Long-term outcomes after radiosurgery for acoustic neuromas

Suggested response criteria for phase II antitumor drug studies for neurofibromatosis type 2 related vestibular schwannoma

Neurofibromatosis type 2 (NF2) is a tumor suppressor gene syndrome characterized by multiple schwannomas, especially vestibular schwannomas (VS), and meningiomas. Anticancer drug trials are now being explored, but there are no standardized endpoints in NF2. We review the challenges of NF2 clinical trials and suggest possible response criteria for use in initial phase II studies. We suggest two main response criteria in such trials. Objective radiographic response is defined as a durable 20% or greater reduction in VS volume based on post-contrast T1-weighted MRI images collected with 3 mm or finer cuts through the internal auditory canal. Hearing response is defined as a statistically significant improvement in word recognition scores using 50-word recorded lists in audiology. A possible composite endpoint incorporating both radiographic response and hearing response is outlined. We emphasize pitfalls in response assessment and suggest guidelines to minimize misinterpretations of response. We also identify research goals in NF2 to facilitate future trial conduct, such as identifying the expectations for time to tumor progression and time to measurable hearing loss in untreated NF2-related VS, and the relation of both endpoints to patient prognostic factors (such as age, baseline tumor volume, and measures of disease severity). These data would facilitate future use of endpoints based on stability of tumor size and hearing, which might be more appropriate for testing certain drugs. We encourage adoption of standardized endpoints early in the development of phase II trials for this population to facilitate comparison of results across trials of different agents.

Conservative management of 386 cases of unilateral vestibular schwannoma: tumor growth and consequences for treatment

Object

The object of this study was to evaluate the natural history, pattern, and occurrence of tumor growth and its consequences for treatment of small-sized vestibular schwannomas (VSs).

Methods

From 1990 to 2005, 386 patients underwent conservative management for VS because of the following: age > 60 years, poor health/medical risks, risk of deterioration of good hearing, small tumor size, minimal or no incapacitating symptoms, and/or patient preference. Tumor size was measured by MR imaging according to the guidelines of the Committee on Hearing and Equilibrium. The first MR imaging study was performed 1 year after diagnosis, and subsequent imaging was performed yearly or every 2 years depending on the appearance of new symptoms, tumor growth, or both.

Results

Sixty-one patients were lost to follow-up the first year after presentation. Of the 325 patients for whom 1-year follow-up data were available, 39 showed tumor growth ≥ 3 mm. Conservative management was discontinued for these 39 patients. The patients who returned for follow-up were evaluated at 1- or 2-year intervals depending on tumor growth. The authors extrapolated to obtain data for 2-year intervals, yielding data for 160, 56, 21, and 8 patients at 3, 5, 7, and 9 years after initial presentation, respectively. The overall mean tumor growth rate (±standard deviation) was 1.15 ± 2.4 mm/year. This rate was estimated by pooling all values of tumor growth that had been determined for all patients and dividing by the total number of “events,” with each assessment constituting an event. In 58.6% of patients, the annual tumor growth rate was < 1 mm/year; in 29.2%, 1–3 mm/year; and in 12.2%, ≥ 3 mm/ year. The growth rates of intrameatal (1.02 ± 1.8 mm/year) and extrameatal (1.40 ± 3.1 mm/year) tumors did not differ significantly. No significant association was found between tumor growth rate and sex, age, initial hearing status, or initial tumor grade. Delay in diagnosis was the only significant factor associated with tumor growth rate. During follow-up, conservative management was discontinued for 77 (23.7%) of the 325 patients for whom at least 12-month follow-up data were available; surgery was performed in 60 (77.9%) and radiation therapy in 17 (22.1%).

Conclusions

The results of this study support the role of a conservative “wait-and-scan” policy of management for small-sized VSs because most have a slow growth rate. Long-term neuroimaging follow-up is needed even with non-growing tumors.

Evolution of techniques for the resection of vestibular schwannomas: from saving life to saving function

The current state of surgery for vestibular schwannomas (VSs) is the result of a century of step-by-step technical progress by groundbreaking surgeons who transformed the procedure from its hazardous infancy and high mortality rate to its current state of safety and low morbidity rate. Harvey Cushing advocated bilateral suboccipital decompression and developed the method of intracapsular tumor enucleation. Walter Dandy supported the unilateral suboccipital approach and developed the technique of gross-total tumor resection. Microsurgical techniques revolutionized VS surgery to its current status. In this article, the authors review the early history of surgery for VSs with an emphasis on contributions from pioneering surgeons. The authors examined the Cushing Brain Tumor Registry for clues regarding the bona fide intention of Cushing for the resection of these tumors.

Control of growth of vestibular schwannomas with low-dose Gamma Knife surgery

OBJECT

The treatment of solitary vestibular schwannomas by performing Gamma Knife surgery is well established. It has been reported that decreasing the surface dose reduces patient morbidity, especially facial weakness and numbness. The authors of this retrospective study examine patient data from a single center to determine if low-dose (< or = 14 Gy) GKS controls tumor growth as effectively as higher doses (> 14 Gy).

METHODS

Based on the formula for ellipsoid volumes, the tumor volumes were calculated using measurements from MR images obtained at follow up in patients treated at the authors' center. Follow-up data were available in 159 patients with a mean age of 59.5 +/- 14.2 years at treatment. Fifty-six percent of the patients were women and 53.5% of the tumors were located on the right side of the brain. The mean tumor volume was 3.3 +/- 4.3 cm3 with 10% of the tumors having volumes larger than 8 cm3. After GKS, smaller tumors (> or = 40% decrease in volume) were observed in 44.8% of patients treated with a low dose and in 48.8% treated with a high dose. Enlarged tumors (> or = 40% increase in volume) were seen in 5.2% of the patients receiving a low dose and 2.3% of those receiving a high dose. These differences were not statistically significant. Patients who had been followed up for longer than 5 years after treatment had median residual volumes of only 28.2% of the starting volume in the low-dose group and 26% in the high-dose group. This difference was statistically not significant.

CONCLUSIONS

No statistically significant differences were observed between tumors given low-dose radiation treatment and those given high-dose radiation treatment.

Repeated treatment of vestibular schwannomas after gamma knife radiosurgery

PURPOSE

When gamma knife radiosurgery (GKS) does not achieve control of the growth of a tumour, the need to repeat treatment is considered. The results and risks of repeat treatment of patients with a vestibular schwannoma were reviewed to assess its efficacy and safety.

METHODS

Between 1992 and 2001, we treated 351 patients with a vestibular schwannoma by GKS, control of the growth of the tumour was not achieved in 32. 26 patients underwntrepeat GKS and five patients had an open microsurgical operation and one stereotactic aspiration of a tumour cyst.

RESULTS

Twenty-four of 26 patients were followed up after the repeat GKS for a median of 43 months. 15 tumours became smaller, seven remained unchanged and two enlarged. After the second GKS one patient's hearing deteriorated, one developed facial weakness and three facial spasms. One patient required insertion of ventriculo-peritoneal drainage. An operation to radically resect the tumour was performed in five patients after the first GKS and for a subtotal removal in one after repeated GKS.

