Gamma knife radiosurgery for intracranial metastatic melanoma: a 6-year experience

In Patients With Melanoma Brain Metastases, Is Combination Immune Checkpoint Inhibition a Safe and Effective First-Line Treatment? A Critically Appraised Topic

BACKGROUND

Combined PD-1/PD-L1 and CTLA-4 immune checkpoint inhibition for the has been shown to produce superior results in the treatment of malignant melanoma when compared to monotherapy. However, patients with intracranial disease were excluded from these studies given their poor prognosis.

OBJECTIVE

The objective of this study was to critically assess current evidence supporting the co-administration of PD-1/PD-L1 and CTLA-4 inhibitors in the treatment of melanoma brain metastases.

METHODS

The objective was addressed through the development of a critically appraised topic that included a clinical scenario, structured question, literature search strategy, critical appraisal, assessment of results, evidence summary, commentary, and bottom-line conclusions. Participants included consultant and resident neurologists, a medical librarian, clinical epidemiologists, and a content expert in the field of neuro-oncology.

RESULTS

A recent, open-label, non-comparative randomized phase II trial was selected for critical appraisal. This trial evaluated the efficacy and safety of nivolumab alone or in combination with ipilimumab in 79 adult patients with untreated, asymptomatic melanoma brain metastases. The rates of the primary outcome (intracranial response at ≥12 wk) in the primary endpoint cohort were 46% for cohort A (combination therapy) and 20% for cohort B (nivolumab monotherapy). No treatment related deaths were observed in the study. Grade 4 adverse events occurred in 9% of patients in cohort A and none in cohort B.

CONCLUSIONS

Co-administration of ipilimumab and nivolumab as first-line therapy is effective in the treatment of asymptomatic melanoma brain metastases, with an acceptable safety profile.

Radiation therapy for melanoma brain metastases: a systematic review

BACKGROUND

Radiation therapy (RT) for melanoma brain metastases, delivered either as whole brain radiation therapy (WBRT) or as stereotactic radiosurgery (SRS), is an established component of treatment for this condition. However, evidence allowing comparison of the outcomes, advantages and disadvantages of the two RT modalities is scant, with very few randomised controlled trials having been conducted. This has led to considerable uncertainty and inconsistent guideline recommendations. The present systematic review identified 112 studies reporting outcomes for patients with melanoma brain metastases treated with RT. Three were randomised controlled trials but only one was of sufficient size to be considered informative. Most of the evidence was from non-randomised studies, either specific treatment series or disease cohorts. Criteria for determining treatment choice were reported in only 32 studies and the quality of these studies was variable. From the time of diagnosis of brain metastasis, the median survival after WBRT alone was 3.5 months (IQR 2.4-4.0 months) and for SRS alone it was 7.5 months (IQR 6.7-9.0 months). Overall patient survival increased over time (pre-1989 to 2015) but this was not apparent within specific treatment groups.

CONCLUSIONS

These survival estimates provide a baseline for determining the incremental benefits of recently introduced systemic treatments using targeted therapy or immunotherapy for melanoma brain metastases.

Radiotherapy and immunotherapy: Can this combination change the prognosis of patients with melanoma brain metastases?

Brain metastases are a common occurrence in patients with melanoma. Prognosis is poor. Radiotherapy is the main local treatment for brain metastases. Recently, immunotherapy (i.e. immune checkpoints inhibitors) showed a significant impact on the prognosis of patients with metastatic melanoma, also in the setting of patients with brain metastases. Despite various possible treatments, survival of patients with melanoma brain metastases is still unsatisfactory; new treatment modalities or combination of therapies need to be explored. Being immunotherapy and radiotherapy alone both efficient in the treatment of melanoma brain metastases, the combination of these two therapies seems logical. Moreover radiotherapy can improve the efficacy of immunotherapy and the immune system plays a relevant role in the action of radiotherapy. Preclinical data support this combination. Clinical data are more contradictory. In this review, we will discuss available therapies for melanoma brain metastases, focusing on the preclinical and clinical available data supporting the possible synergism between radiotherapy and immunotherapy.

