The human acoustic neurinoma in organ culture. II. Tissue changes after gamma irradiation

[Trigeminal neuromas: modern diagnosis and treatment]

Trigeminal neuroma (TN) is a benign neoplasm arising from trigeminal nerve sheath. The tumor can grow from any part of the nerve from the root in posterior cranial fossa to peripheral extracranial branches. Symptoms of trigeminal neuroma are variable and usually depend on location and dimensions of tumor. We present a review devoted to the problem of TN. Surgery was the only possible option in patients with TN for a long time. However, radiotherapy became one of the options and sometimes alternative to surgical treatment since the late 1980s. Besides active management of patients with TN, follow-up with regular radiographic control of small asymptomatic tumors also seems to be reasonable. When evaluating treatment outcomes, physicians consider quality of life and return to previous work and activity in addition to resection quality, neurological impairment, relapse-free period and tumor growth control. However, assessment of these indicators after certain treatment is rare. Thus, it is difficult to determine treatment strategy with maximum ratio of effectiveness and quality of life. Therefore, optimization of TN treatment is currently an urgent problem that requires further study.

Absence of residual tumor tissue after Gamma Knife radiosurgery followed by resection of a vestibular schwannoma: illustrative case

BACKGROUND

Late pathology after vestibular schwannoma radiosurgery is uncommon. The authors presented a case of a resected hemorrhagic mass 13 years after radiosurgery, when no residual tumor was found.

OBSERVATIONS

A 56-year-old man with multiple comorbidities, including myelodysplastic syndrome cirrhosis, received Gamma Knife surgery for a left vestibular schwannoma. After 11 years of stable imaging assessments, the lesion showed gradual growth until a syncopal event occurred 2 years later, accompanied by progressive facial weakness and evidence of intralesional hemorrhage, which led to resection. However, histopathological analysis of the resected specimen showed hemorrhage and reactive tissue but no definitive residual tumor.

LESSONS

This case demonstrated histopathological evidence for the role of radiosurgery in complete elimination of tumor tissue. Radiosurgery for vestibular schwannoma carries a rare risk for intralesional hemorrhage in select patients.

The biological underpinnings of radiation therapy for vestibular schwannomas: Review of the literature

OBJECTIVE

Radiation therapy is a mainstay in the treatment of numerous neoplasms. Numerous publications have reported good clinical outcomes for primary radiation therapy for Vestibular Schwannomas (VS). However, there are relatively few pathologic specimens of VSs available to evaluate post-radiation, which has led to a relative dearth in research on the cellular mechanisms underlying the effects of radiation therapy on VSs.

METHODS

Here we review the latest literature on the complex biological effects of radiation therapy on these benign tumors-including resistance to oxidative stress, mechanisms of DNA damage repair, alterations in normal growth factor pathways, changes in surrounding vasculature, and alterations in immune responses following radiation.

RESULTS

Although VSs are highly radioresistant, radiotherapy is often successful in arresting their growth.

CONCLUSION

By better understanding the mechanisms underlying these effects, we could potentially harness such mechanisms in the future to potentiate the clinical effects of radiotherapy on VSs.

LEVEL OF EVIDENCE

N/A.

Tumor control and trigeminal dysfunction improvement after stereotactic radiosurgery for trigeminal schwannomas: a systematic review and meta-analysis

Trigeminal nerve schwannomas (TS) are uncommon intracranial tumors, frequently presenting with debilitating trigeminal and/or oculomotor nerve dysfunction. While surgical resection has been described, its morbidity and mortality rates are non-negligible. Stereotactic radiosurgery (SRS) has emerged with variable results as a valuable alternative. Here, we aimed at reviewing the medical literature on TS treated with SRS so as to investigate rates of tumor control and symptomatic improvement. We reviewed manuscripts published between January 1990 and December 2019 on PubMed. Tumor control and symptomatic improvement rates were evaluated with separate meta-analyses. This meta-analysis included 18 studies comprising a total of 564 patients. Among them, only one reported the outcomes of linear accelerators (Linac), while the others of GK. Tumor control rates after SRS were 92.3% (range 90.1–94.5; p < 0.001), and tumor decrease rates were 62.7% (range 54.3–71, p < 0.001). Tumor progression rates were 9.4% (range 6.8–11.9, p < 0.001). Clinical improvement rates of trigeminal neuralgia were 63.5% (52.9–74.1, p < 0.001) and of oculomotor nerves were 48.2% (range 36–60.5, p < 0.001). Clinical worsening rate was 10.7% (range 7.6–13.8, p < 0.001). Stereotactic radiosurgery for TS is associated with high tumor control rates and favorable clinical outcomes, especially for trigeminal neuralgia and oculomotor nerves. However, patients should be correctly advised about the risk of tumor progression and potential clinical worsening. Future clinical studies should focus on standard reporting of clinical outcomes.

Clinical Results After Single-fraction Radiosurgery for 1,002 Vestibular Schwannomas

Background

Herein, we report clinical results for patients treated with stereotactic radiosurgery (SRS) for vestibular schwannomas (VS) over a period of 10 years.

Methods

Clinical data and imaging follow-up were stored in a database of 1,378 patients, with 1,384 VS treated consecutively between 2005 and 2018 and analyzed retrospectively. A total of 996 patients with 1,002 tumors with at least one year of follow-up were included for analysis.

