HSC Section 8_April 2017

T. R. MCRACKAN ET AL.

FIG. 3. Hearing change after SRS based on initial hearing class in patients with at least 2-year follow-up. Worsened hearing was defined by a change in AAO-HNS hearing class.

Using intraoperative FN stimulation as a guide, they were able to remove more than 80% of tumor in 90% of patients. Three patients (27.3%) developed poor FN function (HB grade 9 2), whereas eight (72.7%) maintained good func- tion with long-term follow-up. These outcomes are most likely caused by histologic evidence of nerve fascicles running in FNS to a variable degree (6). Given this in- formation, it is our institution’s practice not to perform subtotal resections. Limited surgical options create an opportunity for SRS as a treatment modality for FNS. Overall, 93.3% of pa- tients undergoing SRS for FNS had tumor control (de- fined as either no growth or decreased tumor size). In those studies where tumor shrinkage was clearly defined, 43.3% of patients showed a decrease in size. Like vestibular schwannoma data, most studies included in this analysis did not directly discuss the FNS pretreatment growth pat- tern before SRS. This greatly hinders our ability to deter- mine whether SRS can stop or reverse tumor growth. We recommend that future studies explicitly state this infor- mation to better understand the effect of SRS on FNS. Given that FN paralysis is the most common presenting symptom in FNS patients (9), we were surprised to find that eight patients (21.1%) had improved FN function after SRS. It is difficult to make physiologic sense of this occurrence. Although the easiest explanation would be decreased tumor size and thus decreased pressure on the FN that would allow increased axonal flow, only one of these patients had radiologic evidence of tumor shrinkage.

two (14.2%) from class B to D. Figure 3 displays hearing outcomes based on pre-SRS hearing class in those with at least 2-year follow-up. Longer-Term Outcomes In a separate analysis, 24 patients had follow-up for 36 months or longer after SRS. The mean follow-up time for this cohort was 60.2 months (range, 36 Y 120 mo). The tumor control rate was 91.7%. With regard to FN function, 80.0% were unchanged at last follow-up, 13.3% worsened, and 6.7% improved. Hearing outcomes were unchanged in 72.7% and worsened in 27.3%. Table 2 displayed outcome results based on duration of follow-up. Given that FNS represent 0.15% to 0.8% of all intra- cranial tumors (20), it is understandable that very few institutions have large treatment series especially with re- gard to SRS. In the above meta-analysis, we have com- bined data from multiple published studies to present a better understanding of the results and complication rates from SRS for FNS. Treatment of FNSs is difficult because surgical options are limited. In looking at treatment trends across time, there is a clear modern trend toward a more conservative treat- ment approach (2,4). Patients are typically observed with serial imaging until they become symptomatic (typi- cally FN paralysis). When observed, FN paralysis has been reported to occur in 38% of patients (21). When symptoms occur, patients are left with several op- tions. With regard to surgery, options are limited to FN decompression or debulking versus resection and FN graft. Total resection with graft is typically only performed when patients are HB grade III or worse because a grade III function is the best possible outcome of FN grafting. Subtotal resections have been described with variable outcomes (22,23). Recently, Mowry et al. (24) reported on 11 patients with preoperative HB grades I to II who un- derwent debulking with FNS isolated to the IAC/CPA. DISCUSSION

TABLE 2. Rates are displayed as percentages of available data because hearing and FN function data were not available on all patients

Duration of follow-up n

Worsened hearing (%)

Worsened FN function (%)

Tumor control rate (%)

9 1 yr 9 2 yr 9 3 yr

53 36 24

16.7 22.2 27.3

12.8

94.3 94.4 91.7

8.7

13.3

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