Impact of the number of metastatic brain lesions on survival after Gamma Knife radiosurgery

Effectiveness of Gamma Knife radiosurgery (GKRS: Elekta AB, Stockholm, Sweden) for patients with metastatic brain disease and the prognostic factors influencing their survival were analyzed in a 5 year retrospective data analysis (July 2001 to June 2006). Kaplan-Meier survival curves were constructed using univariate and multivariate analyses with the respective salient prognostic factors. This study analyzed data on 330 patients with brain metastases who underwent GKRS. Lung carcinoma (55%) was the most common primary cancer followed by breast (17.8%), melanoma (9.4%), colorectal (4.8%) and renal (3.9%). The median survival for all patients was 8 months. Survival ranged from 13 months for breast metastases, 10 months for renal, and 8 months for lung to 5 months for colorectal and melanoma. Mean age of patients was 58.5 years (range 18-81). Melanoma patients were younger with a mean age of 49 and also had the highest number of lesions (3.8) when compared to patients with renal (2.5), lung (2.8), colorectal (3) and breast (3.6). When stratified according to the number of lesions patient survival was 8 months (one to three lesions), 7.5 months (four or five lesions) and 7 months (six lesions or more). Mean Karnofsky Performance Status score (KPS) was 77 and survival dropped significantly from 8 months to 4.5 months if KPS was less than 70. Survival improved with a KPS of 70 or more, regardless of the number of lesions treated. Selection of patients based on the number of lesions may not be justified. A prospective trial is required to further define the prognostic factors affecting survival.

Ipilimumab and radiation therapy for melanoma brain metastases

Ipilimumab, an antibody that enhances T-cell activation, may augment immunogenicity of tumor cells that are injured by radiation therapy. We hypothesized that patients with melanoma brain metastasis treated with both ipilimumab and radiotherapy would have improved overall survival, and that the sequence of treatments may affect disease control in the brain. We analyzed the clinical and radiographic records of melanoma patients with brain metastases who were treated with whole brain radiation therapy or stereotactic radiosurgery between 2005 and 2012. The hazard ratios for survival were estimated to assess outcomes as a function of ipilimumab use and radiation type. Seventy patients were identified, 33 of whom received ipilimumab and 37 who did not. The patients who received ipilimumab had a censored median survival of 18.3 months (95% confidence interval 8.1–25.5), compared with 5.3 months (95% confidence interval 4.0–7.6) for patients who did not receive ipilimumab. Ipilimumab and stereotactic radiosurgery were each significant predictors of improved overall survival (hazard ratio = 0.43 and 0.45, with P = 0.005 and 0.008, respectively). Four of 10 evaluable patients (40.0%) who received ipilimumab prior to radiotherapy demonstrated a partial response to radiotherapy, compared with two of 22 evaluable patients (9.1%) who did not receive ipilimumab. Ipilimumab is associated with a significantly reduced risk of death in patients with melanoma brain metastases who underwent radiotherapy, and this finding supports the need for multimodality therapy to optimize patient outcomes. Prospective studies are needed and are underway.

Polychlorinated biphenyls disrupt blood-brain barrier integrity and promote brain metastasis formation

BACKGROUND

Polychlorinated biphenyls (PCBs) comprise a ubiquitous class of toxic substances associated with carcinogenic and tumor-promoting effects as well as neurotoxic properties in the brain. However, the effects of PCBs on the development of tumor metastases are not fully understood.

OBJECTIVE

We evaluated the hypothesis that exposure to individual PCB congeners can facilitate the development of brain metastases in immunocompetent mice via the disruption of the integrity of the blood-brain barrier (BBB).

METHODS

C57/Bl6 mice were exposed to individual PCBs by oral gavage, and 48 hr later they were injected with luciferase-labeled K1735 M2 melanoma cells into the internal carotid artery. The development of metastatic nodules was monitored by bioluminescent imaging. In addition, we evaluated the functional permeability of the BBB by measuring permeability of sodium fluorescein across the brain microvessels. Expression and colocalization of tight junction (TJ) proteins were studied by Western blotting and immunofluorescence microscopy.

RESULTS

Oral administration of coplanar PCB126, mono-ortho-substituted PCB118, and non-coplanar PCB153 (each at 150 micromol/kg body weight) differentially altered expression of the TJ proteins claudin-5, occludin, and zonula occludens-1 in brain capillaries. These alterations were associated with increased permeability of the BBB. Most importantly, exposure to individual PCB congeners enhanced the rate of formation and progression of brain metastases of luciferase-tagged melanoma cells.

