Management of Acoustic Neuromas(Vestibular Schwannomas)
File 2: Surgical Techniques
G. OJEMANN, M.D. © Congress of Neurological Surgeons Honored
Originally Published Clinical Neurosurgery, Volume 40, Chapter
24, Pages 498-535, 1992
Used with permission of the Congress of Neurological Surgeons.
HTML Editor: Stephen B. Tatter, M.D.,
The information and reference materials contained herein are intended
solely to provide background information. They were written for an
audience of physicians. They are in no way intended to constitute
medical advise. For medical advise a physician must, of course, be
- INTRODUCTION (File
- SURGICAL MANAGEMENT
(For surgeons!, This File)
- RESULTS OF SUBOCCIPITAL OPERATION:
Summary of the Series, 1979-1992 (File
- Extent of Tumor Removal and
- Postoperative Complications
- Cochlear Nerve Function
- Management of Tumor in the Only
- Management in Elderly Patients
(70 Years and Older)
- Management in Patients with
- RADIOTHERAPY MANAGEMENT (File
- OBSERVATIONAL MANAGEMENT (File
- MANAGEMENT PLAN (File
- REFERENCES (File
The microsurgical removal of an acoustic
neuroma can be done by a suboccipital, translabrynthine, or middle
fossa approach. Good results from all three approaches have been
reported by experienced groups of neurosurgeons (43). For most patients
we have preferred the suboccipital (posterior fossa) approach because
of the wide visualization it allows, the ability to save hearing
in appropriate cases, and the good results we (35-44) and others
(1, 8, 10, 12, 18, 19, 47, 53) have reported. The technical aspects
of the operation have been reported and illustrated in detail in
previous publications (39, 42, 43). In a few patients with no useful
hearing and intracanalicular tumors or with tumors extending a few
millimeters into the posterior fossa, we have used a translabrynthine
Perioperative Medical Therapy
Steroids are usually started 48 hours
prior to operation and a higher dose (methyprednisolone, 80 mg,
intravenously) is given just before the operation. The blood sugar
is carefully monitored. The high steroid dose is continued every
6 hours during the operation and then is gradually tapered off over
5-10 days depending on the size of the tumor and facial nerve function.
An antibiotic, usually a cephalosporin,
is given intravenously starting just before surgery. This is continued
for 24 hours after the operation.
After anesthesia is induced, an indwelling
Foley catheter is inserted and 10-20 mg of furosemide are given
intravenously. During the preparation and exposure of the dura a
20% solution of mannitol is given intravenously, in a dosage of
1-1.5 g/kg, over 20-30 minutes.
Continuous electrophysiological monitoring
of facial nerve function during the operation has become an established
| FIG-24.1: Monitoring
of facial- and cochlear-nerve function during the operation.
The benefits of this monitoring have
been documented (16). A continuous drip of a muscle relaxant is
carefully administered so facial nerve function can be assessed.
The dosage is monitored by following the twitches elicited with
ulnar nerve stimulation. Facial nerve function is monitored by continuous
recording of electromyographic activity with two recording electrodes,
one in the orbicularis oculi and the other in the orbicularis oculus
muscles (Fig. 24. 1). The muscle contractions, which could occur
from stimulation of the facial nerve during coagulation when the
electrodes are inactive, are recorded from a motion sensor placed
on the cheek. Monopolar stimulation is used to locate the seventh
nerve. Fifth nerve function is monitored with electrodes placed
in the masseter and temporalis muscles.
When auditory evoked responses are
monitored during an attempt to save hearing, we use a system developed
by Dr. Robert Levine (see Cochlear Nerve Function) (21-25, 42).
A transtympanic electrode is placed for electrocochleography, scalp
electrodes are inserted for brainstem auditory evoked potential
monitoring, and a microphone system is placed in the external ear
canal to provide the sound stimulus (Fig. 24. 1).
| FIG-24.2: Position, skin
incision, craniotomy opening, and dural incisions.
