Complications of stereotactic brain surgery

The authors review iatrogenic complications of stereotactic surgery, including tumor biopsy, cyst or abscess aspiration, movement disorder surgery, and radiosurgery. The expected morbidities and steps taken to reduce complications are also discussed.

Analysis of neurological sequelae from radiosurgery of arteriovenous malformations: how location affects outcome

PURPOSE/OBJECTIVE

To elucidate how the risks of developing temporary and permanent neurological sequelae from radiosurgery for arteriovenous malformations (AVM) are related to AVM location, the addition of stereotactic magnetic resonance (MR) imaging to angiographic targeting, and prior hemorrhage or neurological deficits.

MATERIALS AND METHODS

We evaluated follow-up imaging and clinical data in 332 AVM patients who received gamma knife radiosurgery at the University of Pittsburgh between 1987 and 1994. All patients had regular clinical or imaging follow-up for a minimum of 2 years (range: 24-96 months, median = 45 months). There were 83 patients with MR-assisted planning, 187 with prior hemorrhages, and 143 with prior neurological deficits.

RESULTS

Symptomatic postradiosurgery sequelae (any neurological problem including headache) developed in 30 (9%) of 332 patients. Symptoms resolved in 58% of patients within 27 months with a significantly greater proportion (p = 0.006) resolving in patients with Dmin < 20 Gy vs. > or = 20 Gy (89 vs. 36%). The 7-year actuarial rate for developing persistent symptomatic sequelae was 3.8%. We first evaluated the relative risks for different locations to construct a postradiosurgery injury expression (PIE) score for AVM location. Multivariate logistic regression analysis of symptomatic postradiosurgery sequelae identified independent significant correlations with PIE location score (p = 0.0007) and 12 Gy volume (p = 0.008), but with none of the other factors tested (p > 0.3), including the addition of MR targeting, average radiation dose in 20 cc, prior hemorrhage, or neurological deficit. We used these results to construct a risk prediction model for symptomatic postradiosurgery sequelae. The risk of radiation necrosis was significantly correlated with PIE score (p < 0.048), but not with 12-Gy volume.

CONCLUSION

The risks of developing complications from AVM radiosurgery can be predicted according to location with the PIE score, in conjunction with the 12-Gy treatment volume. Further study of factors affecting persistence of these sequelae (progression to radiation necrosis) is needed.

Stereotactic radiosurgery for patients with nonsmall cell lung carcinoma metastatic to the brain

BACKGROUND

A retrospective study of patients undergoing stereotactic radiosurgery for one to four brain metastases from nonsmall lung cell carcinoma (NSCLC) was performed to document outcomes and risks.

METHODS

Seventy-seven patients underwent radiosurgery during a 7-year interval; 71 also underwent whole brain radiation therapy. Univariate and multivariate analyses were used to determine significant prognostic factors affecting survival.

RESULTS

The overall median survival was 10 months after radiosurgery, and 15 months from the diagnosis of brain metastases. Five factors significantly affected survival: extent of systemic disease, presence of a neurologic deficit, size of the intracranial tumor, initial imaging appearance of intratumoral necrosis, and initial resection of the primary tumor of the chest. Median survival time was 26 months in a subgroup of patients with no extracranial metastases, no neurologic deficits, and a small tumor without necrosis. The authors evaluated 91 tumors with imaging. Local tumor control was achieved in 77 lesions (85%) and tumoral radiation necrosis developed in 4 lesions (4.4%). Nineteen new metastatic tumors developed during the observation interval.

CONCLUSIONS

Stereotactic radiosurgery for NSCLC brain metastases is effective and is associated with few complications. The early detection of brain metastases and treatment with radiosurgery combined with radiation therapy provide the opportunity for extended high quality survival.

Lars Leksell. Notes at the side of a raconteur

Lars Leksell was a visionary and creative neurosurgeon who helped to define the origins of functional brain surgery, stereotactic surgery, and radiosurgery. As a neurophysiologist, he described the gamma motor system of the nervous system. He created an evolutionary array of stereotactic guiding devices that were continually updated to meet changes in neurodiagnostic imaging. His interest in furthering the development of neurosurgery led to a unique number of other sophisticated instruments designed to reach the depths of the brain safely and effectively, while remaining simple and practical. Throughout life he remained an outstanding neurosurgical mentor.