CONCLUSIONS

In the small proportion of patients (9%) in whom initial GKS does not control the growth of a vestibular schwannoma, most can be controlled by further GKS with a very low risk of a complications.

HEARING PRESERVATION AFTER GAMMA KNIFE RADIOSURGERY FOR VESTIBULAR SCHWANNOMAS PRESENTING WITH HIGH-LEVEL HEARING

OBJECTIVE

The aim of this study was to evaluate long-term hearing preservation after gamma knife radiosurgery (GKS) for vestibular schwannomas in patients with initially normal or subnormal hearing (Gardner-Robertson Class 1) and to determine the predictive factors for functional hearing preservation.

METHODS

Since July 1992, more than 2053 vestibular schwannomas have been treated by GKS and followed at the Timone University Hospital, Marseille. A minimum of 3 years of follow-up (range, 3–11 years; median, 48 months) is available for 74 patients (without neurofibromatosis Type 2 or previous surgery) with Gardner-Robertson Class 1 hearing.

RESULTS

The average age of the patients was 47.5 years (range, 17–76 years). The number of tumors in Koos Stage I was 8, the average number in Stage II was 21, the average number in Stage III was 43, and the average number in Stage IV was 2. The median number of isocenters was 8 (range, 2–45), and the median marginal dose was 12 Gy (range, 9–13 Gy). At the time of the last follow-up evaluation, 78.4% of the patients had preserved functional hearing. Tumor control was achieved in 93% of the cases. The probability of preserving functional hearing was higher in patients who had an initial symptom other than hearing decrease (91.1%), in patients younger than 50 years (83.7%), and in those treated with a dose to the cochlea of less than 4 Gy (90.9%).

CONCLUSION

This study shows that the probability of preserving functional hearing in the long term after GKS for patients presenting with unilateral vestibular schwannomas is very high. The positive predictive factors appear to be young age, an initial symptom other than hearing decrease, and a low dose to the cochlea.

Hearing preservation in vestibular schwannoma stereotactic radiosurgery: what really matters?

Stereotactic radiosurgery (SRS) for vestibular schwannomas has evolved and improved over time. Although early short-term follow-up reports suggest that fractionation yields hearing preservation rates equivalent to modern single-dose SRS techniques, significant questions remain regarding long-term tumor control after the use of fractionation in a late responding tumor with a low proliferative index and alpha/beta ratio. With single-dose SRS, critical hearing preservation variables include: 1) strict attention to prescription dose 3D conformality so that the ventral cochlear nucleus (VCN) receives <or= 9 Gy; 2) careful delineation of the 3D tumor margin to exclude the cochlear nerve when visualizable with contrast-enhanced T2-weighted MR volumetric imaging techniques and exclusion the dura mater of the anterior border of the internal auditory canal; 3) a tumor margin dose prescription <or= 12 Gy; 4) optimization of the tumor treatment gradient index without sacrificing coverage and conformality; and 5) strict attention to prescription dose 3D conformality so that the modiolus and the basal turn of the cochlea receive the lowest possible dose (ideally < 4-5.33 Gy). Testable correlates for the relative importance of the VCN versus cochlear dose given the tonotopic organization of each structure suggests that VCN toxicity should lead to preferential loss of low hearing frequencies, while cochlear toxicity should lead to preferential loss of high hearing frequencies. The potential after SRS for hearing toxicity from altered endolymph and/or perilymph fluid dynamics either via impaired fluid production and/or absorption has yet to be explored. Serous otitis media, ossicular or temporal bone osteonecrosis, and chondromalacia are not likely to be relevant factors or considerations for hearing preservation after SRS.

REPEAT GAMMA KNIFE SURGERY FOR REGROWTH OF VESTIBULAR SCHWANNOMAS

OBJECTIVE

Gamma knife surgery (GKS) has become established as a minimally invasive treatment modality for patients with vestibular schwannomas. Treatment failure and/or tumor regrowth, however, is occasionally encountered, and microsurgical resection is usually warranted in such cases. The role of repeat GKS in these situations is still unclear. The goal of this study was to investigate whether repeat GKS is an effective treatment for recurrent vestibular schwannomas and to assess the conservation of residual neurological function.

METHODS

Between July 1992 and December 2007, 1951 patients harboring a unilateral vestibular schwannoma were treated with GKS. Of these, 48 patients (2.5%) had to undergo a subsequent intervention because of progression or regrowth of the tumor. Repeat GKS was performed in a total of 15 patients, 8 of whom had more than 2 years of follow-up and were eligible to be enrolled in the present study. The median follow-up period after repeat GKS was 64 months, and the median interval between these interventions was 46 months. The median tumor volume was 0.51 and 1.28 mL at the initial and second GKS treatments, respectively. Patients received a median prescription dose of 12.0 Gy at both interventions.

RESULTS

We report no cases of failure. Six patients demonstrated a significant reduction in tumor volume. In 1 patient, the final tumor volume was less than the initial volume. The other 2 patients showed stabilization of tumor growth. Useful hearing ability was preserved in only 1 of the 3 patients who had serviceable hearing ability at the time of the second GKS. Neither aggravation of facial nerve dysfunction nor other neurological deficits secondary to GKS were observed.

CONCLUSION

This is the first report to address repeat GKS for vestibular schwannomas. After long-term follow-up, repeat GKS with a low marginal dose seems to be a safe and effective treatment in selected patients harboring regrowth of small vestibular schwannomas that have previously been treated with GKS.

Transient expansion of vestibular schwannoma following stereotactic radiosurgery

OBJECT

The authors prospectively analyzed volume changes in vestibular schwannomas (VSs) after stereotactic radiosurgery.

METHODS

One hundred consecutive patients with unilateral VS treated with Gamma Knife surgery (GKS) at Chiba Cardiovascular Center between 1998 and 2006 were analyzed in this study. For each lesion the Gd-enhanced volume was measured serially every 3 months in the 1st year, then every 6 months thereafter, using volumetric software. The frequency and degree of transient tumor expansion were documented and possible prognostic factors were analyzed. Concurrently, neurological deterioration involving trigeminal, facial, and cochlear nerve functions were also assessed.

RESULTS

The mean observation period was 65 months (range 25-100 months). There were 32 men and 68 women, whose mean age was 59.1 years (range 29-80 years). Tumor volumes at GKS averaged 2.7 cm3 (range 0.1-13.2 cm3), and the lesions were irradiated at the mean 52.2% isodose line for the tumor margin (range 50-67%), with a mean dose of 12.2 Gy (range 10.5-13 Gy) at the periphery. The tumor volume was increased by 23% at 3 months and 27% at 6 months. Tumors shrank to their initial size over a mean period of 12 months. The maximum volume increase was < 10% (no significant increase) in 26 patients, 10-30% in 23, 30-50% in 22, 50-100% in 16, and > 100% in 13. The peak tumor expansion averaged 47% (range 0-613%). A high-dose (> or = 3.5 Gy/min) treatment appears to be the greatest risk factor for transient tumor expansion, although the difference did not reach statistical significance. Transient facial palsy and facial dysesthesia correlated strongly with tumor expansion, but only half of the hearing loss was coincident with this phenomenon.

