Risk factors for neurological complications after acoustic neurinoma radiosurgery: refinement from further experiences

The behavior of residual tumors following incomplete surgical resection for vestibular schwannomas

The management of vestibular schwannoma (VS) with residual tumor following incomplete resection remains controversial and little is known regarding postoperative tumor volume changes. The behavior of residual tumors was analyzed for 111 patients who underwent surgery for newly diagnosed VS between September 2006 and July 2017. The postoperative tumor volume changes were assessed during a mean follow-up of 69 months (range 36–147 months). Fifty-three patients underwent imaging surveillance following incomplete resection. There was no residual tumor growth in 44 patients (83%). A significant regression of residual tumor volume was noted in the no growth group at postoperative 1 year (p = 0.028), 2 years (p = 0.012), but not from 3 years onwards. Significant predictors of regrowth were immediate postoperative tumor volume ≥ 0.7 cm³ (HR 10.5, p = 0.020) and residual tumor location other than the internal auditory canal (IAC) (HR 6.2, p = 0.026). The mean time to regrowth was 33 months (range 5–127 months). The 2-, 5-, and 10-year regrowth-free survival rates were 90.6%, 86.8%, and 83%, respectively. In conclusion, significant residual tumor regression could occur within 2 years for a VS with an immediate postoperative tumor volume less than 0.7 cm³ or residual tumor in IAC.

Outcomes of large vestibular schwannomas following subtotal resection: early post-operative volume regression and facial nerve function

INTRODUCTION

Subtotal resection (STR) of vestibular schwannoma (VS) tumors remains controversial and little is known regarding post-operative volume changes.

METHODS

Authors retrospective reviewed the medical records from January 1st 2002 to January 1st 2018, for all patients who had undergone primary STR of large VS at a single tertiary academic institution.

RESULTS

Our series consists of 34 patients with a mean age of 53.9 (median 53; range 21-87) years that had STR of their VS tumor. The mean pre-operative tumor diameter and volume was 3.9 cm (median 3.0 cm; range 1.6-6.0 cm) and 11.7 cm³ (median 9.6 cm³; range 2.8-44.3 cm³), respectively, with a mean extent of resection of 86% (median 90%; range 53-99%). The mean radiographic and clinical follow-up was 40 months (range 6-120 months) and 51 months (range 7-141 months), respectively. 85% of patients had optimal House-Brackmann (HB) scores (Grade 1 & 2) immediately post-operatively, and 91% at 1 year; 94% of patients had normal (HB 1) at last follow-up. There was significant regression of residual tumor volume at 1 year (p = 0.006) and 2 years (p = 0.02), but not at 3 years (p = 0.08), when compared to the prior year. There was significant regression of size over time, with a mean slope estimate of - 0.70 units per year (p < 0.001).

CONCLUSION

Excellent clinical facial nerve outcomes can be obtained with STR of large VS tumors. Maximal reduction in tumor size occurs at 2-year post-operatively. Thus, in patients undergoing surgery for large VS, STR and a "watch and wait" strategy is a reasonable treatment option that may optimize facial nerve outcomes.

Short-Term Surgical Outcome for Vestibular Schwannoma in Sweden: A Nation-Wide Registry Study

Background: Vestibular Schwannoma (VS) is a benign neoplasm arising from the 8th cranial nerve, with surgery one of the treatment modalities. In a nation-wide registry study, we describe the baseline, treatment characteristics, and short-term outcome in patients surgically treated for VS.

Methods: We performed a nationwide study with data from the Swedish Brain Tumor Registry (SBTR) for all adults diagnosed with VS 2009–2015. Patient symptoms, tumor characteristics, and postoperative complications were analyzed.

Results: In total 348 patients underwent surgery for VS. Mean age was 50.6 ± 14.5 years and 165 patients (47.4%) were female. The most common symptom was focal neurological deficit (92.0%), with only 25 (7.2%) being asymptomatic prior to surgery, and 217 (63.6%) had no restriction in activity. Following surgery, 100 (28.7%) patients developed new deficit(s). In terms of postoperative complications; 11 (3.2%) had a hematoma, 35 (10.1%) an infection, 10 (2.9%) a venous thromboembolism, and 23 (6.6%) had a reoperation due to complication. There were no deaths within 30-days after surgery. When grouped according to tumor size (< 4 vs. ≥4 cm), those with ≥4 cm tumors were more often males (p = 0.02), had more often ICP related symptoms (p = 0.03) and shorter time from imaging to surgery (p < 0.01). Analysis of the younger (< 65 years) vs. elderly (≥65 years) revealed no difference in outcome except increased 1-year mortality (p = 0.002) in elderly.

Conclusion: In this nation-wide registry-study, we benchmark the 30-day complication rate after VS surgery as collected by the SBTR. Further, we present the current neurosurgical outcome data from both VS smaller than 40 mm compared to larger tumors, as well as younger vs. elderly VS patients. Since surgical decision making is a careful consideration of short term risk vs. long term benefit, this information can be useful in clinical decision making.

Predictors of Trigeminal Neuropathy After Radiosurgery for Vestibular Schwannomas

PURPOSE

To analyze the relationship between dosimetric characteristics and symptoms related to trigeminal neuropathy (TN) observed after radiosurgery (RS) for vestibular schwannomas (VS); to propose guidelines to optimize planification in VS RS regarding TN preservation; and to detail the mechanism of TN impairment after VS RS.

METHODS AND MATERIALS

One hundred seventy-nine patients treated between 2011 and 2013 for VS RS and without trigeminal impairment before RS were included in a retrospective study. Univariate and multivariate analyses were performed to determine predictors of TN among characteristics of the patients, the dosimetry, and the VS.

