HSC Section 8_April 2017

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

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

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.

CONCLUSION

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.

REFERENCES

1. Lipkin AF, Coker NJ, Jenkins HA, Alford BR. Intracranial and intra-

temporal facial neuroma.

Otolaryngol Head Neck Surg

1987;96:71

2. Wilkinson EP, Hoa M, Slattery WH III, et al. Evolution in the

management of facial nerve schwannoma.

Laryngoscope

2011;

121:2065

74.

3. Pulec JL. Symposium on ear surgery: facial nerve neuroma.

La-

ryngoscope

1972;82:1160

76.

4. McRackan TR, Rivas A, Wanna GB, et al. Facial nerve outcome in

facial nerve schwannomas.

Otol Neurotol

2011;33:78

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

72.

6. Hajjaj M, Linthicum FH Jr. Facial nerve schwannoma: nerve fibre

dissemination.

J Laryngol Otol

1996;110:632

7. Mabanta SR, Buatti JM, Friedman WA, et al. Linear accelerator

radiosurgery for nonacoustic schwannomas.

Int J Radiat Oncol Biol

Phys

1999;43:545

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

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

SRS FOR FACIAL NERVE SCHWANNOMAS

Otology & Neurotology, Vol. 36, No. 3, 2015

170