An image fusion study of the geometric accuracy of magnetic resonance imaging with the Leksell stereotactic localization system.

A special acrylic phantom designed for both magnetic resonance imaging (MRI) and computed tomography (CT) was used to assess the geometric accuracy of MRI-based stereotactic localization with the Leksell stereotactic head frame and localizer system. The acrylic phantom was constructed in the shape of a cube, 164 mm in each dimension, with three perpendicular arrays of solid acrylic rods, 5 mm in diameter and spaced 30 mm apart within the phantom. Images from two MR scanners and a CT scanner were obtained with the same Leksell head frame placement. Using image fusion provided by the Leksell GammaPlan (LGP) software, the coordinates of the intraphantom rod positions from two MRI scanners were compared to that of CT imaging. The geometric accuracy of MR images from the Siemens scanner was greatly improved after the implementation of a special software patch provided by the manufacturer. In general, much better accuracy was achieved in the transverse plane where images were acquired. Most distortion was found around the periphery while least distortion was present in the middle and most other parts of the phantom. For most intracranial lesions undergoing stereotactic radiosurgery, accuracy of target localization can be achieved within size of a voxel, especially with the Siemens scanner. However, extra caution should be taken for imaging of peripheral lesions where the distortion is the greatest.

2001: Things to come.

THIS ARTICLE DISCUSSES elements in the definition of modernity and emerging futurism in neurological surgery. In particular, it describes evolution, discovery, and paradigm shifts in the field and forces responsible for their realization. It analyzes the cyclical reinvention of the discipline experienced during the past generation and attempts to identify apertures to the near and more remote future. Subsequently, it focuses on forces and discovery in computational science, imaging, molecular science, biomedical engineering, and information processing as they relate to the theme of minimalism that is evident in the field. These areas are explained in the light of future possibilities offered by the emerging field of nanotechnology with molecular engineering.

Sine qua non: the formulation of a theory of neurosurgery.

Fundamental postulates underlying the fabric of biomedicine are rarely discussed, much less seen in print. Scientific surgery and its subspecialties are relatively new fields, and their philosophical basis has received little attention since Halsted's day. During the last quarter century, we have "reinvented" neurosurgery, and a concatenation of forces is escalating that is further accelerated by technological change. Social, economic, political, and scientific climates concurrently exert unusually stressful influences on all practitioners, irrespective of the individual setting. This provides a reason to reexamine what neurosurgeons do and why, and to attempt to define the guidelines of theoretical basis for the specialty of neurosurgery and its procedures. This article examines the accomplishments of past generations in an effort to establish surgical substrata and proceeds to attempt to readdress elements of a theoretical basis of our current practice.

Radiosurgical management of benign cavernous sinus tumors: dose profiles and acute complications.

OBJECTIVE: Radiosurgery has emerged as an alternative treatment modality for cranial base tumors in patients deemed not suited for primary surgical extirpation, patients with recurrent or residual tumor after open surgery, or patients who refuse surgical treatment. We review our short-term experience with radiosurgical management of cavernous sinus region tumors with the Leksell gamma knife. METHODS: From August 1994 to February 1999, 69 patients with cavernous sinus lesions were treated in 72 separate treatment sessions. The tumor type distribution was 29 pituitary adenomas, 35 meningiomas, 4 schwannomas, and 1 paraganglioma. The median follow-up was 122 weeks. Lesions were stratified according to a five-level surgical grade. The grade distribution of the tumors was as follows: Grade I, 13; Grade II, 21; Grade III, 19; Grade IV, 12; Grade V, 4. Median tumor volume was 4.7 cm3. The median radiation dose was 15 Gy to the 50% isodose line. Median maximal radiation dose was 30 Gy. RESULTS: Analysis of tumor characteristics and radiation dose to optic nerve and pontine structures revealed a significant correlation between distance and dose. Much lower correlation coefficients were found between tumor volume and dose. One lesion in this series had evidence of transient progression and later regression on follow-up radiographic studies. No other lesions in this series were demonstrated to have exhibited progression. Complications after radiosurgical treatment were uncommon. Two patients had cranial nerve deficits after treatment. One patient with a surgical Grade III pituitary adenoma had VIth cranial nerve palsy 25 months after radiosurgical treatment that spontaneously resolved 10 months later. A patient with a bilateral pituitary adenoma experienced bilateral VIth cranial nerve palsy 3 months after treatment that had not resolved at 35 months after treatment. Six patients with preoperative cranial nerve deficits experienced resolution or improvement of their deficits after treatment. One patient with a prolactin-secreting adenoma experienced normalization of endocrine function with return of menses. CONCLUSION: Radiosurgical treatment represents an important advance in the management of cavernous sinus tumors, with low risk of neurological deficit in comparison with open surgical treatment, even in patients with high surgical grades.

