1. Following stereotactic radiosurgery, tumor size was stable or decreased in 90% of schwannoma cases at last follow-up.
2. Smaller tumor with favorable facial nerve function was correlated with better neurological outcomes following the procedure.
Evidence Rating Level: 2 (Good)
Study Rundown: Facial nerve schwannoma (FNS) is a rare tumor that arises from the facial nerve. Due to a small number of cases and subsequent lack of literature, the optimal management of FNS remains unclear. This study analyzed the outcomes of patients, who received stereotactic radiosurgery (SRS) for FNS, as SRS has been shown to be effective in vestibular schwannoma, a similar disease. The authors found that the tumors remained stable or decreased in size in 90% of cases at last follow-up. The radiographic progression-free survival at 5 years was 90% as well. Furthermore, facial nerve function and hearing were preserved in 38 out of 42 patients (90.5%) and 33 out of 42 patients (78.6%), respectively. Sixty percent of patients had normal function or slight dysfunction of facial nerve following SRS. In addition, small tumor volume (1cm3 or less) was associated with better neurological outcomes following SRS. Lastly, patients with normal function to moderate dysfunction of facial nerve prior to SRS were more likely to maintain their level of neurological function post-SRS. The major strength of this study comes from the large multi-center study cohort for such a rare entity. However, the study is limited by heterogeneity of treatment protocols across different centers and the small statistical power of the study.
In-Depth [retrospective cohort]: This study retrospectively reviewed 42 patients with intracranial FNS managed by SRS between 1988 and 2014 at 8 medical centers in the United States, Canada, and Taiwan. Patients were included if they had either a histological diagnosis or clinical/neuroimaging features of FNS. 15 patients (36%) had previous surgical resection for histologically confirmed FNS. SRS dose was planned by a neurosurgeon in conjunction with a radiation oncologist and a medical physicist. All patients were treated with single session radiotherapy and followed up with neuroimaging and clinical evaluations. The mean follow-up was 42 months. Outcome measures included the FNS volume on imaging, auditory function and facial nerve function assessed with House-Brackmann grades. Kaplan-Meier method and logistic regression were used for univariate and multivariate analysis, respectively. At last follow-up, the FNS volume was stable in 21 patients (52%) and 15 patients (38%) out of 40 patients, who had reliable radiographic follow-ups. The radiographic progression-free survival was 97%, 97%, 97%, and 90% at 1, 2, 3, and 5 years, respectively. There was no statistical difference between those previously treated with surgery and those primarily treated with SRS (p = 0.25). After SRS, 22 out of 37 patients (60%) with available information had House-Backmann grades I or II. Facial nerve and auditory function were preserved in 38 out of 42 patients (90.5%) and 33 out of 42 patients (78.6%), respectively, following SRS. Patients with tumors of 1cm3 or less had significantly fewer events of new or worsened neurological deficits compared to those with tumors greater than 1cm3. In addition, tumors of 1cm3 or less were more likely to result in favorable outcomes, defined as tumor stability or regression in combination with improved facial and auditory function at last follow-up (OR 5.4, 95% confidence interval [CI]: 1.29-22.6). In multivariate analysis, the maintenance of House-Brackmann grade I-III post-SRS was significantly correlated with House-Brackmann grade I-III prior to SRS (OR 6.09; 95%CI: 1.7-22.0).
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