Faculty Bibliography

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.

To analyze the effect of stereotactic radiosurgery on the hemorrhage rate of arteriovenous malformations (AVMs), we reviewed the clinical and angiographic characteristics of 315 patients with AVMs before and after radiosurgery. One hundred ninety-six patients sustained 263 bleeds in 10,939 patient-years before radiosurgery, for an annual nonfatal hemorrhage rate of 2.4%. Clinical follow-up after radiosurgery was available in 312 patients (mean, 47 +/- 20 mo); follow-up > or = 24 months was obtained in 295 patients (94%). Twenty-one patients had AVM bleeds at a median of 8 months (range, 1-60 mo) after radiosurgery. Two additional patients had three aneurysmal bleeds (at 5, 27, and 32 mo, respectively) for a 7.4% total risk of hemorrhage per patient. The actuarial hemorrhage rate until AVM obliteration was 4.8% per year (95% confidence interval, 2.4-7.0%) during the first 2 years after radiosurgery and 5.0% per year (95% confidence interval, 2.3-7.3%) for the third to fifth years after radiosurgery. Multivariate analysis of clinical and angiographic factors demonstrated that the presence of an unsecured proximal aneurysm was associated with an increased risk of postradiosurgical hemorrhage (relative risk, 4.56; 95% confidence interval, 1.77-11.70%; P < 0.001). No AVM hemorrhages were observed after radiosurgery in seven patients with intranidal aneurysms. No protective effect against hemorrhage was observed in patients who received an "optimal" radiation dose (> or = 25 Gy to the AVM margin) compared with patients who received < 25 Gy to the AVM margin (P = 0.36). No patient suffered a hemorrhage after angiography had confirmed complete obliteration (n = 140) or suffered from an early draining vein without residual nidus (n = 19). Stereotactic radiosurgery was not associated with a significant change in the hemorrhage rate of AVMs during the latency interval before obliteration. No protective benefit was conferred on patients who had incomplete nidus obliteration in early (< 60 mo) follow-up after radiosurgery. AVM patients with unsecured proximal aneurysms should have aneurysms obliterated either before radiosurgery or at the time of surgical resection of their AVMs.

BACKGROUND: Treatment options for head and neck cancers that recur at the cranial base are limited. METHODS: Twelve patients with head and neck cancers recurrent after resection and fractionated radiotherapy (n = 11) at the cranial base had stereotactic radiosurgery using the gamma unit. The median dose to the tumor margin was 16 Gy. Imaging follow-up varied from 3 to 17 months; the longest clinical follow-up was at 35 months. RESULTS: Three of 8 tumors studied by postradiosurgery imaging remained unchanged in size, 3 decreased, and 2 were no longer visible. There was no morbidity or worsening of symptoms after radiosurgery. Four patients died between 4 and 8 months and did not have postradiosurgery imaging performed. Mean survival after radiosurgery was 10.5 months, with 7 patients (58%) still living. CONCLUSIONS: Radiosurgery proved safe and effective in providing local control for recurrent cranial base cancers arising from the extracranial head and neck. Radiosurgery should be considered for those patients who have failed prior fractionated radiation or surgical resection, those who have tumors in high-risk cranial locations, or those who are poor medical candidates. Although this study shows its potential adjuvant role, longer follow-up and increased clinical experience will be necessary to evaluate the overall role of radiosurgery in head and neck cancer.

Arteriovenous malformations (AVMs) that are located within the postgeniculate optic radiations or striate cortex are difficult to resect without creating postoperative visual defects. To reduce the risk of an AVM hemorrhage and to enhance the possibility of preserving visual function, the authors performed stereotactic radiosurgery in 34 patients with newly diagnosed or residual AVMs of the visual pathways. The mean AVM volume was 4.7 ml, and the average radiation dose to the AVM margin was 21 Gy. The median follow up was 47 months (range 16-83 months). Two (6%) of 34 patients had documented new visual field defects (central scotoma in one, and partial hemianopsia in one) after single-stage radiosurgery, but no patient developed a new permanent homonymous hemianopsia. Angiography was performed in all patients at a median of 26 months after radiosurgery: 22 (65%) had complete obliteration, 10 (29%) had a significant decrease in AVM volume, one (3%) had only a persistent early draining vein without residual nidus, and one (3%) had no change in the AVM. Thirteen (81%) of 16 patients with AVMs less of than 4 ml had complete obliteration. Five patients had second-stage stereotactic radiosurgery after angiography revealed a persistent AVM nidus; two patients eligible for follow-up angiography had complete obliteration, thereby increasing the overall series obliteration rate to 71%. The calculated annual risk of AVM bleeding (before radiographic evidence of obliteration) was 2.4%. No patient bled after angiographically confirmed obliteration. In most patients stereotactic radiosurgery obliterates visual pathway AVMs and also preserves preoperative visual function. Multimodality management (embolization, microsurgery, or staged radiosurgery) enhances AVM obliteration and visual preservation rates.

