Long-Term Hearing Results in Gamma Knife Radiosurgery for Acoustic Neuromas

Early results with hypofractionated gamma knife radiotherapy for treatment of vestibular schwannoma

OBJECTIVE

Vestibular schwannoma (VS) management with stereotactic radiation previously only included stereotactic radiosurgery with Gamma Knife (GKRS) or LINAC-based radiotherapy (LBR). Hypofractionated Gamma Knife radiotherapy (hfGKRS) is a novel protocol potentially producing less toxicity than the alternatives. This study examines early results in tumor control, complications and hearing preservation outcomes in a consecutive series of VS patients treated with hfGKRS.

STUDY DESIGN

A retrospective review was conducted for all patients with unilateral VS treated with primary hfGKRS at an academic center between 2017 and 2023.

SETTING

Tertiary referral center.

INTERVENTIONS

Therapeutic.

MAIN OUTCOME MEASURES

Pre- and post-treatment imaging, notes and audiograms were analyzed. Tumor volumes were tabulated. Audiometric data recorded were pure-tone average (PTA), word recognition score (WRS), and speech reception threshold (SRT). Collected data included tinnitus, imbalance, House-Brackmann score, and facial spasms. Outcomes obtained were compared to literature controls of GKRS and LBR.

RESULTS

Twenty-five hfGKRS cases were identified. Mean tumor volume was 1.79 cm3 (range 0.14-9.29cm3). Mean patient follow-up was 28 months (range 6-86 months). Pre-treatment versus post-treatment hearing results were: PTA 62.9 dB versus 68.6 dB, WRS 40 % versus 30.8 % and SRT 33.1 dB versus 34.1 dB. The tumor control was 96 % and hearing was preserved in 80 % of patients with pre-treatment serviceable hearing. hfGKRS complications included tinnitus (12.5 %), dizziness (12.5 %), facial pain (8 %), and facial spasms (4 %).

CONCLUSION

Short term results for VS treated with hfGKRS had high rates of tumor control, favorable hearing results and comparable complication rates to literature reports for GKRS and LBR. Further follow-up is needed to adequately evaluate long-term outcomes of hfGKRS in tumor control, toxicity and hearing results in order to compare this technique with GKRS and LBR. However, these results support further evaluation of hfGKRS as a potential technique to improve outcomes in stereotactic radiation treatment of VS.

Schwannomas of Brain and Spinal Cord

Schwannomas are benign tumors originating from the Schwann cells of cranial or spinal nerves. The most common cranial schwannomas originate from the eight cranial nervevestibular schwannomas (VS). VS account for 6-8% of all intracranial tumors, 25-33% of the tumors localized in the posterior cranial fossa, and 80-94% of the tumors in the cerebellopontine angle (CPA). Schwannomas of other cranial nerves/trigeminal, facial, and schwannomas of the lower cranial nerves/are much less frequent. According to the World Health Organization (WHO), intracranial and intraspinal schwannomas are classified as Grade I. Some VS are found incidentally, but most present with hearing loss (95%), tinnitus (63%), disequilibrium (61%), or headache (32%). The neurological symptoms of VSs are mainly due to compression on the surrounding structures, such as the cranial nerves and vessels, or the brainstem. The gold standard for the imaging diagnosis of VS is MRI scan. The optimal management of VSs remains controversial. There are three main management options-conservative treatment or "watch-and-wait" policy, surgical treatment, and radiotherapy in all its variations. Currently, surgery of VS is not merely a life-saving procedure. The functional outcome of surgery and the quality of life become issues of major importance. The most appropriate surgical approach for each patient should be considered according to some criteria including indications, risk-benefit ratio, and prognosis of each patient. The approaches to the CPA and VS removal are generally divided in posterior and lateral. The retrosigmoid suboccipital approach is a safe and simple approach, and it is favored for VS surgery in most neurosurgical centers. Radiosurgery is becoming more and more available nowadays and is established as one of the main treatment modalities in VS management. Radiosurgery (SRS) is performed with either Gamma knife, Cyber knife, or linear accelerator. Larger tumors are being increasingly frequently managed with combined surgery and radiosurgery. The main goal of VS management is preservation of neurological function - facial nerve function, hearing, etc. The reported recurrence rate after microsurgical tumor removal is 0.5-5%. Postoperative follow-up imaging is essential to diagnose any recurrence.

