39Indications for Surgery
Once an acoustic neuroma has been diagnosed
and the patient has elected to undergo surgical
resection, the most important factors when con-
sidering the surgical approach are preoperative
hearing status and tumor size. We use the middle
fossa approach for patients who have a small
tumor, primarily located in the lateral portion of
the internal auditory canal and good preoperative
hearing. The retrosigmoid approach is used for
patients with a small tumor, primarily located in
the cerebellopontine angle that does not extend to
the lateral portion of the internal auditory canal
and good preoperative hearing. The translabyrin-
thine approach is used for patients with large
tumors or patients with poor preoperative
hearing.
Since 1995, the American Academy of
Otolaryngology-Head and Neck Surgery (AAO-
HNS) has broken down hearing status into four
classifications (A–D), as shown in Table 3.1 [ 25 ].
Class A and B hearing (PTA >50 dB, SDS >50%)
are considered “serviceable” hearing, and if pre-
served will facilitate, the use of amplification
postoperatively [ 26 ]. More recent guidelines by
the AAO-HNS have recommended a new mini-
mal standard of reporting hearing results by plot-
ting a scattergram relating average pure-tone
thresholds to word recognition scores; however,
few studies evaluating acoustic neuroma out-
comes have been published to date using these
guidelines [ 27 ]. The audiometric criteria to per-
form hearing conservation surgery vary from sur-
geon to surgeon, and the indications must be
individualized to the needs of each patient [ 28 ].
Many use serviceable hearing, or the “50/50
rule,” as the cutoff to attempt hearing preserva-
tion. Jackler and Pitts consider those with “good
hearing” (>70% SDS, <30 dB speech reception
threshold (SRT)), a CPA component <1 cm, and
shallow IAC involvement as excellent candidates
for hearing conservation surgery. Conversely,
those with what they called “poor” hearing
(<30% SDS, >70 dB SRT), a large (>3 cm) CPA
component, and deep penetration of the IAC are
considered poor candidates for hearing conserva-
tion and undergo a translabyrinthine approach
[ 29 ]. In our practice, we use the arbitrary audio-
metric criteria of a SRT <50 dB and a SDS >70%
as criteria to perform hearing conservation sur-
gery. We do not routinely perform middle fossa
surgery on patients older than 65 years, as they
do not tolerate temporal lobe retraction as well as
younger patients and have more fragile dura than
younger patients.
As has been shown in multiple studies, the
smaller the tumor, the easier it is to remove and
the greater the likelihood that hearing will be pre-
served [ 30 – 32 ]. The middle fossa approach is
ideal for resection of tumors isolated to the IAC
(intracanalicular) with no or limited extension
into the CPA when there is serviceable hearing.
Extension of the tumor further than 1–1.5 cm into
the CPA is a relative contraindication to this
approach, with exceptions made for those with
serviceable hearing in the operative ear and either
poor contralateral hearing or bilateral tumors [ 16 ,
20 ]. In contrast, hearing preservation is very
unlikely with tumors that have a CPA component
measuring greater than 2 cm in its greatest dimen-
sion [ 33 , 34 ]. In such tumors, the translabyrin-
thine approach is ideal because it is associated
with the highest rate of preserving facial nerve
function [ 20 ]. The retrosigmoid approach
(discussed elsewhere) can be used in an attempt
to preserve serviceable hearing in tumors smaller
than 2 cm, so long as they do not extend to the
fundus of the IAC [ 35 ].Patient Counseling
A thorough discussion includes reviewing the
relative anatomy and the options of observation
and stereotactic radiation, in addition to surgery.Table 3.1 AAO-HNS hearing classification system
Class PTA (dB) SDS (%)
A ≤ 30 and ≥ 70
B > 30, ≤50 and ≥ 50
C > 50 and ≥ 50
D Any level < 50
PTA 4-frequency pure-tone average of 500, 1000, 2000,
and 3000 dB, dB decibel, SDS speech-discrimination
score
3 Middle Fossa and Translabyrinthine Approaches