Results

Median follow-up was 3·6 years (1-12·5 years). The three, five, and 10-year Kaplan-Meier estimated local tumor control was 96·6%, 92·3%, and 90·8%, respectively. The median hearing loss of the affected ear as compared to its healthy counterpart was 17 dB at treatment start and increased to 23 and 29 dB at one and five years. Six patients (0·6%) developed symptomatic hydrocephalus and underwent the placement of a ventriculoperitoneal shunt. In 30 patients (3·0%), trigeminal sensory dysfunction developed, five patients (0·5%) had a mild transient weakness, and nine patients (0·9%) had a permanent facial weakness (House-Brackmann Grade > II) after SRS.

Conclusion

Single fraction SRS proves to be highly effective and shows low treatment-related toxicity for VS. SRS should be considered a primary treatment option for small and middle-sized VS.

Persistent Oxidative Stress in Vestibular Schwannomas After Stereotactic Radiation Therapy

OBJECTIVE

Stereotactic radiation therapy is increasingly used to treat vestibular schwannomas (VSs) primarily and to treat tumor remnants following microsurgery. Little data are available regarding the effects of radiation on VS cells. Tyrosine nitrosylation is a marker of oxidative stress following radiation in malignant tumors. It is not known how long irradiated tissue remains under oxidative stress, and if such modifications occur in benign neoplasms such as VSs treated with significantly lower doses of radiation. We immunostained sections from previously radiated VSs with an antibody that recognizes nitrosylated tyrosine residues to assess for ongoing oxidative stress.

STUDY DESIGN

Immunohistochemical analysis.

METHODS

Four VSs, which recurred after excision, were treated with stereotactic radiation therapy. Ultimately each tumor required salvage reresection for regrowth. Histologic sections of each tumor before and after radiation were immunolabeled with a monoclonal antibody specific to nitrotyrosine and compared. Two VSs that underwent reresection of a growing tumor remnant without previous radiation therapy served as additional controls.

RESULTS

Irradiated tumors enlarged in volume by 3.16 to 8.62 mL following radiation. Preradiation sections demonstrated little to no nitrotyrosine immunostaining. Three of four of irradiated VSs demonstrated increased nitrotyrosine immunostaining in the postradiation sections compared with preradiation tumor sections. Nonirradiated VSs did not label with the antinitrotyrosine antibody.

CONCLUSIONS

VSs exhibit oxidative stress up to 7 years after radiotherapy, yet these VSs continued to enlarge. Thus, VSs that grow following radiation appear to possess mechanisms for cell survival and proliferation despite radiation-induced oxidative stress.

Primary culture of human vestibular schwannomas

Vestibular schwannomas (VSs) represent Schwann cell (SC) tumors of the vestibular nerve, compromising 10% of all intracranial neoplasms. VSs occur in either sporadic or familial (neurofibromatosis type 2, NF2) forms, both associated with inactivating defects in the NF2 tumor suppressor gene. Treatment for VSs is generally surgical resection or radiosurgery, however the morbidity of such procedures has driven investigations into less invasive treatments. Historically, lack of access to fresh tissue specimens and the fact that schwannoma cells are not immortalized have significantly hampered the use of primary cultures for investigation of schwannoma tumorigenesis. To overcome the limited supply of primary cultures, the immortalized HEI193 VS cell line was generated by transduction with HPV E6 and E7 oncogenes. This oncogenic transduction introduced significant molecular and phenotypic alterations to the cells, which limit their use as a model for human schwannoma tumors. We therefore illustrate a simplified, reproducible protocol for culture of primary human VS cells. This easily mastered technique allows for molecular and cellular investigations that more accurately recapitulate the complexity of VS disease.

Radiosurgery as neuromodulation therapy!

Radiosurgery is commonly considered to be effective through a destructive physical mechanism acting on neural tissue. However, the results of modern neurophysiological, radiological, and histological studies are providing a basis on which to question this assumption. There are now multiple pieces of evidence pointing to a nonlesional mechanism of the radiosurgical action. It appears that tissue destruction is absent or minimal and in almost all cases insufficient to explain the clinical effects produced. There is a real possibility that radiosurgery induces changes in the functioning of neural tissue by differential effects on various neuronal populations and remodeling the glial environment, leading to modulation of function while preserving basic processing. Hence, the majority of radiosurgical procedures induce the desired biological effect without histological destruction of tissue. These findings may result in a major paradigm shift in the treatment of functional brain disorders.

Therapeutic profile of single-fraction radiosurgery of vestibular schwannoma: unrelated malignancy predicts tumor control

Radiosurgery has become an accepted treatment option for vestibular schwannomas. Nevertheless, predictors of tumor control and treatment toxicity in current radiosurgery of vestibular schwannomas are not well understood. To generate new information on predictors of tumor control and cranial nerve toxicity of single-fraction radiosurgery of vestibular schwannomas, we conducted a single-institution long-term observational study of radiosurgery for sporadic vestibular schwannomas. Minimum follow-up was 3 years. Investigated as potential predictors of tumor control and cranial nerve toxicity were treatment technology; tumor resection preceding radiosurgery; tumor size; gender; patient age; history of cancer, vascular disease, or metabolic disease; tumor volume; radiosurgical prescription dose; and isodose line. Three hundred eighty-six patients met inclusion criteria. Treatment failure was observed in 27 patients. History of unrelated cancer (strongest predictor) and prescription dose significantly predicted tumor control. The cumulative incidence of treatment failure was 30% after 6.5 years in patients with unrelated malignancy and 10% after ≥15 years in patients without such cancer (P < .02). Tumor volume was the only predictor of trigeminal neuropathy (observed in 6 patients). No predictor of facial nerve toxicity was found. On the House and Brackmann scale, 1 patient had a permanent one-level drop and 7 a transient drop of 1 to 3 levels. Serviceable hearing was preserved in 75.1%. Tumor hearing before radiosurgery, recurrence, and prescription isodose predicted ototoxicity. Unrelated malignancy is a strong predictor of tumor control. Tumor recurrence predominantly predicts ototoxicity. These findings potentially will aid future clinical decision making in ambiguous cases.

