Preservation of Useful
Hearing in Resection of
Acoustic Neuroma (Vestibular Schwannoma)
by Robert G Ojemann, M.D.
and Joseph B. Nadol, Jr., M.D.
Stephen B. Tatter,M.D., Ph.D. , HTML
The introduction of computerized tomography
and magnetic resonance imaging has made possible the diagnosis of
small acoustic neuromas. This as well as refinement in microsurgical
technique have made consideration of hearing preservation during
acoustic neuroma resection feasible. Success in preservation of
usable hearing has been reported by the suboccipital and middle
fossa approaches in a number of centers.
Several important questions remain
unresolved. Can truly useful hearing be preserved often enough to
make this worthwhile, particularly in unilateral cases? Are there
preoperative clinical indicators that can identify the likelihood
of success in a given patient? How helpful is intraoperative neurophysiologic
monitoring? Does an attempt to preserve hearing compromise tumor
excision, making recurrence more likely? Is initial success in preserving
measurable hearing rewarded by long term preservation?
In a recent study at the Cranial Base
Center of 144 cases of patients who underwent total removal of unilateral
acoustic neuroma via the suboccipital approach with an attempt to
preserve auditory function, some insight on these questions was
achieved. All cases were done by the suboccipital approach by a
team including neurosurgeon, neurotologist, and neurophysiologic
monitoring using intraoperative evoked potentials and facial nerve
electromyography. Graphic display of pre- and post-operative hearing
as measured by speech discrimination scores is displayed in Figure
3 for the most recent series of 78 cases. As can be seen in 12 patients
(15%) postoperative hearing was within 15 percentage points of preoperative
levels. In 4 patients (5%) hearing was actually improved. In the
entire series, usable hearing is defined by a postoperative speech
discrimination score of 15% or better and was achieved in 25 patients
or 32% of the total.
| Figure. Preoperative
and postoperative speech discrimination scores in the current
series of 78 cases.
The central line corrresponds to parity of preoperative and
postoperative scores; the other parallel lines indicate +/-15
percentage point change. Thus, all cases to the left of the
central line represent postoperative decrenient in speech discnmination
score and all cases to the right of the central line represent
improvement in speech discrimination score.
Logistic regression analysis demonstrated
that there were clear cut predictors of success. The most significant
predictor of preservation of useful hearing was a relatively small
tumor and relatively high preoperative speech discrimination score.
Thus for tumors that extended less than 5 millimeters into the posterior
fossa, hearing was unchanged or better in 41% of cases and deemed
useful in 50% of cases.
lntraoperative monitoring of evoked
potential provided reliable prognostic data concerning hearing outcome
and in the judgement of the operating surgeons was of use in the
attempt to save hearing. Thus, when wave V was unchanged at the
end of the resection, even if it had been transiently lost during
surgery, useful hearing was invariably preserved. In 4 patients
who enjoyed significant improvement in hearing (greater than 15
percentage point increase in speech discrimination) no changes were
detected in intraoperative evoked potentials that would have predicted
this outcome. The strong positive correlation between small tumor
size and preservation of hearing was likewise observed in preservation
of facial nerve function. Thus, in cases where tumor size was 5
millimeters or less 100% had normal facial function at one year,
whereas in those with tumors exceeding 25 millimeters of extension
to the posterior fossa, 75% had normal facial function at one year.
In the overall group of 78 patients, 90% of patients had normal
facial function at one year.
In a recent follow up of a subset
of these patients in whom hearing was initially preserved, stable
hearing was achieved in 78% whereas further deterioration of hearing
was found in 22%, with a mean follow-up period of 5 years.
To date, there is no evidence that
an attempt to save hearing predisposes the patient to an increased
risk of clinical recurrence of tumor. Our current results support
the notion that an attempt to save hearing, particularly in small
acoustic neuromas, is worthwhile and safe for patients.
- Nadol JB,Jr, Chiong CM, Ojemann
RG, McKenna MJ, Martuza RL, Montgomery WW, Levine RA, Ronner SF,
Glyrin RG: Preservation of hearing and facial nerve function in
resection of acoustic neuroma. Laryngoscope 102:1153-1158;1992
- McKenna MJ, Halpin C, Ojemann RG,
Nadol JB Jr., Montgomery WW, Levine RA, Carlisle E, Martuza R:
Long lerm hearing results in patients after surgical removal of
aco~stic tumors with hearing preservation. Am J Otol 13:134-136;1992.
- Ojemann RG, Levine RA, Montgomery
WW, McGaffigan P: Use of intraoperative auditory evoked potentials
to preserve hearing in unilateral acoustic neuroma removal.
J Neurosurg 61: 938-948, 1984
- Ojemann RG: Management of acoustic
neuroma (Vestibular schwannoma) Clin Neurosurg 40:498-533,
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