Hearing Preservation After Intervention in Vestibular Schwannoma

OBJECTIVE

This study aimed to assess the durability of audiological outcomes after radiation and surgery in the management of vestibular schwannoma.

STUDY DESIGN

Retrospective review.

SETTING

Tertiary academic center.

PATIENTS

Adults with sporadic vestibular schwannoma and serviceable hearing at the time of intervention.

INTERVENTIONS

Gamma Knife, middle cranial fossa, or retrosigmoid approaches.

MAIN OUTCOME MEASURES

Pure-tone audiometry and speech discrimination scores.

RESULTS

Postintervention serviceable hearing (class A/B) was preserved in 70.4% (n = 130; mean follow-up, 3.31 yr; range, 0-15.25 yr). Of the 49 patients treated with radiation, 19 (39.6%) had serviceable hearing at last follow-up, compared with 38 (46.9% of 81) who underwent retrosigmoid (n = 36 [44.4%]) and middle cranial fossa (n = 45 [55.6%]) approaches (odds ratio [OR], 1.40; 95% confidence interval [CI], 0.67-2.82; p = 0.47). A matched analysis by age, tumor volume, and preintervention hearing (n = 38) also found no difference in hearing preservation (HP) likelihood between surgery and radiation (OR, 2.33; 95% CI, 0.24-35.91; p = 0.59). After initial HP, 4 (9.5%) surgical versus 10 (37.0%) radiated patients subsequently lost residual serviceable (A/B) hearing (OR, 0.18; 95% CI, 0.06-0.69; p = 0.01) at a mean 3.74 ± 3.58 and 4.73 ± 3.83 years after surgery and radiation, respectively. Overall, 5- and 10-year HP rates (A/B) after initially successful HP surgery were 84.4 and 63.0%, respectively. However, survival estimates declined to 48.9% at 5 years and 32.7% at 10 years when patients with immediate postoperative serviceable hearing loss were also included, which were comparable to radiation-HP rates at 5 and 10 years of 28.0 and 14.2%, respectively ( p = 0.75).

CONCLUSIONS

After vestibular schwannoma intervention, overall HP was similar between radiated and surgical cohorts. However, when successful, surgical approaches offered more durable hearing outcomes at long-term follow-up.

Systematic Review of Hearing Preservation After Radiotherapy for Vestibular Schwannoma

OBJECTIVE

To determine the long-term hearing preservation rate for spontaneous vestibular schwannoma treated by primary radiotherapy.

DATA SOURCES

The MEDLINE/PubMed, Web of Science, Cochrane Reviews, and EMBASE databases were searched using a comprehensive Boolean keyword search developed in conjunction with a scientific librarian. English language papers published from 2000 to 2016 were evaluated.

STUDY SELECTION

Inclusion criteria: full articles, pretreatment and posttreatment audiograms or audiogram based scoring system, vestibular schwannoma only tumor type, reported time to follow-up, published after 1999, use of either Gamma Knife or linear accelerator radiotherapy.

EXCLUSION CRITERIA

case report or series with fewer than five cases, inadequate audiometric data, inadequate time to follow-up, neurofibromatosis type 2 exceeding 10% of study population, previous treatment exceeding 10% of study population, repeat datasets, use of proton beam therapy, and non-English language.

DATA EXTRACTION

Two reviewers independently analyzed papers for inclusion. Class A/B, 1/2 hearing was defined as either pure tone average less than or equal to 50 db with speech discrimination score more than or equal to 50%, American Academy of Otolaryngology-Head & Neck Surgery (AAO-HNS) Hearing Class A or B, or Gardner-Robertson Grade I or II. Aggregate data were used when individual data were not specified.

DATA SYNTHESIS

Means were compared with student t test.

CONCLUSIONS

Forty seven articles containing a total of 2,195 patients with preserved Class A/B, 1/2 hearing were identified for analysis. The aggregate crude hearing preservation rate was 58% at an average reporting time of 46.6 months after radiotherapy treatment. Analysis of time-based reporting shows a clear trend of decreased hearing preservation extending to 10-year follow-up. This data encourages a future long-term controlled trial.

Stereotactic radiosurgery planning of vestibular schwannomas: Is MRI at 3 Tesla geometrically accurate?

