190 / 264
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.
DISCUSSION
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.
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.
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.
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
53
16.7
12.8
94.3
9
2 yr
36
22.2
8.7
94.4
9
3 yr
24
27.3
13.3
91.7
T. R. MCRACKAN ET AL.
Otology & Neurotology, Vol. 36, No. 3, 2015
169