients with conservatively managed VSs, incidental VSs, focusing on both the hearing status at while varying significantly from patient to patient, tends various intervals and how it affects patients’ quality of to follow certain patterns that correlate with certain stag- life and perception of their illness, ultimately using their es of increasing lesion size as well as with the location of subjective hearing experience combined with radiologi- the lesion.27 Given that most patients with incidental VSs cal indicators to guide further management. probably qualify for conservative management, an un- Other symptoms besides hearing loss have also been derstanding of how these tumors progress, the effect that discussed in terms of long-term outcomes of conservative this form of management has on the later development management and patient quality of life. Of these symp- of symptoms, and how conservative management affects toms, tinnitus, vertigo, and balance disturbances have long-term quality of life is paramount to the successful been the most heavily studied. Whitmore et al.39 suggest- long-term management of these lesions. ed that the incidence of tinnitus and vertigo is significant- One of the most heavily studied outcomes in regard ly higher in patients undergoing conservative manage- to conservative management is its effect on long-term ment as opposed to primary intervention. Tinnitus was hearing preservation. Hearing loss has been suggested to also shown to be significantly associated with tumor size be an integral part of the natural history of VSs, possibly and type of hearing loss.2 Interestingly, however, Breivik as a result of ischemia of the inner ear or protein shedding et al.4 suggested that, after a period of conservative man- from the tumor.9 Prior studies have shown that hearing agement, tinnitus was not significantly associated with a may be preserved in up to 49% of individuals undergoing reduced quality of life as compared with baseline condi- conservative management,29 while hearing preservation tions. Additionally, they showed a significant reduction in rates vary between 17% and 68%3 in patients undergoing the number of patients experiencing vertigo after a period primary microsurgery. Whitmore et al.39 suggested that of conservative management. However, the presence of conservative management is associated with a significant- vertigo was also associated with a significant reduction ly higher incidence of functional hearing loss; however, at in quality of life. While it is clearly important to follow this point, the comparison of hearing outcomes between hearing loss and tinnitus as possible indicators of worsen- conservative management and other forms of therapy is ing clinical progression, the presence of vertigo may have largely inconclusive.3 The latest prospective study on con- the greatest impact on patient quality of life since it is servative management by Breivik et al.4 suggested that often a debilitating symptom. Thus, the discussion of ver- hearing deteriorates in patients over time, regardless of tigo in addition to tinnitus and hearing loss is a vital part treatment or tumor growth. of patient follow-up in conservative management.