A phantom study of the geometric accuracy of computed tomographic and magnetic resonance imaging stereotactic localization with the Leksell stereotactic system.

OBJECTIVE: To assess the spatial accuracy of magnetic resonance imaging (MRI) and computed tomographic stereotactic localization with the Leksell stereotactic system. METHODS: The phantom was constructed in the shape of a box, 164 mm in each dimension, with three perpendicular arrays of solid acrylic rod, 5 mm in diameter and spaced 30 mm apart within the phantom. In this study, images from two different MRI scanners and a computed tomographic scanner were obtained using the same Leksell (Elekta Instruments, Stockholm, Sweden) head frame placement. The coordinates of the rod images in the three principal planes were measured by using a tool provided with Leksell GammaPlan software (Elekta Instruments, Norcross, GA) and were compared with the physical phantom measurements. RESULTS: The greatest distortion was found around the periphery, and the least distortion (<1.5 mm) was present in the middle and most other areas of the phantom. In the phantom study using computed tomography, the mean values of the maximum errors for the x, y, and z axes were 1.0 mm (range, 0.2-1.3 mm), 0.4 mm (range, 0.1-0.8 mm), and 3.8 mm (range, 1.9-5.1 mm), respectively. The mean values of the maximum errors when using the Philips MRI scanner (Philips Medical Systems, Shelton, CT) were 0.9 mm (range, 0.4-1.7 mm), 0.2 mm (range, 0.0-0.7 mm), and 1.9 mm (range, 1.3-2.3 mm), respectively. Using the Siemens MRI scanner (Siemens Medical Systems, New York, NY), these values were 0.4 mm (range, 0.0-0.7 mm), 0.6 mm (range, 0.0-1.0 mm), and 1.6 mm (range, 0.8-2.0 mm), respectively. The geometric accuracy of the MRI scans when using the Siemens scanner was greatly improved after the implementation of a new software patch provided by the manufacturer. The accuracy also varied with the direction of phase encoding. CONCLUSION: The accuracy of target localization for most intracranial lesions during stereotactic radiosurgery can be achieved within the size of a voxel, especially by using the Siemens MRI scanner at current specifications and with a new software patch. However, caution is warranted when imaging peripheral lesions, where the distortion is greatest.

Vagus nerve stimulation for control of intractable seizures in childhood.

Vagus nerve stimulation (VNS) is gaining increasing popularity and credibility as a treatment option for children with intractable epilepsy. VNS offers several advantages over extant treatments. Its efficacy is maintained during prolonged stimulation, and seizure control actually improves with time. There is no associated cognitive impairment and no adverse drug interactions. Unlike cerebral surgery, VNS is a potentially reversible form of therapy. The computer-controlled characteristic of the device permits complete and involuntary treatment compliance. VNS is safe and well-tolerated. Its side effects are generally transient and mild, and no physiologic perturbations have been reported despite extensive monitoring. Serious adverse events are rare, and no deaths have been attributed to VNS therapy itself or to the technique of surgical insertion. In this article, we discuss the theoretical background behind VNS and review the clinical studies that substantiate its long-term safety, feasibility, tolerability and potential efficacy in children with refractory epilepsy.

Stereotactic radiosurgery in the treatment of metastatic disease to the brain.

OBJECTIVE: In recent years, stereotactic radiosurgery has been growing in popularity as a treatment modality for metastatic disease to the brain. The technique has advantages of reduced cost and low morbidity compared with open surgical treatment. Furthermore, it avoids the potential cognitive side effects of fractionated whole-brain radiotherapy. We undertook this study to determine the usefulness of adjuvant radiation therapy and to determine prognostic factors in patients treated with stereotactic radiosurgery. METHODS: We reviewed our series of patients with metastatic tumors treated using gamma knife stereotactic radiosurgery from August 1994 to February 1999. Nonparametric methods were used to compare treatment subgroups by demographic features including age, Karnofsky Performance Scale score, diagnosis, and systemic disease status. Univariate and multivariate analyses of survival and freedom from progression were performed using Kaplan-Meier and Cox proportional hazards regression techniques. RESULTS: This study included 190 patients harboring 431 lesions who were treated in 263 treatment sessions. The median follow-up after radiosurgery was 36 weeks for all patients. The median actuarial survival from the time of radiosurgery in all patients was 34 weeks. When patients were stratified according to tumor histology, those without melanoma had a median survival of 39 weeks, and those with melanoma had a median survival of 28 weeks. The cause of death could be determined in 122 (92%) of the patients known to have died during the data capture period. For patients harboring melanoma, death was attributable to systemic disease in 31 (47%), to central nervous system-related processes in 29 (44%), and to unknown causes in 6 (9%). For non-melanoma patients, death was attributable to systemic disease in 45 (68%), to central nervous system-related processes in 17 (26%), and to unknown causes in 4 (6%). Significantly improved survival (P = 0.002) was observed in patients with controlled systemic disease. No significant difference in survival could be ascertained for patients presenting with up to four lesions, although patients with a total tumor volume greater than 9 cc had shortened survival. No survival benefit could be demonstrated for whole-brain radiotherapy administered either concomitantly or after radiosurgery. CONCLUSION: Factors correlated with significantly improved survival included controlled systemic disease and non-melanoma histology. We found no significant survival benefit that could be discerned from adjuvant whole-brain radiotherapy in this patient group.

