Facial nerve preservation and tumor control after gamma knife radiosurgery of unilateral acoustic tumors

Characterization of facial nerve outcomes following radiosurgery for vestibular schwannoma: a meta-analysis

PURPOSE

Gamma Knife radiosurgery (GKRS) is a precise and efficacious treatment modality for vestibular schwannoma (VS) with favorable cranial nerve preservation rates. This study aims to better characterize facial nerve (FN) outcomes in VS after GKRS.

METHODS

A query of six medical databases was conducted following PRISMA guidelines. Eligible studies exclusively reported VS managed with single-fraction GKRS and included House-Brackmann (HB) scale assessments prior to and following GKRS. Data was analyzed using random-effects modeling, and FN preservation was defined as HB I or II at last follow-up.

RESULTS

Data was analyzed from 15 articles with 3,155 patients at an mean age of 55.0 years. Mean tumor volume, radiation dose, follow-up, tumor control, and hearing preservation were 4.28 cm3, 13.3 Gy, 59.4 months, 92.7%, and 62.6%, respectively. The pooled FN preservation rate was 92.9%. Mean preoperative tumor volume > 2.5 cm3 and age > 60 years were significantly associated with worse preoperative FN function (p = 0.019, p = 0.023, respectively). Normal FN function (HB = 1) at last follow up was 95.8% for VS volume < 2.5 cm3 and 89.4% with larger volumes (p < 0.001). Doses ≤ 13 Gy were significantly associated with superior FN preservation (96.5%) compared to higher doses (p < 0.001). Tumor control and hearing preservation were not significantly associated with FN preservation.

CONCLUSION

This meta-analysis identifies tumor volume and radiation dose as prognostic factors for FN preservation. A FN preservation rate of 93% may be expected at five years after GKRS. This study provides a unique characterization of FN outcome that should be considered in the management of VS.

Cranial nerve preservation in surgery for large acoustic neuromas

Facial nerve outcomes and surgical complication rates for other cranial nerves were evaluated retrospectively after the resection of large acoustic neuromas. The charts of all patients who underwent surgical removal of an acoustic neuroma between 1992 and 2001 at New York University Medical Center were reviewed. Fifty-four patients with tumors measuring 3 cm or larger were included in the study. Four patients had neurofibromatosis type 2, two of whom underwent bilateral removal of acoustic neuromas. Translabyrinthine microsurgical removal of tumor was performed in 47 of 56 cases (84%). In all cases, EMG monitoring, improved sharp microdissection, and ultrasonic aspiration were employed. Facial nerve function was assessed using the House-Brackmann facial nerve grading system immediately after surgery and at follow-up visits. A House-Brackmann grade III or better was achieved in 90% of patients, and a grade II or better was achieved in 84% of patients. Ultimate facial nerve outcome was excellent after the surgical resection of large acoustic neuromas. Preoperative cranial nerve palsies also improved after surgery. The translabyrinthine approach for tumor removal is our treatment of choice for acoustic neuromas 3 cm or larger.

Relative indications for radiosurgery and microsurgery for acoustic schwannoma

The physical and biological principles underlying the use of radiosurgery for the treatment of vestibular schwannomas of up to 2.5 cm in diameter are reviewed together with the historical controversies that have surrounded its introduction. The results in terms of mortality, quality of life, preservation of facial movement and hearing, incidence of shunt-dependent hydrocephalus, cancer neogenesis and brain stem damage are compared in the Marseilles series of 600 microsurgical procedures and 830 Gamma knife procedures and with the peer-reviewed literature. The key principles of a steep profile to radiation exposure at the tumour margin, careful topographical planning of the radiation against the tumour shape to minimise the radiation dose to the cranial nerves and brain stem, early tumour swelling, tumour texture and national history of the tumour are analysed. Protocols for the management of unilateral schwannoma, Type II neurofibromatosis (both the Wishart and the Gardner types) and residual/recurrent tumours are presented. In summary, the growth of nearly 97% of vestibular schwannomas (up to 2.5 cm) is arrested by the Gamma knife, the facial nerve is preserved in almost all cases and hearing may be preserved at its pre-operative level in nearly 70% of cases without the complications of microsurgery.

