Stereotactic radiosurgery and vestibular schwannoma: hydrocephalus associated with the development of a secondary arachnoid cyst: a report of two cases and review of the literature

Stereotactic radiosurgery for vesibular schwannoma requires long-term follow-up with complete MR imaging. We report two cases of a large secondary arachnoid cyst developing in the cerebellopontine angle following stereotactic radiosurgery. In one case this was associated with progressive ventriculomegaly and the onset of symptomatic hydrocephalus requiring emergency treatment. The second patient had ventriculomegaly at diagnosis, but developed an arachnoid cyst following treatment. Although both arachnoid cysts and hydrocephalus may also occur spontaneously in patients with vestibular schwanomma, the incidence is higher after stereotactic radiosurgery. As both complications may be associated with sudden clinical deterioration, follow-up with full cranial T1 and T2 weighted MR imaging is required to reveal these complications, in addition to assessing tumour response.     

Stereotactic radiosurgery for well-circumscribed fibrillary grade II astrocytomas: an initial experience

OBJECTIVE: To examine the role of stereotactic radiosurgery in the management of patients with progressive, well-circumscribed grade II fibrillary astrocytomas. METHODS: During a 13-year interval, 12 patients (median age: 25 years) required multimodality management for recurrent or unresectable World Health Organization (WHO) grade II fibrillary astrocytomas. Tumors involved the brainstem (n = 4), thalamus (n = 1), cerebellum (n = 1), frontal lobe (n = 4), temporal lobe (n = 1), and parietal lobe (n = 1). Diagnosis was confirmed by stereotactic biopsy (n = 5), partial resection (n = 5), and near total resection (n = 2). Multimodality management of patients prior to radiosurgery included fractionated radiation therapy (n = 4), stereotactic cyst drainage (n = 1), and ventriculoperitoneal shunt placement (n = 2). Tumor volumes varied from 1.2 to 45.1 cm(3). The median radiosurgical dose to the tumor margin was 16 Gy. RESULTS: After radiosurgery, serial imaging showed complete tumor resolution in 1 patient, reduced tumor volume in 4, stable tumor volume in 3, and delayed tumor progression in 4 (3 patients with increase in cyst size only). Therapy after radiosurgery included additional cytoreductive surgery (n = 1) for recurrence of a higher grade tumor, stereotactic cyst aspiration (n = 1), and stereotactic intracavitary irradiation (n = 1). All patients were alive at a median follow-up of 52 months after radiosurgery and 103 months after diagnosis. In 8 patients, follow-up lasted more than 60 months. CONCLUSION: Stereotactic radiosurgery is a potential alternative or adjunctive strategy in the management of selected patients with WHO grade II fibrillary astrocytomas.     

Malignant squamous degeneration of a cerebellopontine angle epidermoid tumor. Case report

The authors present the case of a woman with a cerebellopontine angle (CPA) epidermoid cyst that degenerated into a squamous cell carcinoma. Malignant degeneration of an epidermoid cyst is an extremely rare occurrence. Malignant transformation must be considered in the differential diagnosis when new contrast enhancement on imaging studies and progressive neurological deficit are seen in a patient harboring an epidermoid cyst. The patient initially presented with a 10-year history of left trigeminal neuralgia, subacute left-sided hearing loss, and with facial weakness of 3 weeks' duration. Initial magnetic resonance (MR) imaging revealed a left CPA mass, consistent with an epidermoid. There was faint contrast enhancement where the tumor was in contact with the lateral brainstem. A subtotal resection was performed. Histopathological findings were consistent with an epidermoid tumor. One year after initial presentation, the patient's neurological deficit had increased, and follow-up MR imaging demonstrated a large contrast-enhancing tumor filling the left CPA and compressing the brainstem. At repeated surgery a squamous cell carcinoma arising from the previous epidermoid was found. The patient was subsequently treated with external-beam radiotherapy and stereotactic radiosurgery. Her tumor stabilized. Three years and 8 months after the patient's initial presentation, a new area of tumor developed at the torcular Herophili. The patient died shortly thereafter. Malignant squamous degeneration is a rare cause of enhancement on MR images, as is progressive neurological deficit in a patient with an epidermoid. The combination of subtotal resection, external-beam radiotherapy, and stereotactic radiosurgery may be useful for local tumor control but the long-term prognosis is guarded.     