The operating table is turned so the
surgeon can sit behind the patient's head and place the feet under
the table. The patient lies supine with the shoulder that is ipsilateral
to the tumor slightly elevated (Fig. 24.2). The head is turned parallel
to the floor, elevated, and held with a three-point skeletal-fixation
headrest. During the operation the line of sight to the brainstem
may be altered by rotating the table from side to side. An arm rest
is placed for the surgeon's arm nearest the vertex. The other arm
rests on the patient. In patients with previous neck pathology,
it may be necessary to elevate the shoulder more or use a lateral
Incision and Exposure
A vertical incision is centered 2 cm
medial to the mastoid process (Fig. 24.2). A graft of peticrartial
tissue, about 4 cm in diameter, is taken from the occipital region
by extending the superior aspect of the incision as needed. This
graft is used in closing the cerebral convexity dura at the end
of the operation. The suboccipital muscles and fascia are incised
in line with the incision and carefully separated from their attachments
to the bone using subperiosteal dissection and electrocautery. Special
care is taken to occlude the arterial vessels as they are encountered
in the muscle. An ernissary vein is usually exposed in the region
of the medial mastoid area.
| FIG-24.3: The dural flaps
have been retracted with sutures. The cerebellum is elevated
and the arachnoid opened to allow drainage of cerebrospinal
fluid. In medium and large size tumors a catheter is placed
in the cistem to drain the fluid during the operation.
The bone over the lateral two thirds
of the cerebellar hemisphere is exposed. It is usually not necessary
to visualize the midline bone or lim of the foramen magnum. A burr
hole is placed, the dura carefully separated from the overlying
bone, and a bone flap cut. This opening exposes the dura over the
lateral two thirds of the cerebellar hemisphere and exposes the
transverse sinus. Further bone is removed as needed to expose the
turn from the transverse sinus to the sigmoid sinus and the edge
of the petrous bone laterally. This allows the edge of the sinus
to be retracted, with the sutures placed to hold the dural flaps,
and yields a direct line of sight down the posterior surface of
the petrous bone. The mastoid air cells are usually entered and
are occluded with bone wax.
The dura is opened vertically, keeping
an area of medial dura intact to protect the retracted cerebellum.
Stellate dural incisions provide superior, lateral, and inferior
flaps of dura, which are held back with sutures (Fig. 24.3).
The cerebellum is then gently elevated,
the arachnoid is opened, and cerebrospinal fluid is allowed to drain
(Fig. 24.3). This usually relieves any bulging of the cerebellum
and allows exposure of the cerebellopontine angle with minimal retraction.
The arachnoid should be opened enough to allow cerebrospinal fluid
to continue to drain during the operation.
In most tumors of >2 cm the tip
of a small catheter (number 10 Bardic) is placed in the cistern
and sutured to the inferior medial comer of the dural opening to
drain cerebrospinal fluid continuously during the operation. In
some patients with large tumors a small portion of the lateral cerebellar
hemisphere is removed to facilitate the exposure. Following placement
of the self-retaining Greenberg refractors, the operating microscope
Removal of Small Tumors and Hearing
| FIG-24.4: In small tumors
where hearing is to be preserved the internal auditory canal
is exposed and a decision is made regarding how best to proceed
with the dissection.With large tumors the cochlear nerve is
divided and the seventh nerve followed back to the meatus.
Under the microscope the arachnoid
over the tumor is opened and the petrosal vein is coagulated and
divided. The refractors are repositioned. With small tumors the
eight nerve complex is seen coming into the inferior medial side
of the tumor. The next step is usually exposure of the tumor in
the internal auditory canal. Dura is removed over the region of
the internal auditory canal and bone is carefully removed using
an air drill, with constant suction-irrigation for cooling. When
hearing preservation is a consideration, the bone removal extends
for a distance of no more than 10 mm laterally. A more lateral exposure
risks entering the labyrinth. Dissection then depends on an assessment
of the relationship of the tumor to the vestibular and cochlear
nerves. In some patients the vestibular nerve fibers entering the
medial edge of the tumor are divided, the cochlear and facial nerves
are identified, and the dissection proceeds from the medial to lateral
sections. In other patients it may be difficult to define the cochlear
nerve medially. The tumor is then carefully rotated near the lateral
end of the canal, with a search for the seventh nerve anteriorly
superiorly and the cochlear nerve anteriorly inferiorly (Fig. 24.4).
