Faculty Bibliography

Alterations in gyral contour made it difficult to identify the motor cortex thought to be near an arteriovenous malformation (AVM) in a 24-year-old man considered for stereotactic radiosurgery. Functional imaging in three modalities was performed preoperatively to compare the reliability of localization using functional magnetic resonance imaging (fMRI) on a conventional scanner with positron emission tomography (PET) and magnetoencephalography (MEG). Similar tasks were used for each imaging modality in an attempt to activate and identify the sensory and motor cortex. Data from all three modalities converged for the sensory task, and fMRI and PET data converged for the motor task. The right hemisphere motor strip was localized adjacent and anterior to the AVM. These data were used in planning the radiosurgery isodose configuration to the AVM in order to reduce the irradiation of motor cortex parenchyma. A postoperative fMRI study was also performed using newer techniques to reduce head motion artifact and to improve signal-to-noise ratio. The data confirmed the conclusions derived from the preoperative evaluations. This study demonstrates how conventional MRI scanners can be used for functional studies of use in surgical planning.

We compared the efficacy and the hospital charges of either single-stage or two-stage stereotactic diagnosis and radiosurgery procedures. Twelve patients underwent either one-stage or two-stage diagnosis and management of their brain tumors. Both techniques utilize high-resolution intraoperative stereotactic image-guided technology and rapid touch preparation (imprint) cytopathological techniques to confirm the presence of neoplasm. Following this pathologic diagnosis, six patients immediately underwent stereotactic radiosurgery employing the same frame application and dose planning based on preoperative and intraoperative images. Six patients underwent two-stage procedures, i.e., discharge from the hospital after histopathological diagnosis followed by readmission, reapplication of the stereotactic head frame, and repeat neuroradiological imaging prior to radiosurgery. Requirements for success of the single-stage procedure include intraoperative stereotactic high-resolution imaging, a hospital-wide ethernet system for transferring neurodiagnostic images, and expertise in rapid touch-preparation histopathological technique for accurate diagnosis. Intraoperative computed tomography imaging after biopsy confirmed the target accuracy and lack of movement of the target after brain biopsy. The advantages of the single-stage approach include reduced length of overall hospital stay, simultaneous histopathological diagnosis and therapy in a single hospital admission, and reduced total hospital charges. For patients highly suspected of having brain tumors and for whom stereotactic radiosurgery will be utilized in the treatment, single-stage stereotactic diagnosis immediately followed by radiosurgery is an accurate, effective, and potentially less costly management strategy than a two-stage approach.

Stereotactic radiosurgery is an increasingly safe and usually effective method of preventing growth of small to moderate-sized primary tumors of the anterior skull base. Tumor growth control is obtained in more than 90% of patients with skull base tumors having benign histology. Neurologic function is maintained in most patients. The risk of temporary or permanent injury to critical neural and vascular structures is significantly lower than the risk associated with microsurgery. The optic nerves, chiasm, and tracts are structures that appear most sensitive to the radiation doses used during radiosurgery of anterior skull base tumors. The incidence of injury to the optic apparatus is low when the dose to the nerve is less than 8 to 9 Gy (27). The incidence of injury to motor nerves, such as the oculomotor, trochlear, trigeminal, and abducens nerves, is extremely low at the doses used in clinical radiosurgery (27). To date no cases of delayed carotid injuries have been reported. Microsurgical complications (e.g., CSF leak, wound infection, and meningitis) do not occur after radiosurgery. Additional attractive features of radiosurgery are a relatively low, hospital-based cost and a rapid return of the patient of work. In the report of our experience with the first 207 patients treated with the Gamma Knife at the University of Pittsburgh, the average length of hospital stay was 2.24 days for a patient undergoing stereotactic radiosurgery for a skull base tumor and 11.44 days for a patient undergoing craniotomy for the same lesion. The total hospital charges were 30 to 70% lower for patients having radiosurgery (19). The average hospital stay and cost of radiosurgery are even lower now, because most radiosurgery patients are released from the hospital on the same day as their procedure. Patients are usually able to return to a full preoperative functional level and employment within 3 to 5 days. There are patients in certain clinical situations in which microsurgery clearly is required. These include patients experiencing rapidly progressive visual deterioration or who have endocrine-active pituitary tumors. A more rapid reduction in endocrine dysfunction is best achieved by microsurgical tumor excision. In patients in whom a tumor recurs despite "gross total removal," and in cases in which tumor is left behind to preserve critical nerve and vessel integrity, stereotactic radiosurgery is a very effective alternative to additional microsurgical operations. Stereotactic radiosurgery may also be the primary treatment of choice in patients who are unable or unwilling to accept the risk:benefit ratio of microsurgery.

