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Nervus intermedius dysfunction following Gamma Knife surgery for vestibular schwannoma.

OBJECT
The purpose of this study was to evaluate the function of the nervus intermedius, the nonmotor component of the facial nerve, following modern Gamma Knife surgery (GKS) for the treatment of vestibular schwannoma.


METHODS
Sixty-five consecutive patients at our center underwent GKS as a primary treatment option for vestibular schwannoma between 2005 and 2010. The authors interviewed patients with a functional questionnaire to evaluate the function of the nervus intermedius before and after radiosurgery from their subjective point of view. Data from 50 patients treated using GKS for a unilateral vestibular schwannoma were obtained.


RESULTS
Nine (18%) of 50 patients presented with at least one preradiosurgical disturbance of the nervus intermedius caused by the vestibular schwannoma itself, with dysfunctions of lacrimation, salivation, nasal secretion, and taste. Of the 41 patients without preradiosurgical disturbances, 9 (22%) experienced the onset of at least one new disturbance after GKS. Specifically for each dysfunction, of the 45 patients without a lacrimal disturbance before GKS, 5 (11.1%) had a new lacrimal disturbance after GKS. New onset of a salivary disturbance after GKS was reported in 3 (6.2%) of 48 patients. In 1 patient (2%), increased nasal secretion was noted 1 year after GKS. Five (10.6%) of 47 patients without a preradiosurgical taste disturbance experienced the symptom after GKS. No facial palsy developed in any patient before or after GKS. There was no significant correlation between postradiosurgical nervus intermedius dysfunction and tumor size, margin dose, or patient age.


CONCLUSIONS
The authors demonstrated that 22% of patients undergoing modern GKS for vestibular schwannoma experience various disturbances of nonmotor components of the facial nerve as a result of the radiosurgery. Through this study, we can provide useful information about the likelihood of certain postradiosurgical symptoms for vestibular schwannoma.