Retrosigmoid removal of small acoustic neuroma: curative tumor removal with preservation of function

Clinical article

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Object

Management of small acoustic neuromas (ANs) consists of 3 options: observation with imaging follow-up, radiosurgery, and/or tumor removal. The authors report the long-term outcomes and preservation of function after retrosigmoid tumor removal in 44 patients and clarify the management paradigm for small ANs.

Methods

A total of 44 consecutively enrolled patients with small ANs and preserved hearing underwent retrosigmoid tumor removal in an attempt to preserve hearing and facial function by use of intraoperative auditory monitoring of auditory brainstem responses (ABRs) and cochlear nerve compound action potentials (CNAPs). All patients were younger than 70 years of age, had a small AN (purely intracanalicular/cerebellopontine angle tumor ≤ 15 mm), and had serviceable hearing preoperatively. According to the guidelines of the Committee on Hearing and Equilibrium of the American Academy of Otolaryngology–Head and Neck Surgery Foundation, preoperative hearing levels of the 44 patients were as follows: Class A, 19 patients; Class B, 17; and Class C, 8. The surgical technique for curative tumor removal with preservation of hearing and facial function included sharp dissection and debulking of the tumor, reconstruction of the internal auditory canal, and wide removal of internal auditory canal dura.

Results

For all patients, tumors were totally removed without incidence of facial palsy, death, or other complications. Total tumor removal was confirmed by the first postoperative Gd-enhanced MRI performed 12 months after surgery. Postoperative hearing levels were Class A, 5 patients; Class B, 21; Class C, 11; and Class D, 7. Postoperatively, serviceable (Class A, B, or C) and useful (Class A or B) levels of hearing were preserved for 84% and 72% of patients, respectively. Better preoperative hearing resulted in higher rates of postoperative hearing preservation (p = 0.01); preservation rates were 95% among patients with preoperative Class A hearing, 88% among Class B, and 50% among Class C. Reliable monitoring was more frequently provided by CNAPs than by ABRs (66% vs 32%, p < 0.01), and consistently reliable auditory monitoring was significantly associated with better rates of preservation of useful hearing. Long-term follow-up by MRI with Gd administration (81 ± 43 months [range 5–181 months]; median 7 years) showed no tumor recurrence, and although the preserved hearing declined minimally over the long-term postoperative follow-up period (from 39 ± 15 dB to 45 ± 11 dB in 5.1 ± 3.1 years), 80% of useful hearing and 100% of serviceable hearing remained at the same level.

Conclusions

As a result of a surgical technique that involved sharp dissection and internal auditory canal reconstruction with intraoperative auditory monitoring, retrosigmoid removal of small ANs can lead to successful curative tumor removal without long-term recurrence and with excellent functional outcome. Thus, the authors suggest that tumor removal should be the first-line management strategy for younger patients with small ANs and preserved hearing.

Abbreviations used in this paper:ABR = auditory brainstem response; AN = acoustic neuroma; CNAP = cochlear nerve compound action potential.

Object

Management of small acoustic neuromas (ANs) consists of 3 options: observation with imaging follow-up, radiosurgery, and/or tumor removal. The authors report the long-term outcomes and preservation of function after retrosigmoid tumor removal in 44 patients and clarify the management paradigm for small ANs.

Methods

A total of 44 consecutively enrolled patients with small ANs and preserved hearing underwent retrosigmoid tumor removal in an attempt to preserve hearing and facial function by use of intraoperative auditory monitoring of auditory brainstem responses (ABRs) and cochlear nerve compound action potentials (CNAPs). All patients were younger than 70 years of age, had a small AN (purely intracanalicular/cerebellopontine angle tumor ≤ 15 mm), and had serviceable hearing preoperatively. According to the guidelines of the Committee on Hearing and Equilibrium of the American Academy of Otolaryngology–Head and Neck Surgery Foundation, preoperative hearing levels of the 44 patients were as follows: Class A, 19 patients; Class B, 17; and Class C, 8. The surgical technique for curative tumor removal with preservation of hearing and facial function included sharp dissection and debulking of the tumor, reconstruction of the internal auditory canal, and wide removal of internal auditory canal dura.

Results

For all patients, tumors were totally removed without incidence of facial palsy, death, or other complications. Total tumor removal was confirmed by the first postoperative Gd-enhanced MRI performed 12 months after surgery. Postoperative hearing levels were Class A, 5 patients; Class B, 21; Class C, 11; and Class D, 7. Postoperatively, serviceable (Class A, B, or C) and useful (Class A or B) levels of hearing were preserved for 84% and 72% of patients, respectively. Better preoperative hearing resulted in higher rates of postoperative hearing preservation (p = 0.01); preservation rates were 95% among patients with preoperative Class A hearing, 88% among Class B, and 50% among Class C. Reliable monitoring was more frequently provided by CNAPs than by ABRs (66% vs 32%, p < 0.01), and consistently reliable auditory monitoring was significantly associated with better rates of preservation of useful hearing. Long-term follow-up by MRI with Gd administration (81 ± 43 months [range 5–181 months]; median 7 years) showed no tumor recurrence, and although the preserved hearing declined minimally over the long-term postoperative follow-up period (from 39 ± 15 dB to 45 ± 11 dB in 5.1 ± 3.1 years), 80% of useful hearing and 100% of serviceable hearing remained at the same level.

Conclusions

As a result of a surgical technique that involved sharp dissection and internal auditory canal reconstruction with intraoperative auditory monitoring, retrosigmoid removal of small ANs can lead to successful curative tumor removal without long-term recurrence and with excellent functional outcome. Thus, the authors suggest that tumor removal should be the first-line management strategy for younger patients with small ANs and preserved hearing.

Abbreviations used in this paper:ABR = auditory brainstem response; AN = acoustic neuroma; CNAP = cochlear nerve compound action potential.

Technological developments and the prevalence of MRI have increased the number of small acoustic neuromas (ANs) that are detected. Currently, the 3 management options for small ANs are observation with imaging follow-up (wait-and-scan), radiosurgery, and/or tumor removal.52 Magnetic resonance imaging can be used to evaluate the size and volume of small ANs accurately, noninvasively, and repeatedly. Because tumor growth of small ANs is usually slow, wait-and-scan has become a common and valid alternative that allows for documentation of the benign natural history of small ANs while offering the safety and feasibility of observation management.2,44 Radiosurgery, which is much less invasive than tumor removal, offers the most control over small ANs, although it does not eradicate the tumor. Radiosurgery achieves a good functional outcome; facial function is preserved for 95%–100% of patients7,35 and useful hearing for 61%–78%.4,31,45 Under certain circumstances, a surgeon might be requested to perform curative tumor removal of a small AN, usually to preserve facial function and hearing. To achieve excellent functional outcome after surgery, we have refined the microsurgical technique and intraoperative auditory monitoring for retrosigmoid removal of small ANs. Our newly designed intracranial electrode enables continuous and reliable auditory monitoring by use of cochlear nerve compound action potentials (CNAPs).49,51,54 We report long-term outcomes of curative tumor removal with preservation of hearing and facial function; thus, we recommend that tumor removal be the first-line management strategy for younger patients with small ANs and preserved hearing.

Methods

During the period of 1998–2012, we consecutively enrolled 44 patients (19 men and 25 women, 22–69 years of age [mean age 52 ± 12 years]) with small ANs and preserved hearing who underwent curative tumor removal in an attempt to preserve facial and hearing functions. To meet the study inclusion criteria, patients needed to have a small AN, have serviceable hearing preoperatively, and be younger than 70 years of age. A small AN was defined as a purely intracanalicular AN without cerebellopontine angle extension (6 patients) or an AN with a cerebellopontine angle extension in which the maximal diameter of the cerebellopontine angle tumor was 15 mm or less (38 patients). During the study period, we performed tumor removal in 240 patients with previously untreated ANs; therefore, these 44 study patients accounted for 18% of our total AN experience. According to the guidelines of the Committee on Hearing and Equilibrium of the American Academy of Otolaryngology–Head and Neck Surgery Foundation,11 serviceable hearing is defined as Class A, B, or C. The preoperative hearing levels of the 44 study patients were Class A, 19 patients; Class B, 17; and Class C, 8 (Table 1). Furthermore, those with a hearing level of Class A or B were designated as the useful hearing group; they had pure tone averages of 50 dB or less and speech discrimination scores of 50% or more.

