Stereotactic radiosurgery of anterior skull base tumors

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.