RESULTS

There were 20 Koos grade 1, 99 grade 2, 57 grade 3, and 3 grade 4. Fourteen patients (7.8%) presented a transitory or permanent TN. Between the patients with and without TN after VS RS, there was no significant difference regarding dosimetry or VS volume itself. Significant differences (univariate analysis P<.05, Mann-Whitney test) were found for parameters related to the cisternal portion of the trigeminal nerve: total integrated dose, maximum dose, mean dose, volume of the Vth nerve (Volv), and volume of the Vth nerve receiving at least 11 Gy (VolVcist>11Gy), but also for maximal dose to the Vth nerve nucleus and intra-axial portion (Dose maxVax). After multivariate analysis, the best model predicting TN included VolVcist>11Gy (P=.0045), Dose maxVax (P=.0006), and Volv (P=.0058). The negative predictive value of this model was 97%.

CONCLUSIONS

The parameters VolVcist>11Gy, Dose maxVax, and Volv should be checked when designing dosimetry for VS RS.

Multisession Radiosurgery for Hearing Preservation

Clinically relevant dose-tolerance limits with reliable estimates of risk in 1-5 fractions for cochlea are still unknown. Timmerman׳s limits from the October 2008 issue of Seminars in Radiation Oncology have served as the basis for clinical practice, augmented by updated constraints in TG-101 and QUANTEC, but the corresponding estimates of risk have not yet been well-reported. A total of 37 acoustic neuroma CyberKnife cases from Medstar Georgetown University Hospital treated in 3 or 5 fractions were combined with single-fraction Gamma Knife data from the 69 cases in Timmer 2009 to form an aggregate dataset of 106 cochlea cases treated in 1-5 fractions. Probit dose-response modeling was performed in the DVH Evaluator software to estimate normal tissue complication probability. QUANTEC recommends keeping single-fraction maximum dose to the cochlea less than 14Gy to maintain less than 25% risk of serviceable hearing loss, and our 17.9% risk estimate for 14Gy in 1 fraction is within their predicted range. In 5 fractions, our estimate of the Timmerman 27.5Gy maximum cochlea dose limit was 17.4%. For cases in which lower risk is required, the Timmerman 12Gy in 1 fraction and the TG-101 limit of 25Gy in 5 fractions had an estimated risk level of 11.8% and 13.8%, respectively. High-risk and low-risk dose tolerance with risk estimates in 1-5 fractions are all presented.

Communicating Hydrocephalus Associated with Intracranial Schwannoma Treated by Gamma Knife Radiosurgery

OBJECTIVE

Gamma knife radiosurgery (GKRS) has been established as an effective and safe treatment for intracranial schwannoma. However, serious complications can occur after GKRS, including hydrocephalus. The pathophysiology and risk factors of this disorder are not yet fully understood. The objective of the study was to assess potential risk factors for hydrocephalus after GKRS.

METHODS

We retrospectively reviewed the medical radiosurgical records of 244 patients who underwent GKRS to treat intracranial schwannoma. The following parameters were analyzed as potential risk factors for hydrocephalus after GKRS: age, sex, target volume, irradiation dose, prior tumor resection, treatment technique, and tumor enhancement pattern. The tumor enhancement pattern was divided into 2 groups: group A (homogeneous enhancement) and group B (heterogeneous or rim enhancement).

RESULTS

Of the 244 patients, 14 of them (5.7%) developed communicating hydrocephalus. Communicating hydrocephalus occurred within 2 years after GKRS in most patients (92.8%). No significant association was observed between any of the parameters investigated and the development of hydrocephalus, with the exception of tumor enhancement pattern. Group B exhibited a statistically significant difference by univariate analysis (P = 0.002); this difference was also significant by multivariate analysis (P = 0.006).

CONCLUSION

Because hydrocephalus is curable, patients should be closely monitored for the development of this disorder after GKRS. In particular, patients with intracranial schwannomas with irregular enhancement patterns or cysts should be meticulously observed.

Results for local control and functional outcome after linac-based image-guided stereotactic radiosurgery in 190 patients with vestibular schwannoma

BACKGROUND

We assessed local control (LC) and functional outcome after linac-based stereotactic radiosurgery (SRS) for vestibular schwannoma (VS).

METHODS

Between 1998 and 2008, 190 patients with VS were treated with SRS. All patients had tumors <2 cm diameter. Patients received 13.5 Gy prescribed to the 80th isodose at the tumor margin. The primary endpoint was LC. Secondary endpoints were symptomatic control and morbidity.

RESULTS

Median follow-up was 40 months. LC was achieved in 88% of patients. There were no acute reactions exceeding Grade I. Trigeminal nerve dysfunction was present in 21.6% (n = 41) prior to SRS. After treatment, 85% (n = 155) had no change, 4.4,% (n = 8) had a relief of symptoms, 10.4% (n = 19) had new symptoms. Facial nerve dysfunction was present in some patients prior to treatment, e.g. paresis (12.6%; n = 24) and dysgeusia (0.5%; n = 1). After treatment 1.1% (n = 2) reported improvement and 6.1% (n = 11) experienced new symptoms. Hearing problems before SRS were present in 69.5% of patients (n = 132). After treatment, 62.6% (n = 144) had no change, 10.4% (n = 19) experienced improvement and 26.9% (n = 49) became hearing impaired.

CONCLUSION

This series of SRS for small VS provided similar LC rates to microsurgery; thus, it is effective as a non-invasive, image-guided procedure. The functional outcomes observed indicate the safety and effectiveness of linac-based SRS. Patients may now be informed of the clinical equivalence of SRS to microsurgery.

Stereotactic radiosurgery and hypofractionated stereotactic radiotherapy for management of vestibular schwannomas: initial experience with 17 cases

BACKGROUND

Nowadays radiation treatment of patients with vestibular schwannomas (VSs) applied either as stereotactic radiosurgery (SRS) or stereotactic radiotherapy (SRT) represents a real alternative to surgical tumor resection.

METHODS

During 2010-2011, 17 consecutive patients (19-75 years old) with a VS underwent treatment with SRS or SRT in our center. Microsurgery was initially offered in all cases but was declined for various reasons. Five lesions recurred after the initial partial resection. Two other patients with neurofibromatosis type 2 underwent initial surgery for a large tumor on the contralateral side and had the only hearing ear on the side of the remaining neoplasm. Three elderly persons had somatic problems that were too severe for them to undergo craniotomy. Five small tumors without brain stem compression underwent single-fraction SRS (12.0-12.5 Gy at the 80 % isodose line). Other patients, mainly with large neoplasms that caused brain stem compression, were treated with hypofractionated SRT (five or six daily fractions at a dose of 4.5-5.0 Gy each). Treatment was performed with a dedicated linear accelerator (Elekta Axesse). Various stereotactic fixation devices were used: Leksell G frame, noninvasive HeadFIX frame, reinforced thermoplastic masks.