Purpose

MRI is a mandatory requirement to accurately plan Stereotactic Radiosurgery (SRS) for Vestibular Schwannomas. However, MRI may be distorted due not only to inhomogeneity of the static magnetic field and gradients but also due to susceptibility‐induced effects, which are more prominent at higher magnetic fields. We assess geometrical distortions around air spaces and consider MRI protocol requirements for SRS planning at 3 T.

Methods

Hardware‐related distortion and the effect of incorrect shimming were investigated with structured test objects. The magnetic field was mapped over the head on five volunteers to assess susceptibility‐related distortion in the naso‐oro‐pharyngeal cavities (NOPC) and around the internal ear canal (IAC).

Results

Hardware‐related geometric displacements were found to be less than 0.45 mm within the head volume, after distortion correction. Shimming errors can lead to displacements of up to 4 mm, but errors of this magnitude are unlikely to arise in practice. Susceptibility‐related field inhomogeneity was under 3.4 ppm, 2.8 ppm, and 2.7 ppm for the head, NOPC region and IAC region, respectively. For the SRS planning protocol (890 Hz/pixel, approximately 1 mm³ isotropic), susceptibility‐related displacements were less than 0.5 mm (head), and 0.4 mm (IAC and NOPC). Large displacements are possible in MRI examinations undertaken with lower receiver bandwidth values, commonly used in clinical MRI. Higher receiver bandwidth makes the protocol less vulnerable to sub‐optimal shimming. The shimming volume and the CT‐MR co‐registration must be considered jointly.

Conclusion

Geometric displacements can be kept under 1 mm in the vicinity of air spaces within the head at 3 T with appropriate setting of the receiver bandwidth, correct shimming and employing distortion correction.

Comparison of 3 ABR Methods for Diagnosis of Retrocochlear Hearing Impairment

BACKGROUND The purpose of this study was to compare the effectiveness of methods for screening for retrocochlear pathologies based on auditory evoked brainstem responses (ABRs). The study compared the sensitivity, specificity, and effectiveness of these 3 techniques. MATERIAL AND METHODS The methods were: (i) standard ABR utilizing click-evoked responses, (ii) stacked ABR based on derived-band responses, and (iii) ABRs evoked by tone-pips (ABR TP). The methods were tested on patients with retrocochlear pathologies confirmed by MRI-Gd, normal-hearing subjects, and patients with cochlear hearing loss. The system and software used in the tests was NavPro AEP v.6.2.0 (BioLogic - Natus). Prior to testing, all subjects were given comprehensive audiologic and otologic examinations, including MR imaging. Sensitivity and specificity functions and predictive values of methods were determined. RESULTS The stacked ABR method as realized in the NavPro system exhibited high sensitivity but specificity was very low, due to the high variability of stacked ABR amplitudes. The standard ABR method had good specificity, but low sensitivity in cases of small tumors (below 1 cm in diameter). Best sensitivity and specificity was obtained with the ABR TP method. CONCLUSIONS The stacked ABR method allows small acoustic tumors to be detected, but produces high percentage of false positive results. The ABR TP method offers good sensitivity and specificity, and relatively high predictive value. The best option would be to use a two-stage screening, consisting of a standard ABR in the first stage and an ABR TP test in the second.

Factors associated with symptom-specific psychological and functional impact among acoustic neuroma patients

INTRODUCTION

The main purpose of this study was to investigate the psychological and functional impact attributed to acoustic neuroma symptoms.

MATERIALS AND METHODS

A sample of 207 acoustic neuroma patients completed a study-specific questionnaire about the severity, frequency, and psychological and functional impact of 9 acoustic neuroma symptoms.

RESULTS

The survey response rate was 56.4 per cent. All symptoms had some degree of psychological impact for the majority of participants; hearing loss was the symptom most often reported to have a severe psychological impact. The majority of respondents reported functional impact attributed to hearing loss, balance disturbance, dizziness, eye problems, headache and fatigue; balance disturbance was the symptom most often reported to have a severe functional impact. For most symptoms, psychological and functional impact were related to severity and frequency.

CONCLUSION

Of the acoustic neuroma symptoms investigated, hearing loss and balance disturbance were the most likely to have a severe psychological and functional impact, respectively.

Microsurgery versus stereotactic radiation for small vestibular schwannomas: a meta-analysis of patients with more than 5 years' follow-up

OBJECTIVE

To compare the long-term outcome of hearing and tumor outcome of small vestibular schwannomas treated with stereotactic radiation and microsurgery.

DATA SOURCES

A thorough search for English-language publications and "in process" articles dating from 1948 to December 2011 was conducted using Ovid MEDLINE.