Second stereotactic radiosurgery procedures were required in 45 patients with arteriovenous malformations (AVMs) who initially had incomplete obliteration. Repeat radiosurgery was performed at a median of 39 months (range, 24-71 mo) after the first stage. The median AVM volume at the first procedure was 6.0 ml (range, 0.2-18.0 ml). Thirty-seven patients (82%) had AVMs of Spetzler-Martin Grades III through VI. A retrospective analysis revealed definite causes for incomplete obliteration after the first procedure in 33 patients (73%). Incomplete angiographic definition of the nidus was the most frequent factor (57%) associated with failed radiosurgery. Three patients (7%) had recanalization of the AVM nidus after prior embolization; four patients (9%) had incomplete nidus recognition, because AVM vessels were not visualized in the presence of a hematoma. "Radiobiological resistance" was another potential factor associated with failed radiosurgery in 17 patients (38%). Our current technique for volume determination and dose planning includes stereotactic magnetic resonance angiography, magnetic resonance imaging, and complete cerebral angiography (including superselective and external carotid artery injections, as indicated). Integrated multiplanar high-resolution imaging will likely increase the rate of AVM obliteration after stereotactic radiosurgery.

Members of the American Society of Stereotactic Functional Neurosurgery were surveyed to determine the current use of magnetic resonance imaging (MRI) for stereotactic coordinate determination. Of 137 respondents, 48% used MRI as the sole technique for some biopsy procedures. Of those performing functional surgery, more surgeons use MRI alone than CT alone for localization. Of those surgeons who used MRI alone for stereotactic surgery, 98.6% were satisfied with this method. Significant factors related to the use of MRI amongst individual surgeons included the performance of > or = 2 stereotactic surgeries per week, the performance of radiosurgery, and being in an academic practice (p < 0.0004). The increasing use of MRI in stereotactic surgery must be coupled with quality assurance testing from frame manufacturers, imaging manufacturers, and surgeons.

The results of Gamma Knife stereotactic radiosurgery in the management of 51 patients who had typical trigeminal neuralgia were evaluated at the University of Pittsburgh. In all cases, a 4-mm isocenter was targeted at the proximal nerve at the root entry zone. The target dose varied from 60 to 90 Gy. Forty-four patients (86%) had undergone prior surgery. The mean follow-up after radiosurgery was 9.6 months (range, 2-29 months). The initial response rate was 86%. At the last follow-up, 19 patients (37%) had excellent control (pain free), 21 (41%) had good control (50-90% relief), and 11 (21%) had failed treatment. No patient developed further sensory loss or deafferentation pain. A maximum radiosurgery dose > or = 70 Gy was associated with a significantly greater chance for complete pain relief. Using magnetic resonance imaging stereotactic targeting, the proximal trigeminal nerve is an appropriate anatomic target for radiosurgery. Gamma Knife radiosurgery is a useful additional surgical approach in the management of medically or surgically refractory trigeminal neuralgia.

The development of computed imaging techniques has revolutionized contemporary neurosurgical procedures. In a 20-year interval, intraoperative imaging was used in more than 4,000 patients at our center. The selection of the appropriate intraoperative imaging tool was dependent on the neurosurgical procedure performed. In our dedicated operating room suite, intraoperative fluoroscopic imaging was used during transsphenoidal, spinal, and functional procedures, e.g. to treat percutaneous trigeminal neuralgia. A dedicated intraoperative computed tomography scanner was first available in 1981 and was used in more than 1,500 stereotactic or image-guided procedures. During radiosurgical procedures with the Gamma Knife (n = 1,560) a variety of intraoperative imaging tools (MRI, CT, angiography, and digital subtraction angiography) were used to define the target. The output of these imaging tools is currently transferred via fiberoptic ethernet to a wide variety of computer workstations designed to facilitate surgical or radiation dose planning. In addition, intraoperative imaging became increasingly important during vascular neurosurgery. Because of its superior patient accessibility and instrument compatibility. CT is likely to remain the most important imaging tool for conventional intraoperative image-guided stereotactic surgery. In contrast, intraoperative MRI proved to be the superior imaging tool for radiosurgery.

Accurate localization of the lesion with respect to functionally significant brain is essential to safe stereotactic radiosurgical dose planning. We report the use of functional MR imaging in 3 patients to identify critical areas of surrounding brain and to provide assistance with dose planning, especially with regard to shaping the peripheral isodose around the lesion. We used a functional MRI system employing a conventional 1.5-tesla MRI unit that can detect decreases in deoxyhemoglobin concentration occurring with performance of specific tasks. Two of the patients had supratentorial arteriovenous malformations and 1 patient had a recurrent parasagittal meningioma. Functional MRI provided information on the location of speech, motor, and sensory cortex in these patients. Radiosurgical dose plans were constructed that kept these cortical areas outside of the 30% isodose curves. We believe that the safety of supratentorial parenchymal radiosurgery will be enhanced by the localization of critical brain regions around the target.