RESULTS

No adverse reactions or complications were seen in any case. Within 3 months after treatment three tumors demonstrated shrinkage accompanied by improvement of the neurological functions.

CONCLUSION

Radiation treatment, particularly hypofractionated SRT, can be safely applied even for large VSs that cause brain stem compression and are accompanied by prominent neurological symptoms.

Management of large vestibular schwannoma. Part I. Planned subtotal resection followed by Gamma Knife surgery: radiological and clinical aspects

OBJECT

In large vestibular schwannoma (VS), microsurgery is the main treatment option, and complete resection is considered the primary goal. However, previous studies have documented suboptimal facial nerve outcomes in patients who undergo complete resection of large VSs. Subtotal resection is likely to reduce the risk of facial nerve injury but increases the risk of lesion regrowth. Gamma Knife surgery (GKS) can be performed to achieve long-term growth control of residual VS after incomplete resection. In this study the authors report on the results in patients treated using planned subtotal resection followed by GKS with special attention to volumetric growth, control rate, and symptoms.

METHODS

Fifty consecutive patients who underwent the combined treatment strategy of subtotal microsurgical removal and GKS for large VSs between 2002 and 2009 were retrospectively analyzed. Patients with neurofibromatosis Type 2 were excluded. Patient charts were reviewed for clinical symptoms. Audiograms were evaluated to classify hearing pre- and postoperatively. Preoperative and follow-up contrast-enhanced T1-weighted MR images were analyzed using volume-measuring software.

RESULTS

Surgery was performed via a translabyrinthine (25 patients) or retrosigmoid (25 patients) approach. The median follow-up was 33.8 months. Clinical control was achieved in 92% of the cases and radiological control in 90%. One year after radiosurgery, facial nerve function was good (House-Brackmann Grade I or II) in 94% of the patients. One of the two patients who underwent surgery to preserve hearing maintained serviceable hearing after resection followed by GKS.

CONCLUSIONS

Considering the good tumor growth control and facial nerve function preservation as well as the possibility of preserving serviceable hearing and the low number of complications, subtotal resection followed by GKS can be the treatment option of choice for large VSs.

Management of large vestibular schwannoma. Part II. Primary Gamma Knife surgery: radiological and clinical aspects

OBJECT

In large vestibular schwannomas (VSs), microsurgery is the main treatment option. A wait-and-scan policy or radiosurgery are generally not recommended given concerns of further lesion growth or increased mass effect due to transient swelling. Note, however, that some patients do not present with symptomatic mass effect or may still have serviceable hearing. Moreover, others may be old, suffer from severe comorbidity, or refuse any surgery. In this study the authors report the results in patients with large, growing VSs primarily treated with Gamma Knife surgery (GKS), with special attention to volumetric growth, control rate, and symptoms.

METHODS

The authors retrospectively analyzed 33 consecutive patients who underwent GKS for large, growing VSs, which were defined as > 6 cm(3) and at least indenting the brainstem. Patients with neurofibromatosis Type 2 were excluded from analysis, as were patients who had undergone previous treatment. Volume measurements were performed on contrast-enhanced T1-weighted MR images at the time of GKS and during follow-up. Medical charts were analyzed for clinical symptoms.

RESULTS

Radiological growth control was achieved in 88% of cases, clinical control (that is, no need for further treatment) in 79% of cases. The median follow-up was 30 months, and the mean VS volume was 8.8 cm(3) (range 6.1-17.7 cm(3)). No major complications occurred, although ventriculoperitoneal shunts were placed in 2 patients. The preservation of serviceable hearing and facial and trigeminal nerve function was achieved in 58%, 91%, and 86% of patients, respectively, with any facial and trigeminal neuropathy being transient. In 92% of the patients presenting with trigeminal hypesthesia before GKS, the condition resolved during follow-up. No patient- or VS-related feature was correlated with growth.

CONCLUSIONS

Primary GKS for large VSs leads to acceptable radiological growth rates and clinical control rates, with the chance of hearing preservation. Although a higher incidence of clinical control failure and postradiosurgical morbidity is noted, as compared with that for smaller VSs, primary radiosurgery is suitable for a selected group of patients. The absence of symptomatology due to mass effect on the brainstem or cerebellum is essential, as are close clinical and radiological follow-ups, because there is little reserve for growth or swelling.

Treatment of large and giant residual and recurrent vestibular schwannomas

This report is a retrospective analysis of the surgical outcome of 15 patients (8 females, 7 males; mean age, 37.8 years) with residual or recurrent vestibular schwannomas operated on between 1987 and 2005. These 15 patients were part of a larger series of 252 consecutive vestibular schwannoma excisions. Tumors were classified as large (10) when their diameter exceeded 3.5 cm and giant (5) when their diameter exceeded 4.5 cm. All patients had previously undergone surgery. Hearing was lost in all cases, 8 had complete facial nerve palsy, 6 had trigeminal nerve deficits, 5 had cranial nerve IX and X palsy, and 10 had ataxic gait. Twelve patients had hydrocephalus. The tumors were reoperated through the retrosigmoid-transmeatal approach. The mean postoperative follow-up was 4.9 years. Complete resection was achieved in all patients. The facial nerve was preserved in 6 of the 7 patients with preoperative facial function. Transient worsening of bulbar cranial nerves palsy occurred in 2 cases. Cerebrospinal fluid leakage occurred in 3 patients. There were no deaths, and the tumors were histologically benign. Surgical removal is the only treatment for these lesions. Total resection associated with a low morbidity rate is possible. Preservation of the facial nerve is difficult due to severe scar tissue.