STUDY SELECTION

The principal criteria were patients having had microsurgery or radiation therapy as their sole treatment, with a follow-up of at least 5 years, and a useful hearing level at diagnosis.

DATA EXTRACTION

Sixteen studies met our criteria. Hearing preservation outcome (worse or preserved) and tumor outcome (failure, control) data, as well as all other significant observations, were collected from the articles. Stereotactic radiation was the only radiation therapy analyzed.

DATA SYNTHESIS

The Pearson χ test was our primary statistical analysis.

CONCLUSION

Stereotactic radiation showed significantly better long-term hearing preservation outcome rates than microsurgery (p < 0.001). However, long-term tumor outcome was not significantly different in stereotactic radiation as compared with microsurgery (p = 0.122). Although stereotactic radiation demonstrates a more favorable long-term hearing preservation outcome as compared with microsurgery, additional studies are required to provide the medical field with a better understanding of vestibular schwannoma treatment.

Longitudinal analysis of hearing before and after radiosurgery for vestibular schwannoma

OBJECT

The aim of this study was to perform an accurate analysis of changes in hearing in patients with vestibular schwannoma (VS) who have undergone Gamma Knife surgery (GKS) and distinguish the impact of radiosurgery from the natural course of hearing deterioration due to the tumor itself.

METHODS

This study was a retrospective review of prospectively collected patient data. A group of 154 patients with unilateral nonsurgically treated VS was conservatively monitored for more than 6 months and then treated with GKS between July 1997 and September 2005. They were followed up with serial clinical examination, MRI, and audiometry. The annual hearing decrease rate (AHDR) was measured before and after radiosurgery, and the possible prognostic factors for hearing preservation were investigated.

RESULTS

The mean dose prescribed to the tumor margins was 12.1 Gy. The mean radiological follow-up period after GKS was 60 months (range 7-123 months). The tumor control rate was 94.8%, and 8 patients underwent subsequent intervention due to tumor progression. The mean audiological follow-up times before and after GKS were 22 and 52 months, respectively. The mean AHDRs before and after GKS were 5.39 dB/year (95% CI 3.31-7.47 dB/year) and 3.77 dB/year (95% CI 3.13-4.40 dB/year), respectively (p > 0.05). The mean pre- and post-GKS AHDRs in patients who initially had Gardner-Robertson (GR) Class I hearing were -0.57 dB/year (95% CI -2.95 to 1.81 dB/year) and 3.59 dB/year (95% CI 2.52-4.65 dB/year), respectively (p = 0.007). The mean pre- and post-GKS AHDRs in patients who initially had GR Class II hearing were 5.09 dB/year (95% CI 1.36-8.82 dB/year) and 4.98 dB/year (95% CI 3.86-6.10 dB/year), respectively (p > 0.05). A subgroup of 80 patients had both early and late post-intervention AHDR assessment (with early referring to the period from GKS to the assessment closest to the 2-year follow-up point and late referring to the period from that assessment to the most recent one); in these patients, the mean early post-GKS AHDR was 5.86 dB/year (95% CI 4.25-7.50 dB/year) and the mean late post-GKS AHDR was 1.86 dB/year (95% CI 0.77-2.96 dB/year) (p < 0.001). A maximum cochlear dose of less than 4 Gy was found to be the sole prognostic factor for hearing preservation.

CONCLUSIONS

The present study demonstrated the absence of an increase in AHDR after radiosurgery as compared with the preoperative AHDR. There was even a trend indicating a reduction in the annual hearing loss after radiosurgery over the long term. To fully elucidate a possible protective effect of radiosurgery, longer-term follow-up with a larger group of patients will be required.

Hearing Preservation Using the Middle Fossa Approach for the Treatment of Vestibular Schwannoma

BACKGROUND:

The incidence of small vestibular schwannomas in patients with serviceable hearing is increasing because of the widespread use of MRI. The middle fossa approach provides the patient with an opportunity for tumor removal with hearing preservation.

OBJECTIVE:

To determine the rate of hearing preservation and facial nerve outcomes after removal of a vestibular schwannoma with the use of the middle fossa approach.

METHODS:

A retrospective case review at a tertiary, academic medical center was performed identifying patients from 1998 through 2008 that underwent removal of a vestibular schwannoma by the middle fossa approach. Preoperative and postoperative audiograms were compared to determine hearing preservation rates. In addition, facial nerve outcomes at last follow-up were recorded.

