Faculty Bibliography

OBJECT: Schwannomas from the motor cranial nerves controlling eye movement are rare. The authors evaluated the role of Gamma Knife surgery (GKS) in the management of schwannomas originating from cranial nerves III, IV, and VI. METHODS: Over a 7-year period, 8 patients with schwannomas originating from the oculomotor (2 patients), trochlear (5 patients), or abducent (1) nerve underwent GKS. The mean patient age was 46.1 years (range 19-59 years). The presenting symptoms included diplopia in 5 patients, ptosis in 1 patient, ophthalmoplegia in 1 patient, and headache in 1 patient. Two patients had a history of neurofibromatosis Type 2. Gamma Knife surgery was performed as primary management in 7 patients and after prior resection in 1 patient. The median and mean tumor volumes were 0.22 and 1.32 cm(3) (range 0.03-7.4 cm(3)). A median margin dose of 12.5 Gy (range 11.0-13.0 Gy) was prescribed to the tumor margin. Clinical and imaging follow-up data were available for all 8 patients. RESULTS: Magnetic resonance imaging showed tumor regression in all patients. The progression-free period varied from 4 to 42 months, with a mean of 21 months. Over a mean of 23 months, 4 of the 5 patients with a trochlear schwannoma and symptoms of diplopia noted symptomatic improvement. No improvement was noted in the 2 patients with oculomotor nerve palsies. Headache was improved in the 1 patient with an abducent neuroma. CONCLUSIONS: Gamma Knife surgery is an effective and minimally invasive approach capable of inactivating schwannomas originating from the oculomotor, trochlear, and abducent nerves. Accompanying trochlear function may improve. Longer follow-up and larger patient samples are needed to confirm the authors' initial observations.

OBJECTIVE: Tumor control, facial function preservation, and hearing preservation are important criteria for successful management of intracanalicular vestibular schwannomas, whether observation, microsurgery, or radiosurgery is chosen. We collected data prospectively to assess hearing preservation after intracanalicular vestibular schwannoma radiosurgery. METHODS: Between 1987 and 2003, 96 patients (65 men and 31 women) underwent gamma knife stereotactic radiosurgery (SRS) for intracanalicular tumors. The median patient age was 54 years (range, 22-80 years). Hearing was graded using the Gardner-Robertson (GR) and the American Academy of Otolaryngology-Head and Neck Surgery classifications. Dose planning was performed on intraoperative stereotactic images using multiple 4-mm isocenters. The median tumor volume was 0.112 mm3 (range, 0.05-0.447 mm3), and the median margin dose was 13 Gy (range, 10-18 Gy). RESULTS: The mean and median audiologic follow-up periods were 42 months and 28 months (range, 12-144 months), respectively. Serviceable hearing was preserved in 31 of 40 (77.5%) patients with initial American Academy of Otolaryngology-Head and Neck Surgery Class A hearing. Serviceable hearing was preserved in 40 of 79 (64.5%) patients with GR Grade I or II pre-SRS hearing. Ninety-two patients had GR Grade I, II, or III hearing before SRS, and GR Grade I, II, or III hearing was maintained in 78 patients (85%). Hearing grades improved in 7 patients. Facial and trigeminal nerve function was preserved in all patients. The tumor control rate (freedom from additional intervention) was 99.0% (95 of 96) at a median follow-up of 28 months (range, 12-144 months). One patient underwent tumor resection 18 months after radiosurgery. CONCLUSION: SRS is a minimally invasive first-line management option for patients with intracanalicular tumors and provides high rates of hearing preservation with minimal morbidity.

BACKGROUND: Metastases to the brain from ovarian and endometrial carcinoma are uncommon and to the authors' knowledge consensus regarding optimal management is lacking. Stereotactic radiosurgery (SRS) has proven useful for the treatment of many benign and malignant brain tumors. In the current study, the authors evaluated outcomes after SRS in patients with ovarian and endometrial carcinoma. METHODS: Twenty-seven patients with brain metastases underwent gamma-knife SRS. Six patients had endometrial carcinoma, whereas 21 patients had ovarian carcinoma. Eighteen patients also received whole-brain radiotherapy. A total of 68 tumors were treated with gamma-knife SRS. RESULTS: At the time of last follow-up, 1 patient was still alive and 26 had died. The median survival was 7 months after the initial diagnosis of brain metastasis and 5 months after SRS. The 1-year survival rate after radiosurgery was 15% and that from the diagnosis of brain metastases was 22%. On final imaging, all tumors were controlled without further growth. Two patients (7.4%) developed new or progressive neurologic deficits after SRS. CONCLUSIONS: SRS is an acceptable choice for the treatment of brain metastases resulting from ovarian and endometrial carcinoma, and provides local tumor control with limited morbidity. Careful patient selection is warranted in the setting of patients with uncontrolled systemic disease in whom a limited survival benefit is expected.

OBJECTIVE: One of the key limitations of gamma knife surgery arises from the radiation safety tolerance limit of the brainstem. The authors conducted an analysis of patients with intra-axial brainstem lesions and documented the incidence of adverse radiation imaging effects (ARIE) and new neurological deficits after gamma knife surgery. METHODS: Thirty-eight patients (39 lesions) with intra-axial brainstem astrocytomas or vascular malformations underwent gamma knife surgery during a 6-year interval. Brainstem exposure volume was calculated by subtracting the volume within the 12-Gy isodose line (12 Gray volume) from the prescription volume. ARIE was defined as a new parenchymal signal alteration on follow-up magnetic resonance imaging sequences. RESULTS: The average prescription volume was 1.46 cm, 12 Gy volume was 2.03 cm, and brainstem exposure volume was 0.57 cm. Seven (18.4%) patients developed ARIE. ARIE correlated only with the presence of new neurological deficits and age younger than 40 years. Three (7.9%) patients developed minor residual deficits without any ARIE. There was no mortality. CONCLUSION: Exposure of the brainstem to more than 12 Gy at volumes as low as 0.1 cm can produce ARIE and new neurological deficits. The tolerance of the brainstem to radiosurgery is related to patient age, lesion volume, and pathology. Analysis of the exposed volume of brainstem tissue may be useful in radiosurgical planning for individual patients.

OBJECTIVE: To report the results of gamma knife radiosurgery (GKR) for treatment resistant choroid plexus papillomas. METHODS: Six patients (median age 55 years; range 29-75) with residual (n = 2) or recurrent (n = 4) choroid plexus papillomas underwent GKR. All failed prior surgery and one failed prior proton beam radiation therapy. These six patients had a total of 11 locally or distant recurrent intracranial tumors. The median and mean tumor volumes were 2.7 and 3.9 cc (range, 0.23-21.1). A median margin dose of 12.0 Gy (range, 11.5-15) was prescribed to the tumor margin. RESULTS: The progression-free periods varied from 7 to 108 months (mean: 36.9). Four tumors were stable after GKR but seven showed progression. Four recurrent tumors in two patients were managed with repeat radiosurgery and three were observed. At the second GKR, the tumor volume varied from 1.3 to 12.4 cc, and the marginal radiation dose varied from 11 to 14 Gy. The overall survival after the first GKR varied from 15 to 120 months. Four patients were alive at the end of the study period. CONCLUSIONS: Radiosurgery represents an additional management strategy for patients who progress despite surgical removal. It may especially be useful for patients with small deep seated residual choroid plexus papillomas, and for tumors that recur at a site distant from their origin.