Linac Radiosurgery for Skull Base Meningiomas

Summary  Introduction. Skull base meningiomas present a difficult surgical challenge because of the high potential morbidity of radical surgical extirpation and their low potential for incapacitating symptomatology. The focal character of meningiomas makes stereotactic radiosurgery an attractive adjuvant treatment modality to resection. The purpose of this study was to evaluate the local control rates and complications in 56 patients with base of skull meningiomas undergoing radiosurgery.  Methods. Patients underwent radiosurgery using the dedicated stereotactic linear accelerator at the Brigham and Women's Hospital. Minimal peripheral doses of radiosurgery ranged from 12 to 18.5 Gy (mean 15 Gy). Doses were designed to conform to the frequently irregular tumor volumes using the X-Knife treatment planning system. Multiple isocenters were used when required to increase conformality of dose. For 36 patients (64%), radiosurgery was used as an adjunct to surgery; for 20 patients (36%) it was the primary treatment.  Results. Median followup was five years. Nineteen patients (34%) were improved clinically at follow-up; 32 (57%) were unchanged; and 5 patients (9%) developed new or worsened neurologic deficits. Serial imaging studies after radiosurgery showed a reduction in tumor volume in 23 patients (41%); 30 (54%) showed stable disease; 3 patients (5%) had tumors which increased in size (2 being outside the radiosurgery treatment site). The actuarial freedom from progression rate (defined as further tumor growth) was thus 95%, with a median imaging follow-up of 26 months (range, 6–66 months).  Although further follow-up is necessary, the results of this series clearly demonstrate that these lesions are feasible for treatment by modern radiosurgical techniques. Linac radiosurgery can stabilize skull base meningiomas, with decreased or unchanged tumor volumes on radiologic follow-up in approximately 95% of patients. Radiosurgery is a low-morbidity, effective technique as adjunct and sometimes primary treatment of small to moderate-sized meningiomas of the skull base.     

Gamma knife radiosurgery for intracranial haemangioblastomas

Summary Background. The results of gamma knife radiosurgery for haemangioblastomas were retrospectively studied to assess the efficacy for tumour growth control and clarify the clinical indications for gamma knife radiosurgery in these tumours. Methods. The medical records of 22 patients with 67 tumours, 12 men and 10 women aged 20–73 years (mean 51.9 years), who underwent gamma knife radiosurgery for haemangioblastomas between January 1993 and January 2006, were retrospectively reviewed. Ten patients with 54 lesions had von Hippel-Lindau disease. The mean tumour volume was 1.69 cm³ (range 0.0097–16.4 cm³). Nineteen patients had undergone 1–4 open surgery procedures (mean 1.5) before gamma knife radiosurgery. Tumours without a cystic component, (the solid type), were found in 54 lesions and tumours associated with cyst, (the mural nodule with cyst type), in 13 lesions. The marginal dose was 8–30 Gy (mean 14.0 Gy). Findings. Follow-up magnetic resonance (MR) imaging was performed at 9–146 months (mean 63 months). The control rate for tumour growth was 83.6%. The only factor affecting tumour growth control was the presence of a cystic component at the time of gamma knife radiosurgery in both univariate and multivariate analysis. No complication such as radiation-induced peritumoural oedema or radiation necrosis occurred. Conclusion. The presence of cystic components at the time of gamma knife radiosurgery was the only factor significantly correlated with unfavourable tumour growth control by gamma knife radiosurgery for haemangioblastomas. Gamma knife radiosurgery is effective for solid type tumours, even if the marginal dose is relatively low. Surgical removal is recommended for mural nodule with cyst type tumours, when possible.     