Numbness matters: a clinical review of trigeminal neuropathy

AIM

Trigeminal neuropathies are a group of clinical disorders that involve injury to primary first-order neurons within the trigeminal nerve. We review the spectrum of etiologies underlying both painful and non-painful trigeminal neuropathies, with attention to particularly dangerous processes that may elude the clinician in the absence of a meticulous evaluation. Complications and management issues specific to patients with trigeminal neuropathy are discussed.

METHODS

Retrospective literature review.

RESULTS

Facial or intraoral numbness, the hallmark of trigeminal neuropathy, may represent the earliest symptomology of malignancy or autoimmune connective tissue disease as sensory neurons are destroyed. Such numbness, especially if progressive, necessitates periodic evaluation and vigilance even years after presentation if no diagnosis can be made.

CONCLUSIONS

In the routine evaluation of patients with facial pain, the clinician will inevitably be confronted with secondary pathology of the trigeminal nerves and nuclei. The appearance of numbness, even when pain continues to be the most pressing complaint, necessitates clinical assessment of the integrity of all aspects of the trigeminal pathways, which may also include neurophysiologic, radiographic, and laboratory evaluation.

Clinical outcome after hypofractionated stereotactic radiotherapy (HSRT) for benign skull base tumors

OBJECTIVE

Surgical resection of skull base tumors can be associated with significant morbidity. In cases where the risks outweigh the benefits, radiation therapy can offer an alternative means to effectively control tumor growth. However, the optimal dose regime for radiation therapy remains controversial. The objective of this study was to assess the neurological outcome, local control rate and morbidity associated with a 5-fraction regime of hypofractionated stereotactic radiotherapy (HSRT) for benign skull base tumors.

METHODS

Twenty-six patients presenting with two of the most prevalent benign skull base tumors were included in the study. The tumors comprised 16 meningiomas and 10 acoustic neuromas. All patients exhibited preserved cranial nerve function prior to treatment, and a detailed audiological assessment was performed pre- and post-treatment for those patients with acoustic neuroma. Stereotactic radiosurgery was administered with the frameless CyberKnife Robotic Radiosurgery System. In each case, a 5-fraction HSRT regime was used: a dose of 5 Gy × 5 = 25 Gy to 6 Gy × 5 = 30 Gy was prescribed for skull base meningiomas, and 5 Gy × 5 = 25 Gy was prescribed for acoustic neuromas.

RESULTS

The clinical and radiographic median follow-up was 22 months (range: 6-54 months). Radiological assessment showed local control in all 26 tumors (100%), and in 5/26 patients (20%) the tumor showed a decrease in size. Cranial nerve function was preserved in all cases thus far studied; however, 28% of patients had transient Grade II side effects, including fatigue, headaches, unsteadiness and transient subjective worsening of hearing. In two of these patients, the period of transient worsening of hearing was associated with a temporary increase in the size of the tumor on control T2 MR images, consistent with radiation-induced edema. One patient had transient decrease in visual acuity from treatment-related edema. At the last follow-up, 3/16 patients with meningiomas (19%) and 2/10 with acoustic neuromas (20%) showed a decrease in tumor volume and improvement in hearing.

CONCLUSION

A 5-fraction stereotactic radiotherapy regime, as used in this study, seems to be effective for local control of benign skull base tumors in this early follow-up evaluation. Neurological function preservation is excellent with this short regime in the early post-treatment period, but long-term follow-up is crucial for validation.

Stereotactic radiation therapy for large vestibular schwannomas

BACKGROUND AND PURPOSE

To evaluate the morbidity and tumor-control rate in the treatment of large vestibular schwannomas (VS) after stereotactic radiation therapy in our institution.

MATERIAL AND METHODS

Twenty-five consecutive patients (17 men, 8 women) with large VS (diameter 3.0 cm or larger), treated with stereotactic radiotherapy (SRT) or stereotactic radiosurgery (SRS) between 1992 and 2007, were retrospectively studied after a mean follow-up period of three years with respect to tumor-control rate and complications.

RESULTS

Actuarial 5-year maintenance of pre-treatment hearing level probability of 30% was achieved. Five of 17 patients suffered permanent new facial nerve dysfunction. The actuarial 5-year facial nerve preservation probability was 80%. Permanent new trigeminal nerve neuropathy occurred in two of 15 patients, resulting in an actuarial 5-year trigeminal nerve preservation probability of 85%. Tumor progression occurred in four of 25 (16%) patients. The overall 5-year tumor control probability was 82%.

CONCLUSION

Increased morbidity rates were found in patients with large VS treated with SRT or SRS compared to the published series on regular sized VS and other smaller retrospective studies on large VS.

A comprehensive analysis of hearing preservation after radiosurgery for vestibular schwannoma

Object

Gamma Knife surgery (GKS) has evolved into a practical alternative to open microsurgical resection in the treatment of patients with vestibular schwannoma (VS). Hearing preservation rates in GKS series suggest very favorable outcomes without the possible acute morbidity associated with open microsurgery. To mitigate institutional and practitioner bias, the authors performed an analytical review of the published literature on the GKS treatment of vestibular schwannoma patients. Their aim was to objectively characterize the prognostic factors that contribute to hearing preservation after GKS, as well as methodically summarize the reported literature describing hearing preservation after GKS for VS.

Methods

A comprehensive search of the English-language literature revealed a total of 254 published studies reporting assessable and quantifiable outcome data obtained in patients who underwent radiosurgery for VSs. Inclusion criteria for articles were 4-fold: 1) hearing preservation rates reported specifically for VS; 2) hearing status reported using the American Association of Otolaryngology–Head and Neck Surgery (AAO-HNS) or Gardner-Robertson classification; 3) documentation of initial tumor size; and 4) GKS was the only radiosurgical modality in the treatment. In the analysis only patients with AAO-HNS Class A or B or Gardner-Robertson Grade I or II status at the last follow-up visit were defined as having preserved hearing. Hearing preservation and outcome data were then aggregated and analyzed based on the radiation dose, tumor volume, and patient age.