CONCLUSIONS

Our results show for the first time that exposure to individual PCBs can facilitate the formation of bloodborne metastases via alterations of the integrity of the brain capillary endothelium.

Stereotactic radiosurgery with or without whole brain radiotherapy for patients with a single radioresistant brain metastasis

PURPOSE

To examine the outcomes of patients with a single brain metastasis from radioresistant histologies (renal cell carcinoma and melanoma) treated with stereotactic radiosurgery (SRS) with or without whole brain radiotherapy (WBRT).

METHODS AND MATERIALS

We reviewed the medical records of 27 patients treated at our institution between 2000 and 2007 with a single radioresistant brain metastasis. Patients were treated with Gamma Knife based SRS. Tumor histologies included renal cell carcinoma and melanoma.

RESULTS

Patients were treated to a median marginal dose was 20 Gy (range, 15-22 Gy). At follow-up intervals ranging from 1.8 to 23.2 months, the radiographic responses were as follows: progression in 7 patients; stable in 5 patients; and shrinkage in 15 patients. Fifteen patients (56%) developed distant brain failure. Seven of the 27 patients were alive at last follow-up. The 3-, 6-, 9-, 12-, and 18-months after SRS local control rates were 82.8%, 77.9%, 69.3%, 69.3%, and 55.4%, respectively. None of the 5 patients who received WBRT developed distant brain failure although the follow-up intervals were short (range, 3.5-13.7 months; median, 5.1 months). WBRT did not appear to affect local control, progression free survival, and overall survival (P = 0.32, 0.87, 0.69). One patient developed worsening of symptoms attributable to SRS.

CONCLUSIONS

Gamma Knife SRS is a safe and feasible strategy for treatment of patients with a single radioresistant brain metastasis. Radiosurgery alone is a reasonable treatment option, but may carry a greater likelihood of distant brain recurrence.

Multiple intracranial melanoma metastases: case report and review of the literature

Although intracerebral metastases of malignant melanoma are common, those located in the sellar region and within the pontocerebellar area are extremely rare. Furthermore, to our knowledge, there is no report about melanoma metastasis to the epiphysis published so far. We report here a 46-year-old patient who had metastatic lesions in the sellar region, cerebellopontine area and epiphysial gland, preceded by a primary melanoma at her left shoulder. The diagnosis of sellar metastasis was confirmed histopathologically following a stereotactic biopsy. The patient received whole-brain irradiation therapy combined with chemotherapy. After 10 months, she died from a severe hemorrhage in the cerebellopontine angle. Autopsy findings confirmed melanoma metastases both in the cerebellopontine angle and additionally in the epiphysial gland. To our knowledge, this is the first case of multiple intracranial melanoma metastases including the suprasellar region, the pontocerebellar and epiphysial area.

Gamma Knife surgery for the treatment of melanoma metastases: the effect of intratumoral hemorrhage on survival

OBJECT

Gamma Knife surgery (GKS) improves overall survival in patients with malignant melanoma metastatic to the brain. In this study the authors investigated which patient- or treatment-specific factors influence survival of patients with melanoma brain metastases; they pay particular interest to pre- and post-GKS hemorrhage.

METHODS

Demographic, treatment, and survival data on 59 patients with a total of 208 intracranial metastases who underwent GKS between 1998 and 2007 were abstracted from treatment records and from the Connecticut Tumor Registry. Multivariate analysis was used to identify factors that independently affected survival.

RESULTS

Survival was significantly better in patients with solitary metastasis (p = 0.04), lesions without evidence of pre-GKS hemorrhage (p = 0.004), and in patients with total tumor volume treated < 4 cm(3) (p = 0.02). Intratumoral bleeding occurred in 23.7% of patients pre-GKS. Intratumoral bleeding occurred at a mean of 1.8 months post-GKS at a rate of 15.2%. Unlike the marked effect of pretreatment bleeding, posttreatment bleeding did not independently affect survival. Sex, systemic control, race, metastases location, whole-brain radiation therapy, chemotherapy, history of antithrombotic medications, and cranial surgery had no independent association with survival.

CONCLUSIONS

These data corroborate previous findings that tumor burden (either as increased number or total volume of lesions) at the time of GKS is associated with diminished patient survival in those with intracerebral melanoma metastases. Patients who were noted to have hemorrhagic melanoma metastases prior to GKS appear to have a worse prognosis following GKS compared with patients with nonhemorrhagic metastases, despite similar rates of bleeding pre- and post-GKS treatment. Gamma Knife surgery itself does not appear to increase the rate of hemorrhage.