Radiation optic neuropathy after stereotactic radiosurgery

PURPOSE

The purpose of the study is to report the occurrence of optic neuropathy after stereotactic radiosurgery for perichiasmal tumors.

METHODS

Records of four patients with visual deterioration after stereotactic radiosurgery were reviewed, including clinical findings, neuroimaging results, and treatment methods.

RESULTS

Optic neuropathy developed 7 to 30 months after gamma knife radiosurgery. All patients experienced an abrupt change in visual function. Clinical findings indicated anterior visual pathway involvement. Patterns of field loss included nerve fiber bundle and homonymous hemianopic defects. Gadolinium-enhanced magnetic resonance imaging (MRI) showed swelling and enhancement of the affected portion of the visual apparatus in three patients. Systemic corticosteroids were administered in all patients and one partially recovered. One patient also received hyperbaric oxygen without improvement.

CONCLUSIONS

Although rare, optic neuropathy may follow radiosurgery to lesions near the visual pathways. Careful dose planning guided by MRI with restriction of the maximal dose to the visual pathways to less than 8 Gy will likely reduce the incidence of this complication.

Survival benefit of stereotactic radiosurgery for patients with malignant glial neoplasms

OBJECTIVE

During an 8-year interval, we evaluated the survival benefit of stereotactic radiosurgery performed in 64 patients with glioblastomas multiforme (GBM) and 43 patients with anaplastic astrocytomas (AA).

METHODS

Adjuvant radiosurgery was performed either before disease progression or for recurrent tumor at the time of disease progression. Clinical and imaging follow-up data were obtained for all patients. The diagnosis of GBM was obtained by performing craniotomies in 41 patients and by performing stereotactic biopsies in 23. The diagnosis of AA was obtained by performing craniotomies in 19 patients (44%) and by performing biopsies in 24.

RESULTS

Of the entire series, the median survival time after initial diagnosis for patients with GBM was 26 months (standard deviation [SD], 19 mo; range, 5-79 mo) and the median survival time after radiosurgery was 16 months (SD, 16 mo; range, 1-74 mo). The 2-year survival rate was 51%. No survival benefit was identified for patients who underwent intravenously administered chemotherapy in addition to radiosurgery (P = 0.97). After undergoing radiosurgery, 12 patients (19%) underwent craniotomies and resections and 4 (6%) underwent subsequent radiosurgery for regional or remote recurrence. For 45 patients who underwent radiosurgery as part of the initial management plan, the median survival time after diagnosis was 20 months. Of the entire series, the median survival time after diagnosis for patients with anaplastic astrocytomas was 32 months (SD, 23 mo; range 5-96 mo) and the median survival time after radiosurgery was 21 months (SD, 18 mo; range 3-93 mo). The 2-year survival rate was 67%. Ten patients (23%) underwent subsequent craniotomies at a mean of 8 months after initial surgery, and two underwent subsequent radiosurgery. There was no acute neurological morbidity after radiosurgery. Histologically proven radiation necrosis occurred in one patient with GBM (1.6%) and two patients with AA (4.7%). For 21 patients for whom radiosurgery was part of the initial management plan, the median survival time after diagnosis was 56 months.

CONCLUSION

In comparison to historical controls, improved survival benefit after radiosurgery was identified for patients with GBM and patients with AA. Although this survival benefit may be related to our selection of patients for radiosurgery based on their having smaller tumor volumes, no selection was made based on location. We observed that radiosurgery was safe and well tolerated. Its effectiveness as an adjuvant therapy deserves a properly stratified randomized trial.

Radioprotective effects of the 21-aminosteroid U-74389G for stereotactic radiosurgery

OBJECTIVE

Future improvements in the results of stereotactic radiosurgery will be related to better patient selection, dose planning, radiosensitization of the target, and, possibly, protection of the brain surrounding the target. 21-Aminosteroids may provide protection against brain radiation injury by inhibition of lipid peroxidation and a selective action on vascular endothelium. We hypothesized that the 21-aminosteroid U-74389G would reduce radiosurgery-related brain injury without attenuating the target volume response.