TABLE 1:

Preoperative and postoperative hearing of 44 patients with small ANs

Preop Hearing Class*Postop Hearing Class*Rate of Postop Serviceable Hearing PreservationTotal
ABCD
A4122195%19
B195288%17
A & B92%
C004450%§8
total52111784%44

American Academy of Otolaryngology–Head and Neck Surgery Classification.

p = 0.01 (chi-square test).

p < 0.01 (chi-square test).

50% (4/8), the rate of postoperative serviceable hearing preservation among the 8 patients with preoperative Class C hearing, is statistically significant (p = 0.01) compared with 95% (18/19), the rate of postoperative serviceable hearing preservation among the patients with preoperative Class A hearing, and 88% (15/17), the rate of postoperative serviceable hearing preservation among the patients with preoperative Class B hearing. Moreover, 50% (4/8) is statistically significant (p < 0.01) compared with 92% (33/36), the rate of postoperative serviceable hearing preservation among the patients with Class A or B hearing.

Curative Tumor Removal With Preservation of Function via the Retrosigmoid Approach

All patients underwent retrosigmoid tumor removal. The goals were curative (total) tumor removal and preservation of hearing and facial function.

Surgical Technique for Functional Preservation

Because the retrosigmoid AN removal surgical technique has been reported elsewhere,53,54 herein we list several points with regard to curative total tumor removal and preservation of function, especially hearing.

Minimal Cerebellopontine Angle Arachnoid Dissections

In patients with a small AN, especially those with a pure intracanalicular tumor, the cerebellopontine angle arachnoid dissection was limited to the minimal area near the porus acusticus. The restricted arachnoid dissection prevented the cerebellum from sinking downward from gravity, which has been shown to be the typical cause of hearing loss because of longitudinal traction of the acoustic nerve.10

Petrous Dura Flap to Protect the Cerebellopontine Angle

Before the posterior wall of the internal auditory canal was drilled, the dura of the petrous bone that forms the posterior wall was peeled off as a flap from the fundus side to the porus side. The petrous dura flap, secured by using a brain retractor, protected the cerebellopontine angle during posterior wall drilling (Fig. 1A).

Fig. 1.
Fig. 1.

A: The petrous dura flap (arrows) protecting the cerebellopontine angle. B: Trimming both sides of the internal auditory canal by using a small diamond bur head. C: Sufficient internal auditory canal drilling caused meatal tumor bulging. D: Using the petrous dura flap (arrows) to reconstruct the new roof of the internal auditory canal.

Posterior Wall Drilling

The petrous bone was drilled wide enough on both sides of the internal auditory canal to provide a sufficient extraction area; however, to preserve the common crus, we limited drilling on the lateral (fundus) end. We began drilling with a large (3-mm) steel bur head and then used a 3-mm diamond bur head to skeletonize the internal auditory canal dura. The last stage of internal auditory canal skeletonization comprised trimming the sides and fundus area of the internal auditory canal by using a smaller (2-mm) diamond bur head (Fig. 1B). Sufficient drilling caused the meatal tumor to bulge out by itself; however, at this time, the tumor was still covered by the dura (Fig. 1C).

Harvesting of the Petrous Dura Flap for Internal Auditory Canal Reconstruction

After completing adequate posterior wall drilling, we removed the petrous dura flap and preserved it for subsequent internal auditory canal reconstruction.

Wide Removal of the Internal Auditory Canal Dura

To gain wide exposure of the intrameatal nerves and tumor, after cutting the sides and lateral end, we removed the exposed internal auditory canal dura in its entirety as a single sheet.

Sharp Tumor Dissection

We then dissected the tumor from the nerves (vestibular, cochlear, and facial) by using microscissors and microknives in the same way that they would be used for dissecting the arachnoid membrane and trabeculae.

Tumor Debulking

The tumor and the surrounding nerves were tightly packed in the internal auditory canal. Dissection of the tumor without first debulking it would have caused unexpected compression or damage to the preserved nerve. Therefore, intracapsular tumor debulking is always mandatory, even in patients with small ANs. Tumor debulking using ring or blunt dissectors can compress and damage the nerves surrounding the tumor. Thus, we debulked the tumor by using microscissors and microknives. Last, the tumor was removed piece by piece by using microscissors throughout the dissection.

Tumor Removal Near the Fundus of the Internal Auditory Canal

Tumor excision near the fundus was the last and most hazardous stage of tumor removal. With direct visualization of the fundus area, we cautiously and sharply dissected the tumor out by using microscissors.

Preservation of Nerve Function

For hemostasis, we used oxidized cellulose, surgical patties, saline irrigation, and, sometimes, an application of gentle pressure, which was sufficient.

Internal Auditory Canal Reconstruction and Restoring the CSF Space in the Internal Auditory Canal

As mentioned, the petrous dura flap was harvested for internal auditory canal reconstruction (Fig. 1D).50 After completion of the tumor removal, the roof of the internal auditory canal was reconstructed by using the harvested dura flap. Thereafter, muscle or fat grafts were placed on this roof to fill up the removed posterior wall. The new internal auditory canal roof separated the preserved cochlear and facial nerves from the grafts and restored the space in the internal auditory canal (Fig. 2).

Fig. 2.
Fig. 2.

A patient with left small AN. Before tumor removal, the left internal auditory canal was filled with tumor (T1-weighted axial Gd-enhanced image [A]; T2-weighted coronal image [B]). Tumor was totally removed via the retrosigmoid approach, and function was preserved; preoperative and postoperative hearing levels were 35 and 30 dB, respectively. At 2 years after tumor removal, T2-weighted coronal image (C) showed that the intrameatal tumor was removed and that the left internal auditory canal restored the cerebrospinal fluid space after internal auditory canal reconstruction. Arrows indicate left internal auditory canal. R = right.

Intraoperative Monitoring of Auditory and Facial Function

During surgery, we performed simultaneous and continuous monitoring of the auditory brainstem responses (ABRs) and CNAPs.51,54 In brief, ABRs were monitored throughout the duration of the surgery, and CNAPs were monitored continuously throughout intradural microsurgery by using our newly developed intracranial electrodes. Facial function was monitored by intermittent electrical stimulation of the intracranial facial nerve with the NIM nerve monitoring system (Medtronic).

Postoperative Follow-Up

After tumor removal, all patients were regularly examined at the outpatient clinic every 3–6 months. To confirm the extent of tumor removal, they underwent the first postoperative Gd-enhanced MRI 12 months after surgery; to evaluate tumor recurrence, they underwent follow-up Gd-enhanced MRI every year thereafter. Data analysis was performed by using StatView software (SAS Institute Inc.), and statistical significance was defined as p ≤ 0.05. Data are expressed as means and standard deviations.

This study adhered to the World Medical Association Declaration of Helsinki and the guidelines for clinical research published by the ethical committee of Chiba Central Medical Center. All patients gave informed consent before inclusion in this study.

Results

Outcomes of Tumor Removal and Preservation of Function

Total tumor removal was achieved for all patients and confirmed by surgical records and the first postoperative Gd-enhanced MRI (12 months after surgery). Postoperative hearing levels were Class A, B, C, and D for 5, 21, 11, and 7 patients, respectively (Table 1). Postoperative rates of preservation of serviceable and useful hearing were 37/44 (84%) and 26/36 (72%), respectively. The postoperative rate for preservation of serviceable hearing was 95% among patients with preoperative Class A hearing, 88% among those with Class B hearing, and 50% among those with Class C hearing (p = 0.01). Serviceable hearing was preserved for 92% of patients with preoperative Class A or B hearing and 50% of patients with preoperative Class C hearing (p < 0.01). A mild facial palsy (House-Brackmann Grade II) occurred in 2 patients (5%) during the first postoperative week, but normal facial function had been recovered (House-Brackmann Grade I) when they were seen in the outpatient clinic. No deaths or other postoperative complications occurred.