Results

The 45 articles that met the authors' inclusion criteria represented 4234 patients in whom an overall hearing preservation rate was 51%, irrespective of radiation dose, patient age, or tumor volume. Practitioners who delivered an average ≤ 13-Gy dose of radiation reported a higher hearing preservation rate (60.5% at ≤ 13 Gy vs 50.4% at > 13 Gy; p = 0.0005). Patients with smaller tumors (average tumor volume ≤ 1.5 cm3) had a hearing preservation rate (62%) comparable with patients harboring larger tumors (61%) (p = 0.8968). Age was not a significant prognostic factor for hearing preservation rates as in older patients there was a trend toward improved hearing preservation rates (56% at < 65 years vs 71% at ≥ 65 years of age; p < 0.1134). The average overall follow-up in the studies reviewed was 44.4 ± 32 months (median 35 months).

Conclusions

These data provide a methodical overview of the literature regarding hearing preservation with GKS for VS and a less biased assessment of outcomes than single-institution studies. This objective analysis provides insight into advising patients of hearing preservation rates for GKS treatment of VSs that have been reported, as aggregated in the published literature. Analysis of the data suggests that an overall hearing preservation rate of ~ 51% can be expected approaching 3–4 years after radiosurgical treatment, and the analysis reveals that patients treated with ≤ 13 Gy were more likely to have preserved hearing than patients receiving larger doses of radiation. Furthermore, larger tumors and older patients do not appear to be at any increased risk for hearing loss after GKS for VS than younger patients or patients with smaller tumors.

Non-audiofacial morbidity after Gamma Knife surgery for vestibular schwannoma

OBJECT

While many studies have been published outlining morbidity following radiosurgical treatment of vestibular schwannomas, significant interpractitioner and institutional variability still exists. For this reason, the authors conducted a systematic review of the literature for non-audiofacial-related morbidity after the treatment of vestibular schwannoma with radiosurgery.

METHODS

The authors performed a comprehensive search of the English-language literature to identify studies that published outcome data of patients undergoing radiosurgery treatment for vestibular schwannomas. In total, 254 articles were found that described more than 50,000 patients and were analyzed for satisfying the authors' inclusion criteria. Patients from these studies were then separated into 2 cohorts based on the marginal dose of radiation: < or = 13 Gy and > 13 Gy. All tumors included in this study were < 25 mm in their largest diameter.

RESULTS

A total of 63 articles met the criteria of the established search protocol, which combined for a total of 5631 patients. Patients receiving > 13 Gy were significantly more likely to develop trigeminal nerve neuropathy than those receiving < 13 Gy (p < 0.001). While we found no relationship between radiation dose and the rate of developing hydrocephalus (0.6% for both cohorts), patients with hydrocephalus who received doses > 13 Gy appeared to have a higher rate of symptomatic hydrocephalus requiring shunt treatment (96% [> 13 Gy] vs 56% [< or = 13 Gy], p < 0.001). The rates of vertigo or balance disturbance (1.1% [> 13 Gy] vs 1.8% [< or = 13 Gy], p = 0.001) and tinnitus (0.1% [> 13 Gy] vs 0.7% [< or = 13 Gy], p = 0.001) were significantly higher in the lower dose cohort than those in the higher dose cohort.

CONCLUSIONS

The results of our review of the literature provide a systematic summary of the published rates of nonaudiofacial morbidity following radiosurgery for vestibular schwannoma.

Optimal dose of stereotactic radiosurgery for acoustic neuromas: a systematic review

Radiosurgery is increasingly employed in the treatment of acoustic neuroma, but the optimal dose in terms of long-term tumour control and minimal adverse effects has not been established. We performed a systematic review of the published literature of radiosurgery of acoustic neuroma to assess whether the use of low dose radiosurgery is as effective as high dose treatment. Reports of radiosurgery for acoustic neuroma were identified through a Medline search. Studies with at least 15 patients and a median follow-up longer than 12 months were included. The relationship between actuarial 5-year progression-free survival (PFS), and tumour and treatment parameters was examined. Forty-two studies were included. Tumour control following lower radiosurgery doses was similar to that reported following high doses. Only 12 studies reported actuarial outcomes at 5 years. There was no relationship between PFS at 5 years and dose to the tumour margin. Radiosurgery of larger tumours was associated with lower 5 year PFS (p < 0.05). Although on initial inspection radiosurgery of acoustic neuroma with doses of 12 - 13 Gy seems to be as effective as higher dose treatment, the available reports are subject to a number of confounding factors, are not sufficiently statistically powered and there is only limited long-term actuarial outcome data. Currently, available studies do not provide sufficient confidence to support the claim that low dose radiosurgery is equally effective as higher doses in the long-term control of acoustic neuroma.

Neurological complications after acoustic neurinoma radiosurgery: revised risk factors based on long-term follow-up

CONCLUSIONS

The precise risk factors for neurological complications after acoustic neurinoma radiosurgery were identified on long-term follow-up. Type 2 neurofibromatosis was found to be a risk factor for hearing loss and peripheral tumor dose was a risk factor for seventh and fifth cranial nerve injuries. These risk factors corresponded to those reported at other institutions. At the present time, controversy exists regarding history of prior surgical resection and tumor size as risk factors for cranial nerve complications.

OBJECTIVES

To identify more precisely the risk factors for neurological complications after stereotactic radiosurgery (SRS) based on long-term follow-up.

PATIENTS AND METHODS

Between June 1990 and September 1998, 138 patients with acoustic neurinomas had SRS at Tokyo University Hospital. Of these, the 125 patients who were followed up for at least 6 months were entered into the present study. The patients' ages ranged from 13 to 77 years (median 53 years). The average tumor diameter ranged from 6.7 to 25.4 mm (mean 13.9 mm). The maximum tumor doses ranged from 20 to 40 Gy (mean 29.8 Gy), and the peripheral doses ranged from 12 to 25 Gy (mean 15.4 Gy). One to 12 isocenters were used (median 4). The follow-up period ranged from 6 to 191 months (median 60 months). The potential risk factors for neurological complications were analyzed using two univariate actuarial analyses. The neurological complications studied included hearing loss, facial palsy, and trigeminal nerve dysfunction. The variables analyzed were age, gender, prior operation, neurofibromatosis type 2 (NF2), tumor diameter, maximum tumor dose, peripheral tumor irradiation dose, and the number of isocenters. Variables with significant p values (<0.05) on both actuarial analyses were considered risk factors.

