Faculty Bibliography

In early experience, radiosurgery proved to be a relatively safe and effective therapy for selected patients with symptomatic meningiomas, including those for whom surgical resection failed. Radiosurgery also has been an effective primary treatment alternative for patients whose advanced age, medical condition, or high-risk tumor location preclude microsurgery. The long-term response to treatment, as defined by imaging and clinical findings, is not yet available. In addition, further clinical and laboratory work is necessary to determine the appropriate tumoricidal radiosurgical dose, dose-volume relationships for individual tumors, and the variable radiation tolerance of the different brain structures that closely surround meningiomas.

Stereotactic radiosurgery is an important alternative treatment for carefully selected patients with acoustic tumors. We perform radiosurgery under local anesthesia, and 91% of our patients have been discharged from the hospital within 24 hours after treatment. All returned to their preoperative level of function or employment within 5 to 7 days after treatment. Our current tumor control rate is 97%, but reduction in tumor size, judged by strict, objective criteria, was achieved in only 23%. Our actuarial rate of useful hearing preservation after radiosurgery is 38% at 1 year. Three tumors increased in size after treatment. Only one of the three demonstrated increased mass effect on surrounding brain structures by neuroimaging criteria. No increase has led to worsened clinical symptoms or has required surgical excision at this point in follow-up. The 1-year rates for developing new facial or trigeminal neuropathies after radiosurgery were 30% and 33%, respectively. Cranial neuropathies had a delayed onset, with the median onset occurring after 5 to 6 months. The vast majority were partial at onset, and most improved over time. Communicating hydrocephalus requiring ventriculoperitoneal shunts developed after radiosurgery in four patients. Eight patients developed increased signal within adjacent brain parenchyma on T2-weighted MR imaging, consistent with edema or blood-brain barrier breakdown. It is unlikely that stereotactic radiosurgery using the gamma knife will obviate the need for microsurgical removal performed by skilled and experienced microsurgeons. However, radiosurgery is a safe and effective treatment for patients whose medical problems make surgery unacceptably dangerous, those with bilateral tumors or a tumor in their only hearing ear, those who have recurrent tumor despite surgical resection, or patients who refuse microsurgical excision.

Diagnosis and treatment of tumours and vascular malformations in the region of the pineal gland continue to challenge the neurosurgeon's skill. Due to vital vascular and brain structures in the region, microsurgical removal of such masses is often impossible. During the past nine years, we have managed 47 patients with pineal region mass lesions using stereotactic techniques for diagnosis and treatment. In order to determine further therapeutic options, 15 patients underwent stereotactic biopsy of pineal region tumours. In all patients, the histologic diagnosis obtained served to direct further therapy. Thirty-two patients were treated with stereotactic radio-surgery for pineal region tumours or vascular malformations. During the follow-up period, one patient underwent delayed microsurgical resection of a midbrain angiographically occult vascular malformation. No other patient required microsurgical intervention after a stereotactic procedure. In all 47 patients, no significant morbidity or mortality occurred after stereotactic biopsy or radiosurgery. Empiric treatment of pineal region tumours with fractionated radiation therapy is no longer warranted. Image-guided stereotactic technology provides a safe method to accurately diagnose and effectively treat selected pineal region masses. After definitive histologic diagnosis is established, proper treatment may be instituted. Options for treatment include stereotactic radiosurgery for selected tumours and vascular malformations, microsurgical resection of benign tumours or fractionated external beam radiation therapy for malignant germ cell and glial tumours. Stereotactic surgery should be the first option in the diagnosis and therapy of pineal region masses.

In order to analyze complications and the factors responsible for the development of serial imaging changes after stereotactic radiosurgery for intracranial arteriovenous malformations, we reviewed serial post-treatment magnetic resonance imaging scans in 72 patients. Median follow-up was 23 months (range 12 to 35 months). Twenty patients developed post-radiosurgical imaging changes consisting of new regions of increased T2 signal on magnetic resonance imaging in brain surrounding the arteriovenous malformation (two year actuarial incidence of 31%). Imaging changes were associated with headache or new neurological deficits in nine of these 20 (45%) and remained asymptomatic in 11 (55%). Symptoms developed in three of 13 patients with imaging changes in the cerebral cortex or cerebellum, in contrast to six of seven patients who had symptoms with imaging changes in the brainstem (p = .028). The onset of imaging changes varied from five to 18 months after radiosurgery (median, 12 months). Serial follow-up scans four to 25 months after the onset of imaging changes were available for review in 16 patients. Post-radiosurgical imaging changes completely resolved within 4 to 19 months in ten patients and have not yet completely resolved after 6 to 25 months in six patients. The projected actuarial rate for resolution of imaging changes was 88%, 19 months after onset; the median time for resolution was 14 months. Univariate analysis revealed that the development of imaging changes was significantly associated with treatment volume (p = .025), the risk predicted from the integrated logistic formula (p = .042), and the number of isocenters treated (p = .042). In multivariate analysis, volume was the only factor significantly associated with the development of imaging changes.

Stereotactic radiosurgery has an important role as primary or adjuvant therapy for selected cerebral vascular malformations and brain tumors. Over the next decade, both extended clinical experience, basic radiobiologic studies, and improvements in dose planning are expected to enhance its overall efficacy and safety.

Stereotactic aspiration is a valuable surgical alternative for colloid cysts, but due to cyst heterogeneity, it is not uniformly successful as the sole treatment in all patients. Since 1981, we performed CT-guided stereotactic aspiration as the initial procedure in 25 patients with colloid cysts. We retrospectively reviewed our experience in the first 22 patients and found that preoperative CT imaging studies accurately determined size and predicted cyst viscosity. The preoperative CT appearance of a hypodense or isodense cyst correlated favorably with successful aspiration. Preoperative MRI provided excellent anatomic definition of the cyst and its relationship to other structures, but failed to correlate successful aspiration. Unsuccessful aspiration was related to the high viscosity of the intracystic material or deviation of the cyst away from the aspiration probe. These factors were used prospectively in 3 additional patients to accurately predict success of cyst aspiration.