The value of image coregistration during stereotactic radiosurgery

Background  Coregistration of any neuroimaging studies into treatment planning for stereotactic radiosurgery became easily applicable using the Leksell Gamma Knife 4C, a new model of gamma knife. The authors investigated the advantage of this image processing. Method  Since installation of the Leksell Gamma Knife 4C at the authors’ institute, 180 sessions of radiosurgery were performed. Before completion of planning, coregistration of frameless images of other modalities or previous images was considered to refine planning. Treatment parameters were compared for planning before and after refinement by use of coregistered images. Findings  Coregistered computed tomography clarified the anatomical structures indistinct on magnetic resonance imaging. Positron emission tomography visualized lesions disclosing metabolically high activity. Coregistration of prior imaging distinguished progressing lesions from stable ones. Diffusion-tensor tractography was integrated for lesions adjacent to the corticospinal tract or the optic radiation. After refinement of planning in 36 sessions, excess treated volume decreased (p = 0.0062) and Paddick conformity index improved (p < 0.001). Maximal dose to the white matter tracts was decreased (p < 0.001). Conclusion  Image coregistration provided direct information on anatomy, metabolic activity, chronological changes, and adjacent critical structures. This gathered information was sufficiently informative during treatment planning to supplement ambiguous information on stereotactic images, and was useful especially in reducing irradiation to surrounding normal structures.     

Cerebral Germinoma with Hemiatrophy of the Brain: Report of Three Cases

Summary. Summary.   Background: The authors report three cases of cerebral germinoma that occurred in young adults with unusual presentation.   Method: All three patients presented with hemiparesis and were treated at Seoul National University. A histological diagnosis of germinoma was made by a stereotactic biopsy in all three cases.   Findings: Magnetic resonance (MR) images showed that their tumors were located in the internal capsule and thalamus, and were associated with ipsilateral cerebral hemisphere and brain stem atrophy. The hemiparesis slowly progressed and this was accompanied by a haemorrhagic cyst in each patient.   Interpretation: Clinical diagnosis was not easy because of the unusual clinical presentations and atypical MR imaging findings. It is suggested that cerebral germinoma should be included in the differental diagnosis of a haemorrhagic mass which is associated with cerebral atrophy in the thalamus, basal ganglia, or internal capsule, especially in adolescents or young adults.     

Polymer gel in rat skull to assess the accuracy of a new rat stereotactic device for use with the Gamma Knife

Purpose  Accurate targeting is crucial for the irradiation of a small-volume animal brain. We propose an original method, based on a polymer gel, to determine the accuracy and reproducibility of irradiation using a new stereotactic frame. Methods  An in-house designed rat stereotactic frame, compatible with the Gamma Knife, was constructed. The rat brain was then removed through a small burr hole and the intracranial cavity was washed and filled with a polymer gel. This “gel brain” was irradiated by Gamma Knife and the irradiated volumes and coordinates were measured after the irradiation. Results  The position of the polymerized areas revealed that the stereotactic frame was able to accurately reproduce the same position of irradiation in each animal. The small standard deviation demonstrated the high reproducibility. Conclusion  The polymer gel confirmed the ability of the rat stereotactic frame to accurately and reproducibly position a small animal for precise radiosurgery procedures.     