RESULTS

NF2 was significantly correlated with both total hearing loss and pure tone threshold (PTA) elevation; a history of prior surgical resection, tumor size, and the peripheral tumor dose were significantly correlated with facial palsy; and the peripheral tumor dose was significantly correlated with trigeminal neuropathy.

Long-term follow-up reveals low toxicity of radiosurgery for vestibular schwannoma

AIM

The long-term effects of radiosurgery of vestibular schwannomas were investigated in a group of consecutively treated patients.

METHODS AND MATERIALS

Between 1995 and 2001, 26 patients (median age: 67, range: 30-82) with a vestibular schwannoma were treated by Linac-based stereotactic radiosurgery (SRS). The median follow-up was 49 months (16-85 months). Only progressive tumours were treated. The median size of tumours was 18 mm (range 9-30 mm). Before SRS, 11 patients had a useful hearing (Gardner-Robertson classes 1 and 2). Single doses of 10-14 Gy were prescribed at the 80% isodose at the tumour margin. The follow-up consisted of regular imaging with MRI the first 3-6 months after the intervention, followed by additional yearly MRIs, a hearing test and a neurological examination.

RESULT

The 5-year-probability of tumour control (defined as stabilization or decrease in size) was 95%. Five-year-probability of preservation of hearing and facial nerve function was 96% and 100%, respectively. Hearing was preserved in 10 out of 11 patients who had a normal or useful hearing at the time of treatment. Mild and transient trigeminal toxicity occurred in 2 (8%) patients. It appeared to be significantly correlated to the dose used (p=0.044). However, only a tendency to significance could be demonstrated in the relationship between the two factors when using the Cox analysis (hazard ratio=1.7; 95% CI: 0.7-3.9; p=0.23).

CONCLUSIONS

With the doses used, our study demonstrates that SRS provides an equivalent tumour control rate when compared to surgery, as well as on a long-term basis, an excellent preservation of the facial and the acoustic nerves. Although no permanent trigeminal toxicity was observed, our data confirm that doses below 14 Gy can avoid transient dysesthesias.

Long-term outcome of stereotactic radiosurgery (SRS) in patients with acoustic neuromas

PURPOSE

To evaluate the effectiveness and long-term outcome of stereotactic radiosurgery (SRS) for acoustic neuromas (AN).

PATIENTS AND METHODS

Between 1990 and 2001, we treated 26 patients with 27 AN with SRS. Two patients suffered from neurofibromatosis type 2. Before SRS, a subtotal or total resection had been performed in 3 and in 5 patients, respectively. For SRS, a median single dose of 13 Gy/80% isodose was applied.

RESULTS

The overall actuarial 5-year and 10-year tumor control probability in all patients was 91%. Two patients developed tumor progression after SRS at 36 and 48 months. Nineteen patients (73%) were at risk of treatment-related facial nerve toxicity; of these, 1 patient developed a complete facial nerve palsy after SRS (5%). A total of 93% of the lesions treated were at risk of radiation-induced trigeminal neuralgia. Two patients (8%) developed mild dysesthesia of the trigeminal nerve after SRS. The hearing preservation rate in patients with useful hearing before SRS was 55% at 9 years.

CONCLUSION

Stereotactic radiosurgery results in good local control rates of AN and the risk of cranial nerve toxicities is acceptable. As toxicity is lower with fractionated stereotactic radiotherapy, SRS should be reserved for smaller lesions.

Low-dose radiosurgery for large vestibular schwannomas: long-term results of functional preservation

Object.The author conducted a study to assess the long-term results obtained in patients who underwent GKS for large vestibular schwannomas (> cochlear nerve functions were evaluated.

Methods.Twenty consecutive large tumors in 18 patients (including two cases of neurofibromatosus Type 2 [NF2]) were followed for more than 6 years. There were eight tumors that were more than 4 cm in maximum diameter. Microsurgery had already been performed prior to GKS in 11 patients (nine recurrent and two residual tumors).

Four patients (including one with NF2) died during the follow-up period of other diseases or by accident. Fourteen of 15 tumors were stable or decreased in size. Microsurgery was performed in one patient 2 years after radiosurgery. Facial nerve function was preserved in all patients and hearing preserved in four of five patients with cochlear nerve function prior to radiosurgery. No adverse effects of radiosurgery have been observed to date.

Conclusions.Gamma knife surgery seems to have a place in the low-dose treatment of selected large vestibular schwannoma in patients with a reasonable chance of retaining facial function and pretreatment hearing level. Patients with severe brainstem compression should first be undergo microsurgery.

Low-dose radiosurgery for large vestibular schwannomas: long-term results of functional preservation

Object. The author conducted a study to assess the long-term results obtained in patients who underwent GKS for large vestibular schwannomas (> cochlear nerve functions were evaluated.

Methods. Twenty consecutive large tumors in 18 patients (including two cases of neurofibromatosus Type 2 [NF2]) were followed for more than 6 years. There were eight tumors that were more than 4 cm in maximum diameter. Microsurgery had already been performed prior to GKS in 11 patients (nine recurrent and two residual tumors).

Four patients (including one with NF2) died during the follow-up period of other diseases or by accident. Fourteen of 15 tumors were stable or decreased in size. Microsurgery was performed in one patient 2 years after radiosurgery. Facial nerve function was preserved in all patients and hearing preserved in four of five patients with cochlear nerve function prior to radiosurgery. No adverse effects of radiosurgery have been observed to date.

Conclusions. Gamma knife surgery seems to have a place in the low-dose treatment of selected large vestibular schwannoma in patients with a reasonable chance of retaining facial function and pretreatment hearing level. Patients with severe brainstem compression should first be undergo microsurgery.