Intraoperative Auditory Monitoring (Fig. 3)

Monitoring of ABRs during tumor removal was often disrupted by artifacts from various surgical equipment and procedures. Among the 44 patients, reliable monitoring of ABRs with the distinct wave V was consistently obtained in 14 (32%), was intermittently obtained in 10 (23%), and was either unreliable or not obtained in 20 (45%) (Table 2). Consistently reliable ABR monitoring was obtained in 11 (58%) of 19 patients with preoperative Class A hearing, 3 (18%) of 17 with preoperative Class B hearing, and 0 of 8 with preoperative Class C hearing (p < 0.01). Useful hearing was preserved postoperatively in 12 (86%) of 14 patients with consistently reliable ABRs, but in only 9 (45%) of 20 patients with unreliable/not obtained ABRs (p < 0.05).

Fig. 3.
Fig. 3.

Intraoperative auditory monitoring of a 46-year-old man with a small AN. This patient's preoperative hearing level was Class A, and his hearing level was preserved after tumor removal. Continuously reliable monitoring of ABRs (left) and CNAPs (right) was obtained throughout surgery. Black arrow indicates CNAP with latency of 3.2 msec.

Cochlear nerve compound action potentials were not affected by artifacts of surgical equipment and procedures. Reliable CNAPs were obtained consistently throughout microsurgical tumor removal in 29 (66%) of the 44 patients, and reliable auditory monitoring was achieved more frequently with CNAPs than with ABRs (66% vs 32%, p < 0.01). Cochlear nerve compound action potentials were intermittently reliable in 7 patients and unreliable/not obtained in 8 patients (Table 2). Useful hearing was preserved postoperatively in 22 (76%) of 29 patients with consistently reliable CNAPs and in 4 (27%) of 15 patients with intermittently reliable or unreliable/not obtained CNAPs (p < 0.01).

TABLE 2:

Results of intraoperative auditory monitoring versus preoperative and postoperative hearing among 44 patients who underwent retrosigmoid removal of small AN

Type of MonitoringNo. of CasesHearing Level*
PreoperativePostoperative
ABCABCD
ABRs
 consistently reliable1411304811
 intermittently reliable103520541
 unreliable/not obtained205961865
 total4419178521117
CNAPs
 consistently reliable291710241852
 intermittently reliable72410340
 unreliable/not obtained80351025
 total4419178521117

American Academy of Otolaryngology–Head and Neck Surgery Classification.

Long-Term Postoperative Follow-Up Results of Gd-Enhanced MRI and Audiological Examinations

During the long-term Gd-enhanced MRI follow-up period (81 ± 43 months [range 5–181 months], median 7 years), no tumor recurred in any patient. However, for 1 patient (a 42-year-old woman) hearing suddenly worsened 30 months after surgery. No tumor recurrence was demonstrated on Gd-enhanced MRI, so the patient underwent treatment for sudden deafness, which did not ameliorate her hearing impairment (from 36 dB to 70 dB in pure tone averages). No sudden deterioration of the preserved hearing occurred in any other patient; postoperative audiological follow-up examinations for preserved hearing showed a decline of pure tone averages from 39 ± 15 dB to 45 ± 11 dB over 5.1 ± 3.1 years (range 2–13 years); that is, the rate of annual hearing decrease was 1.2 dB per year. Preserved useful hearing remained the same for 12 (80%) of 15 patients, and preserved serviceable hearing was maintained for all 37 patients.

Discussion

Wait-and-Scan for Patients With Small ANs and Preserved Hearing

Observation management with imaging follow-up (wait-and-scan) has become the prevalent strategy for managing small ANs. This approach has revealed that the natural history of ANs as a whole is benign and that the mean tumor growth rate is 1.0–3.0 mm per year.2,44,52 However, the wait-and-scan strategy has also revealed that the growth rate and pattern of small ANs vary widely among patients. Growth rates are less than 1 mm per year for more than 60% of patients and more than 3 mm per year for 12% of patients.2 Moreover, no significant association has been found between tumor growth rate and factors such as sex, age, initial hearing status, or preliminary tumor grade.2,52 Because the tumor growth of each patient is unpredictable, the ideal interval for imaging follow-up studies is not fixed.12

Previous reports of the wait-and-scan approach for patients with small ANs and preserved hearing have indicated that hearing progressively declines regardless of tumor growth. Specifically, 1 study showed that pure tone averages among 47 patients with intracanalicular AN deteriorated from 38 dB to 51 dB and that 26% of useful hearing was lost during the 3.6-year duration of the wait-and-scan management strategy.33 Another study revealed that over a follow-up period of more than a decade, most patients with preserved useful hearing lost the useful hearing regardless of tumor growth.43 These studies provide compelling evidence that, to avoid the progressive hearing decline that has been reported for the prevalent wait-and-scan approach, tumor removal should be the first treatment option for younger patients with small ANs and preserved hearing.

Long-Term Outcome of Curative Small AN Removal With Preservation of Function

In our study, retrosigmoid removal of small ANs in 44 patients with preserved hearing was accomplished with excellent functional outcomes. Curative tumor removal was confirmed by long-term MRI follow-up examinations.

One of the main and most challenging focuses in the management of small ANs is preservation of hearing. In our study, the rates of postoperative preservation of useful and serviceable hearing were 72% and 84%, respectively. Table 3 summarizes the outcome of hearing and facial function after tumor removal and radiosurgery of small ANs. Two surgical approaches (the retrosigmoid approach and the middle fossa approach) are currently used for small AN removal in cases where hearing preservation is desired. Although it has previously been claimed that a higher rate of hearing preservation can be accomplished with the middle fossa approach than with the retrosigmoid approach,22 recent publications have suggested that there is no difference between the 2 approaches (that is, hearing is preserved for 50%–77% of patients after the retrosigmoid approach9,25,29,36 and for 52%–73% after the middle fossa approach9,13,21,39). By using the retrosigmoid approach, we achieved the same level of preservation (72%) in the study reported here.

TABLE 3:

Outcome of hearing and facial function after treatment of small ANs*

Treatment ModalityHearing After TreatmentRate of Good Facial Function Preservation
Rate of Useful Hearing PreservationProgressive Hearing Decline
%(%) Author & YearAmount of DeclineAuthor & Year%(%) Author & Year
surgery50–77no/rare/minimal88–100
middle fossa approach52–73(52) Sanna 2004,39(53) Satar 2002,40(59) Hillman 2010,21(62) Gjurić 2001,18(66) Colletti 2005,9(73) Arts 2006,1(73) De-Monte 201213no/minimalFriedman 2003,16 Woodson 20104988–100(88) Hillman 2010,21(89) Kutz 2012,23(93) DeMonte 2012,13(94) Friedman 2003,16(97) Meyer 2006,27(99) Gjurić 2001,18(100) Sameshima 201036
retrosigmoid approach50–77(50) Mohr 2005,29(57) Colletti 2005,9(72) Mangham 2004,25(77) Sameshima 201036rareMazzoni 20122690–100(90) Samii 2006,37(91) Colletti 2005,9(92) Staechker 2000,42(100) Magnan 2002,24(100) Sameshima 201036
current series72rare/minimal100
radiosurgery61–78(61) Niranjan 2008,31(68) Franzin 2009,15(78) Tamura 200945usual/definiteChopra 2007,7 Hasegawa 2011,19 Roos 20123495–100(95) Rowe 2003,35(95) Murphy 2011,30(99) Hasegawa 2013,19(100) Chopra 20077

Data from a series of studies published in 2000 or later.

