HSC Section 8_April 2017

SRS FOR FACIAL NERVE SCHWANNOMAS

on FNS with respect to hearing, FN function, and tumor control rates. We tried to be stringent with the data included in our analysis by excluding patients who did not have standard- ized outcome measurements reported (AAO-HNS hearing class, HB grade, definitions of tumor growth/regression). This unfortunately eliminated multiple patients from inclu- sion in the subgroup outcome measures reported in this study. We recommend that these reporting measures be used in the future for standardization of results. We noticed three other notable faults in the literature on this topic. First, three studies did not report hearing out- come data. This is a major weakness of these studies be- cause both the cochlear nerve and the cochlea are adjacent and often intimately involved with these lesions. It is im- portant that we understand the effects of SRS on hearing for these tumors to compare with surgical options. Second, there is lack of uniformity in reporting tumor size and lo- cation. This factor may likely play a role in SRS outcomes, but the variability in literature precludes any evaluation. Third, the reasons for choosing SRS over surgical therapy were not clear in the literature. Stereotactic radiation may have been chosen because of advanced patient age or medical comorbidities. The lack of this information makes appli- cation of these data to the general population difficult. Using standard definitions of tumor control, it seems that SRS is an effective therapy for FNS in the short-term. Re- ports of improved FN function are intriguing, but more data and longer follow-up are needed to determine conclusive results.The above meta-analysis provides information re- garding the effect of SRS on FNS growth, hearing outcome, and FN function that can be used to counsel patients before choosing treatment options. 1. Lipkin AF, Coker NJ, Jenkins HA, Alford BR. Intracranial and intra- temporal facial neuroma. Otolaryngol Head Neck Surg 1987;96:71 Y 9. 2. Wilkinson EP, Hoa M, Slattery WH III, et al. Evolution in the management of facial nerve schwannoma. Laryngoscope 2011; 121:2065 Y 74. 3. Pulec JL. Symposium on ear surgery: facial nerve neuroma. La- ryngoscope 1972;82:1160 Y 76. 4. McRackan TR, Rivas A, Wanna GB, et al. Facial nerve outcome in facial nerve schwannomas. Otol Neurotol 2011;33:78 Y 82. 5. Barrs DM, Brackmann DE, Hitselberger WE. Facial nerve anastamosis in the cerebellopontine angle: a review of 24 cases. Am J Otol 1984; 5:269 Y 72. 6. Hajjaj M, Linthicum FH Jr. Facial nerve schwannoma: nerve fibre dissemination. J Laryngol Otol 1996;110:632 Y 3. 7. Mabanta SR, Buatti JM, Friedman WA, et al. Linear accelerator radiosurgery for nonacoustic schwannomas. Int J Radiat Oncol Biol Phys 1999;43:545 Y 8. 8. Zabel A, Debus J, Thilmann C, et al. Management of benign cranial non-acoustic schwannomas by fractionated stereotactic radiothera- py. Int J Cancer 2001;96:356 Y 62. 9. Jacob JT, Driscoll CL, Link MJ. Facial nerve schwannomas of the cerebellopontine angle: the Mayo Clinic experience. J Neuro Surg Part B 2012;73:230 Y 5. CONCLUSION REFERENCES

The possibility exists, however, that a decrease in tumor size may escape the detection ability of MRI. There were also five patients (13.2%) who developed worsened FN function after SRS. Given that the SRS dose is given in the area, and directly to the FN, reason would suggest that this would be a more likely occurrence than FN improvement. Although this rate is lower than FN im- provement, this risk should be discussed with patients be- fore performing SRS. There were minimal data available with regard to tumor location. FNSs may arise at different locations within the parotid, temporal bone, and CPA. These tumors are known to affect different portions of the FN or may involve mul- tiple segments of the FN in the parotid, temporal bone, and CPA. Tumors traveling very close to the cochlea or adjacent to the cochlear nerve in the IAC may be at higher risk for associated hearing loss. There also may be factors related to location of which we are unaware that may lead to higher or lower SRS success rates. We suspect that the majority of cases treated with SRS involved the GG/middle fossa, the labyrinthine segment, IAC, or CPA. We could not find reports that included treatment of FNS that arose within the parotid or temporal bone. Unfortunately, the location data were not readily reported and could not be included for evaluation. Outcome comparison with surgical treatment is diffi- cult to perform for multiple reasons. First, several patients in the literature received a primary surgical decompression before SRS. This was done either purposefully or after the tumor was discovered to be of FN origin during the op- eration. Analysis of this cohort is impossible because these individual patients are not clearly identified in the litera- ture. Second, when patients do ultimately undergo surgery, it is only after they have had significant deterioration of FN function. These patients often undergo FNS resection with FN graft, which yields repaired FN recovery scale class C at best (25). Conversely, published data on FN decom- pression for FNS show similar FN outcomes compared with those undergoing SRS (both 9 95% HB grade III) (2,4). Again, these values include patients who have had surgery before SRS, so direct comparison is imperfect. As with any meta-analysis, the conclusions are only as good as the data available. There is a wide range of follow- up duration for patients undergoing SRS for FNS. We have attempted to display results based on follow-up period, but many studies did not have long-term follow-up. This is certainly needed to fully understand the results of SRS for FNS with regard to tumor control, FN function, and hearing. Specifically, with hearing outcomes, there was a trend to- ward worsening hearing results in patients with longer than 3-year follow-up compared with those with longer than 12 months (27.3% worsened hearing compared with 17.2%, respectively). Given that hearing at last follow-up is the only data reported, it is impossible to know whether this increased rate of hearing loss is a delayed result from SRS or function of lack of data. Delayed hearing loss from SRS has been reported in the literature (26), so this is certainly in the realm of possibility. Clearly, long follow-up periods are required to better understand the effect of SRS

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