A rational surgical approach to the treatment of distant melanoma metastases

The optimal treatment of melanoma involves multidisciplinary care. To many, this means surgical resection of early, localized disease and treatment of metastatic disease with chemotherapy, immunotherapy, or radiation. Because it is effective, results in little morbidity and may be repeated, surgery should have a central role in the treatment of selected patients with American Joint Committee on Cancer (AJCC) stage IV melanoma.

Can surgeons improve survival in stage IV melanoma?

Successful systemic management of stage IV melanoma continues to be elusive because of the paucity of effective therapies. This has fueled the continued interest in surgical resection. Several single-institution studies and a current, large, multi-institutional phase III trial have demonstrated a survival benefit for patients who underwent surgical resection for melanoma metastases. Incorporating these results into new approaches using multimodality treatment may enhance survival in patients with stage IV melanoma.

Management of metastatic melanoma patients with brain metastases

Brain metastases seem to be an almost inevitable complication in patients with metastatic melanoma. Except for the rare patients who can undergo successful surgical resection of brain metastases, current management strategies do not appear adequate and result in a poor outcome (median survival, 2-4 months). In recent small series, stereotactic radiosurgery or gamma-knife treatment has suggested improvement in local control compared with whole brain radiation therapy. We have recently shown prolonged survival (11.1 months) using a multimodality treatment approach in 44 sequential patients with melanoma brain metastases. A subsequent study demonstrated that the outcome of biochemotherapy for metastatic melanoma is not affected by the presence or absence of brain metastases. Our results suggest that the outcome of patients with melanoma brain metastases can be improved using a multidisciplinary management strategy.

Multimodality treatment of melanoma brain metastases incorporating stereotactic radiosurgery (SRS)

BACKGROUND

Brain metastases are a frequent complication in advanced melanoma. A 3.6 to 4.1-month median survival has been reported after treatment with whole brain radiotherapy. We performed a retrospective analysis of our institutional experience of multimodality treatment utilizing linear accelerator (Linac)-based stereotactic radiosurgery (SRS).

METHODS

Forty-four melanoma patients with brain metastases underwent 66 SRS treatments for 156 metastatic foci between 1999 and 2004. Patients were treated with initial SRS if <or=5 brain metastases were present. All patients had Karnofsky Performance Status (KPS)>or=70, but 37 patients had active systemic metastases (Recursive Partition Analysis Class 2). Survival was calculated from the time of diagnosis of brain metastases. Minimum follow-up was 1 year after SRS. The potential role of prognostic factors on survival was evaluated including age, sex, interval from initial diagnosis to brain metastases, surgical resection, addition of whole brain radiotherapy (WBRT), number of initial metastases treated, and number of SRS treatments using Cox univariate analysis.

RESULTS

The median survival of melanoma patients with brain metastases was 11.1 months (95% confidence interval [CI]: 8.2-14.9 months) from diagnosis. One-year and 2-year survivals were 47.7% and 17.7%, respectively. There was no apparent effect of age or sex. Surgery or multiple stereotactic radiotherapy treatments were associated with prolonged survival. Addition of WBRT to maintain control of brain metastases in a subset of patients did not improve survival.

CONCLUSIONS

Our results suggest that aggressive treatment of patients with up to 5 melanoma brain metastases including SRS appears to prolong survival. Subsequent chemotherapy or immunotherapy after SRS may have contributed to the observed outcome.

GAMMA KNIFE RADIOSURGERY IN THE MANAGEMENT OF MALIGNANT MELANOMA BRAIN METASTASES

OBJECTIVE

Radiosurgery is increasingly used to manage malignant melanoma brain metastases. We reviewed our series of patients who underwent radiosurgery for melanoma brain metastases to assess clinical outcomes and identify prognostic factors for survival and cerebral disease control.

METHODS

Two hundred forty-four patients had radiosurgery for the management of 754 metastatic tumors. A mean of 2.6 tumors were irradiated per procedure. The median tumor volume was 4.4 cm3. The median margin and maximum doses used were 18 and 32 Gy, respectively.