Long-term outcomes after radiosurgery for acoustic neuromas

BACKGROUND

Stereotactic radiosurgery is the principal alternative to microsurgical resection for acoustic neuromas (vestibular schwannomas). The goals of radiosurgery are the long-term prevention of tumor growth, maintenance of neurologic function, and prevention of new neurologic deficits. Although acceptable short-term outcomes have been reported, long-term outcomes have not been well documented.

METHODS

We evaluated 162 consecutive patients who underwent radiosurgery for acoustic neuromas between 1987 and 1992 by means of serial imaging tests, clinical evaluations, and a survey between 5 and 10 years after the procedure. The average dose of radiation to the tumor margin was 16 Gy, and the mean transverse diameter of the tumor was 22 mm (range, 8 to 39). Resection had been performed previously in 42 patients (26 percent); in 13 patients the tumor represented a recurrence of disease after a previous total resection. Facial function was normal in 76 percent of the patients before radiosurgery, and 20 percent had useful hearing.

RESULTS

The rate of tumor control (with no resection required) was 98 percent. One hundred tumors (62 percent) became smaller, 53 (33 percent) remained unchanged in size, and 9 (6 percent) became slightly larger. Resection was performed in four patients (2 percent) within four years after radiosurgery. Normal facial function was preserved in 79 percent of the patients after five years (House-Brackmann grade 1), and normal trigeminal function was preserved in 73 percent. Fifty-one percent of the patients had no change in hearing ability. No new neurologic deficits appeared more than 28 months after radiosurgery. An outcomes questionnaire was returned by 115 patients (77 percent of the 149 patients still living). Fifty-four of these patients (47 percent) were employed at the time of radiosurgery, and 37 (69 percent) remained so. Radiosurgery was believed to have been successful by all 30 patients who had undergone surgery previously and by 81 (95 percent) of the 85 who had not. Thirty-six of the 115 patients (31 percent) described at least one complication, which resolved in 56 percent of those cases.

CONCLUSIONS

Radiosurgery can provide long-term control of acoustic neuromas while preserving neurologic function.

Preliminary results of linear accelerator radiosurgery for acoustic schwannomas

In this paper the authors evaluate the results of linear accelerator (LINAC)-based stereotactic radiosurgery for acoustic schwannomas. Fifty-six patients underwent LINAC-based stereotactic radiosurgery for acoustic schwannomas at the University of Florida between July 1988 and November 1994. Each patient was followed for a minimum of 1 year or until death; no patient was lost to follow up. One or more follow-up magnetic resonance images or computerized tomography scans were obtained in 52 of the 56 patients. Doses ranged between 10 and 22.5 Gy with 69.6% of patients receiving 12.5 to 15 Gy. Thirty-eight patients (68%) were treated with one isocenter and the dose was specified to the 80% isodose line in 71% of patients. Fifty-five patients (98%) achieved local control after treatment. The 5-year actuarial local control rate was 95%. At the time of analysis, 48 patients were alive and free of disease, seven had died of intercurrent disease, and one was alive with disease. Complications developed in 13 patients (23%). The likelihood of complications was related to the dose and treatment volume: 10 to 12.5 Gy to all volumes, three (13%) of 23 patients; 15 to 17.5 Gy to 5.5 cm3 or less, two (9%) of 23 patients; 15 to 17.5 Gy to more than 5.5 cm3, five (71%) of seven patients; and 20 to 22.5 Gy to all volumes, three (100%) of three patients. Linear accelerator-based stereotactic radiosurgery results in a high rate of local control at 5 years. The risk of complications is related to the dose and treatment volume.

Tumors of the cerebellopontine angle. Changing policy in treatment

One hundred and twenty-six cases of cerebellopontine angle tumors with various histologies are presented. Results of 75 operated vestibular neurinomas, 22 meningiomas, and 16 tumors with other histologies are discussed. The method of irradiation and non-radical surgery may be an alternative for treatment.

The retrosigmoid approach to acoustic neurinomas: technical, strategic, and future concepts

The retrosigmoid approach continues to be the most widely employed strategy for the surgical resection of acoustic neuromas. The results with respect to facial nerve function are uniformly reported to be quite high. The great emphasis currently is upon improving results with regard to the conservation of useful hearing. This paper focuses on the anatomical and strategic surgical factors that we currently consider to be important to maximizing our current results. The future aspects of this trend toward improved success in conserving hearing in these patients is also discussed.