We believe that every patient who has clinical symptoms and neurodiagnostic imaging signs suggesting a low-grade glial neoplasm should undergo early diagnosis and treatment. Observation is not warranted for a tumor that has a median survival of 5 years. The value of cytoreductive surgery for many patients has yet to be proven. It is incumbent on neurosurgeons who advocate this approach to show that this more aggressive treatment strategy is preferable to minimally invasive techniques, such as stereotactic biopsy followed by radiation therapy. Clearly, some patients who have a glial tumor require early cytoreductive surgery: those with mass effect and significant neurologic deficits. Otherwise, they will not be able to tolerate fractionated radiation therapy. Because the long-term survival rate is very poor, observation is not warranted in patients with suspected glial neoplasm. Early stereotactic biopsy immediately identifies those patients who, in fact, have more anaplastic tumors and a much worse prognosis. Such patients may benefit from early, aggressive treatments such as cytoreductive surgery, chemotherapy, and radiation. Applying this philosophy, we have achieved a median survival of more than 10 years in patients with astrocytoma. Most patients maintain a high KPS rating, and most do not require delayed cytoreductive surgery. Although we believe that the outcomes of future patients with astrocytomas will improve, we must establish whether such improvement is related to better therapeutic options, earlier recognition enabled by advanced neuroimaging, or the availability of corticosteroids (28, 30). We also believe that neurosurgeons and neuro-oncologists should stop arguing over whether cytoreductive surgery is warranted. For some patients it is, and for others it is not. This prolonged controversy indicates the basic impotence with which neurosurgeons approach glial tumors. Our energy and efforts should be devoted toward more concrete and positive goals in terms of glial tumor management. These goals include prolonged and higher-quality survival, reduced surgical and postoperative morbidity, and the development of new surgical, chemotherapeutic, and molecular tools that will allow us to improve clinical outcomes. Needless and senseless arguing over cytoreductive surgery versus biopsy, radiation versus no radiation, or any of these procedures versus observation alone trivialize the issues that face us and our patients: astrocytomas of the brain are neither indolent nor benign. The vast majority of our patients with astrocytomas are dead within 5 years, and almost all within 10. Our papers, our meetings, our approach should encourage us to pursue new basic science and clinical strategies to fight glial neoplasms. Surgery alone cures no patient with a glioma. Radiation therapy cures relatively few, and chemotherapy cures none. New ideas and new approaches are needed to improve the plight of our patients.

We reviewed our initial stereotactic radiosurgery experience in 10 patients with intracanalicular acoustic tumors managed by radiosurgery during a 5-year period. These patients constitute 4.7% of acoustic tumor patients who underwent Gamma Knife radiosurgery during this period. Tumor volume stabilization was achieved in 8. Two patients had initial growth followed by delayed growth arrest. Preservation of preoperative hearing was achieved in all patients in the immediate postoperative period and in 8 of 10 at 1 year. No patient had developed facial or trigeminal nerve dysfunction at the last follow-up, which varied from 3 to 64 months (mean 25 months). Tumor growth was delayed in 2 patients, but neither has required delayed microsurgical resection. All patients returned to their preoperative functional status within 3-5 days after radiosurgery. Stereotactic radiosurgery using the Gamma Knife is a safe and effective management strategy for intracanalicular acoustic tumor patients. Our initial results indicate that high cranial nerve preservation rates and a rapid return to previous activity and employment are benefits of radiosurgery.