It is important to avoid stretching or putting tension on these
nerves. The position of the seventh nerve is confirmed with stimulation.
An internal decompression of the tumor may be done using sharp dissection
to facilitate the exposure. Dissection along the facial and cochlear
nerves is done with fine straight or curved microdissectors or canal
knives and sharp dissection is done with microscissors. Dissection
is alternated from different directions depending on what seems
to give the best exposure, the easiest plane of dissection, and
the least traction on the nerves. When the cochlear and facial nerves
have been clearly defined, the vestibular nerves coming into the
tumor are divided on both the medial and lateral aspects of the
tumor. In some patients the lateral end of the tumor may not be
exposed because of the limitation in bone removal. In these patients
the tumor is transacted near the end of the canal and the lateral
extent of the tumor is removed with a small ring curette.
During the dissection there may be
intermittent bleeding along the nerves. A fine suction keeps the
field clean and does not damage the nerves. Most of the bleeding
stops spontaneously. When trying to save hearing, an attempt is
made to preserve any significant arterial vessel entering the internal
Removal of Medium and Large Size
| FIG-24.5: The facial
nerve may be displaced in different directions on the anterior
capsule of the turner (see text). In some patients a portion
of the nerve may be directly over the fifth nerve.
The arachnoid over the posterior capsule
of the tumor is opened. A separate cystic collection of cerebrospinal
fluid may occasionally be loculated in relation to the tumor capsule,
with thickened arachnoid and xanthochromic fluid. The petrosal vein,
which usually comes off the cerebellum or middle cerebellar peduncle
to the petrosal sinus just above the tumor, is coagulated and divided.
In order to complete the initial exposure of the posterior capsule
it is usually necessary to shrink the cerebellar tissue next to
the tumor with bipolar coagulation or to remove a small amount of
cerebellar tissue which may obscure the inferior medial pole. In
some large tumors up to 1 cm of lateral cerebellum may be resected.
The posterior capsule is stimulated
to locate the facial nerve. In almost all patients the facial nerve
is on the anterior surface of the tumor and there is no response
on this first stimulation. The most common direction of displacement
is directly anteriorly (Fig. 24.5). The next most common location
is a anterior medial displacement along the brainstem and over the
anterior superior aspect of the tumor. In this circumstance the
facial nerve may be displaced against the fifth nerve. On rare occasions
the nerve is inferior or across the posterior surface. Only one
patient in my series of 410 cases had the facial nerve displaced
posteriorly. The ninth, 10th, and llth cranial nerves are identified
and arachnoid adjacent to the cerebellum is carefully dissected
to aid exposure of the inferior medial capsule. With larger tumors
the ninth and 10th nerves are carefully reflected off the tumor
capsule and a small rubber dam is placed over them for protection
during the rest of the operation.
| FIG-24.6: Internal decompression
of the tumor has been done. The tumor capsule is being reflected
laterally and superiorly to bring into view the eight nerve
The next step is internal decompression
of the tumor, which is done intermittently as needed. This allows
all the pressure to be placed on the tumor capsule while it is separated
from the cranial nerves and brainstem. The ultrasonic aspirator,
bipolar coagulation, and sharp dissection are used for internal
Dissection begins inferiorly and medially.
In medium size tumors, the eight nerve complex can usually be defined
with moderate dissection (Fig. 24.6). In larger tumors these nerves
are usually not seen initially. After carefully reflecting the capsule
laterally and superiorly into the area of decompression, one looks
for the eight nerve complex along the inferior medial capsule. Being
a right-handed surgeon, I prefer having fine suction in my left
hand to retract the tumor and keep the area of dissection clean.