RESULTS

The median survival was 5.3 months after radiosurgery (mean, 10 mo; range, 0.2–114.3 mo). Patients survived a median of 7.8 months (mean, 13.4 mo) from the diagnosis of brain metastases and 44.9 months (mean, 69 mo) after the diagnosis of the primary tumor. Survival was better in patients with controlled systemic disease (12.7 mo), single brain metastasis (6.8 mo), and a Karnofsky performance score of 90 or 100% (6.3 mo). Sustained local control was achieved in 86.2% of tumors. Increased tumor volume and previous evidence of hemorrhage increased the risk of local failure. Multiple lesions and failure to provide systemic immunotherapy were predictors for the occurrence of new brain metastases, which developed in 41.7% of the patients. Symptomatic radiation changes occurred in 6.6% of the patients. Overall, 71.4% of the patients improved or remained clinically stable. Brain disease was the cause of death in 40.5% of the patients, usually from the development of new metastases.

CONCLUSION

Gamma knife radiosurgery for malignant melanoma brain metastases is safe and effective and provides a high rate of durable local control. Improved survival can be achieved in patients with single metastasis, controlled systemic disease, and a high Karnofsky performance score.

Atypical teratoid/rhabdoid tumor: the controversy behind radiation therapy

To date, approximately 200 cases of atypical teratoid/rhabdoid tumor (AT/RT) of the central nervous system have been described in the literature. This CNS tumor tends to present at an age of less than 3 years, and most patients succumb to their disease within 1 year of diagnosis. Prior to the rise in utilization of immunohistochemical (IHC) testing in the late 1990s, this tumor was likely mistaken as medulloblastoma and treated as such. However, lessons learned from regimens based upon medulloblastoma have revealed that AT/RT requires more aggressive treatment. A significant portion of patients die of local recurrence in spite of aggressive surgery and chemotherapy. As most patients with AT/RT present as infants or young children, radiation therapy has been a less than standard treatment option. However, recent evidence suggests that long-term survival can occur with use of more aggressive treatment approaches including dose-intense chemotherapy as well as adjuvant radiation therapy. A standardized and effective approach to treating this usually fatal tumor remains elusive, and the role of radiation therapy presents a particular dilemma as young patients with this disease may experience devastating late effects of therapy if they achieve a long-term survival. Review of the literature reveals an association between initial radiation therapy and the ability to achieve a prolonged survival. Our review underscores the importance or enrolling patients in multi-institutional prospective studies to further investigate the value of radiation to treat this pediatric neoplasm.

Gamma-Knife radiosurgery in the management of melanoma patients with brain metastases: A series of 106 patients without whole-brain radiotherapy

PURPOSE

To assess retrospectively a strategy that uses Gamma-Knife radiosurgery (GKR) in the management of patients with brain metastases (BMs) of malignant melanoma (MM).

METHODS

GKR without whole-brain radiotherapy (WBRT) was performed for patients with Karnofsky Performance Status (KPS) of 60 or above who harbored 1 to 4 BMs of 30 mm or less and was repeated as often as needed. Survival was assessed in the whole population, whereas local-control rates were assessed for patients with follow-up longer than 3 months.

RESULTS

A total of 221 BMs were treated in 106 patients; 61.3% had a single BM. Median survival from the time of GKR was 5.09 months. Control rate of treated BMs was 83.7%, with 14% of complete response (14 BMs), 42% of partial response (41 BMs), and 43% of stabilization (43 BMs). In multivariate analysis, survival prognosis factors retained were KPS greater than 80, cortical or subcortical location, and Score Index for Radiosurgery (SIR) greater than 6. On the basis of KPS, BM location, and age, a score called MM-GKR, predictive of survival in our population, was defined.

CONCLUSION

Gamma-Knife radiosurgery provides a surgery-like ability to obtain control of a solitary BM and could be consider as an alternative treatment to the combination of GKR+WBRT as a palliative strategy. MM-GKR classification is more adapted to MM patients than are SIR, RPA and Brain Score for Brain Metastasis.