METHODS

One hundred and forty-five rats were divided into four experimental groups before undergoing radiosurgery: control (n = 47); low-dose U-74389G (5 mg/kg of body weight, n = 30); high-dose U-74389G (15 mg/kg, n = 20); and methylprednisolone (2 mg/kg, n = 48). The drug was administered 1 hour before radiosurgery (4-mm gamma knife collimator) of the normal rat frontal lobe (single-fraction maximum doses of 50, 100, or 150 Gy) was performed. All brains underwent histological examination at 90 or 150 days to evaluate the diameters of necrosis and the findings of radiation-induced vasculopathy, brain edema, and gliosis.

RESULTS

None of the animals that received 50-Gy radiation developed histological changes, whereas all of the animals that received 150-Gy radiation developed radiation necrosis without drug-induced protection from vascular changes or edema. In animals receiving 100-Gy radiation, high-dose aminosteroid reduced radiation-induced vasculopathy at 90 days (P = 0.06) and at 150 days (P = 0.02) and prevented regional edema at 90 days (P = 0.01) and at 150 days (P = 0.03). Low-dose aminosteroid and corticosteroid provided no protection.

CONCLUSION

The 21-aminosteroid U-74389G provided protection after a single intravenously administered dose of 15 mg/kg against radiation-induced vasculopathy and edema. High-dose 21-aminosteroids seem to have optimal properties for radiosurgery, surrounding brain protection without reducing the therapeutic effect desired within the target volume.

Hemangioblastoma of the posterior fossa. The role of multimodality treatment

The authors made a review of a series of patients with hemangioblastomas of the posterior fossa treated between 1973 and 1993. A total of 32 patients were analyzed with 24 patients receiving resection, 8 patients receiving radiosurgery and 2 patients receiving conventional radiotherapy. The mortality in the patients with a resection was considered acceptable with 2 deaths (8%) and with a morbidity of 3 patients (12.5%). A review of the literature suggests that conventional radiotherapy with high doses (45-60 Gy) may have a role in the post-operative control of hemangioblastomas and in some cases could be employed even before the resection in order to facilitate the surgery. The radiosurgical treatment is regarded like adjuvant. Poor results were obtained with radiosurgery in large tumors where low doses (less than 20 Gy) were used. Because of the rarity and complexity of these tumors, mainly when associated with von Hippel-Lindau disease, a multicenter study could be useful with the assessment of the optimal utilization and combination of these treatment modalities.

Complications from arteriovenous malformation radiosurgery: multivariate analysis and risk modeling

PURPOSE/OBJECTIVE

To assess the relationships of radiosurgery treatment parameters to the development of complications from radiosurgery for arteriovenous malformations (AVM).

METHODS AND MATERIALS

We evaluated follow-up imaging and clinical data in 307 AVM patients who received gamma knife radiosurgery at the University of Pittsburgh between 1987 and 1993. All patients had regular clinical or imaging follow up for a minimum of 2 years (range: 24-96 months, median = 44 months).

RESULTS

Post-radiosurgical imaging (PRI) changes developed in 30.5% of patients with regular follow-up magnetic resonance imaging, and were symptomatic in 10.7% of all patients at 7 years. PRI changes resolved within 3 years developed significantly less often (p = 0.0274) in patients with symptoms (52.8%) compared to asymptomatic patients (94.8%). The 7-year actuarial rate for developing persistent symptomatic PRI changes was 5.05%. Multivariate logistic regression modeling found that the 12 Gy volume was the only independent variable that correlated significantly with PRI changes (p < 0.0001) while symptomatic PRI changes were correlated with both 12 Gy volume (p = 0.0013) and AVM location (p = 0.0066).

CONCLUSION

Complications from AVM radiosurgery can be predicted with a statistical model relating the risks of developing symptomatic post-radiosurgical imaging changes to 12 Gy treatment volume and location.

Flash visual evoked potential monitoring of optic tract function during macroelectrode-based pallidotomy

