Cranial Nerve Side Effects of Vestibular Schwannoma Radiosurgery

Keywords: vestibular schwannoma, cranial nerve, gamma knife, complications, outcome

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     Vestibular schwannomas are benign neoplasms of the sheath of the vestibulo-acoustic nerve which typically present with unilateral hearing loss. For many years the morbidity of surgery for such tumors has been recognized and the alternative of Gamma Knife radiosurgery often considered. 
     This report analyzes the results of our treatment of vestibular schwannomas with traditional (single fraction) radiosurgery in terms of tumor control and the non-auditory side effects of treatment to further substantiate the valuable role played by this modality.
     Between February, 1989 and December, 2010 246 patients with vestibular schwannomas have been treated with radiosurgery at our institution.
     We reviewed clinical and imaging outcomes in our patients after radiosurgery.
     Significant, new facial nerve dysfunction occurred following radiosurgery in 5% of patients and was transient in at least one quarter of these. Factors related to the incidence of facial nerve dysfunction included advanced age, prior surgery, and prescription dose > 14 Gy. Trigeminal nerve dysfunction occurred in three percent and also appeared related to tumor size and dose. Although major hearing loss was present prior to radiosurgery in almost all patients, new vestibular dysfunction in the form of dizziness, ataxia, and tinnitus occurred in several patients. Overall tumor control was 95% at a median follow up time of 7 years. Contrary to other published reports, facial nerve dysfunction, usually temporary, did occur at the 12 Gy prescription dose inspite of careful conformal planning always using MRI as well as CT on the day of the procedure. We saw no instances of cyst formation causing hydrocephalus.
     This was a retrospective study.
     Radiosurgery with the Gamma Knife at a prescription dose of 12 Gy was highly effective and generally safe, as was the strategy of subtotal resection followed by radiosurgery on the remnant. 
     Based on our experience with other sites, the Gamma Knife Extend System may offer a potentially even more favorable therapeutic ratio for larger tumors.


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