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resection, although follow-up in all these series is lim- ited. Together, these data demonstrate that in many cases incomplete tumor resection is required in order to preserve facial nerve integrity, and that more aggressive resection is associated with poorer postoperative facial nerve function. In a previous study, the authors found that at 3, 5, and 10 years following SRS for treatment of sporadic VS, 45%, 52%, and 77% of patients developed nonserviceable hearing, respectively. 16 In the current study, 15 of 17 (88%) patients with serviceable hearing prior to SRS lost useful hearing at a median of 40 months following treat- ment, which is even greater than prior estimates. 16–19 The higher percentage of cases that lost serviceable hearing following radiation in the current study is most likely attributable to the added effects of tumor growth. 16–20 The small number of patients with preoperative serviceable hearing in our study precluded analysis of hearing preser- vation surgery after failed radiation therapy; however, this would seem like an unrealistic goal in most cases. 8 The merit of gross total tumor resection in the set- ting of recurrent VS has been a subject of ongoing debate. 6,8 Our data suggest that gross total tumor resec- tion is less frequently achievable in previously radiated tumors compared to nonradiated controls. We acknowl- edge that our GTR rate of 49% seems low for the patients presented here. However, we want to emphasize that we are very stringent about not considering NTR in which there is no residual tumor visible on the 3-month follow-up MRI as a complete resection. If we were to include NTR and GTR together, the rate would be 76%. Irradiation inevitably delivers a minimum of the pre- scribed marginal dose to the facial nerve–tumor plane, leading to formation of adhesions and poor surgical planes. As a general strategy, our group enters surgical salvage cases with the intent to remove the tumor in its entirety; however, we utilize intraoperative impression and results of intraoperative electroprognostic testing to assist in determining when less-than-complete resection should be performed in order to preserve facial nerve integrity. 14 The limited cumulative data suggest that short- and intermediate-term tumor control is good even following subtotal resection. Long-term data will be required to ascertain the risk of delayed recurrence. Theoretically, reirradiation carries an increased risk of cranial neuropathy, hydrocephalus, and radiation- induced cerebral edema or necrosis. Furthermore, tumors that initially fail radiation therapy may be considered more radioresistant and less likely to respond to addi- tional radiation treatment. Despite these considerations, preliminary data suggest that retreatment with low-dose SRS is well tolerated and provides tumor control in the majority of cases. 21–23 Until more data are available docu- menting the long-term safety and efficacy of this strategy, the authors favor microsurgical salvage in most cases. With the increasing number of VS cases worldwide receiving primary radiation therapy, and the ongoing trend toward dose deescalation to limit treatment mor- bidity, our ability to manage radiation failure is becoming increasingly relevant. 3 In the authors’ experience, approximately 6% of patients who receive primary SRS

experience treatment failure at 5 to 7 years following radiation. 12,24 This number may be greater for cystic, large, or rapidly growing tumors—or in cases where less than 12 Gy to the tumor margin is prescribed. 2,25–27 Data regarding the utility of radiation therapy for treat- ment of residual progressive disease following subtotal resection is mixed. Several studies have demonstrated that the results following subtotal resection are on par with primary radiation treatment. 28,29 However, in a recent preliminary report of a large prospective multicen- ter study, Monfared et al. found that four of 11 (36%) cases failed salvage radiation therapy, leading to the con- clusion that radiation control of growing tumor remnants following microsurgery is suboptimal. 30 Our study has several strengths and limitations. We included a relatively large and homogenous cohort of spo- radic VS and excluded patients with NF2 given the signifi- cant difference in tumor biology and behavior. Control subjects, matched by age, tumor size, and center, were included for comparison. Additionally, patients were included from two separate institutions on separate conti- nents to try and reduce surgeon specific biases. Finally, both institutions have a strong track record of utilizing SRS and microsurgery in the management of VS. Limitations include retrospective review of data, which carries a risk of selection bias, heterogeneous and incomplete data points, and inconsistent follow-up. When previous SRS has failed, much longer follow-up is necessary to truly determine the fate of tumor remnants following less than GTR. CONCLUSION Microsurgical resection of VS following SRS is tech- nically challenging. Nevertheless, facial nerve preserva- tion with effective tumor control remains an attainable goal in most patients. Intraoperative surgical judgment about when to perform less than GTR and how to maxi- mize tumor removal in such cases remains extremely important and is very difficult to objectify. Acknowledgment The authors would like to thank Amy E. Glasgow, MHA, for her valuable assistance with statistical analysis. BIBLIOGRAPHY 1. Carlson ML, Tveiten OV, Driscoll CL, et al. Long-term quality of life in patients with vestibular schwannoma: an international multicenter cross-sectional study comparing microsurgery, stereotactic radiosurgery, observation, and nontumor controls. J Neurosurg 2015;122:833–842. 2. Carlson ML, Link MJ, Wanna GB, Driscoll CL. Management of sporadic vestibular schwannoma. Otolaryngol Clin N Am 2015;48:407–422. 3. Carlson ML, Habermann EB, Wagie AE, et al. The Changing Landscape of Vestibular Schwannoma Management in the United States--A Shift Toward Conservatism. Otolaryngology Head Neck Surg 2015;153:440–446. 4. Jacob JT, Pollock BE, Carlson ML, Driscoll CL, Link MJ. Stereotactic radiosurgery in the management of vestibular schwannoma and glomus jugulare: indications, techniques, and results. Otolaryngol Clin N Am 2015;48:515–526. 5. Society LGK (2014) Leksell Gamma Knife: Indications Treated 1986 to 2013 (68%–100% of sites reporting). Leksell Gamma Knife Society. Available at: https://http://www.lgksociety.com/uploads/media/1968-2013- statistics-report.pdf. Last accessed 1 January 2015. 6. Friedman RA, Berliner KI, Bassim M, et al. A paradigm shift in salvage surgery for radiated vestibular schwannoma. Otol Neurotol 2011;32: 1322–1328. 7. Friedman RA, Brackmann DE, Hitselberger WE, Schwartz MS, Iqbal Z, Berliner KI. Surgical salvage after failed irradiation for vestibular schwannoma. Laryngoscope 2005;115:1827–1832.

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