Posteroventral pallidotomy (PVP) has received renewed interest as an ablative procedure for the symptomatic treatment of Parkinson's disease. In previous reports, the proximity of the optic tract to the lesion target in the globus pallidus internus has resulted in the occurrence of visual field deficits in as much as 14% of patients. The authors have used intraoperative visual evoked potentials (VEPs) during PVP to reduce this risk. All procedures were performed in awake patients. Flash stimuli were delivered to each eye via fiberoptic sources. Baseline flash VEPs were recorded at O1/Cz (left visual cortex to vertex), Oz/Cz (midline visual cortex to vertex), and O2/Cz (right visual cortex to vertex) for OS, OU, and OD stimulation. Epochs were acquired before and after localization, after macroelectrode stimulation, after temporary thermal lesioning, and after permanent thermal lesioning. Forty-seven patients underwent a total of 59 procedures. Visual evoked potentials were recorded reproducibly in all patients. In 11 procedures, VEP changes were reported, including six amplitude changes (10-80%), six latency shifts (3-10 msec), and one report of “variability.” In four procedures, VEP changes prompted a change in target coordinates. One false-positive and one false-negative VEP change were encountered. The only confirmed visual deficit was a superior quadrantanopsia, present on formal fields, but clinically asymptomatic. The authors conclude that VEPs may be useful for procedures performed in the awake patient because of the lack of anesthetic-induced variability. The 1.7% visual morbidity reported here (one in 59 patients) compares favorably with other series using microelectrodes. Visual evoked potentials may be a useful monitoring technique to reduce the incidence of clinically significant visual morbidity during pallidotomy, especially during formal lesioning of the ventral pallidum adjacent to the optic tract.

Percutaneous retrogasserian glycerol rhizotomy. Current technique and results

Despite the establishment of the vasculoneural compression as a frequent cause of trigeminal neuralgia, minimally invasive surgical techniques to treat medically refractory trigeminal neuralgia are needed in order to minimize the risks associated with craniotomy. Percutaneous retro gasserian glycerol rhizotomy (PRGR) is one of the alternative surgical treatments to microvascular decompression. Technical simplicity, less chance of trigeminal sensory loss, no need of intraoperative sensory testing, and no attempted deliberate destruction of the trigeminal nerve are advantages over other percutaneous trigeminal operations.

Gamma knife radiosurgery for trigeminal neuralgia

Radiosurgery is one of the surgical treatments of trigeminal neuralgia. Through precise irradiation of the proximal trigeminal nerve identified on high-resolution imaging, pain relief can be achieved after a short latency interval. This image-guided approach has been useful for both patients with persistent pain after other surgeries, and as a primary surgical option. A minimum dose of 70 Gy delivered with the gamma knife has been associated with low risk for facial numbness, and no other morbidity. Management of trigeminal neuralgia without an incision, transfacial needle placement or nerve section may prove useful to increasing numbers of patients.

Gamma knife for glioma: selection factors and survival

PURPOSE

To determine factors associated with survival differences in patients treated with radiosurgery for glioma.

METHODS AND MATERIALS

We analyzed 189 patients treated with Gamma Knife radiosurgery for primary or recurrent glioma World Health Organization (WHO) Grades 1-4.

RESULTS

CONCLUSION

The median minimum tumor dose was 16 Gy (8-30 Gy) and the median tumor volume was 5.9 cc (1.3-52 cc). Brachytherapy selection criteria were satisfied in 65% of patients. Median follow-up of all surviving patients was 65 weeks after radiosurgery. For primary glioblastoma patients, median survival from the date of pathologic diagnosis was 86 weeks if brachytherapy criteria were satisfied and 40 weeks if they were not (p = 0.01), indicating that selection factors strongly influence survival. Multivariate analysis showed that increased survival was associated with five variables: lower pathologic grade, younger age, increased Karnofsky performance status (KPS), smaller tumor volume, and unifocal tumor. Survival was not found to be significantly related to radiosurgical technical parameters (dose, number of isocenters, prescription isodose percent, inhomogeneity) or extent of preradiosurgery surgery. We developed a hazard ratio model that is independent of the technical details of radiosurgery and applied it to reported radiosurgery and brachytherapy series, demonstrating a significant correlation between survival and hazard ratio.

CONCLUSIONS

Survival after radiosurgery for glioma is strongly related to five selection variables. Much of the variation in survival reported in previous series can be attributed to differences in distributions of these variables. These variables should be considered in selecting patients for radiosurgery and in the design of future studies.

Dose and diameter relationships for facial, trigeminal, and acoustic neuropathies following acoustic neuroma radiosurgery

PURPOSE AND OBJECTIVE

To define the relationships between dose and tumor diameter for the risks of developing trigeminal, facial, and acoustic neuropathies after acoustic neuroma radiosurgery, a large single-institution experience was analyzed.