Stereotactic Radiosurgery for Hemangioblastomas of the Brain

Summary  Objective. To assess the effectiveness of stereotactic radiosurgery in achieving tumor control and improving survival in patients with hemangioblastoma, we evaluated results from patients who were managed at the University of Pittsburgh and the Mayo Clinic.  Patients and Methods. Twenty-seven patients with 29 hemangioblastomas had stereotactic radiosurgery over a 10 year interval. The mean patient age was 32 years (range, 14–75 years). The tumor volumes varied from 0.36 to 27 ml (mean, 3.2 ml), and the mean tumor margin dose was 16 Gy (range, 11.7–20). Clinical and neuroimaging follow-up was obtained for all patients between 0.5 and 9 years (mean, 4 years) after radiosurgery.  Results. At this assessment, 21 patients (79%) were alive and six (21%) had died. The median survival after radiosurgery was 6.5 years (actuarial 5 year survival=75.1±11.5%). The median survival from the initial diagnosis was 15 years. Twenty two of 29 evaluable tumors were controlled locally. The two-year actuarial control rate was 84.5±7.1% and at five years, 75.2±8.9%. Multivariate testing of factors affecting good outcome indicated that smaller tumor volume and higher radiosurgical dose (>18 Gy) were significant.  Conclusion. For small to moderate size hemangioblastomas, multiple or recurrent tumors, and for patients who are not surgical candidates, radiosurgery is a safe and effective option to control disease and improve survival.     

Glioblastoma multiforme occurring in a patient treated with gamma knife surgery. Case report and review of the literature

Stereotactic radiosurgery is being increasingly advocated as the primary modality for treatment of vestibular schwannomas (VS). This modality has been shown to arrest tumor growth, with few associated short-term morbidities, and with possibly better hearing and facial nerve preservation rates than microsurgery. Radiation-induced oncogenesis has long been recognized, although stereotactic radiosurgery de novo induction of a secondary tumor has never been clearly described. The authors report on a patient with a VS who did not have neurofibromatosis Type 2 and who underwent gamma knife surgery (GKS). This patient required microsurgical removal of the VS within 8 months because of development of a tumor cyst with associated brainstem compression and progressive hydrocephalus. The operation resulted in clinical stabilization and freedom from tumor recurrence. Seven and a half years after undergoing GKS, the patient presented with symptoms of raised intracranial pressure. Magnetic resonance imaging demonstrated a new ring-enhancing lesion in the inferior temporal lobe adjacent to the area of radiosurgery, which on craniotomy was confirmed to be a glioblastoma multiforme (GBM). Despite additional conventional external-beam radiation to the temporal lobe, the GBM has progressed. Whereas this first reported case of a GBM within the scatter field of GKS does not conclusively prove a direct causal link, it does fulfill all of Cahan's criteria for radiation-induced neoplasia, and demands increased vigilance for the potential long-term complications of stereotactic radiosurgery, and reporting of any similar cases.     

Tube angulation improves angiographic targeting of arteriovenous malformations during stereotactic radiosurgery.

Stereotactic radiosurgery using the 201 Cobalt-60 source Gamma Knife has been an effective method for obliterating selected cerebral arteriovenous malformations (AVMs). For more than 20,000 patients worldwide, angiography under stereotactic conditions has been the main imaging modality for defining and targeting the AVM nidus. The role of angulation of the X-ray tube for angiographic localization of the AVM during stereotactic Gamma Knife radiosurgery was studied with a phantom. Using current dose-planning software, tube angulation facilitated target visualization, improved three-dimensional dose planning, and has been consistent with the increased probability of complete nidus obliteration.     

Cyst formation after stereotactic radiosurgery for intracranial meningioma

The authors report 2 cases of delayed cyst formation after gamma knife radiosurgery for 3 meningioma lesions. All 3 lesions reported here had a distinctive feature before gamma knife treatment of small and spotty intratumoral cysts. One patient experienced an intriguing clinical course of spontaneous regression of the enlarged cyst, and 2 of the 3 lesions became symptomatic requiring surgical interventions. Cyst formation as a postradiosurgical complication is relatively rare in meningioma patients in the literature, and its pathogenesis is unclear. We describe herein the clinical courses of these 2 patients and review the relevant literature in this report. From our experience of these 2 cases, we suggest that we should be aware of the possible development of spotty intratumoral cysts into larger cysts after stereotactic radiosurgery and that we should carefully observe such patients after the treatment.     