RESULTS:

Forty-six patients underwent a middle fossa craniotomy for the removal of a vestibular schwannoma. Of the 38 patients that had class A or class B hearing preoperatively, 24 (63.2%) retained class A or B hearing and 29 (76.3%) retained class A, B, or C hearing. When tumors were 10 mm or less in patients with class A or B preoperative hearing, 22 of 30 patients (73.3%) retained class A or B hearing. When the tumor size was greater than 10 mm in patients with class A or B preoperative hearing, 2 of 8 patients (25%) retained class A or B hearing. At most recent follow-up, 76.1% of patients had House-Brackmann grade I facial function, 13.0% had House-Brackmann grade II facial function, and 10.9% had House-Brackmann grade III facial function.

CONCLUSION:

Hearing preservation rates are excellent using the middle fossa approach, especially for smaller tumors. No patient experienced long-term facial nerve function worse than House-Brackmann grade III.

Management of patients with acoustic neuromas: a Markov decision analysis

OBJECTIVES/HYPOTHESIS

The management of patients with small (<1.5 cm) acoustic neuromas is controversial. Immediate treatment via microsurgical resection or radiosurgery is often advocated. A period of observation is sometimes advised followed by microsurgery or radiosurgery for tumors that demonstrate growth during the observation period. The purpose of this study is to calculate quality-adjusted life expectancy for the most commonly applied management strategies in hypothetical cohorts of patients of various ages.

STUDY DESIGN

Markov decision analysis; societal perspective.

METHODS

Assumptions used in creating this model and event probabilities were obtained from a thorough literature review. Key parameters were identified and defined by the best available evidence. The main outcome measure is the benefit derived from each management strategy in quality-adjusted life years (QALYs). Sensitivity analysis was used to define benchmark performance information for these parameters.

RESULTS

The benefit of a period of observation followed by radiosurgery, if needed, for significant tumor growth is greater then all other strategies for all age groups and both sexes. When compared to observation followed by microsurgery, the additional benefit is small. QALY totals for the two immediate treatment groups were significantly lower than that for the observation groups.

CONCLUSIONS

For patients of all ages, a period of observation during which tumor growth and hearing thresholds are closely monitored is the superior strategy. For tumors that grow substantially or when hearing deteriorates, definitive management via radiosurgery is recommended.

Vestibular schwannoma: surgery or gamma knife radiosurgery? A prospective, nonrandomized study

OBJECTIVE

To conduct a prospective, open, nonrandomized study of treatment-associated morbidity in patients undergoing microsurgery or gamma knife radiosurgery (GKRS) for vestibular schwannomas.

METHODS

Ninety-one patients with vestibular schwannomas with a maximum tumor diameter of 25 mm in the cerebellopontine angle were treated according to a prospective protocol either by GKRS (63 patients) or open microsurgery (28 patients) using the suboccipital approach. Primary end points included hearing function, according to the Gardner-Robertson scale, and facial nerve function, according to the House-Brackmann scale at 2 years. Clinical data included a balance platform test, score for tinnitus and vertigo using a visual analog scale, and working ability. Patients responded to the quality-of-life questionnaires Short-Form 36 and Glasgow Benefit Inventory.

RESULTS

Three elderly GKRS patients withdrew; all remaining patients were followed for 2 years. Both primary end points were highly significant in favor of GKRS (P < 0.001). Evidence of reduced facial nerve function (House-Brackmann grade 2 or poorer) at 2 years was found in 13 of 28 open microsurgery patients and 1 of 60 GKRS patients. Thirteen of 28 patients who underwent surgery had serviceable hearing (Gardner-Robertson grade A or B) preoperatively, but none had serviceable hearing postoperatively. Twenty-five of 60 GKRS patients had serviceable hearing before treatment, and 17 (68%) of them had serviceable hearing 2 years after treatment. The tinnitus and vertigo visual analog scale score, as well as balance platform tests, did not change significantly after treatment, and working status did not differ between the groups at 2 years. Quality of life was significantly better in the GKRS group at 2 years, based on the Glasgow Benefit Inventory questionnaire. One GKRS patient required operative treatment within the 2-year study period.

CONCLUSION

This is the second prospective study to demonstrate better facial nerve and hearing outcomes from GKRS than from open surgery for small- and medium-sized vestibular schwannomas.