Radiobiology of vestibular schwannomas: mechanisms of radioresistance and potential targets for therapeutic sensitization

Vestibular schwannomas (VS) are benign tumors arising from the Schwann cells of cranial nerve VIII. Historically the prevailing therapy for patients with VS has been microsurgical resection. More recently, stereotactic radiosurgery (SRS) and fractionated stereotactic radiotherapy have gained acceptance as effective alternatives. Although the side effect profile and rates of tumor control appear to be favorable for SRS, there is a subset of radioresistant tumors that continue to progress despite properly administered radiation treatment. In this review, the authors summarize what is known about the mechanism of radioresistance in VS at the clinical and molecular level. An improved understanding of the radiobiological behavior of VS may help guide appropriate patient selection for SRS and potentially aid in the design of novel therapies to treat radioresistant tumors.

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.

Surgical Salvage after Failed Irradiation for Vestibular Schwannoma

OBJECTIVES/HYPOTHESIS

Compare vestibular schwannoma (VS) surgical outcome between patients with prior irradiation and those not previously treated.

STUDY DESIGN

Retrospective review with matched control group.

METHODS

Review of tumor adherence to the facial nerve, facial nerve grade, and complications in 38 patients with radiotherapy as a primary procedure before VS surgical removal and a matched random sample of 38 patients with primary surgery. The majority of the irradiated group had gamma knife radiation therapy. Mean time from irradiation to surgical salvage was 3.3 years (SD = 3.2), with a minimum of 5.2 months and a maximum of 15.8 years. Most (89.5%) patients in each group underwent a translabyrinthine approach. Mean tumor size at surgery was 2.6 cm in each group.

RESULTS

The irradiated group had more moderate to severe adherence of tumor than the controls (89% vs. 63%, P < or = .01). They also had a lower rate of good facial function (House-Brackmann grade I/II) (37% vs. 70%) and a higher rate of poor function (grades V or VI) (50% vs. 18%) at follow-up (P < or = .019). Results were similar when including only those with good preoperative function (50% vs. 72% and 32% vs. 15%) but did not achieve statistical significance. Surgical time and complications did not differ.

CONCLUSION

Patients who have undergone irradiation for VS and require surgical salvage may have a more difficult surgery and poorer outcomes than those not previously irradiated. When making their initial choice of treatment, patients should be counseled that surgery might be more difficult after failed stereotactic irradiation.

Radiosurgery for vestibular schwannomas

BACKGROUND

Radiosurgery has been established as an important alternative to microsurgery. We report our experience with radiosurgery for tumor control and the complications of unilateral vestibular schwannomas.

METHODS

We reviewed our early experience regarding clinical presentation, management and outcomes in 45 patients with acoustic schwannomas who underwent gamma knife stereotactic radiosurgery. The median follow-up period was 25 months (range, 6-48 months). Thirteen patients had undergone 1 or more previous resections before radiosurgery; 32 underwent radiosurgery as the first procedure. Median tumor volume was 4.5 mL (range, 0.5-30.0), and median radiotherapy dose was 11.5 Gy (range, 10.5-14.0 Gy).

RESULTS

Tumor control was achieved in 43 patients (95.6%). Loss of central contrast enhancement was a characteristic change and was noted in 29 patients (64.4%). Reduction in tumor size was shown in 15 patients (33.3%). Thirteen patients (28.9%) had good or serviceable hearing preoperatively, and in all of these, the preoperative status was retained immediately after radiosurgery. At follow-up, however, 10 patients (76.9%) had preserved hearing and 3 (23.1%) had reduced hearing on the treated side. Hearing in 1 patient that was not serviceable preoperatively later improved to a serviceable level. No patients had delayed facial palsy or lower cranial nerve dysfunction, but one had delayed trigeminal sensory loss.

CONCLUSION

Radiosurgery achieved a high tumor control rate and a relatively low post-radiosurgical complication rate for acoustic neuromas.

Long-term results of Leksell gamma knife surgery for trigeminal schwannomas

Object. The authors evaluated the long-term efficacy of gamma knife surgery (GKS) in patients with trigeminal schwannomas.

Methods. Fifty-six patients, 31 women and 25 men (mean age 42 years), underwent GKS for trigeminal schwannomas. Fourteen had previously undergone surgery, and GKS was the primary treatment in the remaining 42 patients. The mean target volume was 8.7 cm3 (range 0.8–33 cm3); the mean maximum dose was 27 Gy (range 20–40 Gy); the mean tumor margin dose was 13.3 Gy (range 10–15 Gy); and the mean follow-up period was 68 months (range 27–114 months).