We showed that better preoperative hearing resulted in a higher rate of postoperative hearing preservation: 95% preservation for patients with preoperative Class A hearing, 88% for Class B, and 50% for Class C. Therefore, hearing preservation after tumor removal is associated with the preoperative hearing level.4

Intraoperative auditory monitoring during this study showed that reliable auditory monitoring was more frequently obtained for patients with better preoperative hearing. Moreover, reliable monitoring was also associated with higher rates of postoperative hearing preservation. In this study, intraoperative auditory monitoring with ABRs and CNAPs was performed simultaneously and reliable auditory monitoring more frequently with CNAPs than with ABRs (66% vs 32%, p < 0.01). Because of their large amplitude, CNAPs can almost be monitored in real time, thus giving the surgeon intraoperative feedback.8,51 This feedback enables the surgeon to refine the surgical technique in an attempt to preserve hearing and facial function intraoperatively, thereby improving functional outcome. Several points with regard to surgical technique for preservation of hearing and facial function are detailed above. However, the most critical point for preservation of hearing and facial function is sharp dissection with microscissors and microknives. Blunt dissection not only damages nerves by indirect compression but also damages small vessels that have mild adhesions.

Although removal of medium or large ANs carries a considerable risk for facial palsy,38 a series of recent studies of removal of small ANs reported high rates of facial function preservation (88%–100%)9,13,16,18,21,23,24,27,36,37,42 (Table 3). In our study, the rate of normal facial function preservation (House-Brackmann Grade I) was 100%. In reports published during the 1980s–1990s, the rates of good facial function preservation after small AN removal were unsatisfactory (72%–94%).3,17,22,38 The increased success can be attributed to the development of surgical and monitoring techniques. With regard to surgical approaches, we and others have found that the retrosigmoid approach can offer better postoperative facial function than the middle fossa approach.32,36 This is so because for the access route of the middle fossa approach, the facial nerve is located in front of the tumor, but for the retrosigmoid approach, the nerve is located behind the tumor; thus, during tumor removal, the middle fossa approach requires greater manipulation of the facial nerve.32 Preservation of facial function is also excellent (95%–100%) after radiosurgery.7,30,35

Progressive Hearing Decline After AN Treatment

The highest rates of hearing preservation after treatment of small ANs are achieved with radiosurgery; useful hearing is preserved for 61%–78% of patients15,31,45 However, preserved hearing after radiosurgery has been shown to progressively decline. This progressive decline is typical and definite; hearing preservation rates are 43%–57% at 5 years after radiosurgery and decrease to 34%–45% at 10 years.7,20,34

In our study, after retrosigmoid tumor removal, the occurrence of postoperative decline of preserved hearing was rare and the level of the postoperative decline was minimal; that is, over the long term, useful hearing and serviceable hearing were preserved for 80% and 100% of patients, respectively. Yomo et al. reported that the rate of annual hearing decrease among AN patients was 5.39 dB per year and 3.77 dB per year before and after radiosurgery, respectively.55 In our study, the rate of annual hearing decrease after retrosigmoid small AN removal was 1.2 dB per year, which is much lower than that after radiosurgery. In addition, it is possible that the postoperative hearing decline found in this study might represent natural hearing decline from aging (presbycusis). Postoperative declines in hearing after tumor removal through the middle fossa approach have been documented.41 After tumor removal, scarring of the preserved cochlear nerve occurs as a consequence of fat or muscle graft packing of the internal auditory canal and results in delayed hearing declines.6,41 We reconstructed the internal auditory canal after tumor removal by using the petrous dura flap to restore the CSF space of the internal auditory canal.50 Recovery of the CSF space prevents scarring of the preserved nerve, and this method of internal auditory canal reconstruction can contribute to long-term hearing preservation after tumor removal. Mazzoni et al. recently reported that after retrosigmoid AN removal, 87% of preserved useful hearing was maintained at the same level over a long-term follow-up period of 6–21 years.26 Recent studies of the middle fossa approach tumor removal showed no or minimal hearing decline in the postoperative follow-up period.16,49

Learning Curve for Microsurgery and Radiosurgery

Surgical removal of ANs requires a profound knowledge of anatomy and long-standing experience with sophisticated microsurgical technique. The expertise of the surgeon and/or surgical teams affects the outcome of this technically demanding procedure, and the existence of a learning curve has been reported.14,46 To attain surgical results similar to those reported by expert surgeons, experience with 20–50 cases is necessary.5,28,47 Before starting the series of cases reported here, the senior author had removed more than 60 ANs, most of which were large/giant tumors.53 Despite the relatively small number of patients in this series, we removed 240 previously untreated ANs during the same period. Our study shows excellent results regarding preservation of hearing and facial function as well as total tumor removal; therefore, no learning curve was observed. Radiosurgical treatment of ANs requires precise anatomical definition and optimal dose distribution. Because of continuous advances in imaging technology and the refinement of radiosurgical technology, radiosurgery requires improvement of skill and knowledge. A learning curve exists for radiosurgical dose planning of AN treatment, although the effect on the clinical outcome has not yet been elucidated.56

Management Paradigm for Small ANs

In this study, we analyzed the long-term outcome of 44 patients with preserved hearing who had undergone removal of small ANs; we showed that retrosigmoid tumor removal with auditory monitoring can accomplish curative tumor removal and excellent functional outcome without deaths or other postoperative complications. During wait-and-scan of small ANs in patients with preserved hearing, progressive hearing decline occurs frequently, irrespective of tumor growth. After radiosurgery, progressive hearing decline is inevitable. Therefore, we propose that tumor removal, with preservation of hearing and facial function, should be the first-line management for small ANs in younger patients with preserved hearing. Figure 4 outlines this management algorithm. Briefly, patients younger than 70 years of age with preserved hearing and a small AN should be offered tumor removal with preservation of hearing and facial function. For patients 70 years of age or older, the wait-and-scan approach should be offered; thereafter, patients with tumor growth during the wait-and-scan period should be offered either tumor removal or radiosurgery.

Fig. 4.
Fig. 4.

Management algorithm for a patient with small AN. RS = radiosurgery; S = surgery (tumor removal); S/RS = surgery or radiosurgery; W&S = wait-and-scan. Age is represented in years.

Study Limitations and Strengths

This study has some limitations and several strengths. The limitations include the retrospective nature of the study, limited number of patients, potential biases of patient selection, and unknown natural history of AN. At the start of this study, we determined the inclusion criteria for patients who would undergo curative tumor removal with preservation of hearing and facial function (small AN, serviceable hearing, and age younger than 70 years). However, not all patients conforming to the inclusion criteria underwent this surgery because each patient selected his or her own treatment plan after being informed of the 3 treatment options (wait-and-scan, radiosurgery, or tumor removal). Not being a prospectively controlled trial, this study could not evade patient selection bias. Although the natural history of hearing and tumor growth of small ANs is discussed above in relation to the results of wait-and-scan study series, the real natural history of small ANs is unknown. The long-term outcomes after tumor removal and radiosurgery should be determined with regard to the real natural history of small ANs by using a well-controlled, randomized trial. However, the nature of ANs makes a well-controlled, randomized trial unpractical because attaining statistical significance would require sample sizes of more than 6700 patients in each study group.48 Despite the limited number of patients in our study, the auditory monitoring using CNAPs and ABRs might have contributed to the excellent functional results achieved in this study. A major strength of this study is the long-term postoperative follow-up result obtained by Gd-enhanced MRI and audiological examinations.

Conclusions

Using the surgical technique, including sharp dissection and internal auditory canal reconstruction, in concert with intraoperative auditory monitoring of CNAPs and ABRs, we found that removal of small ANs via a retrosigmoid approach accomplished curative removal and excellent functional outcomes. No tumor recurred and the preserved hearing demonstrated no decline or minimal decline during the long-term follow-up period. Hearing decline during wait-and-scan and after radiosurgery is common and inevitable for patients with small ANs; therefore, we propose that curative tumor removal with preservation of hearing and facial function should be the first-line management strategy recommended for younger patients with a small AN and preserved hearing.