CONCLUSIONS

Transient expansion of VSs after GKS was found to be much more frequent than previously reported, strongly suggesting a correlation with deterioration of facial and trigeminal nerve functions.

Complications of Gamma Knife surgery: an early report from 2 Canadian centers

Object

Gamma Knife surgery (GKS) is used to treat benign and malignant brain tumors, arteriovenous malformations, trigeminal neuralgia, and other conditions. Patients experience reduced neurological morbidity from GKS compared with open microneurosurgery, but risks of radiation injury and technical limitations persist. The authors report treatment complications from the early experience of 2 Canadian GKS programs in Toronto and Sherbrooke.

Methods

In Toronto, a prospective administrative database was searched for adverse events and incomplete treatment administrations. In Sherbrooke, data were acquired by chart review. Patients were accrued until August 1, 2007, and a total of 973 patients were included in this report.

Results

During the radiosurgical procedure, 19 patients (2%) suffered anxiety or syncopal episodes, and 2 patients suffered acute coronary events. Treatments were incompletely administered in 12 patients (1.2%). Severe pain was a delayed complication: 8 patients suffered unexpected headaches, and 9 patients developed severe facial pain. New motor deficits developed in 11 patients, including edema-induced ataxia in 4 and one case of facial weakness after treatment of a vestibular schwannoma. Four patients required shunt placement for symptomatic hydrocephalus, and 16 patients suffered delayed seizures.

Conclusions

Gamma Knife surgery is a minimally invasive treatment modality for many intracranial diseases. Treatment is not risk free, and some patients will develop complications; these are likely to decrease as institutional experience matures. Expanding availability and indications necessitate discussion of these risks with patients considering treatment.

Normal pressure hydrocephalus after radiosurgery for sphenoid ridge meningioma

Normal pressure hydrocephalus after radiosurgery for meningioma has rarely been reported. We report such a case and discuss the role of radiosurgery in the development of hydrocephalus. A 75-year-old man with a growing tumor underwent linac-based radiosurgery. The tumor received 16 Gy to the 80% isodose line. He exhibited the triad of symptoms of normal pressure hydrocephalus and became bedridden three months after radiosurgery. Dilated ventricles were demonstrated with MRI. Examination of the cerebrospinal fluid revealed a high level of protein. The patient underwent a ventriculoperitoneal shunt and recovered well.

[An improved case of bedridden mental impairment with normal pressure hydrocephalus associated with acoustic neurinoma after tumor resection]

A 67-year-old woman developed gait disturbance, dysarthria, cognitive impairment and incontinence at age 65, and became bedridden. She showed mutism, stupor and lower limb spasticity. Cranial CT and MRI revealed marked ventricular enlargement and a cerebellopontine angle tumor. CSF study showed normal pressure (125 mmH2O) and elevated protein (143 mg/dl). Radionuclide cisternography showed redistribution of radionuclide to the ventricles and intraventricular residual radionuclide after 72 hours, which allowed a diagnosis of normal pressure hydrocephalus. After removal of the tumor, ventricle size and CSF protein decreased, and the symptoms of cognitive impairment and motor dysfunction resolved. Histological examination showed acoustic neurinoma. Over the half of hydrocephalus following acoustic neurinoma shows a tendency to improve by surgical resection of the tumor. Neurologists who see cognitively impaired spastic bedridden patients should not overlook this pathology.

Guiding patients through the choices for treating vestibular schwannomas: balancing options and ensuring informed consent. 2007

Counseling patients who are diagnosed with vestibular schwannomas, formerly known as acoustic neuromas, can be challenging. The health care provider has the responsibility to explain, in understandable language, to the patient or legal representative the proposed treatment options, risks and complications associated with each form of treatment, and alternatives to treatment, including no therapy. Patients should be encouraged to gather information before making a treatment decision. For the physicians managing these patients, information should be delivered in a balanced way to ensure patient understanding of their options leading to adequate informed consent.

The implementation of ablative hypofractionated radiotherapy for stereotactic treatments in the brain and body: observations on efficacy and toxicity in clinical practice

Radiosurgery has a long history dating back to the 1950s. Only in the last decade or so have advances in radiation delivery and visualization allowed export of this paradigm to extracranial sites. This review evaluates the efficacy and safety of such ablative radiation courses using dose per fraction schedules of 10 Gy or above. Retrospective published experience in functional and benign tumor radiosurgery is reviewed. Prospective controlled clinical trials in ablative cancer therapy of early-stage lung cancer and metastatic disease in the brain, liver, and spine are reviewed.

STEREOTACTIC RADIOSURGERY AND FRACTIONATED STEREOTACTIC RADIOTHERAPY FOR THE TREATMENT OF NONACOUSTIC CRANIAL NERVE SCHWANNOMAS

OBJECTIVE

To review outcomes after fractionated stereotactic radiotherapy (FSR) and stereotactic radiosurgery (SRS) for nonacoustic cranial nerve schwannomas.

METHODS

We reviewed medical records of 39 patients who received FSR or SRS for nonacoustic cranial nerve schwannomas at our institution during the period from 1996 to 2007.

RESULTS

Tumors involved Cranial Nerves V (n = 19), III (n = 2), VI (n = 3), VII (n = 5), IX (n = 2), X (n = 5), and XII (n = 2) and the cavernous sinus (n = 1). Irradiation was performed after partial resection, biopsy, or no previous surgery in 16, 2, and 21 patients, respectively. Twenty-four patients received FSR, delivered in 1.8- to 2.0-Gy fractions to a median dose of 50.4 Gy (range, 45.0–54.0 Gy). Fifteen patients received SRS to a median dose of 12.0 Gy (range, 12–15 Gy). Mild acute toxicity occurred in 23% of the patients. The 2-year actuarial tumor control rate after FSR and SRS was 95%. The median follow-up period was 24 months. Changes in cranial nerve deficits after stereotactic irradiation were analyzed for patients with follow-up periods greater than 12 months (n = 26); cranial nerve deficits improved in 50%, were stable in 46%, and worsened in 4% of the patients. No significant difference was observed for FSR compared with SRS with regard to local control or to improvement of cranial nerve-related symptoms (P = 0.17).

CONCLUSION

SRS and FSR are both well-tolerated treatments for nonacoustic cranial nerve schwannomas, providing excellent tumor control and a high likelihood of symptomatic improvement.

Radiosurgery for benign intradural spinal tumors

OBJECTIVE

The role of stereotactic radiosurgery for the treatment of intracranial benign tumors is well established. There is less experience and more controversy regarding its use for benign tumors of the spine. This study evaluated the clinical efficacy of radiosurgery as part of the treatment paradigm of selected benign tumors of the spine.