Gamma knife stereotactic radiosurgery for unilateral acoustic neuromas

OBJECTIVE

To evaluate the clinical results achievable using current techniques of gamma knife stereotactic radiosurgery to treat sporadic unilateral acoustic neuromas.

METHODS

A retrospective review of 234 consecutive patients treated for unilateral acoustic neuromas between 1996 and 1999, with a mean (SD) follow up of 35 (16) months. Tumour control was assessed with serial radiological imaging and by the need for surgical intervention. Hearing preservation was assessed using Gardner-Robertson grades. Details of complications including cranial neuropathies and non-specific vestibulo-cochlear symptoms are included.

RESULTS

A tumour control rate in excess of 92% was achieved, with only 3% of patients undergoing surgery after radiosurgery. Results were less good for larger tumours, but control rates of 75% were achieved for 35-45 mm diameter lesions. Of patients with discernible hearing, Gardner-Robertson grades were unchanged in 75%. Facial nerve function was adversely affected in 4.5%, but fewer than 1% of patients had persistent weakness. Trigeminal symptoms improved in 3%, but developed in 5% of patients, being persistent in less than 1.5%. Transient non-specific vestibulo-cochlear symptoms were reported by 13% of patients.

CONCLUSIONS

Tumour control rates, while difficult to define, are comparable after radiosurgery with those experienced after surgery. The complications and morbidity after radiosurgery are far less frequent than those encountered after surgery. This, combined with its minimally invasive nature, may make radiosurgery increasingly the treatment of choice for small and medium sized acoustic neuromas.

Radiotherapy-induced ear toxicity

Despite their particular functional consequences, radiotherapy-induced ear injuries remain under-evaluated and under-reported. These reactions may have acute or late character, may affect all structures of the hearing organ, and result in conductive, sensorineural or mixed hearing loss. Up to 40% of patients have acute middle ear side effects during radical irradiation including acoustic structures and about one-third of patients develop late sensorineural hearing loss (SNHL). Total radiotherapy dose and tumour site seem to be among the most important factors associated with the risk of hearing impairment. Thus, reduction in radiation dose to the auditory structures should be attempted whenever possible. New radiotherapy techniques (3-dimensional conformal irradiation, intensity modulated radiotherapy, proton therapy) allow better dose distribution with lower dose to the non-target organs. Treatment of acute and late external otitis is mainly conservative and includes the anti-inflammatory agents (applied topically and systematically). Post-radiation chronic otitis media and the eustachian tube pathology may be managed with tympanic membrane incision with insertion of a tympanostomy tube (grommet), although the benefit of such approach is controversial and some authors advocate a more conservative approach. In these patients the functional deficit can be alleviated by application of bone conduction hearing aids such as, e.g., the bone anchored hearing aid (BAHA). There is no standard therapy for post-irradiation sudden or progressive SNHL yet corticosteroid therapy, rheologic medications, hyperbaric oxygen or carbogen therapy are usually employed (as for idiopathic SNHL), although controversial data on the efficacy of these treatment modalities have been published. In selected cases with bilateral profound hearing loss or total deafness, cochlear implants may prove effective. Further improvements in radiotherapy techniques and progress in otologic diagnostics and therapy may allow better prevention and management of radiation-related acoustic injury.

Radiosurgery for acoustic neuromas: results of low-dose treatment

OBJECTIVE

The results of radiosurgical treatment of acoustic neuromas have improved by reducing the tumor marginal doses. We report relatively long-term follow-up results (>5 yr) for patients who underwent low-dose radiosurgery.

METHODS

We treated and followed 51 consecutive patients with unilateral acoustic neuromas who were treated from January 1994 to December 1996 by gamma knife radiosurgery at low doses (</=12 Gy to the tumor margin). The average age of the patients was 55 years (range, 32-76 yr). The treatment volume was 0.7 to 24.9 cm(3) (median, 3.6 cm(3)). The marginal radiation dose was 8 to 12 Gy (median, 12 Gy), and the follow-up period ranged from 18 to 96 months (median, 60 mo).

RESULTS

Clinical tumor growth control (without tumor resection) was achieved in 96% of patients, and the 5-year tumor growth control rate was 92%. Hearing was preserved in 59% of those with preradiosurgical hearing preservation (Gardner-Robertson Classes 1-4), and improvements (>20 dB of improvement) were noted in 9% of the patients with any hearing. Hearing was preserved at a useful level (Gardner-Robertson Classes 1 and 2) in 56% of patients. Although preexisting trigeminal neuropathy worsened in 4% of the patients, our patients did not experience new facial palsies or trigeminal neuropathies after radiosurgery. Facial spasm occurred in 6% of the patients, and intratumoral bleeding occurred in 4% of patients.

CONCLUSION

Low-dose radiosurgery (</=12 Gy at the tumor margin) can achieve a high tumor growth control rate and maintain low postradiosurgical morbidity (including hearing preservation) for acoustic neuromas.

Gamma knife model C with the automatic positioning system and its impact on the treatment of vestibular schwannomas

Object. The aim of this study was to assess the effects of the gamma knife automatic positioning system (APS) on the treatment of patients, particularly effects of this system on the treatment of patients with vestibular schwannomas (VSs), with a view to reducing loss of hearing.

Methods. The dose delivery with an increased number of shots was checked with GAFChromic Film for various numbers of shots (one to 129). The results in the first 549 patients were recorded. In addition a series of 59 patients with VSs treated with 13 Gy to the 65% isodose is presented. The authors have termed this the “13 on 65” concept.

The film dosimetry showed that a large number of small shots did not materially affect the dose and dose distribution produced by gamma knife treatment.

The APS was used alone in 72% of arteriovenous malformations, 71% of meningiomas, 94% of VSs, and 84% of pituitary adenomas. Metastatic tumors were accessible in a pure APS mode in 59% of all cases, glioma in 58%, and uveal melanoma in 10% of the cases. Thus two thirds of patients could be treated using APS alone. It was possible to use the APS and manual systems together for complex or very eccentrically placed targets. The APS resulted in the use of a larger number of isocenters.