Disclosure

The authors report no conflict of interest concerning the materials or methods used in this study or the findings specified in this paper.

Author contributions to the study and manuscript preparation include the following. Conception and design: Yamakami, Ito. Acquisition of data: all authors. Analysis and interpretation of data: all authors. Drafting the article: Yamakami, Ito. Critically revising the article: all authors. Reviewed submitted version of manuscript: all authors. Approved the final version of the manuscript on behalf of all authors: Yamakami. Statistical analysis: Yamakami, Higuchi. Administrative/technical/material support: Yamakami. Study supervision: Yamakami.

This article contains some figures that are displayed in color online but in black-and-white in the print edition.

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    • Export Citation
  • 3

    Brackmann DEHouse JR IIIHitselberger WE: Technical modifications to the middle fossa craniotomy approach in removal of acoustic neuromas. Am J Otol 15:6146191994

    • Search Google Scholar
    • Export Citation
  • 4

    Brackmann DEOwens RMFriedman RAHitselberger WEDe la Cruz AHouse JW: Prognostic factors for hearing preservation in vestibular schwannoma surgery. Am J Otol 21:4174242000

    • Search Google Scholar
    • Export Citation
  • 5

    Buchman CAChen DAFlannagan PWilberger JEMaroon JC: The learning curve for acoustic tumor surgery. Laryngoscope 106:140614111996

    • Search Google Scholar
    • Export Citation
  • 6

    Chee GHNedzelski JMRowed D: Acoustic neuroma surgery: the results of long-term hearing preservation. Otol Neurotol 24:6726762003

    • Search Google Scholar
    • Export Citation
  • 7

    Chopra RKondziolka DNiranjan ALunsford LDFlickinger JC: Long-term follow-up of acoustic schwannoma radiosurgery with marginal tumor doses of 12 to 13 Gy. Int J Radiat Oncol Biol Phys 68:8458512007

    • Search Google Scholar
    • Export Citation
  • 8

    Colletti VBricolo AFiorino FGBruni L: Changes in directly recorded cochlear nerve compound action potentials during acoustic tumor surgery. Skull Base Surg 4:191994

    • Search Google Scholar
    • Export Citation
  • 9

    Colletti VFiorino F: Is the middle fossa approach the treatment of choice for intracanalicular vestibular schwannoma?. Otolaryngol Head Neck Surg 132:4594662005

    • Search Google Scholar
    • Export Citation
  • 10

    Colletti VFiorino FGCarner MTonoli G: Mechanisms of auditory impairment during acoustic neuroma surgery. Otolaryngol Head Neck Surg 117:5966051997

    • Search Google Scholar
    • Export Citation
  • 11

    Committee on Hearing and Equilibrium: Committee on Hearing and Equilibrium guidelines for the evaluation of hearing preservation in acoustic neuroma (vestibular schwannoma). Otolaryngol Head Neck Surg 113:1791801995

    • Search Google Scholar
    • Export Citation
  • 12

    Deen HGEbersold MJHarner SGBeatty CWMarion MSWharen RE: Conservative management of acoustic neuroma: an outcome study. Neurosurgery 39:2602661996

    • Search Google Scholar
    • Export Citation
  • 13

    DeMonte FGidley PW: Hearing preservation surgery for vestibular schwannoma: experience with the middle fossa approach. Neurosurg Focus 33:3E102012

    • Search Google Scholar
    • Export Citation
  • 14

    Foroughi MPitkäniemi JNannapaneni RNath F: Excision of vestibular schwannomas—is there a learning curve and how best to demonstrate it?. Br J Neurosurg 24:5475542010

    • Search Google Scholar
    • Export Citation
  • 15

    Franzin ASpatola GSerra CPicozzi PMedone MMilani D: Evaluation of hearing function after Gamma Knife surgery of vestibular schwannomas. Neurosurg Focus 27:6E32009

    • Search Google Scholar
    • Export Citation
  • 16

    Friedman RAKesser BBrackmann DEFisher LMSlattery WHHitselberger WE: Long-term hearing preservation after middle fossa removal of vestibular schwannoma. Otolaryngol Head Neck Surg 129:6606652003

    • Search Google Scholar
    • Export Citation
  • 17

    Gantz BJParnes LSHarker LAMcCabe BF: Middle cranial fossa acoustic neuroma excision: results and complications. Ann Otol Rhinol Laryngol 95:4544591986

    • Search Google Scholar
    • Export Citation
  • 18

    Gjurić MWigand MEWolf SR: Enlarged middle fossa vestibular schwannoma surgery: experience with 735 cases. Otol Neurotol 22:2232312001

    • Search Google Scholar
    • Export Citation
  • 19

    Hasegawa TKida YKato TIizuka HKuramitsu SYamamoto T: Long-term safety and efficacy of stereotactic radiosurgery for vestibular schwannomas: evaluation of 440 patients more than 10 years after treatment with Gamma Knife surgery. Clinical article. J Neurosurg 118:5575652013

    • Search Google Scholar
    • Export Citation
  • 20

    Hasegawa TKida YKato TIizuka HYamamoto T: Factors associated with hearing preservation after Gamma Knife surgery for vestibular schwannomas in patients who retain serviceable hearing. Clinical article. J Neurosurg 115:107810862011

    • Search Google Scholar
    • Export Citation
  • 21

    Hillman TChen DAArriaga MAQuigley M: Facial nerve function and hearing preservation acoustic tumor surgery: does the approach matter?. Otolaryngol Head Neck Surg 142:1151192010

    • Search Google Scholar
    • Export Citation
  • 22

    Irving RMJackler RKPitts LH: Hearing preservation in patients undergoing vestibular schwannoma surgery: comparison of middle fossa and retrosigmoid approaches. J Neurosurg 88:8408451998

    • Search Google Scholar
    • Export Citation
  • 23

    Kutz JW JrScoresby TIsaacson BMickey BEMadden CJBarnett SL: Hearing preservation using the middle fossa approach for the treatment of vestibular schwannoma. Neurosurgery 70:3343412012

    • Search Google Scholar
    • Export Citation
  • 24

    Magnan JBarbieri MMora RMurphy SMeller RBruzzo M: Retrosigmoid approach for small and medium-sized acoustic neuromas. Otol Neurotol 23:1411452002

    • Search Google Scholar
    • Export Citation
  • 25

    Mangham CA Jr: Retrosigmoid versus middle fossa surgery for small vestibular schwannomas. Laryngoscope 114:145514612004

  • 26

    Mazzoni AZanoletti ECalabrese V: Hearing preservation surgery in acoustic neuroma: long-term results. Acta Otorhinolaryngol Ital 32:981022012

    • Search Google Scholar
    • Export Citation
  • 27

    Meyer TACanty PAWilkinson EPHansen MRRubinstein JTGantz BJ: Small acoustic neuromas: surgical outcomes versus observation or radiation. Otol Neurotol 27:3803922006

    • Search Google Scholar
    • Export Citation
  • 28

    Moffat DAHardy DGGrey PLBaguley DM: The operative learning curve and its effect on facial nerve outcome in vestibular schwannoma surgery. Am J Otol 17:6436471996

    • Search Google Scholar
    • Export Citation
  • 29

    Mohr GSade BDufour JJRappaport JM: Preservation of hearing in patients undergoing microsurgery for vestibular schwannoma: degree of meatal filling. J Neurosurg 102:152005

    • Search Google Scholar
    • Export Citation
  • 30

    Murphy ESBarnett GHVogelbaum MANeyman GStevens GHCohen BH: Long-term outcomes of Gamma Knife radiosurgery in patients with vestibular schwannomas. Clinical article. J Neurosurg 114:4324402011. (Erratum in J Neurosurg 114: 560 2011)