The vestibular and cochlear nerve fibers entering the tumor are
divided using bipolar coagulation and sharp dissection (Fig. 24.7).
Arterial vessels adjacent to the tumor are preserved, dividing only
branches entering the tumor.
| FIG-24.7: The eighth
nerve has been divided. A small arterial branch entering the
tumor is being coagulated, preserving the main arterial trunk.
As the dissection of the capsule progresses,
not only is further internal decompression done as indicated but
sections of the tumor capsule are removed to allow room to reflect
the capsule laterally. It may also be advantageous to alternate
dissection of the inferior medial capsule with dissection superiorly
and medially to defme the fifth nerve and brainstem attachments
(Fig. 24.8). There are often vascular attachments and significant
compressionin the region of the fifth nerve root entry zone. Small
rubber darns may be placed on the brainstem for protection as the
| FIG-24.8: The fifth nerve
is visualized with gentle inferior and lateral traction on the
If the seventh nerve has not yet been
localized, intermittent stimulation is used. In some patients spontaneous
electromyographic activity indicates when one is on or near that
nerve. This nerve is usually located by reflecting the inferior
and medial tumor capsule further laterally and superiorly. The nerve
is seen anterior to the divided eighth nerve complex (Fig. 24.9).
It often can be recognized by its slight grayish color, which is
different from that of the adjacent brainstem. In some patients
the facial nerve may be displaced against the brainstem and take
a superior course before turning and heading laterally. When displaced
superiorly it may lie against the fifth nerve. Usually the facial
nerve forms a solid band on the tumor capsule but it may be spread
out over a wide area and occasionally is surrounded by the tumor.
| FIG-24.9: The seventh
nerve is identified anterior to the divided eighth nerve as
it angles superiorly and laterally. In such cases a thin layer
of tumor capsule is left (radical subtotal removal).
Dissection extends along the seventh
nerve toward the internal auditory meatus. We use fine straight
or curved microdissectors, canal knives, and sharp dissection with
microscissors as needed (Fig. 24.10). When the point is reached
where the bone over the internal auditory canal is impeding further
dissection or the dissection is difficult, attention is directed
to the tumor in the internal auditory canal. The exposure is the
same as described for small tumors. In some patients the tumor extends
quite far laterally in the canal and it is advisable to make the
usual exposure, remove a portion of the tumor, and then do further
drilling within the lateral end of the canal as needed. When drilling
along the inferior margin one must remember that, occasionally,
the jugular bulb may come over this area.
| FIG-24.10: Dissection
along the seventh and eighth nerves is often facilitated by
After separation of the tumor from
the facial nerve in the internal auditory canal, the attachments
along the edge of the internal auditory meatus are divided. The
facial nerve starts to turn anteriorly as the posterior fossa is
entered. The surgeon can then decide how best to proceed. The dissection
may be continued medially along the brainstem and cere bellapeducle,
by dividing arachnoid and vascular attachments as they are encountered
and gradually freeing the facial nerve. On occasion a large branch
of the anterior inferior cerebellar artery is embedded in the tumor
capsule but it can usually be dissected free by dividing the small
branches directly supplying the tumor. In large tumors the trochlear
nerve and superior cerebellar artery may be adherent superiorly,
the sixth nerve adherent anteriorly, and the ninth and 10th nerves
adherent inferiorly. The objective is to reduce the bulk and attachments
of the tumor so that finally the surgeon is dealing only with dissection
from the facial nerve. The facial nerve is usually most adherent
to the tumor capsule in the posterior fossa near the internal auditory
meatus, where the nerve may be splayed over the anteiior-supeiior
capsule or occasionally surrounded by tumor. The dissection in this
area is often complicated by vasctflar and fibrous attachments.
The surgeon must adapt to the characteristics of the tumor and it
may be necessary to work alternately from vaidous angles.
