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.

INTRODUCTION: Meningiomas are common intracranial benign tumors that can be surgically excised. However, their intimate involvement with critical neurovascular structures often prevent their complete resection. Gamma Knife radiosurgery is a minimally invasive option which provides excellent tumor control as both an adjunct and primary therapy. MATERIALS AND METHODS: Between September 1987 and December 2004, 964 patients underwent Gamma Knife radiosurgery at the University of Pittsburgh for the diagnosis of meningioma. The majority of patients had tumors located at the skull base. All imaging and clinical follow-up was reviewed. RESULTS: Overall, Gamma Knife radiosurgery provides 5- and 10-year actuarial tumor control rates of 93% for benign meningiomas. The 5-year actuarial control rate for patients with atypical and malignant meningiomas was 83 +/- 7 and 72 +/- 10%, respectively. The incidence of adverse radiation effect ranged from 5.7 to 16%; however, the incidence was gradually reduced with the advent of magnetic resonance imaging and lower dosing since 1991. CONCLUSION: Gamma Knife radiosurgery is an attractive option for patients with intracranial meningiomas. It can be used as both primary treatment based on imaging diagnosis alone, or as an adjunct treatment after craniotomy. It provides long-term tumor control with minimal adverse sequelae.

Selecting optimal doses for radiosurgery requires a thorough consideration of existing dose-response data for radiation injury of brain and surrounding structures and of the doseresponse for the desired endpoint (tumor control, obliteration of a vascular malformation, relief of trigeminal neuralgia, etc.). This paper reviews the radiobiological and physics principles that should be considered in dose selection as well as information from retrospective and prospective clinical investigations of radiosurgery.

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.