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Conversion to Active Treatment Conclusions Understanding the frequency of treatment failure as With the advent of advanced imaging technologies, well as when to intervene is an integral aspect of adopting an increasing number of patients have been diagnosed a conservative management strategy. The overall failure with VSs as incidental findings on studies conducted for rate, defined as conversion to an active treatment, has been alternate reasons. These patients probably represent a sig- found to be 15%–50%.5,21,29,39,40 Smouha et al.29 reported nificant fraction of all patients presenting for the manage- that 43% of patients undergoing conservative management ment of VSs. Because these lesions are smaller, produce ultimately demonstrate positive tumor growth. However, minimal symptoms, and are relatively indolent, a trial of only 20% of the patients undergoing a conservative regi- conservative management is probably appropriate in the men required definitive treatment, suggesting that treat- majority of cases. And although current data indicate that ment failure is not directly linked to tumor growth. When tumor growth occurs in a minority of patients, long-term analyzed prospectively, the likelihood of requiring treat- growth is largely unpredictable and may follow a wide ment is 13.3% at 2 years and 41.3% at 5 years, suggesting variety of specific patterns. Furthermore, patients under- that during a longer follow-up period more patients will going conservative management can later present with require secondary intervention.4 Fortunately, secondary symptoms that significantly affect their quality of life and intervention has been shown to be relatively safe. Numer- everyday functioning. Numerous protocols for the selec- tion of and follow-up in conservative management have ous studies have also demonstrated that the incidence of been proposed, but no large-scale multiinstitutional pro- postoperative complications is similar between patients spective studies have compared the various options or ad- undergoing primary surgery and those undergoing sur- 3 dressed specific risk factors for tumor growth, symptom gery due to failure of conservative management. Note, onset, or overall treatment failure. Thus, we recommend however, that there was an increased risk of hearing 3 that practitioners take an individualized approach with deterioration with delayed surgery. Furthermore, up to early initial follow-up and continued lifelong manage- 83% of patients in whom conservative therapy fails will 39 ment, emphasizing the importance of continued contact disproportionately undergo microsurgery. This finding and observation for both clinical and radiological dete- is interesting, suggesting that further investigation into rioration. factors determining the selection of microsurgery versus radiotherapy in secondary management, as well as the Disclosure outcomes that these two strategies have on these patients, The authors report no conflict of interest concerning the mate- would be useful in guiding future management decisions. rials or methods used in this study or the findings specified in this Numerous indicators suggest the failure of conser- paper. vative management and the commencement of second- Author contributions to the study and manuscript prepara- ary intervention. Overt clinical deterioration is a clear tion include the following. Conception and design: Liu, Schmidt, Boghani. Acquisition of data: Schmidt. Analysis and interpretation indicator to cease conservative management and imple- of data: Schmidt, Boghani, Choudhry. Drafting the article: Schmidt, ment secondary treatment. However, other less obvious Boghani. Critically revising the article: all authors. Reviewed sub- indicators can be used as well. Currently, tumor growth mitted version of manuscript: all authors. Administrative/technical/ rate is a commonly used parameter to indicate the failure material support: Liu, Choudhry, Eloy. Study supervision: Liu. of conservative management. Most studies suggest that in patients with small conservatively managed tumors, References growth rates > 2–3 mm/year or significant worsening 1. Anderson TD, Loevner LA, Bigelow DC, Mirza N: Prevalence 3,16,35 of symptoms should signal the need for treatment. of unsuspected acoustic neuroma found by magnetic reso- Bakkouri et al.3 found that conservative management nance imaging. Otolaryngol Head Neck Surg 122:643–646, failed in 23.7% of their patients. They characterized treat- 2000 ment failure by a tumor growth rate ≥ 3 mm between two 2. Baguley DM, Humphriss RL, Axon PR, Moffat DA: The clinical characteristics of tinnitus in patients with vestibular consecutive MRI studies, disabling vertigo, hearing de- schwannoma. Skull Base 16:49–58, 2006 terioration, patient choice, or seeking a second opinion 3. Bakkouri WE, Kania RE, Guichard JP, Lot G, Herman P, from another provider. When utilizing hearing loss as a Huy PT: Conservative management of 386 cases of unilateral parameter of failure, it has been suggested that a growth vestibular schwannoma: tumor growth and consequences for rate > 2.5 mm/year is a strong predictor of failed con- treatment. Clinical article. J Neurosurg 110:662–669, 2009 servative management at the 3-year follow-up in patients 4. Breivik CN, Varughese JK, Wentzel-Larsen T, Vassbotn F, < 35 Lund-Johansen M: Conservative management of vestibular with tumors 25 mm on presentation. However, it was schwannoma—a prospective cohort study: treatment, symp- shown that regardless of the presentation, more than half toms, and quality of life. Neurosurgery 70:1072–1080, 2012 of the patients managed with observation did not show 5. Deen HG, Ebersold MJ, Harner SG, Beatty CW, Marion MS, tumor enlargement (52%–57%), and only 16%–21% re- Wharen RE, et al: Conservative management of acoustic neu- quired therapy within a period of 3 years.41 In general, roma: an outcome study. Neurosurgery 39:260–266, 1996 secondary intervention was required in only a minority 6. Flint D, Fagan P, Panarese A: Conservative management of spo- radic unilateral acoustic neuromas. J Laryngol Otol 119:424– of patients managed conservatively and tended to be suc- 428, 2005 cessful in most of these patients. Thus, we suggest that 7. Fucci MJ, Buchman CA, Brackmann DE, Berliner KI: Acoustic conservative management with careful follow-up is an tumor growth: implications for treatment choices. Am J Otol appropriate therapy in almost all cases of incidental VSs. 20:495–499, 1999

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Selesnick SH, Jackler RK, Pitts LW: The changing clinical pre- Medicine and Dentistry of New Jersey–New Jersey Medical School, sentation of acoustic tumors in the MRI era. Laryngoscope 90 Bergen Street, Suite 8100, Newark, New Jersey 07101. email: 103:431–436, 1993 [email protected].

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