In some patients with large tumors
the capsule is so intimately adherent to the brainstem and cranial
nerves that a plane cannot be developed.
Once the tumor is removed, hemostasis
is checked. The area of bone removal over the internal auditory
meatus is carefully waxed to occlude air cells. In addition, an
adipose tissue graft taken from a superficial incision on the lower
abdomen is carefully placed in the area where bone has been removed.
Surgicel is used to hold this graft in place and is also used to
cover the area of resected or retracted cerebellum.
I like to close the dura in a water-tight
fashion using the graft of pericranial tissue taken at the beginning
of the operation. The dura is covered with Gelfoa.m. The bone flap
is replaced and held with number 28 wire, which does not interfere
with any future imaging, and a dural tenting suture. The wound is
thoroughly irrigated with Bacitracin solution prior to closure.
Management of Postoperative Complications
Hematoma and Cerebellar
During the initial exposure particular
attention is focused on occluding the arterial vessels in the muscles
as they are encountered. Then during the closure the muscles are
again carefully checked for bleeding. A significant epidural hematoma
can result with hemorrhage from these blood vessels.
Prior to closure of the dura, the systemic
blood pressure is elevated to approximately 140-150 mm Hg. On more
than one occasion this maneuver has provoked hemorrhage, which is
controlled with bipolar coagulation. Postoperatively the blood pressure
is controlled, beginning in the operating room with an intravenous
antihypertensive medication, and is monitored continuously for as
long as necessary.
If the cerebellum is unusually full
at the end of the operation and there has been good cerebrospinal
fluid drainage, cerebellar infarction or hematoma should be considered.
In this situation a resection of the lateral 1-2 cm ofcerebellum
may need to be done.
If the patient does not recover promptly
fron, anesthesia or there is an unexpected significant neurological
deficit or delayed neurological deterioration, a CT scan is done
immediately to look for cerebellar hematoma or infarction. Prompt
removal of a significant hematoma or area of infarction can lead
to a dramatic recovery.
Cerebrospinal Fluid Fistula
If a cerebrospinal fluid leak develops,
a lumbar drain is placed for 72 hours; this often resolves the problem.
When the leak persists, a transmastoid repair using an adipose tissue
graft is done.
In the Postoperative period the patient
my develop neurological syrnptoms that suggest that hydrocephalus
or a tense subgaleal fluid collection may be present. Ventricular
size is followed by CT scan. Fortunately, persistent hydrocephalus
is a rare complication. Most patients recover spontaneously, a few
require a temporary lumbar drain, and only occasionally is a ventriculoperitoneal
When there is Postoperative fever with
headache or stiffness in the neck, the possibility of either aseptic
or bacterial meningitis must be considered. CT with contrast is
done to look for an area that might suggest a local infection. A
lumbar puncture is then done and administration of broad-spectrum
antibiotics is started. Subsequent treatment is guided by the results
of the cerebrospinal fluid examination and cultures. If the findings
suggest aseptic meningitis, steroids are used.
When the infection is superficial and
the organism is sensitive to antibiotics, it may not be necessary
to remove the bone flap. ff the infection is extensive, debridement
of the wotmd and removal of the bone flap is necessary.
If there is any significant Postoperative
disability the patient is seen by physical and occupational therapists.
Difficulty swallowing due to impaired function in the ninth and
tenth nerves should be Carefully evaluated with a modified barium
swallow and followed by a specialist in swallowing disorders. Often
the patient can be given instructions that facilitate their swallowing
and prevent aspiration. On rare occasion a gastrostomy is needed.
After suboccipital operation a small
percentage of patients complain of persistent headache. The magnetic
resonance imaging (MRI) scan rarely shows a structural abnormality
such as hydrocephalus. In most patients it seems to be a myofascial
problem, in a few a neuroma of the occipital nerve, and in some
cervical spine degenerative disease. Many patients are benefited
by a program of physical therapy and local blocks as indicated.