    • Search Google Scholar
    • Export Citation
  • 31

    Niranjan AMathieu DFlickinger JCKondziolka DLunsford LD: Hearing preservation after intracanalicular vestibular schwannoma radiosurgery. Neurosurgery 63:105410632008

    • Search Google Scholar
    • Export Citation
  • 32

    Noudel RGomis PDuntze JMarnet DBazin ARoche PH: Hearing preservation and facial nerve function after microsurgery for intracanalicular vestibular schwannomas: comparison of middle fossa and retrosigmoid approaches. Acta Neurochir (Wien) 151:9359452009

    • Search Google Scholar
    • Export Citation
  • 33

    Pennings RJMorris DPClarke LAllen SWalling SBance ML: Natural history of hearing deterioration in intracanalicular vestibular schwannoma. Neurosurgery 68:68772011

    • Search Google Scholar
    • Export Citation
  • 34

    Roos DEPotter AEBrophy BP: Stereotactic radiosurgery for acoustic neuromas: what happens long term?. Int J Radiat Oncol Biol Phys 82:135213552012

    • Search Google Scholar
    • Export Citation
  • 35

    Rowe JGRadatz MWWalton LHampshire ASeaman SKemeny AA: Gamma knife stereotactic radiosurgery for unilateral acoustic neuromas. J Neurol Neurosurg Psychiatry 74:153615422003

    • Search Google Scholar
    • Export Citation
  • 36

    Sameshima TFukushima TMcElveen JT JrFriedman AH: Critical assessment of operative approaches for hearing preservation in small acoustic neuroma surgery: retrosigmoid vs middle fossa approach. Neurosurgery 67:6406452010

    • Search Google Scholar
    • Export Citation
  • 37

    Samii MGerganov VSamii A: Improved preservation of hearing and facial nerve function in vestibular schwannoma surgery via the retrosigmoid approach in a series of 200 patients. J Neurosurg 105:5275352006

    • Search Google Scholar
    • Export Citation
  • 38

    Samii MMatthies C: Management of 1000 vestibular schwannomas (acoustic neuromas): surgical management and results with an emphasis on complications and how to avoid them. Neurosurgery 40:11231997

    • Search Google Scholar
    • Export Citation
  • 39

    Sanna MKhrais TRusso APiccirillo EAugurio A: Hearing preservation surgery in vestibular schwannoma: the hidden truth. Ann Otol Rhinol Laryngol 113:1561632004

    • Search Google Scholar
    • Export Citation
  • 40

    Satar BJackler RKOghalai JPitts LHYates PD: Risk-benefit analysis of using the middle fossa approach for acoustic neuromas with >10 mm cerebellopontine angle component. Laryngoscope 112:150015062002

    • Search Google Scholar
    • Export Citation
  • 41

    Shelton CHitselberger WEHouse WFBrackmann DE: Hearing preservation after acoustic tumor removal: long-term results. Laryngoscope 100:1151191990

    • Search Google Scholar
    • Export Citation
  • 42

    Staecker HNadol JB JrOjeman RRonner SMcKenna MJ: Hearing preservation in acoustic neuroma surgery: middle fossa versus retrosigmoid approach. Am J Otol 21:3994042000

    • Search Google Scholar
    • Export Citation
  • 43

    Sughrue MEKane AJKaur RBarry JJRutkowski MJPitts LH: A prospective study of hearing preservation in untreated vestibular schwannomas. Clinical article. J Neurosurg 114:3813852011

    • Search Google Scholar
    • Export Citation
  • 44

    Sughrue MEYang IAranda DLobo KPitts LHCheung SW: The natural history of untreated sporadic vestibular schwannomas: a comprehensive review of hearing outcomes. Clinical article. J Neurosurg 112:1631672010

    • Search Google Scholar
    • Export Citation
  • 45

    Tamura MCarron RYomo SArkha YMuraciolle XPorcheron D: Hearing preservation after gamma knife radiosurgery for vestibular schwannomas presenting with high-level hearing. Neurosurgery 64:2892962009

    • Search Google Scholar
    • Export Citation
  • 46

    Wang AYWang JTDexter MDa Cruz M: The vestibular schwannoma surgery learning curve mapped by the cumulative summation test for learning curve. Otol Neurotol 34:146914752013

    • Search Google Scholar
    • Export Citation
  • 47

    Welling DBSlater PWThomas RDMcGregor JMGoodman JE: The learning curve in vestibular schwannoma surgery. Am J Otol 20:6446481999

    • Search Google Scholar
    • Export Citation
  • 48

    Whitmore RGUrban CChurch ERuckenstein MStein SCLee JYK: Decision analysis of treatment options for vestibular schwannoma. Clinical article. J Neurosurg 114:4004132011

    • Search Google Scholar
    • Export Citation
  • 49

    Woodson EADempewolf RDGubbels SPPorter ATOleson JJHansen MR: Long-term hearing preservation after microsurgical excision of vestibular schwannoma. Otol Neurotol 31:114411522010

    • Search Google Scholar
    • Export Citation
  • 50

    Yamakami IKobayashi EOno JYamaura A: Prevention of cerebrospinal fluid leakage and delayed loss of preserved hearing after vestibular schwannoma removal: reconstruction of the internal auditory canal in the suboccipital transmeatal approach—technical note. Neurol Med Chir (Tokyo) 40:5976012000

    • Search Google Scholar
    • Export Citation
  • 51

    Yamakami IOka NYamaura A: Intraoperative monitoring of cochlear nerve compound action potential in cerebellopontine angle tumour removal. J Clin Neurosci 10:5675702003

    • Search Google Scholar
    • Export Citation
  • 52

    Yamakami IUchino YKobayashi EYamaura A: Conservative management, gamma-knife radiosurgery, and microsurgery for acoustic neurinomas: a systematic review of outcome and risk of three therapeutic options. Neurol Res 25:6826902003

    • Search Google Scholar
    • Export Citation
  • 53

    Yamakami IUchino YKobayashi EYamaura AOka N: Removal of large acoustic neurinomas (vestibular schwannomas) by the retrosigmoid approach with no mortality and minimal morbidity. J Neurol Neurosurg Psychiatry 75:4534582004

    • Search Google Scholar
    • Export Citation
  • 54

    Yamakami IYoshinori HSaeki NWada MOka N: Hearing preservation and intraoperative auditory brainstem response and cochlear nerve compound action potential monitoring in the removal of small acoustic neurinoma via the retrosigmoid approach. J Neurol Neurosurg Psychiatry 80:2182272009

    • Search Google Scholar
    • Export Citation
  • 55

    Yomo SCarron RThomassin JMRoche PHRégis J: Longitudinal analysis of hearing before and after radiosurgery for vestibular schwannoma. Clinical article. J Neurosurg 117:8778852012

    • Search Google Scholar
    • Export Citation
  • 56

    Yomo STamura MCarron RPorcheron DRégis J: A quantitative comparison of radiosurgical treatment parameters in vestibular schwannomas: the Leksell Gamma Knife Perfexion versus Model 4C. Acta Neurochir (Wien) 152:47552010

    • Search Google Scholar
    • Export Citation

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Article Information

Contributor Notes

Address correspondence to: Iwao Yamakami, M.D., Department of Neurosurgery, Chiba Central Medical Center, 1835-1 Kasoricho, Wakaba-ku, Chiba 264-0017, Japan. email: yamakami@ccmc.seikei-kai.or.jp.Please include this information when citing this paper: published online July 4, 2014; DOI: 10.3171/2014.6.JNS132471.
Headings
Figures
  • View in gallery

    A: The petrous dura flap (arrows) protecting the cerebellopontine angle. B: Trimming both sides of the internal auditory canal by using a small diamond bur head. C: Sufficient internal auditory canal drilling caused meatal tumor bulging. D: Using the petrous dura flap (arrows) to reconstruct the new roof of the internal auditory canal.