METHODS

Seventy-three benign intradural extramedullary spinal tumors were treated with a radiosurgery technique and prospectively evaluated. Patient ages ranged from 18 to 85 years (mean age, 44 yr); the follow-up period was 8 to 71 months (median, 37 mo). Lesion location included 43 cervical, five thoracic, 19 lumbar, and six sacral. Tumor histology included neurofibroma (25 cases), schwannoma (35 cases), and meningioma (13 cases). Twenty-one cases were associated with neurofibromatosis Type 1, and nine patients had neurofibromatosis Type 2. Nineteen tumors (26%) had previously undergone open surgical resection, and six tumors (8%) had previously been treated with conventional external beam irradiation techniques.

RESULTS

Similar radiation doses were prescribed for all three histopathologies. The maximum intratumoral dose was 1500 to 2500 cGy (mean, 2164 Gy). Tumor volume ranged from 0.3 to 93.4 cm (mean, 10.5 cm; median, 4.11 cm). Radiosurgery was used for the treatment of postsurgical radiographic progression in 18 cases; it was used as the primary treatment modality in 14 cases; it was used for treatment of radiographic tumor progression in nine cases; and it was used for the treatment of postsurgical residual tumor in two cases. Long-term pain improvement occurred in 22 out of 30 cases (73%). Long-term radiographic tumor control was demonstrated in all cases. Three patients experienced new symptoms attributed to radiation-induced spinal cord toxicity 5 to 13 months after treatment.

CONCLUSION

Single fraction radiosurgery was found to be clinically effective for the treatment of benign extramedullary spinal neoplasms. Although surgical extirpation remains the primary treatment option for most benign spinal tumors, radiosurgery was demonstrated to have short-term clinical benefits for the treatment of such lesions. The long-term efficacy of spinal radiosurgery for such tumors will be determined with longer follow-up periods. Its role in patients with neurofibromatosis will also be further defined with greater clinical experience.

Comparison of the surgical and follow-up costs associated with microsurgical resection and stereotactic radiosurgery for vestibular schwannoma

OBJECT

The best approach to the management of vestibular schwannoma (VS) remains controversial. The aim of this study is to analyze the initial and follow-up costs of resection and stereotactic radiosurgery for patients with VS.

METHODS

Initial and follow-up costs in 53 cases in which patients with unilateral, previously unoperated VSs > 3 cm underwent resection (21 cases) or radiosurgery (32 cases) at the Mayo Clinic from June 2000 until July 2002 were analyzed for 36 months. Follow-up treatment-specific utilization records were gathered prospectively for patients not returning to the Mayo Clinic after treatment. Six-month moving averages of incremental follow-up costs were calculated for the 2 patient groups.

RESULTS

The mean cost of surgery in the microsurgery group was $23,788 (95% confidence interval $22,280-$24,842) compared with $16,143 (95% confidence interval $15,277-$17,545) for the radiosurgical group. Mean incremental follow-up costs per month for patients in the microsurgery group started just > $1,000 per month, decreased steadily, and remained < $70 per month by the 10th month of follow-up. Mean incremental follow-up costs per month for patients in the radiosurgery group were <$10 per month for the first few months and thereafter increased to as much as $200 per month.

CONCLUSIONS

Although the total cost of microsurgery is higher due to the costs of hospitalization, follow-up costs for radiosurgery are greater in general. From a societal perspective, radiosurgery is less expensive than microsurgical resection provided that the rate of tumor progression after radiosurgery remains low with long-term follow-up.

Gamma knife radiosurgery for intracanalicular acoustic neuromas

In the present study we reviewed our long-term experience with radiosurgery for intracanalicular acoustic neuromas. The study involved 25 patients with unilateral intracanalicular acoustic neuromas. The treatment volume was 0.07 to 0.8 cm(3) (median: 0.27 cm(3)). The marginal radiation dose used for treatment was 12 Gy for all patients. The follow-up period ranged from 36 to 132 months (mean: 89 months). The actuarial rate of tumour growth control at 5 and 10 years after radiosurgery was 96%. Hearing preservation was achieved in 16 patients (64%) and improvement (>20 dB relative to presurgical values) was noted in one patient (4%). No patients experienced post-radiosurgery facial palsy or other cranial nerve deficits. Based on our study and long-term follow-up, radiosurgery can produce high rates of tumour growth control and hearing preservation for intracanalicular acoustic neuromas, and is an alternative to surgical resection given its low level of invasiveness. When determining treatment for intracanalicular acoustic neuromas, the condition's benign natural course and the likelihood of hearing preservation must be taken into account.

Tumor-volume changes after radiosurgery for vestibular schwannoma: implications for follow-up MR imaging protocol

BACKGROUND AND PURPOSE

The outcome of radiosurgery for vestibular schwannoma (VS) is assessed by posttreatment measurement of tumor size and could be influenced by the timing and quality of the assessment. This study evaluates the volumetric changes of VS after radiosurgery and proposes a radiologic follow-up program.

MATERIALS AND METHODS

Of 142 patients with VS treated with radiosurgery, we selected patients who were followed at least 3 times during a minimum of 32 months with a T1-weighted gadolinium-enhanced high-resolution 3D MR imaging examination identical to the pretreatment MR imaging. Forty-five patients were identified with a mean follow-up of 50 months (range, 32-78 months). Pre- and posttreatment tumor volumes were calculated by using BrainSCAN software by manually contouring tumors on each MR imaging study. Volume changes of >13% were defined as events.

RESULTS

At last follow-up MR imaging, volumes were smaller in 37 (82.2%) of the 45 patients. Eleven (29.7%) of these 37 tumors showed transient swelling preceding regression, with a median time to regression of 34 months (range, 20-55 months). Seven (15.6%) of the 45 tumors had volume progression compared with the tumor on pretreatment MR imaging studies. Of these 7 tumors, 3, however, had volume regression compared with the preceding MR imaging study, and in 4, volume progression was ongoing. One tumor remained the same.

CONCLUSIONS

Tumor-volume measurements by standardized T1-weighted gadolinium-enhanced high-resolution 3D MR imaging follow-up protocols revealed good local control of VS after radiosurgery. The first-follow-up MR imaging at 2 years and the second at 5 years postradiosurgery differentiated transient progression from ongoing progression and may prevent unnecessary therapeutic interventions.

THE APPLICATION OF STEREOTACTIC RADIOSURGERY TO DISORDERS OF THE BRAIN

STEREOTACTIC RADIOSURGERY IS the first widely used “biological surgery.” The opportunity for surgeons working with radiation oncologists and medical physicists to affect cell structures with both direct and indirect vascular effects has transformed neurosurgery. As a minimal access surgical approach, it fits well into the patient goals of functional preservation, risk reduction, and cost-effectiveness. Longer-term results have been published for many indications. For many disorders, it may be better to “leave the tumor in rather than take it out.” Radiosurgery has had an impact on the management of patients with vascular malformations, all forms of cerebral neoplasia, and selected functional disorders such as trigeminal neuralgia and tremor. It can be performed alone when lesion volume is not excessive or as part of a multimodality strategy with resection or endovascular surgery. Epilepsy, behavioral disorders, and other novel indications are the topics of current investigation. The combination of high-resolution imaging, high-speed computer workstations, robotics, patient fixation techniques, and radiobiological research has put radiosurgery into the practice of almost all neurosurgeons.