MATERIALS AND METHODS

Two hundred and thirty-eight patients with unilateral acoustic neuromas who underwent Gamma knife radiosurgery between 1987-1994 with 6-91 months of follow-up (median 30 months) were studied. Minimum tumor doses were 12-20 Gy (median 15 Gy). Transverse tumor diameter varied from 0.3-5.5 cm (median 2.1 cm). The relationships of dose and diameter to the development of cranial neuropathies were delineated by multivariate logistic regression.

RESULTS

The development of post-radiosurgery neuropathies affecting cranial nerves V, VII, and VIII were correlated with minimum tumor dose and transverse tumor diameter (P < 0.01 for all except Dmin for VIII where P = 0.10). A comparison of the dose-diameter response curves showed the acoustic nerve to be the most sensitive to doses of 12-16 Gy and the facial nerve to be the least sensitive.

CONCLUSION

The risks of developing trigeminal, facial, and acoustic neuropathies following acoustic neuroma radiosurgery can be predicted from the transverse tumor diameter and the minimum tumor dose using models constructed from data presently available.

Magnetic resonance imaging: an accurate method to evaluate arteriovenous malformations after stereotactic radiosurgery

To determine the accuracy of magnetic resonance (MR) imaging in comparison to cerebral angiography after radiosurgery for an arteriovenous malformation (AVM), the authors reviewed the records of patients who underwent radiosurgery at the University of Pittsburgh Medical Center before 1992. All patients in the analysis had AVMs in which the flow-void signal was visible on preradiosurgical MR imaging. One hundred sixty-four postradiosurgical angiograms were obtained in 140 patients at a median of 2 months after postradiosurgical MR imaging (median 24 months after radiosurgery). Magnetic resonance imaging correctly predicted patency in 64 of 80 patients in whom patent AVMs were seen on follow-up angiography (sensitivity 80%) and angiographic obliteration in 84 of 84 patients (specificity 100%). Overall, 84 of 100 AVMs in which evidence of obliteration was seen on MR images displayed angiographic obliteration (negative predictive value, 84%). Ten of the 16 patients with false-negative MR images underwent follow-up angiography: in seven the lesions progressed to complete angiographic obliteration without further treatment. Exclusion of these seven patients from the false-negative MR imaging group increases the predictive value of a negative postradiosurgical MR image from 84% to 91%. No AVM hemorrhage was observed in clinical follow up of 135 patients after evidence of obliteration on MR imaging (median follow-up interval 35 months; range 2-96 months; total follow up 382 patient-years). Magnetic resonance imaging proved to be an accurate, noninvasive method for evaluating the patency of AVMs that were identifiable on MR imaging after stereotactic radiosurgery. This imaging modality is less expensive, more acceptable to patients, and does not have the potential for neurological complications that may be associated with cerebral angiography. The risk associated with follow-up cerebral angiography may no longer justify its role in the assessment of radiosurgical results in the treatment of AVMs.

A dose-response analysis of arteriovenous malformation obliteration after radiosurgery

PURPOSE

Although radiosurgery is effective in obliterating the pathologic vessels of intracranial arteriovenous malformations (AVM), the relationships of both dose and volume to obliteration have not been well defined.

METHODS AND MATERIALS

The results of radiosurgery in 197 AVM patients with 3-year angiographic follow-up were analyzed. Volume varied from 0.06-18 cc (median: 4.1 cc), and minimum target dose (Dmin) varied from 12.0-25.6 Gy (median: 20.0 Gy).

RESULTS

Follow-up angiography revealed complete AVM obliteration in 142 out of 197 patients (72%). The targeted AVM nidus failed to obliterate in 20 patients (10%), but in-field obliteration was complete in the remaining 35 patients (18%) discovered to have residual untargeted AVM nidus. Multivariate logistic regression analysis of in-field obliteration revealed a significant independent correlation with Dmin (p = 0.04), but not with volume or maximum dose. A sigmoid dose-response curve for in-field obliteration was constructed that significantly differed from the dose-volume-response relationships that would have been expected from overall obliteration data.

CONCLUSIONS

The success rate for in-field obliteration of AVM after radiosurgery depends on Dmin but does not appear to change appreciably with volume or maximum dose. Success rates for complete obliteration additionally are limited by problems defining the complete AVM nidus.

Microsurgical resection of colloid cysts using a stereotactic transventricular approach

BACKGROUND

Several surgical approaches have proven effective in the management of colloid cysts. Cited disadvantages of the transventricular route are its difficulty in patients with small ventricles, and the risk of postoperative seizures; advantages include the avoidance of interhemispheric retraction and venous injury, and callosal section in the transcallosal route.