De novo formation of cavernoma after radiosurgery for adult cerebral arteriovenous malformation--case report

A 47-year-old male underwent stereotactic radiosurgery (25 Gy) for a cerebral arteriovenous malformation located in the right caudate nucleus, using a linear accelerator. Complete obliteration of nidus was confirmed 20 months after radiosurgery. However, a hypointense mass on T(2)-weighted magnetic resonance imaging developed in the area adjacent to the nidus after approximately 80 months. The mass gradually increased in size and induced severe perifocal edema over 2 years. The mass was successfully excised. Histological examination revealed that the mass consisted of dilated sinusoid vessels attached to the hematoma capsule, and the hematoma included clots in various stages of organization encapsulated by dense collagenous tissue. The histological diagnosis was cavernoma. De novo formation of cavernoma is well known to occur after radiation surgery for intracranial tumor, especially in pediatric patients, but is rare in adults. Based on the radiological and histological findings in the present case, the radiation-induced cavernoma underwent repeated bleedings resulting in chronic encapsulated expanding hematoma.     

A case of cerebral arteriovenous malformation revealing repeated intranidal hemorrhage accompanying neovascularization after stereotactic radiosurgery

We report a patient with cerebral arteriovenous malformation (AVM) revealing growing mass lesion after stereotactic radiosurgery. This 12-year-old female presented headache. CT scan showed hematoma at the head of the right caudate nucleus and angiography showed AVM at the site. LINAC-based stereotactic radiosurgery was performed with the patient. Twenty-three months after the radiosurgery the patient complained headache and CT scan showed hematoma again at the same site, although angiography did not show AVM. Thirty-five months after the radiosurgery mass lesion with enhancement effect was observed at the site and the mass lesion grew gradually thereafter. Thirty-nine months after the radiosurgery the mass lesion was evacuated. Histological examination revealed fibrotic core and surrounding neovascularized area with hemorrhage. The histology shows a new etiology of growing mass lesion after radiosurgery for AVM.     

The effective application of segmental image fusion in spinal radiosurgery for improved targeting of spinal tumours

Purpose  As a result of experiences of failed image fusion, an improved protocol for effective CT and MRI image fusion was developed. Image fusion is a critical part of image-guided stereotactic radiosurgery (IG-SRS) and greatly influences the accurate measurement of gross tumour volume (GTV) and optimal dosimetry. Avoidance of any positional discrepancy is vital for optimal image fusion and results in improved targeting, which improves clinical results. This paper describes a protocol for effective image fusion and how it impacted on the clinical outcome of stereotactic radiosurgery for spinal tumours. Methods  Fused MRI/CT images from 20 patients were examined and compared. A protocol for fusing images from thin slice MR images and CTs was developed for improved identification and measurement of tumour volume. Differences in individual GTV values both before and after image fusion were evaluated. The effectiveness of tumour targeting was also assessed by comparing discrepancies in individual and overall GTV values. Results  Differences in mean GTVs using either CT or MRI alone compared with the mean found through combined CT/MR image fusion showed a difference of 30.5 ± 4.8% and 14.5 ± 3.3% respectively. Additionally, the median GTV values from CT- and MR-based imaging were 11.64 ± 7.8 cm³ and 11.72 ± 6.6 cm³ vs 14.06 ± 8.0 cm³. Median GTV from CT–MR fusion was 14.06 ± 8.0 cm³. Improved information provided by the fused images enabled us to prescribe more effective dosages, as the fused images gave more accurate information about tumour se due to better delineation of tumour perimeters. Conclusions  This protocol provides improved visualisation of spinal tumours and enables better treatment planning. Segmented image fusion was shown to provide significant advantages for planning stereotactic radiosurgery. Fused images provided more precise and accurate data and allowed better targeting of tumours, with improved tumour coverage that resulted in better clinical outcomes.     

In vivo biological effects of stereotactic radiosurgery: a primate model.