  • View in gallery

    A patient with left small AN. Before tumor removal, the left internal auditory canal was filled with tumor (T1-weighted axial Gd-enhanced image [A]; T2-weighted coronal image [B]). Tumor was totally removed via the retrosigmoid approach, and function was preserved; preoperative and postoperative hearing levels were 35 and 30 dB, respectively. At 2 years after tumor removal, T2-weighted coronal image (C) showed that the intrameatal tumor was removed and that the left internal auditory canal restored the cerebrospinal fluid space after internal auditory canal reconstruction. Arrows indicate left internal auditory canal. R = right.

  • View in gallery

    Intraoperative auditory monitoring of a 46-year-old man with a small AN. This patient's preoperative hearing level was Class A, and his hearing level was preserved after tumor removal. Continuously reliable monitoring of ABRs (left) and CNAPs (right) was obtained throughout surgery. Black arrow indicates CNAP with latency of 3.2 msec.

  • View in gallery

    Management algorithm for a patient with small AN. RS = radiosurgery; S = surgery (tumor removal); S/RS = surgery or radiosurgery; W&S = wait-and-scan. Age is represented in years.

References
  • 1

    Arts HATelian SAEl-Kashlan HThompson BG: Hearing preservation and facial nerve outcomes in vestibular schwannoma surgery: results using the middle cranial fossa approach. Otol Neurotol 27:2342412006

    • Search Google Scholar
    • Export Citation
  • 2

    Bakkouri WEKania REGuichard JPLot GHerman PHuy PT: Conservative management of 386 cases of unilateral vestibular schwannoma: tumor growth and consequences for treatment. Clinical article. J Neurosurg 110:6626692009

    • Search Google Scholar
    • Export Citation
  • 3

    Brackmann DEHouse JR IIIHitselberger WE: Technical modifications to the middle fossa craniotomy approach in removal of acoustic neuromas. Am J Otol 15:6146191994

    • Search Google Scholar
    • Export Citation
  • 4

    Brackmann DEOwens RMFriedman RAHitselberger WEDe la Cruz AHouse JW: Prognostic factors for hearing preservation in vestibular schwannoma surgery. Am J Otol 21:4174242000

    • Search Google Scholar
    • Export Citation
  • 5

    Buchman CAChen DAFlannagan PWilberger JEMaroon JC: The learning curve for acoustic tumor surgery. Laryngoscope 106:140614111996

    • Search Google Scholar
    • Export Citation
  • 6

    Chee GHNedzelski JMRowed D: Acoustic neuroma surgery: the results of long-term hearing preservation. Otol Neurotol 24:6726762003

    • Search Google Scholar
    • Export Citation
  • 7

    Chopra RKondziolka DNiranjan ALunsford LDFlickinger JC: Long-term follow-up of acoustic schwannoma radiosurgery with marginal tumor doses of 12 to 13 Gy. Int J Radiat Oncol Biol Phys 68:8458512007

    • Search Google Scholar
    • Export Citation
  • 8

    Colletti VBricolo AFiorino FGBruni L: Changes in directly recorded cochlear nerve compound action potentials during acoustic tumor surgery. Skull Base Surg 4:191994

    • Search Google Scholar
    • Export Citation
  • 9

    Colletti VFiorino F: Is the middle fossa approach the treatment of choice for intracanalicular vestibular schwannoma?. Otolaryngol Head Neck Surg 132:4594662005

    • Search Google Scholar
    • Export Citation
  • 10

    Colletti VFiorino FGCarner MTonoli G: Mechanisms of auditory impairment during acoustic neuroma surgery. Otolaryngol Head Neck Surg 117:5966051997

    • Search Google Scholar
    • Export Citation
  • 11

    Committee on Hearing and Equilibrium: Committee on Hearing and Equilibrium guidelines for the evaluation of hearing preservation in acoustic neuroma (vestibular schwannoma). Otolaryngol Head Neck Surg 113:1791801995

    • Search Google Scholar
    • Export Citation
  • 12

    Deen HGEbersold MJHarner SGBeatty CWMarion MSWharen RE: Conservative management of acoustic neuroma: an outcome study. Neurosurgery 39:2602661996

    • Search Google Scholar
    • Export Citation
  • 13

    DeMonte FGidley PW: Hearing preservation surgery for vestibular schwannoma: experience with the middle fossa approach. Neurosurg Focus 33:3E102012

    • Search Google Scholar
    • Export Citation
  • 14

    Foroughi MPitkäniemi JNannapaneni RNath F: Excision of vestibular schwannomas—is there a learning curve and how best to demonstrate it?. Br J Neurosurg 24:5475542010

    • Search Google Scholar
    • Export Citation
  • 15

    Franzin ASpatola GSerra CPicozzi PMedone MMilani D: Evaluation of hearing function after Gamma Knife surgery of vestibular schwannomas. Neurosurg Focus 27:6E32009

    • Search Google Scholar
    • Export Citation
  • 16

    Friedman RAKesser BBrackmann DEFisher LMSlattery WHHitselberger WE: Long-term hearing preservation after middle fossa removal of vestibular schwannoma. Otolaryngol Head Neck Surg 129:6606652003

    • Search Google Scholar
    • Export Citation
  • 17

    Gantz BJParnes LSHarker LAMcCabe BF: Middle cranial fossa acoustic neuroma excision: results and complications. Ann Otol Rhinol Laryngol 95:4544591986

    • Search Google Scholar
    • Export Citation
  • 18

    Gjurić MWigand MEWolf SR: Enlarged middle fossa vestibular schwannoma surgery: experience with 735 cases. Otol Neurotol 22:2232312001

    • Search Google Scholar
    • Export Citation
  • 19

    Hasegawa TKida YKato TIizuka HKuramitsu SYamamoto T: Long-term safety and efficacy of stereotactic radiosurgery for vestibular schwannomas: evaluation of 440 patients more than 10 years after treatment with Gamma Knife surgery. Clinical article. J Neurosurg 118:5575652013

    • Search Google Scholar
    • Export Citation
  • 20

    Hasegawa TKida YKato TIizuka HYamamoto T: Factors associated with hearing preservation after Gamma Knife surgery for vestibular schwannomas in patients who retain serviceable hearing. Clinical article. J Neurosurg 115:107810862011

    • Search Google Scholar
    • Export Citation
  • 21

    Hillman TChen DAArriaga MAQuigley M: Facial nerve function and hearing preservation acoustic tumor surgery: does the approach matter?. Otolaryngol Head Neck Surg 142:1151192010

    • Search Google Scholar
    • Export Citation
  • 22

    Irving RMJackler RKPitts LH: Hearing preservation in patients undergoing vestibular schwannoma surgery: comparison of middle fossa and retrosigmoid approaches. J Neurosurg 88:8408451998

    • Search Google Scholar
    • Export Citation
  • 23

    Kutz JW JrScoresby TIsaacson BMickey BEMadden CJBarnett SL: Hearing preservation using the middle fossa approach for the treatment of vestibular schwannoma. Neurosurgery 70:3343412012

    • Search Google Scholar
    • Export Citation
  • 24

    Magnan JBarbieri MMora RMurphy SMeller RBruzzo M: Retrosigmoid approach for small and medium-sized acoustic neuromas. Otol Neurotol 23:1411452002

    • Search Google Scholar
    • Export Citation
  • 25

    Mangham CA Jr: Retrosigmoid versus middle fossa surgery for small vestibular schwannomas. Laryngoscope 114:145514612004

  • 26

    Mazzoni AZanoletti ECalabrese V: Hearing preservation surgery in acoustic neuroma: long-term results. Acta Otorhinolaryngol Ital 32:981022012

    • Search Google Scholar
    • Export Citation
  • 27

    Meyer TACanty PAWilkinson EPHansen MRRubinstein JTGantz BJ: Small acoustic neuromas: surgical outcomes versus observation or radiation. Otol Neurotol 27:3803922006