Modernity and the emerging futurism in neurosurgery.

This article discusses the emergence of neurosurgery in its 'modern' form during the second half of the 20th century and presents the apertures to the 21st century that are apparent in establishing an evolving futurism in the field. Factors of primary positive impetus and challenges are discussed.

Treatment of central nervous system infections: a neurosurgical perspective.

Almost any microorganism has the potential to infect the human central nervous system. Neurosurgical intervention may be required for tissue assay, to establish a microbiologic diagnosis, for decompression of space-occupying lesions with significant mass effects, or for definitive treatments such as cerebrospinal fluid diversion. This article surveys the surgical management of intracranial infections with special emphasis on subdural and epidural empyema, brain abscesses, mycotic aneurysms, and neurocysticercosis.

Radiosurgical salvage therapy for patients presenting with recurrence of metastatic disease to the brain.

OBJECTIVE: Radiosurgery has emerged as an important modality in the management of metastatic disease to the brain. A number of groups have published results suggesting that high local control rates can be achieved, with improvements in overall survival that rival the results of open surgical treatment. Typically, however, whole-brain radiotherapy has been used in the salvage therapy of patients who have undergone previous craniotomy or radiosurgery. We describe our experience with radiosurgical salvage in this group of patients. METHODS: From August 1994 to February 1999, 190 patients with brain metastasis were treated with gamma unit radiosurgery at our institution. A subset of 45 patients, who underwent radiosurgical salvage for new tumors in a region remote from an initially treated tumor, form the population base for this study. The usual criteria for repeat treatment were recurrence with five or fewer discrete lesions outside of the previously treated radiosurgical volume and Karnofsky Performance Scale score of at least 70. Survival and freedom from progression were measured from the time of radiosurgical treatment and were computed by the Kaplan-Meier product-limit method. Two or more curves were compared using the log-rank method. RESULTS: In this subgroup of patients, a total of 176 tumors were treated. The median time from first radiosurgical procedure to first salvage was 17.4 weeks. Median survival from the second radiosurgical intervention was 28 weeks. Of the 45 study patients, 34 patients underwent a single salvage procedure, 10 patients underwent two salvage procedures, and 1 patient had three salvage procedures. The actuarial freedom from progression for treated tumors at 52 weeks was 92.4%. Patients undergoing upfront whole-brain irradiation were less likely to require salvage therapy (P = 0.008). There were 33 deaths after salvage radiosurgery during the reporting period. Central nervous system causes accounted for 13 deaths, whereas 19 deaths resulted from systemic disease. The cause of death in one patient could not be determined. No statistically significant advantage in overall survival could be demonstrated in patients treated with whole-brain irradiation. CONCLUSION: Radiosurgical salvage represents a valuable means of treatment for central nervous system recurrence for patients who have undergone previous treatment for metastatic disease to the brain. Whole-brain irradiation may reduce the need for salvage therapy, but no advantage in overall survival could be demonstrated in this subgroup.

The metamorphosis of communication, the knowledge revolution, and the maintenance of a contemporary perspective during the 21st century.

OBJECTIVE: To define and discuss elements of the escalation in scientific data availability and their importance to neurosurgery. METHODS: This multifactorial essay describes the evolution of communication methodologies, the information revolution, and the advent and effect of Internet communication with its potential effect on the practice of neurosurgery, professional assemblies, journals, and the infrastructure of the discipline. Practical and philosophical viewpoints are rendered to assess the existing and developing availability of information to the neurosurgical community. CONCLUSION: Knowledge must be discerned from information. The individual does not have the luxury of detachment and must remain consistently, intellectually, and actively involved in the adaptations required to stay truly informed and current.