Hypofractionated CyberKnife stereotactic radiosurgery for acoustic neuromas with and without association to neurofibromatosis Type 2

CyberKnife stereotactic radiosurgery (CKSRS) has been proved effective in treating intra-cranial lesions. To treat acoustic neuroma (AN) patients with or without neurofibromatosis Type 2 (NF2) associations, the functional preservation of hearing, trigeminal nerve, and facial nerve are important. Twenty-one patients were treated with hypofractionated CKSRS. Fourteen non-NF2 and seven NF2 patients were enrolled. Cranial nerve function, audiograms, and magnetic resonance images (MRI) were monitored. Mean follow-up was 15 month. Tumors with volumes ranging from 0.13 to 24.8 cm3 (mean 5.4 cm3) were irradiated with the marginal dose 1800-2000 cGy/3 fractions. Tumors were treated with an 80 to 89% isodose line (mean 83%) and mean 97.9% tumor coverage. Two patients experienced hearing deterioration (16.7%) in the non-NF2 group, and 3 patients (50%) in the NF2 group. No facial or trigeminal dysfunction, brain stem toxicity, or cerebellar edema occurred. Tumor regression was seen in 9 patients (43%) and stable in 12 patients (57%). 100% tumor control rate was achieved. Hypofractionated CKSRS was not only effective in tumor control but also excellent in hearing preservation for non-NF2 AN. But for NF2 patients, although the tumor control was remarkable, hearing preservation was modest as in non-NF2 patients.

Gamma-knife radiosurgery in the treatment of trigeminal schwannomas

BACKGROUND

Trigeminal nerve schwannomas account for 0.07%-0.28% of all intracranial tumours. Advances in skull base surgery have led to more aggressive resection of these tumours, but surgery may associated with development of new neurological deficits.

METHODS

In this report, we analyse the long-term results 15 patients with newly diagnosed or residual/recurrent trigeminal schwannoma who underwent gamma-knife treatment.

FINDINGS

During a mean 61 months of follow-up, MRI revealed reduction of tumour size in 13 and no size change in 2 patients. The tumour growth control rate was 100% and only 1 patient had transient facial numbness and diplopia.

CONCLUSIONS

For patients with small to moderate size trigeminal schwannomas, gamma-knife radiosurgery is associated with good tumour control and a minimal risk of adverse radiation effects.

Long-term Outcomes of Gamma Knife Stereotactic Radiosurgery of Vestibular Schwannomas

OBJECTIVE

Gamma Knife Stereotactic Radiosurgery (GK SRS) has become an important treatment modality for vestibular schwannomas. We evaluated the tumor control rate, patterns of tumor volume change and preservation of hearing following low-dose radiation for vestibular schwannomas in a homogeneous cohort group in which the mean marginal dose was 12 Gy.

METHODS

A total of 59 patients were enrolled in this study. All enrolled patients were followed-up for at least 5 years and the radiation dose was 11-13 Gy. Regular MRI, audiometry and clinical evaluations were done and tumor volumes were obtained from MRI using the OSIRIS program.

RESULTS

The tumor control rate was 97%. We were able to classify the patterns of change in tumor volume into three categories. Transient increases in tumor volume were detected in 29% of the patients and the maximum transient increase in tumor volume was identified at 6 to 30 months after GK SRS. The transient increases in tumor volume ranged from 121% to 188%. Hearing was preserved in 4 of the 12 patients who had serviceable hearing prior to treatment. There were no other complications associated with GK SRS.

CONCLUSION

Low-dose GK SRS was an effective and safe mode of treatment for vestibular schwannomas in comparison to the previously used high-dose GK SRS. Transient increases in tumor volume can be identified during the follow-up period after low-dose GK SRS for vestibular schwannomas. Physicians should be aware that these increases are not always indicative of treatment failure and that close observation is required following treatments. Unfortunately, a satisfactory hearing preservation rate was not achieved by reducing the radiation dose. It is thought that hearing preservation is a more sophisticated problem and further research is required.

Gamma Knife surgery and trigeminal schwannoma: is it possible to preserve cranial nerve function?

Object

The current study was undertaken to evaluate the tumor control rate and functional outcome after Gamma Knife surgery (GKS) in patients with a trigeminal schwannoma. The conditions associated with the development of cranial neuropathies after radiosurgery were scrutinized.

Methods

The authors reviewed the clinical records and radiological data in 22 consecutive patients who received GKS for a trigeminal schwannoma. The median tumor volume was 4.1 ml (0.2–12.0 ml), and the mean tumor margin dose was 13.3 ± 1.3 Gy at an isodose line of 49.9 ± 0.6% (mean ± standard deviation). The median clinical follow-up period was 46 months (range 24–89 months), and the median length of imaging follow-up was 37 months (range 24–79 months).

Results

Tumor growth control was achieved in 21 (95%) of the 22 patients. Facial pain responded best to radio-surgery, with two thirds of patients showing improvement. However, only one third of patients with facial hypesthesia improved. Six patients (27%) experienced new or worsening cranial neuropathies after GKS. Ten patients (46%) showed tumor expansion after radiosurgery, and nine of these also showed central enhancement loss. Loss of central enhancement, tumor expansion, and a tumor in a cavernous sinus were found to be significantly related to the emergence of cranial neuropathies.

Conclusions

The use of GKS to treat trigeminal schwannoma resulted in a high rate of tumor control and functional improvement. Cranial neuropathies are bothersome complications of radiosurgery, and tumor expansion in a cavernous sinus after radiosurgery appears to be the proximate cause of the complication. Loss of central enhancement could be used as a warning sign of cranial neuropathies, and for this vigilant patient monitoring is required.

Fractionated Conformal Radiotherapy in Vestibular Schwannoma: Early Results from a Single Centre

AIMS

To assess the local control and cranial nerve toxicity in vestibular schwannoma patients treated with fractionated conformal radiotherapy delivered using a linear accelerator.

MATERIALS AND METHODS

Ninety-five patients were referred for consultation to the Oncology Department in Addenbrookes Hospital between 1996 and 2005. The 42 cases who received fractionated conformal radiotherapy are the subject of this analysis. All patients had radiological or symptomatic progression. Conformal radiotherapy was prescribed at 50Gy in 30 fractions over 6 weeks, delivered using a linear accelerator. Patients were immobilised using either a beam direction shell or a Gill Thomas Cosman relocatable stereotactic head frame.

RESULTS

The median age was 63 years (range 28-81) with 57% men. The average tumour size was 21.5mm on magnetic resonance imaging. Before treatment, 20 (48%) patients were deemed to have useful hearing on the affected side. The median follow-up was 18.6 months (range 0.3-6.5 years) and the actuarial local control rate at 2.5 years was 96.9% (one patient progressed after treatment). In previously hearing patients, the actuarial rate of useful hearing preservation was 100%, and the rate of mild hearing loss was 20% at 1 year and 26.7% at 2.5 years of follow-up. There were five neurofibromatosis type 2 patients treated, two of whom had useful hearing before radiotherapy. In one patient this was affected, with a 20dB loss, although he still has useful hearing. In those with normal facial nerve function before radiotherapy (n=40), this was preserved in 96.8% at 2.5 years. Trigeminal nerve function was preserved in all patients (n=38) who had normal nerve function before radiotherapy.