Disappearance of the tumor occurred in seven patients. An obvious decrease in tumor volume was observed in 41 patients, four tumors remained unchanged, and four tumors progressed at 5, 26, 30, and 60 months, respectively. One patient with disease progression died of tumor progression at 36 months after GKS. The tumor growth control rate in this group was 93% (52 of 56 cases).

Mild numbness or diplopia was relieved completely in 14 patients. Improvement of other neurological deficits was demonstrated in 25 patients. Trigeminal nerve dysfunction was either unchanged or slightly worse in 13 patients after GKS. Four patients experienced mild symptom deterioration related to tumor progression.

Conclusions. Radiosurgery proved to be an effective treatment for small- and medium-sized trigeminal schwannomas. Some larger tumors are also suitable for radiosurgery if there is no significant brainstem compression.

Long-term results of Leksell gamma knife surgery for trigeminal schwannomas

Object. The authors evaluated the long-term efficacy of gamma knife surgery (GKS) in patients with trigeminal schwannomas.

Methods. Fifty-six patients, 31 women and 25 men (mean age 42 years), underwent GKS for trigeminal schwannomas. Fourteen had previously undergone surgery, and GKS was the primary treatment in the remaining 42 patients. The mean target volume was 8.7 cm3 (range 0.8–33 cm3); the mean maximum dose was 27 Gy (range 20–40 Gy); the mean tumor margin dose was 13.3 Gy (range 10–15 Gy); and the mean follow-up period was 68 months (range 27–114 months).

Disappearance of the tumor occurred in seven patients. An obvious decrease in tumor volume was observed in 41 patients, four tumors remained unchanged, and four tumors progressed at 5, 26, 30, and 60 months, respectively. One patient with disease progression died of tumor progression at 36 months after GKS. The tumor growth control rate in this group was 93% (52 of 56 cases).

Mild numbness or diplopia was relieved completely in 14 patients. Improvement of other neurological deficits was demonstrated in 25 patients. Trigeminal nerve dysfunction was either unchanged or slightly worse in 13 patients after GKS. Four patients experienced mild symptom deterioration related to tumor progression.

Conclusions. Radiosurgery proved to be an effective treatment for small- and medium-sized trigeminal schwannomas. Some larger tumors are also suitable for radiosurgery if there is no significant brainstem compression.

Clinical and histopathologic features of recurrent vestibular schwannoma (acoustic neuroma) after stereotactic radiosurgery

OBJECTIVE

Stereotactic radiosurgery for vestibular schwannoma entails uncertain long-term risk of tumor recurrence and delayed cranial neuropathies. In addition, the underlying histopathologic changes to the tumor bed are not fully characterized. We seek to understand the clinical and histologic features of recurrent vestibular schwannoma after stereotactic radiation therapy.

STUDY DESIGN

Retrospective review.

SETTING

Tertiary referral center.

PATIENTS

Four patients who underwent microsurgical resection of vestibular schwannoma after primary stereotactic radiation therapy.

INTERVENTION

Patients were treated primarily with gamma knife radiosurgery or fractionated stereotactic radiotherapy followed by salvage microsurgery. Retrosigmoid craniotomy was used in all cases.

MAIN OUTCOME MEASURES

Histopathologic review. Preoperative and postoperative facial nerve function was assessed with the House-Brackmann scale.

RESULTS

We observed highly inconsistent radiation changes in the cerebellopontine angle and internal auditory canal. Fibrosis outside and within the tumor bed varied markedly, complicating microsurgical dissection. Light microscopy confirmed the presence of viable tumor in all cases. Histopathologic features were typical of vestibular schwannoma, and there was no significant scarring that could be attributed to radiation effect.

CONCLUSIONS

The variable fibrosis in the cerebellopontine angle and lack of radiation changes seen histopathologically in irradiated vestibular schwannoma suggest that a uniform treatment effect was not achieved in these cases. Although all four patients with preoperative cranial neuropathies were found intraoperatively to have fibrosis in the cerebellopontine angle, excellent preservation of facial nerve anatomy and function was possible with salvage microsurgical resection. Additional analyses are needed to clarify the histopathologic and molecular characteristics associated with vestibular schwannoma growth after stereotactic radiation.

Analysis of risk factors associated with radiosurgery for vestibular schwannoma

OBJECT

The aim of this study was to identify factors associated with delayed cranial neuropathy following radiosurgery for vestibular schwannoma (VS or acoustic neuroma) and to determine how such factors may be manipulated to minimize the incidence of radiosurgical complications while maintaining high rates of tumor control.

