Faculty Bibliography

Stereotactic radiosurgery has become an integral part of conventional and advanced skull base surgery. Despite the advances in skull base techniques, the goal of total resection of such tumors is often problematic and associated with significant risk to critical structures of the skull base, including those within the cavernous sinus, those in the petrous apex, and the jugular bulb. Aggressive resection of such tumors sometimes results in severe adverse neurological events, ranging from permanent extraocular movement deficits to hearing loss, facial weakness, and difficulties with vagal and glossopharyngeal function. Gamma Knife radiosurgery is a primary alternative option for these patients. It minimizes the risks of open surgical techniques and preserves existing cranial nerve function in most patients and achieves tumor growth arrest. Adjuvant radiosurgery is used for larger tumors after their initial partial resection. Gamma Knife radiosurgery becomes an adjuvant tool to provide longterm tumor growth control of a significantly reduced tumor volume.

The role of radiosurgery for cavernous malformations of the brain remains to be fully defined. We have used Gamma Knife radiosurgery for selected patients with symptomatic, hemorrhagic malformations in high-risk brain locations. Indications, techniques, and results are presented.

Advances in neuroimaging, stereotactic techniques, and robotic technology in the last decade have significantly expanded the applications of radiosurgery. Radiosurgery has become a preferred management modality for many intracranial tumors such as schwannomas, menigiomas and metastatic tumors. While indications of radiosurgery continue to expand, further investigations are critical to understand the mechanism of biological response of CNS tissues to radiation as well as the potential of long-term adverse effects. The effects and the pathogenesis of biologic effects following radiosurgery may be unique. The need for basic research concerning the radiobiology of high-dose single-fraction ionizing radiation on nervous system tissue is crucial. The development of future applications of radiosurgery will depend upon our understanding of radiobiology of radiosurgery. The present review examines the state of radiobiological investigations into the nature of CNS effects, the newer techniques developed, and the use of radiosurgery as a tool for understanding basic CNS biology.

BACKGROUND AND PURPOSE: The authors characterize the detection of additional intracranial metastases in cancer patients at the time of stereotactic radiosurgery (SRS) using a specialized high-resolution magnetic resonance imaging (MRI) protocol. METHODS: A retrospective review of 150 consecutive radiosurgical procedures for patients with < or =5 known metastatic intracranial tumors diagnosed using MRI was undertaken at a single center. On the day of SRS, all patients underwent rigid head fixation in a stereotactic frame followed by a specialized MRI using a 3-dimensional fast spoiled-gradient sequence on a 1.5-tesla magnet with double-dose gadolinium. Axial imaging was performed using 2-mm cuts and no gap. RESULTS: Additional metastases were detected in 29.3% of patients. The number of known tumors before SRS was predictive of additional metastases being found (p = 0.014). In multivariate analysis, we more frequently found additional metastases at radiosurgery in patients with 3-5 previously known metastases (p = 0.005), in patients with non-small cell lung cancer (p = 0.012) and in patients with a longer time interval between their diagnostic MRI and their stereotactic MRI (p = 0.030). Age, sex and prior fractionated radiation therapy were not predictive factors. CONCLUSION: Our specialized protocol of high-resolution, double-dose contrast-enhanced MRI is a reliable method to evaluate the extent of intracranial disease in patients with known brain metastasis. Treatment planning for radiosurgery, radiation therapy and open surgical therapy are all impacted by improved metastasis detection.