CONCLUSION

Although follow-up was relatively short in this single institution series, fractionated linear accelerator radiotherapy gave excellent local control, useful hearing preservation and retained cranial nerve function in vestibular schwannoma.

Guiding patients through the choices for treating vestibular schwannomas: balancing options and ensuring informed consent

Counseling patients who are diagnosed with vestibular schwannomas, formerly known as acoustic neuromas, can be challenging. The health care provider has the responsibility to explain, in understandable language, to the patient or legal representative the proposed treatment options, risks and complications associated with each form of treatment, and alternatives to treatment, including no therapy. Patients should be encouraged to gather information before making a treatment decision. For the physicians managing these patients, information should be delivered in a balanced way to ensure patient understanding of their options leading to adequate informed consent.

Radiosurgery in patients with bilateral vestibular schwannomas

BACKGROUND

Patients with bilateral vestibular schwannomas offer a unique opportunity to determine the effectiveness of radiosurgery. By using the untreated tumor as an internal control, one can determine whether radiosurgery was able to interrupt the natural history of the treated tumor.

METHODS

From September 1998 to November 2004, 13 patients with neurofibromatosis type 2 had 14 tumors treated with radiosurgery at the University of Florida. A retrospective analysis was performed on these patients. Actuarial statistics were used to analyze local control in both the treated and untreated tumor.

RESULTS

The average follow-up length was 38 months. One patient failed to send a follow-up MRI. Actuarial local control in the treated tumors was 100% at 1 year and 92% at 2 and 5 years. Only 1 of the treated tumors continued to grow. In the untreated tumors, actuarial local control was 100% at 1 year, 78% at 2 years and 21% at 5 years. None of the untreated tumors decreased in size.

CONCLUSION

In all but 1 patient with follow-up data, radiosurgery successfully prevented or reversed tumor growth. Additionally, half of the untreated tumors continued to grow. This study shows that radiosurgery alters the natural history of vestibular schwannomas.

Treatment of a Facial Nerve Neuroma with Fractionated Stereotactic Radiotherapy

BACKGROUND

Facial nerve neuromas are extremely rare and are often mistaken for acoustic neuromas when located near the vestibular nerve. Usually presenting with facial weakness and hearing loss, facial nerve neuromas of the cerebellopontine angle have commonly been managed by surgery. We present the first reported case of a facial nerve neuroma treated with fractionated stereotactic radiotherapy (FSRT).

METHODS

The patient was a 40-year-old woman who presented with tinnitus, dizziness and decreased hearing that was associated with a right intracanalicular mass on magnetic resonance imaging (MRI). She underwent a middle fossa craniotomy only to reveal a facial nerve tumor rather than an acoustic neuroma that was not resected due to the high risk of facial paralysis. Following surgery, her facial function worsened and was associated with tumor enlargement on MRI. She was referred for FSRT and received 54 Gy in daily 1.8-Gy fractions with a prescription isodose line of 90%.

RESULTS

Three months after treatment she had no worsening of her pretreatment symptoms, and at the 1-year follow-up, she experienced facial weakness improvement accompanied by an absence of tumor growth on MRI. These clinical and imaging findings persisted at 48 months of follow-up.

CONCLUSION

In the first report of a facial nerve neuroma treated with FSRT, this treatment resulted in excellent long-term (4-year) tumor control with improvement of pretreatment symptomatology and absence of morbidity. This report demonstrates the potential for using FSRT to treat facial nerve neuromas of the cerebellopontine angle that could otherwise be associated with significant operative morbidity.

Surgery after radiosurgery for acoustic neuromas: surgical strategy and histological findings

OBJECTIVE

To retrospectively review the authors' experience with surgical resections after failed radiosurgery for acoustic neuromas.

METHODS

The study group consisted of six patients with acoustic neuromas. The median age was 61 years (range, 18-72 yr). The median marginal radiation dose was 11 Gy (range, 10-12.5 Gy). The median interval between radiosurgery and surgical resection was 28 months (range, 4-74 mo). The operative indications were cerebellar ataxia and symptoms associated with increased intracranial pressure. The median follow-up period was 36 months (range, 11-72 mo) after surgical resection.

RESULTS

The tumors were subtotally removed (> or = 80%) in four patients and partially removed (< 80%) in the other two patients. Three patients had intratumoral bleeding. Preexisting facial nerve palsy improved in two patients and deteriorated in one patient, and one patient experienced new facial palsy. No other new neurological deficits emerged after surgery. Histological features were typical of acoustic schwannoma, and some tumors were associated with foamy macrophages, myxoid degeneration, and necrosis attributed to radiation effects. At follow-up, the residual tumor was decreased in five patients and increased in one patient with an expanding intratumoral hematoma.

CONCLUSION

Surgical resection after radiosurgery is indicated in the presence of such symptoms as cerebellar ataxia and increased intracranial pressure. It must be carefully considered because of the natural regression of transient tumor swelling over time. Surgical resection should be limited to subtotal removal for functional preservation. In patients with tumor enlargement several years after radiosurgery, the possibility of chronic intratumoral bleeding resulting from delayed radiation injury must be considered.

Safety and efficacy of fractionated stereotactic radiotherapy for acoustic neuromas

BACKGROUND

The treatment of acoustic neuromas (AN) has historically involved surgical excision or stereotactic radiosurgery, with a relatively limited number of reports available describing the use of fractionated stereotactic radiotherapy (FSRT). To enhance the existing knowledge regarding the safety and efficacy of this treatment modality, we describe our initial experience with FSRT for AN.

METHODS

From 1999-2005, 20 patients (12F, 8M) with AN underwent FSRT. All patients were treated using the Radionics X-Knife 4.0 3D planning system, receiving 54 Gy in 1.8 Gy daily fractions with a prescription isodose line of 90%. Treatments were delivered stereotactically using a dedicated Varian 6/100 linear accelerator, with immobilization achieved via the Gill-Thomas-Cosman relocatable frame. Median tumor size (maximum diameter) was 2.1 cm (range, 1.1-3.4 cm). Median patient age was 49.5 years, with median follow-up of 22 months (range, 1-66 months). All patients were evaluated with pre- and post-gadolinium-enhanced magnetic resonance imaging.

RESULTS

Following FSRT, local tumor control was achieved in every patient, with the treatment well-tolerated by all patients. No patient experienced acute complications or facial nerve weakness. Two patients experienced permanent trigeminal nerve morbidity manifesting as facial numbness. All nine patients with preserved hearing before treatment had hearing preservation at last follow-up, although four of these patients experienced hearing decline following FSRT.

CONCLUSION

In our series of 20 patients with AN, all had local tumor control following FSRT, with minimal morbidity. These results support the growing body of literature demonstrating the safety and efficacy of FSRT in achieving local control for AN, further validating the viability of FSRT as a treatment modality for this patient population.

