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doi:10.1016/j.nec.2008.02.009
Neurosurg Clin N Am 19 (2008) 279–288
Middle Fossa Approach for Acoustic Tumor Removal
William F. House, MD, Clough Shelton, MD
*
Department of Otolaryngology-Head and Neck Surgery, University of Utah School of Medicine,
Salt Lake City, UT, USA
The middle fossa approach for vestibular nerve
section was reported as early as 1904; however,
hammer and chisel were used for surgery at that
time, which put the facial nerve at risk
[1]
. The mid-
dle fossa approach did not have widespread appli-
cation until refined by the senior author (WFH)
in 1961, when it was used for decompression of
the internal auditory canal in cases of extensive oto-
sclerosis
[2]
. That therapy was later abandoned, but
it became evident that this approach was suitable
for removal of acoustic tumors. Initially the middle
fossa approach was used for tumors of all sizes.
Further experience demonstrated, however, that it
was most suitable for small tumors
[3–5]
and that
preservation of hearing and facial nerve function
was possible in a significant proportion of operated
patients
[6]
. The middle fossa approach was
used infrequently until the development of gado-
linium-enhanced magnetic resonance imaging
(MRI). With this development, a larger number
of acoustic tumors are diagnosed when they are
small and before hearing has been significantly
affected, making an attempt at hearing preserva-
tion desirable.
The primary indications for the middle fossa
approach are a small acoustic tumor, with less
than 5 mm extension into the cerebellopontine
angle, and good preoperative hearing. For hearing
conservation surgery, we use the arbitrary audio-
metric criteria of speech reception threshold better
than 30 dB and speech discrimination score better
than 70%, although these indications must be
individualized to the needs of the patient
[7]
. Some
advocate attempted hearing preservation in the re-
moval of small acoustic tumors if any measurable
preoperative hearing exists
[8]
.
The middle fossa approach provides complete
exposure of the contents of the internal auditory
canal, allowing removal of laterally placed tumors
without the need for blind dissection
[9]
. This
exposure ensures total removal and is well suited
for the removal of very small acoustic tumors
[10]
.
The facial nerve can be located in its bony canal,
allowing positive identification in a location not
involved by tumor.
The middle fossa approach is technically di-
cult because of the lack of robust landmarks and the
limited exposure. Bleeding in the posterior fossa
can be dicult to control because of the limited
access. Because of its location in the superior aspect
of the internal auditory canal, the facial nerve is
subjected to more manipulation than in the other
approaches
[11,12].
In the past, facial nerve results
inmiddle fossa cases have not been as good as those
using the translabyrinthine approach for similar-
sized tumors
[13]
. The routine use of the facial nerve
monitor, however, has helped to improve these
results. Patients older than 60 years do not tolerate
the middle fossa approach as well as younger
patients because of the fragility of the dura and
retraction of the temporal lobe.
Several authors use an extended middle fossa
approach for large tumors
[14–16]
. The tentorium
is divided to give wider access to the posterior
fossa. Some also perform a labyrinthectomy to en-
large the exposure when hearing preservation is
not attempted
[17–19]
.
This article originally appeared in The Otolaryngologic
Clinics of NA; Volume 25, issue 2, April 1992. p. 347–60.
* Corresponding author. 50 North Medical Drive,
Room 3C120, Salt Lake City, Utah 84132.
Perioperative Management
We do not usually use preoperative or
postoperative antibiotics, but despite this, the
1042-3680/08/$ - see front matter 2008 Elsevier Inc. All rights reserved.
doi:10.1016/j.nec.2008.02.009
neurosurgery.theclinics.com
280
HOUSE & SHELTON
incidence of postoperative meningitis is very low.
Because of the long-distance referral nature of our
practices, we prefer that if a patient is to develop
postoperative meningitis, it happen while still in
southern California, instead of a partially treated
meningitis occurring at home.
Intraoperative furosemide and mannitol are
given to allow easier temporal lobe retraction. The
junior author (CS) also routinely uses a single
dose of dexamethasone (Decadron) intravenously
at the beginning of surgery. It is his clinical
impression that the incidence of delayed facial
paralysis is reduced by this measure. This single
dose of steroid does not seem to affect wound
healing adversely. Long-acting muscle relaxants
are avoided during surgery so as not to interfere
with facial nerve monitoring.
greater superficial petrosal nerve. The arcuate
eminence marks the position of the superior
semicircular canal and may be readily apparent
in some patients but obscure in others. Kartush
and colleagues
[20]
have cautioned that the rela-
tionship between the arcuate eminence and the su-
perior semicircular canal may be variable in some
patients, but the superior canal tends to be per-
pendicular to the petrous ridge. Medially the su-
perior petrosal sinus runs along the petrous ridge.
Surgical tolerances are tight in the area of the
lateral internal auditory canal. The labyrinthine
portion of the facial nerve lies immediately
posterior to the basal turn of the cochlea. Bill’s
bar separates the facial and superior vestibular
nerves. Slightly posterior and lateral to this area
are the vestibule and ampullated end of the
superior semicircular canal.
Identification of the geniculate ganglion can be
accomplished by tracing the greater superficial
petrosal nerve posteriorly to it. If the tegmen is
unroofed, the geniculate is found to be slightly
anterior to the head of the malleus.
The internal auditory canal lies approximately
on the same axis as the external auditory canal;
this relationship is useful in orienting the surgical
field
[14]
. The more medial one progresses along
the internal auditory canal, the more space exists
Surgical anatomy
The surgical anatomy of the temporal bone
from the middle fossa approach is compact but
complex (
Fig. 1
). Landmarks are not as apparent as
with other approaches through the temporal bone,
so laboratory dissection is useful for the surgeon to
become familiar with the anatomy from above.