METHODS

We retrospectively evaluated patient outcomes after minimally invasive transventricular microsurgical resection. Twenty patients underwent computed tomography-guided stereotactic resection of a colloid cyst based on trajectory planning through the middle frontal gyrus. The mean patient age was 38 years (range, 14-65 years). The colloid cyst was discovered incidentally in one patient; two patients presented in coma. Fourteen patients (70%) had preoperative hydrocephalus.

RESULTS

Total or near-total (only a small remnant of cyst wall left attached to the fornix or thalamostriate vein) cyst removal was achieved in all patients. Mean follow-up after surgery was 4.3 years (range, 0.5-11 years). All patients had an excellent outcome (100%) with return to full function or employment status. Postoperative morbidity occurred in one patient (5%) who sustained a small caudate nucleus hemorrhagic contusion associated with temporary hemiparesis. A single postoperative seizure occurred in one patient 5 months after surgery; no patient developed a persistent seizure disorder.

CONCLUSIONS

This technique relies on the use of a precisely placed limited craniotomy, a small cortical opening (10-20 mm), a precise trajectory to the foramen of Monro, and standard microsurgical instruments. Stereotactic transventricular microsurgical resection provided safe and effective management of patients with colloid cysts, even in the absence of hydrocephalus.

Microvascular decompression for trigeminal neuralgia in patients with multiple sclerosis

BACKGROUND

Microvascular decompression (MVD) of the trigeminal nerve is a well-established procedure for the treatment of idiopathic trigeminal neuralgia. Multiple sclerosis (MS) has long been considered a contraindication for this procedure, due to the known polycentric nature of the disease. Medical treatment followed by percutaneous procedures provide relief for the great majority of these patients. There exists a small subgroup of patients with trigeminal neuralgia who are diagnosed with MS only after a microvascular decompression procedure has been performed. Furthermore, management of the patient with known MS whose pain continues to recur, despite maximal medical therapy and multiple percutaneous procedures, can be exceedingly difficult.

METHODS

Five patients with MS, three who had undergone multiple unsuccessful percutaneous procedures and two in whom the diagnosis of MS had not been established, underwent exploration of the cerebellopontine angle. Three patients underwent MVD alone, and two (both with known MS) underwent MVD and partial section of the trigeminal nerve.

RESULTS

Patients who underwent microvascular decompression alone did not have satisfactory relief of pain. Patients who underwent partial sectioning of the nerve did better.

CONCLUSIONS

Patients with MS and symptoms of typical trigeminal neuralgia may benefit from exploration of the cerebellopontine angle and partial sectioning of the nerve. MVD alone fails to provide adequate or reliable relief of pain.

A conserved 90 nucleotide element mediates translational repression of nanos RNA

Correct formation of the Drosophila body plan requires restriction of nanos activity to the posterior of the embryo. Spatial regulation of nanos is achieved by a combination of RNA localization and localization-dependent translation such that only posteriorly localized nanos RNA is translated. Cis-acting sequences that mediate both RNA localization and translational regulation lie within the nanos 3′ untranslated region. We have identified a discrete translational control element within the nanos 3′ untranslated region that acts independently of the localization signal to mediate translational repression of unlocalized nanos RNA. Both the translational regulatory function of the nanos 3′UTR and the sequence of the translational control element are conserved between D. melanogaster and D. virilis. Furthermore, we show that the RNA helicase Vasa, which is required for nanos RNA localization, also plays a critical role in promoting nanos translation. Our results specifically exclude models for translational regulation of nanos that rely on changes in polyadenylation.

Evolution in technique for vestibular schwannoma radiosurgery and effect on outcome

PURPOSE

To define changes in treatment technique for vestibular schwannoma radiosurgery and to relate them to changes in outcome, a large single institution experience was reviewed.

METHODS AND MATERIALS

Two hundred seventy-three patients with unilateral vestibular schwannomas underwent Gamma knife radiosurgery: 118 with computed tomography (CT) treatment planning during 1987-1991, and 155 with magnetic resonance imaging (MR) treatment planning in 1991-1994. Mean treatment parameters differed between the CT and MR groups: minimum tumor dose (D(min)) was 17 vs. 14 Gy, number of isocenters was 3.4 vs. 5.8, and volume was 3.5 vs 2.7 cc., respectively.