    • Search Google Scholar
    • Export Citation
  • 28

    Moffat DAHardy DGGrey PLBaguley DM: The operative learning curve and its effect on facial nerve outcome in vestibular schwannoma surgery. Am J Otol 17:6436471996

    • Search Google Scholar
    • Export Citation
  • 29

    Mohr GSade BDufour JJRappaport JM: Preservation of hearing in patients undergoing microsurgery for vestibular schwannoma: degree of meatal filling. J Neurosurg 102:152005

    • Search Google Scholar
    • Export Citation
  • 30

    Murphy ESBarnett GHVogelbaum MANeyman GStevens GHCohen BH: Long-term outcomes of Gamma Knife radiosurgery in patients with vestibular schwannomas. Clinical article. J Neurosurg 114:4324402011. (Erratum in J Neurosurg 114: 560 2011)

    • Search Google Scholar
    • Export Citation
  • 31

    Niranjan AMathieu DFlickinger JCKondziolka DLunsford LD: Hearing preservation after intracanalicular vestibular schwannoma radiosurgery. Neurosurgery 63:105410632008

    • Search Google Scholar
    • Export Citation
  • 32

    Noudel RGomis PDuntze JMarnet DBazin ARoche PH: Hearing preservation and facial nerve function after microsurgery for intracanalicular vestibular schwannomas: comparison of middle fossa and retrosigmoid approaches. Acta Neurochir (Wien) 151:9359452009

    • Search Google Scholar
    • Export Citation
  • 33

    Pennings RJMorris DPClarke LAllen SWalling SBance ML: Natural history of hearing deterioration in intracanalicular vestibular schwannoma. Neurosurgery 68:68772011

    • Search Google Scholar
    • Export Citation
  • 34

    Roos DEPotter AEBrophy BP: Stereotactic radiosurgery for acoustic neuromas: what happens long term?. Int J Radiat Oncol Biol Phys 82:135213552012

    • Search Google Scholar
    • Export Citation
  • 35

    Rowe JGRadatz MWWalton LHampshire ASeaman SKemeny AA: Gamma knife stereotactic radiosurgery for unilateral acoustic neuromas. J Neurol Neurosurg Psychiatry 74:153615422003

    • Search Google Scholar
    • Export Citation
  • 36

    Sameshima TFukushima TMcElveen JT JrFriedman AH: Critical assessment of operative approaches for hearing preservation in small acoustic neuroma surgery: retrosigmoid vs middle fossa approach. Neurosurgery 67:6406452010

    • Search Google Scholar
    • Export Citation
  • 37

    Samii MGerganov VSamii A: Improved preservation of hearing and facial nerve function in vestibular schwannoma surgery via the retrosigmoid approach in a series of 200 patients. J Neurosurg 105:5275352006

    • Search Google Scholar
    • Export Citation
  • 38

    Samii MMatthies C: Management of 1000 vestibular schwannomas (acoustic neuromas): surgical management and results with an emphasis on complications and how to avoid them. Neurosurgery 40:11231997

    • Search Google Scholar
    • Export Citation
  • 39

    Sanna MKhrais TRusso APiccirillo EAugurio A: Hearing preservation surgery in vestibular schwannoma: the hidden truth. Ann Otol Rhinol Laryngol 113:1561632004

    • Search Google Scholar
    • Export Citation
  • 40

    Satar BJackler RKOghalai JPitts LHYates PD: Risk-benefit analysis of using the middle fossa approach for acoustic neuromas with >10 mm cerebellopontine angle component. Laryngoscope 112:150015062002

    • Search Google Scholar
    • Export Citation
  • 41

    Shelton CHitselberger WEHouse WFBrackmann DE: Hearing preservation after acoustic tumor removal: long-term results. Laryngoscope 100:1151191990

    • Search Google Scholar
    • Export Citation
  • 42

    Staecker HNadol JB JrOjeman RRonner SMcKenna MJ: Hearing preservation in acoustic neuroma surgery: middle fossa versus retrosigmoid approach. Am J Otol 21:3994042000

    • Search Google Scholar
    • Export Citation
  • 43

    Sughrue MEKane AJKaur RBarry JJRutkowski MJPitts LH: A prospective study of hearing preservation in untreated vestibular schwannomas. Clinical article. J Neurosurg 114:3813852011

    • Search Google Scholar
    • Export Citation
  • 44

    Sughrue MEYang IAranda DLobo KPitts LHCheung SW: The natural history of untreated sporadic vestibular schwannomas: a comprehensive review of hearing outcomes. Clinical article. J Neurosurg 112:1631672010

    • Search Google Scholar
    • Export Citation
  • 45

    Tamura MCarron RYomo SArkha YMuraciolle XPorcheron D: Hearing preservation after gamma knife radiosurgery for vestibular schwannomas presenting with high-level hearing. Neurosurgery 64:2892962009

    • Search Google Scholar
    • Export Citation
  • 46

    Wang AYWang JTDexter MDa Cruz M: The vestibular schwannoma surgery learning curve mapped by the cumulative summation test for learning curve. Otol Neurotol 34:146914752013

    • Search Google Scholar
    • Export Citation
  • 47

    Welling DBSlater PWThomas RDMcGregor JMGoodman JE: The learning curve in vestibular schwannoma surgery. Am J Otol 20:6446481999

    • Search Google Scholar
    • Export Citation
  • 48

    Whitmore RGUrban CChurch ERuckenstein MStein SCLee JYK: Decision analysis of treatment options for vestibular schwannoma. Clinical article. J Neurosurg 114:4004132011

    • Search Google Scholar
    • Export Citation
  • 49

    Woodson EADempewolf RDGubbels SPPorter ATOleson JJHansen MR: Long-term hearing preservation after microsurgical excision of vestibular schwannoma. Otol Neurotol 31:114411522010

    • Search Google Scholar
    • Export Citation
  • 50

    Yamakami IKobayashi EOno JYamaura A: Prevention of cerebrospinal fluid leakage and delayed loss of preserved hearing after vestibular schwannoma removal: reconstruction of the internal auditory canal in the suboccipital transmeatal approach—technical note. Neurol Med Chir (Tokyo) 40:5976012000

    • Search Google Scholar
    • Export Citation
  • 51

    Yamakami IOka NYamaura A: Intraoperative monitoring of cochlear nerve compound action potential in cerebellopontine angle tumour removal. J Clin Neurosci 10:5675702003

    • Search Google Scholar
    • Export Citation
  • 52

    Yamakami IUchino YKobayashi EYamaura A: Conservative management, gamma-knife radiosurgery, and microsurgery for acoustic neurinomas: a systematic review of outcome and risk of three therapeutic options. Neurol Res 25:6826902003

    • Search Google Scholar
    • Export Citation
  • 53

    Yamakami IUchino YKobayashi EYamaura AOka N: Removal of large acoustic neurinomas (vestibular schwannomas) by the retrosigmoid approach with no mortality and minimal morbidity. J Neurol Neurosurg Psychiatry 75:4534582004

    • Search Google Scholar
    • Export Citation
  • 54

    Yamakami IYoshinori HSaeki NWada MOka N: Hearing preservation and intraoperative auditory brainstem response and cochlear nerve compound action potential monitoring in the removal of small acoustic neurinoma via the retrosigmoid approach. J Neurol Neurosurg Psychiatry 80:2182272009

    • Search Google Scholar
    • Export Citation
  • 55

    Yomo SCarron RThomassin JMRoche PHRégis J: Longitudinal analysis of hearing before and after radiosurgery for vestibular schwannoma. Clinical article. J Neurosurg 117:8778852012

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    Yomo STamura MCarron RPorcheron DRégis J: A quantitative comparison of radiosurgical treatment parameters in vestibular schwannomas: the Leksell Gamma Knife Perfexion versus Model 4C. Acta Neurochir (Wien) 152:47552010

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