Integration of gamma knife surgery in the management of cerebral metastases from melanoma

The aim of this study was to investigate the effect of gamma knife surgery on the local control of cerebral metastases from melanoma and to assess survival. In 29 patients, 105 of 178 cerebral metastases were treated with gamma knife surgery. Only five patients had metastases confined to the brain. Of the 96 metastases with magnetic resonance imaging follow-up, 61.5% regressed by more than 50% of the pretreatment volume, 25% regressing by more than 90% and 13.5% completely. The median survival from gamma knife surgery was 5.7 months (longest survival, 38 months). In multivariate analyses, a larger number of lesions requiring treatment (P < 0.001), recursive partitioning analysis class (P = 0.009) and a long time interval from initial melanoma diagnosis to detection of cerebral metastases (P = 0.001) influenced survival. It can be concluded that gamma knife surgery is a useful adjunct in the management of cerebral metastases from melanoma and has a significant impact on local control. Its greatest potential may be achieved in conjunction with systemic chemotherapy, especially in the presence of extracerebral metastases.

Gamma Knife radiosurgery for intracranial metastatic melanoma: an analysis of survival and prognostic factors

Objective of this study was to evaluate retrospectively the effectiveness of Gamma Knife radiosurgery for intracranial metastatic melanoma and to identify prognostic factors related to survival. Twenty-six patients with intracranial metastases (72 lesions) from melanoma underwent Gamma Knife radiosurgery. In 14 patients (54%) whole-brain radiotherapy (WBRT) was performed as part of the initial treatment, and in 12 patients (38%) immunotherapy and/or chemotherapy was given after Gamma Knife radiosurgery. The median tumor volume for Gamma Knife radiosurgery treated lesions was 1.72 cm3. The median prescribed radiation dose was 18 Gy (range 8-22 Gy) typically prescribed to the isodose at the tumor margin. Univariate and multivariate analyses were used to determine significant prognostic factors affecting survival. Overall median survival was 6 months after Gamma Knife radiosurgery, and 1-year survival was 25%. The median survival from the onset of brain metastases was 9 months and from the original diagnosis of melanoma was 50 months (range 4-160 months). There were no major acute or late GKS complications. In univariate testing, the Karnofsky score equal to or higher than 90% (P < 0.01, log-rank test), supratentorial localization (P < 0.001, log-rank test), intracranial tumor volume less than 1 cm3 (P < 0.02, log-rank test), and absence of neurological signs or symptoms before Gamma Knife radiosurgery (P < 0.003, log-rank test) were significant favorable factors for survival. In multivariate regression analyses, the most important predictors associated with increased survival were a KPS > or = 90 (P < 0.023), female sex (P < 0.004), supratentorial localization (P < 0.01), and absence of neurological symptoms (P < 0.008). Radiosurgery is a noninvasive, safe, and effective treatment option for patients with single or multiple intracranial metastases from melanoma. Female sex, Karnofsky score > or = 90, supratentorial localization and lack of symptoms before the Gamma Knife radiosurgery were good independent predictors of survival.

The expanding role of neurosurgeons in the management of brain metastases

BACKGROUND

Brain metastases are the most common type of intracranial tumor. Until recently, whole brain fractionated radiation therapy (WBRT) was the mainstay of treatment, thereby confining the role of neurosurgeons to resection of an occasional solitary, accessible, and symptomatic brain metastasis. Median survival after surgery and radiation typically ranged from 5 to 11 months.

METHODS

We analyzed various demographic incidence reports and our series of brain metastasis patients treated with radiosurgery. During a 15-year interval (1987-2002), radiosurgery was performed on 5,032 patients of whom 1,088 (21.6%) had metastatic brain tumors.

RESULTS

In the United States, 266,820 to 533,640 new cases of brain metastases will be diagnosed in the year 2003. Evidence to date demonstrates that radiosurgery provides effective local tumor control for brain metastases. Important prognostic factors affecting patient survival include the absence of active systemic disease, the patient's preoperative performance status, age, and the number of metastases. Survival and local tumor control rates attained with radiosurgery are superior to those of either conventional surgery or WBRT. The morbidity associated with radiosurgery of brain metastasis is very low, and the mortality rate approaches zero.

CONCLUSIONS

Compelling evidence indicates that radiosurgery is an effective neurosurgical management strategy for intracranial brain metastases. Quite often, favorable tumor control and survival can be achieved without WBRT. With radiosurgery as a therapeutic option, neurosurgeons now have a vastly expanded armamentarium for treatment of patients with brain metastases. The large number of patients with brain metastases who require care by a neurosurgeon for optimal treatment has significant implications for both the patterns of neurosurgical training and practice in the United States.