METHODS

From July 1988 to June 1998, 149 cases of VS were treated using linear accelerator radiosurgery at the University of Florida. In each of these cases, the patient's tumor and brainstem were contoured in 1-mm slices on the original radiosurgical targeting images. Resulting tumor and brainstem volumes were coupled with the original radiosurgery plans to generate dose-volume histograms. Various tumor dimensions were also measured to estimate the length of cranial nerve that would be irradiated. Patient follow-up data, including evidence of cranial neuropathy and radiographic tumor control, were obtained from a prospectively maintained, computerized database. The authors performed statistical analyses to compare the incidence of posttreatment cranial neuropathies or tumor growth between patient strata defined by risk factors of interest. One hundred thirty-nine of the 149 patients were included in the analysis of complications. The median duration of clinical follow up for this group was 36 months (range 18-94 months). The tumor control analysis included 133 patients. The median duration of radiological follow up in this group was 34 months (range 6-94 months). The overall 2-year actuarial incidences of facial and trigeminal neuropathies were 11.8% and 9.5%, respectively. In 41 patients treated before 1994, the incidences of facial and trigeminal neuropathies were both 29%, but in the 108 patients treated since January 1994, these rates declined to 5% and 2%, respectively. An evaluation of multiple risk factor models showed that maximum radiation dose to the brainstem, treatment era (pre-1994 compared with 1994 or later), and prior surgical resection were all simultaneously informative predictors of cranial neuropathy risk. The radiation dose prescribed to the tumor margin could be substituted for the maximum dose to the brainstem with a small loss in predictive strength. The pons-petrous tumor diameter was an additional statistically significant simultaneous predictor of trigeminal neuropathy risk, whereas the distance from the brainstem to the end of the tumor in the petrous bone was an additional marginally significant simultaneous predictor of facial neuropathy risk. The overall radiological tumor control rate was 93% (59% tumors regressed, 34% remained stable, and 7.5% enlarged), and the 5-year actuarial tumor control rate was 87% (95% confidence interval [CI] 76-98%). Analysis revealed that a radiation dose cutpoint of 10 Gy compared with more than 10 Gy prescribed to the tumor margin yielded the greatest relative difference in tumor growth risk (relative risk 2.4, 95% CI 0.6-9.3), although this difference was not statistically significant (p = 0.207).

CONCLUSIONS

Five points must be noted. 1) Radiosurgery is a safe, effective treatment for small VSs. 2) Reduction in the radiation dose has played the most important role in reducing the complications associated with VS radiosurgery. 3) The dose to the brainstem is a more informative predictor of postradiosurgical cranial neuropathy than the length of the nerve that is irradiated. 4) Prior resection increases the risk of late cranial neuropathies after radiosurgery. 5) A prescription dose of 12.5 Gy to the tumor margin resulted in the best combination of maximum tumor control and minimum complications in this series.

Acoustic neuroma with malignant transformation. Case report

The authors describe the case of a 57-year-old woman who had a right-sided hearing disturbance that had remained untreated for 1 year. The diagnosis was of a right cerebellopontine angle tumor, and the patient underwent its removal via retrosigmoid approach. Pathologically, the tumor was a typical benign neuroma. Growth of residual tumor was detected 4 years after the initial operation, and it was treated with gamma knife surgery (GKS). Six months later, the tumor had grown, and the patient underwent surgery via a combined retrosigmoid-translabyrinthine approach. Abnormal mitotic figures were observed on histological studies, indicating that the tumor had become malignant. Thereafter, the tumor grew rapidly, and the patient died 6.5 years after the initial treatment. It cannot be ruled out that GKS affected the outcome, but the causal sequence was unclear. Because such a patient is rare, documentation of the case was considered clinically important.

Stereotactic radiosurgery versus stereotactic radiotherapy for patients with vestibular schwannoma: a Leksell Gamma Knife Society 2000 debate

✓ By definition, the term “radiosurgery” refers to the delivery of a therapeutic radiation dose in a single fraction, not simply the use of stereotaxy. Multiple-fraction delivery is better termed “stereotactic radiotherapy.” There are compelling radiobiological principles supporting the biological superiority of single-fraction radiation for achieving an optimal therapeutic response for the slowly proliferating, late-responding, tissue of a schwannoma. It is axiomatic that complication avoidance requires precise three-dimensional conformality between treatment and tumor volumes. This degree of conformality can only be achieved through complex multiisocenter planning. Alternative radiosurgery devices are generally limited to delivering one to four isocenters in a single treatment session. Although they can reproduce dose plans similar in conformality to early gamma knife dose plans by using a similar number of isocenters, they cannot reproduce the conformality of modern gamma knife plans based on magnetic resonance image—targeted localization and five to 30 isocenters.

A disturbing trend is developing in which institutions without nongamma knife radiosurgery (GKS) centers are championing and/or shifting to hypofractionated stereotactic radiotherapy for vestibular schwannomas. This trend appears to be driven by a desire to reduce complication rates to compete with modern GKS results by using complex multiisocenter planning. Aggressive advertising and marketing from some of these centers even paradoxically suggests biological superiority of hypofractionation approaches over single-dose radiosurgery for vestibular schwannomas. At the same time these centers continue to use the term radiosurgery to describe their hypofractionated radiotherapy approach in an apparent effort to benefit from a GKS “halo effect.” It must be reemphasized that as neurosurgeons our primary duty is to achieve permanent tumor control for our patients and not to eliminate complications at the expense of potential late recurrence. The answer to minimizing complications while maintaining maximum tumor control is improved conformality of radiosurgery dose planning and not resorting to homeopathic radiosurgery doses or hypofractionation radiotherapy schemes.

Linear accelerator radiosurgery in the management of brain tumours

Radiosurgery is an increasingly popular method for treating a variety of intracranial tumours. A great deal of treatment data has been accumulated suggesting that radiosurgery may be the treatment of choice for small acoustic schwannomas. Moreover, radiosurgery promises excellent tumour control and minimal risk in the treatment of small meningiomas in risky surgical locations such as the cavernous sinus. Radiosurgery offers superior local control rates for many metastatic neoplasms and has promise as an adjuvant 'boost' technique in certain malignant gliomas. This article presents a brief description of the linear accelerator, LINAC, radiosurgical technique, followed by a review of the more common applications of stereotactic radiosurgery in the treatment of intracranial neoplastic disease.