RESULTS

The actuarial 7-year clinical tumor control rate (no requirement for surgical intervention) for the entire series was 96.4 +/- 2.3%, with a radiographic tumor control rate of 91.0 +/- 3.4%; these rates were similar for the CT and MR groups. Significantly lower rates of postradiosurgery facial, trigeminal, and auditory neuropathy were observed in the MR group compared to the CT group. Multivariate analyses found significant independent correlations of increasing rates of facial and trigeminal neuropathy with increasing transverse tumor diameter and D(min), as well as with CT treatment planning (compared to MR). Decreased hearing was similarly correlated with diameter and CT planning but not with D(min).

CONCLUSIONS

Changes in radiosurgery technique and the use of lower doses improved the outcome after vestibular schwannoma radiosurgery by decreasing cranial neuropathy rates. MR-based treatment planning appears to have significantly contributed to this improvement. Despite decreases in radiation dose, no change in the high rate of tumor control has yet been observed.

Early outcomes after stereotactic radiosurgery for growing pilocytic astrocytomas in children

To examine the role of stereotactic radiosurgery in the adjuvant management of children with growing and unresectable deep-seated pilocytic astrocytomas, we reviewed our experience in 9 patients. The tumors were located in the dorsolateral pons (n = 2), midbrain (n = 1, cerebellar peduncle (n = 2), thalamus (n = 1), temporal lobe (n = 1), hypothalamus (n = 1), and caudate nucleus (n = 1). The mean tumor diameter was 16 mm (range, 11-25 mm). Seven patients had prior partial tumor resection, and 2 had a stereotactic biopsy. Two patients had failed fractionated radiotherapy and 7 were considered at risk for adverse radiation effects because of their age. The mean dose to the tumor margin at radiosurgery was 15 Gy (range, 12-18). During mean follow-up of 19 months (range 13-41 months), there was a marked decrease in tumor size in 5 patients; 4 patients had no further growth. No early or delayed morbidity was associated with radiosurgery. Gamma knife radiosurgery proved a safe and effective therapeutic tool in the management of children with deep, small volume pilocytic astrocytomas. Because this tumor often appears well-delineated on contrast-enhanced neuroimaging, we believe that conformal radiosurgical targeting accurately irradiates tumor cells. For small tumor volumes it can be used in place of fractionated larger-field radiotherapy. The ability to treat the tumor yet spare surrounding brain may reduce the surgical morbidity associated with attempted radical resection and the potential cognitive and endocrine disabilities associated with fractionated radiation therapy.

Stereotactic radiosurgery for glial neoplasms of childhood

We evaluated the role of stereotactic radiosurgery (SRS) in 25 children with surgically incurable brain tumors of glial origin. Histological diagnoses were obtained at the time of craniotomy and attempted removal (n = 20) or by stereotactic biopsy (n = 5). Thirteen children had tumors with benign histological characteristics (pilocytic and low-grade astrocytomas), whereas 12 children had tumors with malignant characteristic (malignant astrocytomas and ependymomas). Eleven (10 with malignant tumors) of the 25 children had received fractionated irradiation before SRS. Radiosurgical doses (range to margin, 11-20 Gy) were calculated on the basis of tumor volume and location, with consideration given to prior radiation dose. Follow-up for the 13 children with benign tumors ranged from 6 to 48 months (median, 21 mo). Eleven of the 13 children with "benign" glial neoplasms had tumor control with SRS alone (no evidence of tumor, n = 4; decreased tumor, n = 5; and unchanged tumor, n = 2), and all 13 remain alive. Five children with malignant tumors are alive at 12, 45, 50, 72, and 72 months after radiosurgery. The other seven children with malignant tumors are dead, with a median survival of 6 months after radiosurgery. Three of 12 children with malignant glial neoplasms had tumor control after SRS. Two of these three children received fractionated irradiation as an adjunct to SRS. Complications occurring in four children were transient, associated with peritumoral edema, and responsive to oral glucocorticoids. There was no relationship between tumor volume and local control after radiosurgery. Radiosurgery alone is a safe and effective treatment modality for unresectable benign gliomas of childhood. Radiosurgery may have a role in the adjuvant management of unresectable malignant glial neoplasms of childhood if other therapies (irradiation or chemotherapy) are available.