Long-Term Follow-up of Acoustic Schwannoma Radiosurgery With Marginal Tumor Doses of 12 to 13 Gy

PURPOSE

To define long-term tumor control and clinical outcomes of radiosurgery with marginal tumor doses of 12 to 13 Gy for unilateral acoustic schwannoma.

METHODS AND MATERIALS

A total of 216 patients with previously untreated unilateral acoustic schwannoma underwent Gamma Knife radiosurgery between 1992 and 2000 with marginal tumor doses of 12 to 13 Gy (median, 13 Gy). Median follow-up was 5.7 years (maximum, 12 years; 41 patients with >8 years). Treatment volumes were 0.08-37.5 cm(3) (median, 1.3 cm(3)).

RESULTS

The 10-year actuarial resection-free control rate was 98.3% +/- 1.0%. Three patients required tumor resection: 2 for tumor growth and 1 partial resection for an enlarging adjacent subarachnoid cyst. Among 121 hearing patients with >3 years of follow-up, crude hearing preservation rates were 71% for keeping the same Gardner-Robertson hearing level, 74% for serviceable hearing, and 95% for any testable hearing. For 25 of these patients with intracanalicular tumors, the respective rates for preserving the same Gardner-Robertson level, serviceable hearing, and testable hearing were 80%, 88%, and 96%. Ten-year actuarial rates for preserving the same Gardner-Robertson hearing levels, serviceable hearing, any testable hearing, and unchanged facial and trigeminal nerve function were 44.0% +/- 11.7%, 44.5% +/- 10.5%, 85.3% +/- 6.2%, 100%, and 94.9% +/- 1.8%, respectively.

CONCLUSIONS

Acoustic schwannoma radiosurgery with 12 to 13 Gy provides high rates of long-term tumor control and cranial nerve preservation after long-term follow-up.

Gamma Knife surgery for trigeminal schwannoma

Object

Trigeminal schwannomas are rare intracranial tumors. In the past, resection and radiation therapy were the mainstays of their treatment. More recently, neurosurgeons have begun to use radiosurgery in the treatment of trigeminal schwannomas because of its successful use in the treatment of vestibular schwannomas. In this article the authors evaluate the radiological and clinical outcomes in a series of patients in whom Gamma Knife surgery (GKS) was used to treat trigeminal schwannomas.

Methods

Twenty-six patients with trigeminal schwannomas underwent GKS at the University of Virginia Lars Lek-sell Gamma Knife Center between 1989 and 2005. Five of these patients had neurofibromatosis and one patient was lost to follow up. The median tumor volume was 3.96 cm3, and the mean follow-up period was 48.5 months. The median prescription radiation dose was 15 Gy, and the median prescription isodose configuration was 50%. There was clinical improvement in 18 patients (72%), a stable lesion in four patients (16%), and worsening of the disease in three patients (12%). On imaging, the schwannomas shrank in 12 patients (48%), remained stable in 10 patients (40%), and increased in size in three patients (12%). These results were comparable for primary and adjuvant GKSs. No tumor growth following GKS was observed in the patients with neurofibromatosis.

Conclusions

Gamma Knife surgery affords a favorable risk-to-benefit profile for patients harboring trigeminal schwannomas. Larger studies with open-ended follow-up review will be necessary to determine the long-term results and complications of GKS in the treatment of trigeminal schwannomas.

Two- and three dimensional measures of vestibular schwannomas and posterior fossa--implications for the treatment

BACKGROUND

There is no uniformly accepted method of reporting the size of vestibular schwannomas (VS) and to evaluate the individual tumour behaviour in the posterior fossa (PF). To help the treatment decision we investigated the VS and PF morphometry using a computerized method.

METHOD

Stereotactic fused CISS MR and CT scan images were obtained from 58 adult patients (31 males and 27 females) harbouring an unilateral VS (25 Koos II, 21 Koos III and 12 Koos IV). Using a Gammaplanworking station we screened for the following measures: anteroposterior (AP), craniocaudal (CC), transverse (T) and maximum (Max) diameters (Diam) of the intracisternal part of the tumour, VS and PF volumes.

FINDINGS

The Max Diam was the most accurate way to estimate the tumour volume (Spearman's rho >0.80). Among several parameters, the T Diam was the best measure to assess the brain shift (ROC analysis) with a cut off value at 14.5 mm (91.7% sensitivity and 93% specificity). VS volume and the ratio VS volume/PF volume were also efficient to predict a brain shift.

CONCLUSIONS

Max Diam and T Diam are bedside measured simple data of particular interest to respectively estimate the VS volume and predict the brain shift due to the tumour. The determination of cut-off values correlated to brain shift will provide guidelines at the time of the therapeutic decision between radiosurgical and microsurgical strategy.

STEREOTACTIC RADIOSURGERY FOR VESTIBULAR SCHWANNOMAS IN PATIENTS WITH NEUROFIBROMATOSIS TYPE 2

OBJECTIVE

Vestibular schwannomas present significant management challenges in patients with neurofibromatosis Type 2 (NF2). We evaluated the results of gamma knife radiosurgery for the management of these tumors, focusing on tumor response, hearing preservation, and other factors affecting outcomes.

METHODS

Stereotactic radiosurgery was performed to manage 74 schwannomas in 62 patients. Ipsilateral serviceable hearing was present in 35% of tumors before the procedure. The mean tumor volume was 5.7 cm3. The mean margin and maximum dose used were 14 and 27.5 Gy, respectively. Cox regression analyses were performed to identify factors affecting outcomes.

RESULTS

The median follow-up period was 53 months, and two patients were lost to follow-up. Actuarial local control rates at were 85, 81, and 81% at 5, 10, and 15 years, respectively. Tumor volume was significant as a predictor of local control. Since 1992, using current radiosurgery techniques (magnetic resonance imaging scan targeting and reduced margin dose to 14 Gy or less), the actuarial serviceable hearing preservation rate is 73% at 1 year, 59% at 2 years, and 48% at 5 years after radiosurgery. Facial neuropathy occurred in 8% of tumors, trigeminal neuropathy occurred in 4%, and vestibular dysfunction occurred in 4%. Radiation dose and tumor volume were predictive of development of new deficits. No radiosurgery-associated secondary tumors or atypical or malignant changes were noted.

CONCLUSION

Stereotactic radiosurgery is a safe and effective management modality for neurofibromatosis Type 2 vestibular schwannomas. Although results do not seem to be as good as for patients with sporadic unilateral tumors, gamma knife radiosurgery results seem favorable and indicate that radiosurgery should be strongly considered for primary tumor management in selected patients.