Fractionated stereotactic radiosurgery and preservation of hearing in patients with vestibular schwannoma: a preliminary report

OBJECTIVE

Microsurgery and stereotactic radiosurgery (SRS) for vestibular schwannomas are associated with a relatively high incidence of sensorineural hearing loss. A prospective trial of fractionated SRS was undertaken in an attempt to preserve hearing and minimize incidental cranial nerve injury.

METHODS

Thirty-three patients with vestibular schwannomas were treated with 2100 cGy in three fractions during a 24-hour period using conventional frame-based linear accelerator radiosurgery. The median tumor diameter was 20 mm (range, 7-42 mm). Baseline and follow-up evaluations included audiometry and contrast-enhanced magnetic resonance imaging. End points were tumor progression, preservation of serviceable hearing, and treatment-related complications.

RESULTS

Thirty-one patients (32 tumors) were assessable for tumor progression and treatment-related complications and 21 patients for preservation of serviceable hearing, with a median follow-up interval of 2 years (range, 0.5-4.0 yr). Tumor regression or stabilization was documented in 30 patients (97%) and tumor progression in 1 (3%). The patient with tumor progression remains asymptomatic and has not required surgical intervention. Five patients (16%) developed trigeminal nerve injury at a median of 6 months (range, 4-12 mo) after SRS; two of these patients had preexisting trigeminal neuropathy. One patient (3%) developed facial nerve injury (House-Brackmann Class 3) 7 months after SRS. Preservation of useful hearing (Gardner-Robertson Class 1-2) was 77% at 2 years. All patients with pretreatment Gardner-Robertson Class 1 to 2 hearing maintained serviceable (Class 1-3) hearing as of their last follow-up examination.

CONCLUSION

Three-fraction SRS with a conventional stereotactic frame is feasible and well tolerated in the treatment of acoustic neuroma. This study demonstrates a high rate of hearing preservation and few treatment-related complications among a relatively high-risk patient cohort (tumors >15 mm or neurofibromatosis Type 2). Longer follow-up will be required to assess the durability of tumor control.

Stereotactic radiosurgery for jugular foramen schwannomas

BACKGROUND

Jugular foramen schwannomas pose difficult management problems because of the surgical risk of lower cranial neuropathy. The indications and results of stereotactic radiosurgery are not well documented.

METHODS

We reviewed our 10-year experience in the management of 17 patients who had jugular foramen schwannomas managed with the gamma knife. Thirteen patients previously had undergone surgery (range, 1-6 resections). Four patients had multiple cranial nerve deficits before microsurgical resection; 12 developed multiple lower cranial nerve palsies after resection. Four patients underwent radiosurgery based on imaging criteria alone. Conformal dose planning (tumor margin dose of 12-18 Gy) successfully encompassed the irregular tumor volumes in all patients.

RESULTS

Follow-up varied from 6 to 74 months. Tumor size decreased in eight patients, remained stable in eight, and increased in one patient during the average follow-up interval of 3.5 years. Six patients improved and 10 others retained their preradiosurgery clinical status. One patient had an increase in tumor size and clinical deterioration 6 months after radiosurgery and underwent microsurgical resection. No patient developed new cranial nerve or other neurological deficits after radiosurgery.

CONCLUSIONS

We believe that gamma knife radiosurgery is an effective alternative to microsurgical resection for patients who have small tumors and intact lower cranial nerve function. It is also effective for patients who have residual or recurrent tumors after microsurgical resection.

Stereotactic radiosurgery for trigeminal schwannomas

OBJECTIVE

Schwannomas that arise from the trigeminal nerve are rare and are usually managed by surgical resection. The role of radiosurgery in the care of patients with these basal tumors remains to be defined.

METHODS

We reviewed the clinical presentation, management, and outcomes for 16 trigeminal schwannoma patients who underwent gamma knife stereotactic radiosurgery. Fifteen of the 16 patients presented with trigeminal sensory dysfunction. Nine patients had tumors in the region of the ganglion, six in the region of the trigeminal nerve root, and one in the region of the mandibular branch. Six patients had undergone one or more previous resections before radiosurgery. Ten underwent radiosurgery as the first procedure. The mean tumor volume was 5.3 cc (range, 1-17.8 cc). The mean tumor margin dose was 15.3 Gy (range, 12-20 Gy).

RESULTS

During the average imaging follow-up of 44 months (range, 8-116 mo), the tumor control rate was 100% (regression in nine patients and no further tumor growth in seven patients). Five patients had improvement of clinical symptoms, and 11 remained unchanged. No new cranial nerve deficit developed in any patient.

CONCLUSION

As a minimally invasive alternative to microsurgery, gamma knife radiosurgery proved to be an alternative primary or adjuvant strategy that controlled tumor growth, did not cause new deficits, and often improved presenting symptoms.