After a mean follow-up period of 15 months, the results in patients with the VSs in whom 13 Gy was delivered to the 65% isodose were similar to those in patients treated with the more conventional 50% margin isodose. There was no change in the incidence of hearing loss within the study period, and the incidence of trigeminal and facial neuropathies remained unchanged after treatment as well.

Conclusions. The APS encourages the design of more conformal dose plans. The greater use of smaller collimators results in a steeper dose gradient with a smaller amount of radiation outside the target volume. Because the APS is able to apply a large number of smaller isocenters in an acceptable time, the number of isocenters used is increased. An increased number of isocenters can also be used to reduce the maximum radiation dose and increase the homogeneity in a given dose plan.

Stereotactic radiosurgery of acoustic tumors

Stereotactic radiotherapy has an inherent disadvantage in that it does not directly reduce tumor volume. In this increasing environment of cost-containment, however, this modality offers several advantages (see box). Some investigators believe that, over the next generation, stereotactic radiotherapy will be the mainstay of vestibular schwannoma care, with microsurgery being the exception and being reserved for patients needing urgent decompression and for very young patients [12]. Increasing numbers of patients are undergoing stereotactic radiotherapy as a matter of preference following the provision of sufficient information on the two treatment procedures. When counseling younger patients, it is important to remember that no long-term data about the control rate for stereotactic radiotherapy with the most recent, lower doses are available. Also, surgical salvage, which is necessary in some patients, produces a poor outcome following radiation therapy. Published reports have demonstrated similar facial nerve, hearing preservation, and tumor control rates in the short term only [32,33]. Data is insufficient to assess the risk for inducing a secondary, treatment-related malignancy. Until long-term results are available, stereotactic radiotherapy should be reserved for medically infirm patients, elderly patients, patients with contralateral deafness or bilateral tumors, and patients who have failed prior microsurgery. Radiotherapy is not the preferred primary treatment modality for vestibular schwannoma based on currently published results.

Hearing restoration with auditory brainstem implants after radiosurgery for neurofibromatosis type 2

The auditory brainstem implant (ABI) is designed to restore useful auditory sensations in patients with neurofibromatosis Type 2 (NF2). The implantation is usually performed at the time of tumor removal in patients who do not undergo radiation treatment. The authors evaluated the performance of ABIs in three patients with NF2 in whom vestibular schwannoma continued to grow after radiation treatment. These three patients with NF2 received a 21-channel ABI; a translabyrinthine approach was used for both the tumor removal and the ABI placement. The interval between radiosurgery and the tumor removal plus device implantation ranged from 2 to 11 years. In all cases, the tumor was growing and the patients presented with total deafness. The mean number of active electrodes in these three patients was equivalent to the average results reported in other patients who received ABIs. The patients in this study used the ABI regularly for everyday life and obtained useful levels of environmental sound recognition. It is concluded that hearing function can be rehabilitated using ABIs in patients with NF2, even if radiosurgery fails to control the tumor growth.

Reduced-dose radiosurgery for vestibular schwannomas

OBJECTIVE

To evaluate tumor control and complications associated with low-dose radiosurgery for vestibular schwannomas.

METHODS

Between December 1993 and January 2000, 47 patients with vestibular schwannomas were treated at our center with gamma knife radiosurgery. The marginal tumor doses ranged from 7.5 to 14.0 Gy (median, 12.0 Gy) for patients treated after microsurgery and from 10.0 to 15.0 Gy (median, 12.0 Gy) for patients in whom radiosurgery was the primary treatment. The median maximum tumor diameter was 18 mm (range, 3-50 mm). Evaluation included audiometry, neurological examination, and serial imaging tests. A survey was conducted at the time of analysis.

RESULTS

Follow-up data were available for 45 patients and ranged from 1 to 7 years (median, 3.6 yr). In 43 patients (96%), tumor control (no radiographic progression or surgical resection) was observed. All 33 previously untreated patients had tumor control. Transient facial weakness, experienced in two patients (4%), had resolved completely within 6 months. No patient developed trigeminal neuropathy. Hearing was diminished from baseline in 12% of patients with useful hearing (Gardner-Robertson Class III). However, all patients with pretreatment hearing Gardner-Robertson Class I or II maintained testable hearing (Class I to III) at the most recent examination.

CONCLUSION

Low-dose radiosurgery in this series provided comparable local control and decreased incidences of complications in relation to other reports. Additional follow-up will allow more definitive conclusions to be reached regarding the ultimate rates of tumor control and hearing preservation. Nevertheless, the current dose used for vestibular schwannomas at the University of Maryland Medical Center is 12.0 Gy to the tumor periphery.

Medication for hearing loss after fractionated stereotactic radiotherapy (SRT) for vestibular schwannoma

PURPOSE

To investigate the effectiveness of corticosteroid treatments for patients showing decreases in hearing levels after stereotactic radiotherapy for vestibular schwannoma.

METHODS AND MATERIALS

Twenty-one patients experienced a hearing loss in pure-tone average at greater than 20 dB or less than 10 dB within 1 year after irradiation administration of 44 Gy/22 fractions followed by a 4 Gy boost. Eight received oral prednisone at a daily dose of 30 mg, which was gradually decreased (medicated group), and 13 received none (nonmedicated group). The average observation period was 26.7 +/- 16.6 (range: 6--69) months.

RESULTS

Hearing recovery was seen after initial onset of the hearing loss in all 8 patients in the medicated group and in 2 of 13 patients in the nonmedicated group (p = 0.001). The hearing recovery, that is, the change in pure-tone average (dB) at the last follow-up from the onset of hearing loss, was 9.8 +/- 6.9 dB (recovery) in the medicated group and -9.4 +/- 12.8 dB (further loss) in the nonmedicated group (p = 0.0013). The hearing recovery rate, normalizing to the degree of the hearing loss before medication, was also significantly higher in the medicated group than in the nonmedicated group (p = 0.0014).

CONCLUSIONS

Corticosteroidal intake is suggested to be effective in improving hearing loss after stereotactic radiotherapy, at least in young patients having a useful pretreatment hearing level, if the treatment for hearing loss is administered immediately after the hearing loss is first detected.