Anteriorly the limit of the dissection is the
middle meningeal artery, which is lateral to the
Fig. 1. Surgical anatomy of the temporal bone as viewed from the middle fossa approach. (Reprinted by permission of
the House Ear Institute, Los Angeles.)
MIDDLE FOSSA APPROACH FOR ACOUSTIC TUMOR REMOVAL
281
around it,
[21]
allowing for safe dissection in this
area.
Several methods can be used to locate the
internal auditory canal, which are reviewed in
detail elsewhere
[14,20]
. We prefer to follow the
facial nerve in a retrograde fashion to the internal
auditory canal (see later). In some cases, after the
geniculate ganglion has been identified, the junior
author (CS) employs the technique of Garcia-
Ibanez,
[22]
which involves drilling on the bisec-
tion of the angle formed by the blue line of the
superior semicircular canal and greater superficial
petrosal nerve. The internal auditory canal can be
initially located in the ‘‘safe’’ medial area of the
temporal bone and followed laterally.
thirds anterior and one third posterior to the exter-
nal auditory canal and is approximately 2.5 cm
square. This bone flap is based on the root of
the zygoma as close to the floor of the middle
fossa as possible. During creation of this flap,
care is taken to avoid laceration of the underly-
ing dura. The bone flap is set aside for later
replacement.
The dura is elevated from the floor of the
middle fossa. The initial landmark is the middle
meningeal artery, which marks the anterior extent
of the dissection. Frequently venous bleeding is
encountered from this area and can be controlled
with oxidized cellulose (Surgicel). Dissection of
the dura proceeds in a posterior to anterior
fashion. In approximately 5% of cases, the
geniculate ganglion of the facial nerve is dehis-
cent, but injury can be avoided with dural
elevation in this manner. The petrous ridge is
identified with care not to injure the superior
petrosal sinus. The arcuate eminence and greater
superficial petrosal nerve are identified. These are
the major landmarks to the subsequent intra-
temporal dissection. Once the dura has been
elevated, typically with a suction irrigator and
a blunt dural elevator, the House-Urban retractor
is placed to support the temporal lobe. To
maintain a secure position, the teeth of the
retaining retractor should be locked against the
Surgical technique
The patient is placed in the supine position
with the head turned to the side. The surgeon is
seated at the head of the table, and the anesthe-
siologist is at the foot. An incision is made in the
pretragal area and extended superiorly in a gently
curving fashion (
Fig. 2
). An inferiorly based
U-shaped flap is fashioned of the temporalis mus-
cle and fascia. This flap is reflected inferiorly.
Using a cutting bur, a craniotomy opening is
made in the squamous portion of the temporal
bone (
Fig. 3
). It is located approximately two
Fig. 2. Incision begins in the pretragal area and extends 7 to 8 cm superiorly in a gently curving fashion. (Reprinted by
permission of the House Ear Institute, Los Angeles.)
282
HOUSE & SHELTON
Fig. 3. Two thirds of the craniotomy window is located anterior to the external auditory canal. (Reprinted by permission
of the House Ear Institute, Los Angeles.)
bony margins of the craniotomy window (
Fig. 4
).
Using a large diamond bur and continuous
suction irrigation, the blue line of the semicircular
canal is identified at the arcuate eminence. This
structure makes an approximately 45 to 60 degree
angle with the internal auditory canal.
The greater superficial petrosal nerve is located
medial to the middle meningeal artery (
Fig. 5
)
then followed posteriorly to the geniculate gan-
glion (
Fig. 6
). The labyrinthine portion of the
facial nerve is identified medial to the ganglion.
Care must be taken to avoid the cochlea, which
lies only a few millimeters anterior to the labyrin-
thine portion of the facial nerve.
Bone is removed from the superior surface of
the internal auditory canal down to the porus
acusticus. The lateral end of the internal auditory
canal is dissected with identification of Bill’s bar
and the superior vestibular nerve (
Fig. 7
). Medially
180 degrees of bone can be removed from its cir-
cumference (
Fig. 8
). This exposure must narrow
laterally because of the location of the inner ear.
The dura of the internal auditory canal is
divided along the posterior aspect (
Fig. 9
). The
facial nerve is clearly identified in the anterior
portion of the internal auditory canal.
The superior vestibular nerve is cut at its
lateral end, and the vestibulofacial anastomotic
fibers are divided. The tumor is separated from
the facial and cochlear nerves (
Fig. 10
). Using
a right angle hook, the inferior vestibular nerve
is divided, and the tumor is gently freed from
the lateral end of the internal auditory canal.
The tumor is separated from the cochlear and
facial nerves and removed (
Fig. 11
). To preserve
hearing, it is essential to preserve the internal
auditory artery. The vessel typically runs between
the facial and cochlear nerves but may not be
visible during the dissection.
After irrigation of the tumor bed and estab-
lishment of hemostasis, abdominal fat is used to
close the defect in the internal auditory canal. The
House-Urban retractor is removed and the
temporal lobe is allowed to reexpand.
The wound is closed with absorbable subcuta-
neous sutures over a Penrose drain if indicated.
This drain is typically removed on the 1st post-
operative day. A mastoid-type pressure dressing is
maintained for 4 days postoperatively.
Postoperative care
The patient is observed in the intensive care
unit for the initial 2 postoperative days and
typically has a hospitalization of 6 to 7 days.
Once leaving the intensive care unit, ambulation is
MIDDLE FOSSA APPROACH FOR ACOUSTIC TUMOR REMOVAL
283
Fig. 4. Temporal lobe is supported by House-Urban retractor. (Reprinted by permission of the House Ear Institute, Los
Angeles.)
Fig. 5. The greater superficial petrosal nerve is identified medial to the middle meningeal artery. (Reprinted by permis-
sion of the House Ear Institute, Los Angeles.)
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