Death from a malignant cerebellopontine angle triton tumor despite stereotactic radiosurgery. Case report

Malignant vestibular nerve tumors are rare: to date, only three cases have been reported in the literature. The authors report a case of an eighth cranial nerve tumor that progressed 5 years after stereotactic radiosurgery. The patient was a 44-year-old man who underwent stereotactic radiosurgery for a 27-mm cerebellopontine angle tumor that was discovered on investigation of tinnitus and hearing loss. He developed facial weakness after 5 years, and repeated imaging revealed tumor enlargement. Despite complete microsurgical excision, the tumor rapidly recurred locally and subsequently disseminated within the neuraxis. The patient died 1 year after tumor progression was detected. Histopathological analysis revealed a malignant spindle cell neoplasm with frequent mitotic figures. The presence of positive rhabdoid elements on immunohistochemical studies confirmed that it was a triton tumor. The authors review the relevant literature concerning the classification and management of malignant vestibular nerve tumors and discuss the implications of tumor progression after stereotactic radiosurgery.

Outcome analysis of acoustic neuroma management: a comparison of microsurgery and stereotactic radiosurgery

Currently, microsurgical resection of acoustic neuromas by an experienced, multidisciplinary team is thought to be the treatment of choice. During the past 20 years stereotactic radiosurgery has been used as an alternative to surgical removal. To compare the results of both microsurgery and stereotactic radiosurgery, we conducted a study of 87 patients with unilateral, previously unoperated acoustic neuromas with an average diameter less than 3 cm treated by the neurosurgical service during 1990 and 1991. Preoperative patient characteristics and average tumor size were similar between the treatment groups. State of the art microsurgical or radiosurgical techniques were used by experienced surgeons in both treatment groups. The treatment groups were compared based on cranial nerve preservation, tumor control, postoperative complications, patient symptomatology, length of hospital stay, total management charges, effect on employment status, and overall patient satisfaction. Stereotactic radiosurgery was more effective in preserving normal postoperative facial function (P < 0.05), and hearing preservation (P < 0.03) with less treatment associated morbidity (P < 0.01). Effect on preoperative symptoms were similar between the treatment groups. Postoperative functional outcomes and patients' satisfaction of their tumor management were greater after stereotactic radiosurgery when compared to the microsurgical group, although they did not reach statistical significance (P = 0.07 and P = 0.10, respectively). Patients returned to independent functioning sooner after stereotactic radiosurgery (P < 0.001). Hospital length of stay and total management charges were less in the radiosurgical group (P < 0.001). When compared to microsurgical removal, stereotactic radiosurgery proved to be an effective and less costly management strategy of unilateral acoustic neuromas less than 3 cm in diameter. For many acoustic neuroma patients, stereotactic radiosurgery should be offered as an alternative management strategy.

Stereotactic radiosurgery of vestibular schwannomas with a linear accelerator

The authors describe their initial experience with stereotactic radiosurgery of 22 cases with vestibular schwannomas using a linear accelerator. 14 of them with a follow-up of at least one year were studied. 6-9 months after treatment 86% had central tumour necrosis, 71% tumour shrinkage and none of them evidence of tumour growth 3 patients developed reversible facial nerve impairment, 2 had permanent facial numbness. Hearing diminished in one case out of three with normal hearing and in two out of three with already diminished hearing. Although there is a general consensus that microsurgery is the treatment of choice for these benign tumours, stereotactic radiosurgery challenges this opinion. Stereotactic radiosurgery not only proves to be a valuable alternative for selected cases not suitable for microsurgery, but it is conceivable that it will become the treatment of choice for small vestibular tumours. Tumour control can be obtained in the majority of treated patients with fewer complications and with a higher rate of cranial nerve sparing. This series indicates that linear accelerators can achieve results similar to the Gamma Unit in the treatment of vestibular schwannomas.

The radiobiology of human acoustic schwannoma xenografts after stereotactic radiosurgery evaluated in the subrenal capsule of athymic mice

An experimental model with xenograft transplantation into the subrenal capsule of athymic (nude) mice was used to evaluate the early response of human acoustic schwannomas to stereotactic radiosurgery. After xenograft placement, 45 mice underwent radiosurgery with single doses of 10, 20, or 40 Gy using a 201-source 60Co gamma unit (4-mm collimator, single isocenter, 80% isodose line). The 45 radiosurgery-treated xenografts were compared with 15 untreated xenografts and 15 xenografts in mice that underwent "sham radiosurgery." All five study groups were matched for the following pretreatment variables: patient of origin, animal weight, average xenograft diameter, and percentage of xenograft surface vascularity. Immediately prior to sacrifice of the mice all xenografts were evaluated in situ to determine the average tumor diameter, tumor volume, and percentage of surface vascularity. Mice were sacrificed 2 weeks, 1 month, or 3 months after radiosurgery. Blinded histological review was performed by an independent neuropathologist. Tumor volume was reduced 33.6% after 2 weeks (p = 0.023) and 45% after 3 months (p = 0.018) in the 40-Gy radiosurgery group. Tumor volume was reduced by 46.2% after 1 month (p = 0.0002) and 35.2% after 3 months (p = 0.032) in the 20-Gy radiosurgery group. An average volume reduction of 16.4% was observed after 3 months (p = 0.17) in the 10-Gy radiosurgery group. At 3 months after surgery, tumor surface vascularity was reduced by an average of 19.7% (p = 0.043) in the 40-Gy radiosurgery group and 5.8% (p = 0.12) in the 20-Gy radiosurgery group and was unchanged in the 10-Gy radiosurgery group and both control groups. Histological examination demonstrated a higher incidence of hemosiderin deposits (p = 0.026) and vascular mural hyalinization (p = 0.032) in radiosurgery xenografts versus control. The subrenal capsule xenograft in nude mice was an excellent model for studying the in vivo radiobiology of acoustic schwannomas after radiosurgery. Both cellular and vascular effects could be assessed serially in situ and the model was stable even 4 months after transplantation. Additional studies investigating radiobiology over periods better approximating the time course of clinical neuroimaging changes (6 to 12 months) are warranted.