Expression of transforming growth factor-beta receptor type 1 and type 2 in human sporadic vestibular Schwannoma

Expression of the transforming growth factor-beta (TGF-beta) protein family in the peripheral nervous system is well established, but the role of their cognate receptors TGF-beta receptor type 1 (R1) and type 2 (R2) has been less well studied. TGF-beta plays an essential role in Schwann cell proliferation and differentiation, and is involved in neurotrophic effects of several neurotrophic substances. TGF-beta is also expressed in benign peripheral nervous system tumors such as vestibular schwannomas. In the present study, we aimed to detect TGF-beta R1 and R2 in a total of 40 sporadic vestibular schwannomas using immunohistochemistry, and correlated the findings to essential clinicopathologic data. TGF-beta, TGF-beta R1, and TGF-beta R2 mRNA was further analyzed by RT-PCR in six vestibular schwannomas. TGF-beta R1 immunoexpression was found in about 95% of the tumors. TGF-beta R1 was equally present in Antoni A and Antoni B areas of the tumors. TGF-beta R2 was found immunohistochemically in 77%. In addition, all tumors showed strong expression of TGF-beta. No correlation between TGF-beta R1 or R2 expression and clinicopathologic parameters such as age, sex, clinical symptoms, growth pattern, and proliferation acitivity as measured by Ki-67 (MIB-1) staining was found. Moreover, all schwannomas studied contained TGF-beta, TGF-beta R1, and TGF-beta R2 mRNA. Therefore, the TGF-beta/TGF-beta R1 and -R2 system is present in human schwannomas, but its biologic role for tumor development and growth remains unclear.

Microsatellite analysis of recurrent vestibular schwannoma (acoustic neuroma) following stereotactic radiosurgery

HYPOTHESIS

Genetic and immunohistochemical studies may provide insight into the mechanisms of vestibular schwannoma (VS) recurrence following radiation therapy.

BACKGROUND

Stereotactic radiation therapy is an increasingly common alternative to microsurgical resection for the primary management of sporadic VS. The molecular mechanisms associated with recurrent vestibular schwannoma (VS) following radiation therapy are not known.

METHODS

Primary or irradiated VS tumors were fresh-frozen at the time of surgical resection and microdissected to undergo DNA extraction. Lymphocytic control DNA was isolated from blood obtained by venipuncture. Paired normal and tumor DNA specimens were analyzed for allelic loss by PCR amplification of polymorphic dinucleotide repeat sequences. Immunohistochemical studies were performed on paraffin-embedded, irradiated surgical specimens.

RESULTS

Using 16 polymorphic microsatellite markers, 20 of 26 non-irradiated VS demonstrated loss of heterozygosity (LOH) in at least one locus of chromosome 22q. In contrast, none of the four irradiated recurrent VS demonstrated LOH on chromosome 22q (p = 0.008). No allelic loss was seen in either the primary or irradiated VS utilizing markers mapping to chromosome 10. Deletions on chromosome 10 are seen in both benign and higher-grade meningiomas and intracranial malignancies associated with radiotherapy. Immunohistochemical studies were performed to detect the protein product of the NF2 gene, merlin, in the four irradiated VS. NF2 staining was not observed.

CONCLUSION

This study represents the first microsatellite and immunohistochemical analysis of recurrent VS following radiation therapy. Our preliminary observations suggest an alternative mechanism of NF2 inactivation that may correlate with radioresistance in VS.

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.

Trigeminal schwannomas: results of Gamma Knife surgery in 37 cases

Object

Information on outcomes of Gamma Knife surgery (GKS) for patients harboring trigeminal schwannomas is limited because these tumors are rare. The authors evaluated tumor control and functional outcomes in patients who underwent GKS for trigeminal schwannomas to clarify the efficacy of this treatment.

Methods

Forty-two patients with trigeminal schwannomas but no evidence of neurofibromatosis Type 2 were treated with GKS at Komaki City Hospital between November 1991 and December 2003. Of these, 37 patients were assessed. The mean tumor volume in these patients was 10 cm3. The mean maximum radiation dose directed to the tumor was 27.9 Gy and the mean dose directed to the tumor margin was 14.2 Gy. The mean follow-up period was 54 months. In four patients (11%) there was complete tumor remission; in 20 (54%) there was partial tumor remission; in eight (22%) the disease remained stable; and in five (14%) the tumor enlarged or uncontrollable facial pain developed with radiation-induced edema requiring resection. The actuarial 5- and 10-year tumor control rates were both 84%. With respect to functional outcomes, 40% of patients noted an improvement in their symptoms, and one patient experienced new symptoms despite good tumor control.

Conclusions

Gamma Knife surgery was a safe and effective treatment for a select group of patients harboring trigeminal schwannomas. Large tumors that compress the brainstem and cause deviation of the fourth ventricle should first be removed surgically and any remnant should be treated by GKS.

Long-term outcomes after Gamma Knife surgery for vestibular schwannomas: a 10-year experience

Object

The authors sought to assess the results of Gamma Knife surgery (GKS) in patients with vestibular schwannomas (VSs).

Methods

Seventy-four consecutive patients (33 men and 41 women) were evaluated by means of serial imaging studies, clinical examinations, and questionnaires. Nineteen patients had undergone resection of their VS. Facial nerve function was normal in 63 patients (85.1%) before GKS, and 63.5% of them had useful hearing. The prescription peripheral dose varied between 10 and 14 Gy (mean 12.27 ± 0.96 Gy); the corresponding central dose was 21 to 30 Gy (mean 24.9 ± 2.18 Gy). The mean volume of the tumor at GKS was 10.79 ± 5.52 ml (range 0.11–27.8 ml). A mean of eight isocenters (range 3–17) was used for treating these lesions.

At a median follow-up period of 68.3 months (range 30–122 months), tumor shrinkage was observed in 60 patients (81.1%), and the tumor size was stable in 11 (14.8%). Persistent neuroimaging demonstrated evidence of progression in only three patients (4.1%): two underwent repeated GKS after an interval of 18 months and one continues to be observed. Five patients experienced trigeminal dysfunction: in three the dysfunction was transient and in the other two the dysfunction persists. Three patients suffered facial palsy. Useful hearing was preserved in 34 patients. Thirteen patients experienced some degree of hearing improvement. Deterioration of hearing was found in 13 of 62 patients who had Class I or II hearing before treatment.

Conclusions

Gamma Knife surgery prevents tumor growth; it achieves excellent neurological function preservation and produces few treatment-related complications.

Historia magistra vitae (Cic. De or. 2.36). The Prime Objective of Radiosurgery in Acoustic Neurinomas

The central question of stereotaxic radiosurgery in acoustic neurinomas is how to pinpoint its main objective: is it a better alternative to neurosurgery or an option when surgery is unfeasible? This study is a continuation of the article published in 1995 in Acta Neurochirurgica, but benefits from greater experience, more complete analysis and longer supervision of results. The conclusions that can be drawn to date from our own findings and from others in the literature are the following: radiosurgery can be used not only to prevent neurinoma growth and at the same time to preserve the patient's neurological conditions without the risk of complications, but it can also be counted on to provide a cure. However, radiosurgery as an excising device is more insidious than the microsurgical scalpel, since the narrow beam of radiation, directed to a limited target without opening the skull, is invisible. The expression coined by Lars Leksell regarded precisely the innovation he himself conceived in the 'closed skull operation', with reference to its use in cases of acoustic neurinoma as an alternative to traditional surgery. Hence, whatever technique or instruments are involved, it is always a question of interventional neuroradiology or minimally invasive neurosurgery.