Single-fraction, closed skull, small-volume irradiation (radiosurgery) of intact intracranial structures requires accurate knowledge of radiation tolerance. We have developed a baboon model to assess the in vivo destructive radiobiological effects of stereotactic radiosurgery. Three baboons received a single-fraction, 150-Gy lesion of the caudate nucleus, the thalamus, or the pons using the 8-mm diameter collimator of the gamma unit. Serial standard neurodiagnostic tests (neurological examination, computed tomographic scan, magnetic resonance imaging, stable xenon-enhanced computed tomographic scan of cerebral blood flow, somatosensory and brain stem evoked potentials, and myelin basic protein levels of cerebrospinal fluid) were compared with preoperative studies. Magnetic resonance imaging revealed the development of a lesion at the target site between 45 and 60 days after irradiation. Deterioration of the brain stem evoked potentials preceded imaging changes when the lesion encroached on auditory pathways. Myelin basic protein levels increased subsequent to imaging changes. Postmortem neuropathological examination confirmed a well-demarcated radionecrosis of the target volume. The baboon model appears to be an excellent method to study the in vivo biological effects of radiosurgery.     

Stereotactic radiosurgery for residual neurocytoma. Report of four cases.

The purpose of this report was to review the results of stereotactic radiosurgery in the management of patients with residual neurocytomas after initial resection or biopsy procedures. Four patients underwent stereotactic radiosurgery for histologically proven neurocytoma. Clinical and imaging studies were performed to evaluate the response to treatment. Radiosurgery was performed to deliver doses to the tumor margin of 14, 15, 16, and 20 Gy, depending on tumor volume and proximity to critical adjacent structures. More than 3 years later, imaging studies revealed significant reductions in tumor size. No new neurological deficits were identified at 53, 50, 42, and 38 months of follow up. The authors' initial experience shows that stereotactic radiosurgery appears to be an effective treatment for neurocytoma.     

LINAC Radiosurgery for Patients with a Limited Number of Brain Metastases

Patients (pts) with brain metastases have a high risk of cancer-related death due to extra- or intracranial tumor manifestations. The present retrospective analysis demonstrates the ability of linear accelerator (LINAC)-based radiosurgery to control intracranial disease and prolong survival in pts with one to three metastases. From 1991 to 1996, 106 pts (42 females, 64 males; median age, 57 years) with cerebral metastases were treated by stereotactic radiosurgery with a LINAC (8 MeV) equipped with tertiary collimators. In 70 pts, a single metastasis was present; 36 pts had two or three metastases. Fifty-nine pts were treated for their first occurrence of brain metastases; 47 pts had been treated prior to radiosurgery by resection and/or whole-brain irradiation. Histology of the primary tumor was non–small cell lung cancer (36 pts), melanoma (20 pts), breast cancer (15 pts), hypernephroma (15 pts), and other (20 pts). All together, 157 metastases (0.04–69.0 ml; median, 2.7 ml) were irradiated with marginal doses of 12–25 Gy (median, 20 Gy) referred to the 65–80% isodose. Seventy-two percent of the lesions were treated with a single isocenter. Adjuvant whole-brain irradiation was applied in six pts. One hundred thirty-five of 157 metastases were evaluated for response: complete response (CR), 24%; partial response, 31%; no change, 30%; and progression of disease, 15%. CR rates were highest (48%) in small metastases (<1-cm diameter), independent of histological type and dose. The overall median survival was 8 months. Multivariate Cox regression analysis revealed a significant impact on survival for Karnofsky performance score, presence of extracranial tumor, and volume of largest metastasis. Freedom from neurological death was determined only by the volume of the largest metastasis. Patients with multiple metastases and/or extracranial disease had a higher risk of developing new outfield brain metastases. Due to salvage therapy (second or third course of stereotactic radiosurgery, whole-brain irradiation, surgery), the overall survival in pts with two or three metastases did not significantly differ from that in pts with single metastases. LINAC-based stereotactic radiosurgery in pts with up to three cerebral metastases results in survival rates approaching those of pts with resected single brain metastases. As pts with both single and multiple metastases can effectively be salvaged after receiving radiosurgery, extracranial tumor activity becomes a major determinator of survival.