Tumor control after stereotactic radiosurgery in neurofibromatosis patients with bilateral acoustic tumors

During a 4-year interval, 17 patients with bilateral acoustic tumors (vestibular schwannomas) underwent unilateral stereotactic radiosurgery using a multisource gamma unit; 2 patients underwent radiosurgery of both tumors in separate sessions. Eleven patients with unoperated contralateral tumors served as concurrent controls to compare the effects of radiosurgery with the natural history of acoustic tumors. After radiosurgery, the tumor control and regression rates were 89.5 and 21.1%, respectively (median neuroimaging follow-up, 1.4 years; range, 0.3-3.9). The tumor regression rate increased to 40% for patients evaluated at least 12 months after radiosurgery. In comparison to the unoperated contralateral tumors, stereotactic radiosurgery achieved tumor control, as assessed by the ultimate change in tumor size at follow-up (P, 0.012), the change in tumor size over time (P, 0.006), and tumor growth rates (P, 0.003). This study provided convincing evidence that tumor stabilization after radiosurgery (as assessed by neuroimaging) truly represented tumor control. The incidence of delayed facial neuropathy after radiosurgery compared favorably with the incidence reported after microsurgical removal. Some hearing was preserved in one-third of the patients who had preoperative hearing, including three patients who were contralaterally deaf. Stereotactic radiosurgery should be considered as a primary surgical modality for many patients with neurofibromatosis Type II.

Radiosurgery of acoustic neurinomas

Eighty-five patients with acoustic neurinomas underwent stereotactic radiosurgery with the gamma unit at the University of Pittsburgh (Pittsburgh, PA) during its first 30 months of operation. Neuroimaging studies performed in 40 patients with more than 1 year follow-up showed that tumors were smaller in 22 (55%), unchanged in 17 (43%), and larger in one (2%). The 2-year actuarial rates for preservation of useful hearing and any hearing were 46% and 62%, respectively. Previously undetected neuropathies of the trigeminal (n = 12) and facial nerves (n = 14) occurred 1 week to 1 year after radiosurgery (median, 7 and 6 months, respectively), and improved at median intervals of 13 and 8 months, respectively, after onset. Hearing loss was significantly associated with increasing average tumor diameter (P = 0.04). No deterioration of any cranial nerve function has yet developed in seven patients with average tumor diameters less than 10 mm. Radiosurgery is an important treatment alternative for selected acoustic neurinoma patients.

Granular cell tumour of the appendix in a patient irradiated for a rectal carcinoma

We report on a 47-year-old man with a granular cell tumour of the appendix, discovered incidentally during surgery for a rectal adenocarcinoma that had been irradiated preoperatively. A detailed immunocytochemical analysis revealed positivity for S-100 and neuron-specific enolase (NSE). Electron microscopically, the cytoplasm of the tumour cells contained numerous pleomorphic lysosomes. In the appendix tissue adjacent to the tumour a neuroma and the histological features of radiation injury were present. Our findings suggest that this granular cell tumour may have originated from a pre-existing appendix neuroma which underwent granular degeneration, possibly as a result of radiation.

Physics of gamma knife approach on convergent beams in stereotactic radiosurgery

The Presbyterian-University Hospital of Pittsburgh installed the first clinically designated Leksell gamma knife in the U.S. in August 1987. Gamma knife radiosurgery involves stereotactic target localization with the Leksell frame and subsequent closed-skull single-treatment session irradiation of a lesion with multiple highly focused gamma ray beams produced from 60Co sources. The hemispherical array of sources, the large number of small-diameter beams, and the steep dose gradients surrounding a targeted lesion make physical characterization of the radiation field complex. This paper describes the physical features and the operation of the gamma knife as well as the calibration procedures of the very small, well-collimated beams. The results of studies using in-phantom ion chamber, diode, film, and lithium fluoride thermoluminescent dosimetry were all in close agreement. Both single-beam and multiple-beam dose profiles were measured and reported for the interchangeable helmets, which have 4-, 8-, 14-, and 18-mm-diameter collimators. We also describe the dose calculation and treatment planning algorithm in the treatment planning system. Measurements of the accuracy of mechanical and radiation alignment are also performed and discussed.

Gamma knife: an alternative treatment for acoustic neurinomas

Despite surgical advances and technologic means of better monitoring seventh and eighth nerve function intraoperatively, there remains a group of patients for whom alternative methods of treatment are desirable. These include the elderly, those with bilateral tumors or tumors in only hearing ears, individuals with medical contraindications to major surgery, and those who refuse surgical resection. The University of Pittsburgh became the fifth world center and the first in the United States to install the "gamma knife" for stereotactic radiosurgery. On the basis of the pioneering work done at the Karolinska Institute in Stockholm, acoustic tumor patients who fulfill the above criteria are being treated. A tumoricidal single treatment closed-skull radiation dose is given through 201 sharply focused cobalt 60 sources, minimizing the effects on surrounding brain or other tissues. Our early results are discussed and compared to those from more than 200 cases in Stockholm. Complications and expected long-term results are presented.