s1042368008000028.pdf

Neurosurg Clin N Am 19 (2008) 331–343

Surgical Approaches and Complications

in the Removal of Vestibular Schwannomas

Marc Bennett, MD, David S. Haynes, MD *

The Otology Group of Vanderbilt, Nashville, TN, USA

Vestibular schwannomas (VS) are benign tu-

mors of Schwann cells that originate on the

vestibular portion of the eighth cranial nerve.

Found in the internal auditory canal (IAC) and

cerebellopontine angle, VS account for nearly 6%

of intracranial tumors. Although surgical excision

previously had high mortality rates, the advent of

the operating microscope and neurotologic and

neurologic monitoring has allowed surgical tech-

niques to evolve and morbidity and mortality to be

reduced signiﬁcantly. Currently, complete surgical

excision with preservation of facial nerve function

is often an achievable goal. The increasing sensi-

tivity of MRI has allowed for diagnosis of smaller

tumors and has increased the ability to preserve

hearing. Three basic surgical approaches are used

for removal of VS: the translabyrinthine, retro-

sigmoid, and middle cranial fossa (MCF) ap-

proaches, which are described in this article.

Although many factors inﬂuence the choice of

surgical approach, personal experience of the

surgeon often determines the surgical approach.

This article presents the diﬀerent approaches, their

advantages and disadvantages, common compli-

cations, and mechanisms to prevent complications.

by Eduard Sandifort [1] . It was nearly 100 years

later when Thomas Annandale performed the ﬁrst

complete surgical excision with patient survival.

Surgical excision had high mortality ratesdin ex-

cess of 50%duntil the early 1920s, when Harvey

Cushing reﬁned techniques and lowered mortality

rates to 21% [2] . Cushing’s prote´ ge´ , Walter

Dandy, further lowered mortality rates to 10%

by the early 1940s [3] .

The modern era of tumor dissection began in

the early 1960s with the introduction of the

operating microscope and the introduction of

the translabyrinthine and MCF approaches by

William House. Sterile technique, microscopic

magniﬁcation, and precise otologic drills have

continued to lower mortality rates to approxi-

mately 1%. Continued earlier diagnosis with the

advent of MRI with gadolinium has changed the

goals of surgery from complete excision and

survival to maintenance of facial nerve function

and preservation of hearing when possible [4] .

Treatment options

After proper diagnosis, four treatment options

are available for VS: observation, stereotactic

radiation therapy, complete surgical excision,

and subtotal resection with planned radiation

therapy.

Surgical history

The ﬁrst documented case of VS was an

autopsy report during the late eighteenth century

Observation

The indolent nature of VS has led many

physicians to observe tumors that may remain

dormant or grow slowly enough to never require

treatment. Treatment decisions may be based on

patient characteristics, such as age, general health,

status of hearing in the contralateral ear, and

patient preference, or tumor characteristics, such

A version of this article originally appeared in

Otolaryngologic Clinics of NA, volume 40, issue 3.

* Corresponding author. Vanderbilt University, The

Otology Group of Vanderbilt, 300 20th Avenue, North,

Suite 502, Nashville, TN 37203-2115.

E-mail address: david.haynes@vanderbilt.edu

(D.S. Haynes).

doi:10.1016/j.nec.2008.02.002

neurosurgery.theclinics.com

332

BENNETT & HAYNES

as size, location, and growth rate [5] . Observation

is performed via a set schedule of MRI. We scan

our patients initially at 6 months and then every

year until a general growth rate can be estab-

lished. If minimal growth has been observed, the

MRI every 2 years is possible.

The natural history of VS is enigmatic. The

percentage of tumors that grow is generally un-

known and has varied widely in studies from 40%

to 80% [5–7] . A long-term follow-up of 14 years in

more than 1800 patients with observed acoustic

neuroma was published recently in which 83%

of intrameatal tumors remained intrameatal and

70% of extrameatal tumors did not grow more

than 2 mm [6] . All tumors that exhibited growth

did so in the ﬁrst 4 years and maintained consis-

tent growth rates throughout observation [6] .

Tumor growth rates can be stratiﬁed into slow

growing (!2 mm/y) and fast growing (O2 mm/y).

Tumors with slower growth rates often do not

require treatment [5] .

There are diculties with observation. First,

MRI is expensive and patients may be lost to

follow-up. Rarely, tumors may undergo acceler-

ated rates of growth after multiple years of stable

growth. Patients who require surgery after obser-

vation also are older and may suﬀer from more

comorbidities, which makes surgery potentially

more risky. Finally, tumors with continued

growth may no longer meet criteria for hearing

preservation approaches or radiation therapy and

may make facial nerve preservation more dicult.

Advantages to observation are the obvious

delay and potential elimination of the need for

surgical or radiosurgical intervention. Older

patients may develop or have exacerbation of

existing disease that may take precedence over

treatment of the tumor (ie, cancer, stroke, cardiac

disease). Younger patients may choose to observe

the tumor to determine growth and choose in-

tervention only when growth has been established.

Economic reasons, such as retirement, job

changes, or insurance issues, may compel a patient

to choose observation as an initial option. Family

issues, such as a wife/husband or child with an

illness or other family issues (child starting school/

college), also may compel a patient to choose

observation.

1969. Techniques have evolved and outcomes with

fewer side eﬀects are currently possible. Although

most tumors are controlled successfully, nearly

9% of tumors exhibit growth after radiation

therapy. Surgery after failed radiation therapy is

more dicult to perform because intense scarring

and ﬁbrosis obscure surgical planes. As a result,

facial nerve outcomes are poorer than in patients

with nonirradiated tumors [8–10] . Because VS are

known to be slow growing, it is dicult to study

techniques (radiation therapy) that slow or elimi-

nate tumor growth. Long-term studies are needed

to determine the eﬀectiveness of radiation therapy

over observation and surgery to treat VS.

Surgery

The goal of surgery is complete tumor removal

while preserving neurologic function and hearing,

if possible. Each of the three main approaches for

surgical removal of VS has advantages and

disadvantages ( Table 1 ). The retrosigmoid and

MFC are the two surgical techniques most

commonly used in VS surgery when attempting

to preserve hearing. Hearing preservation may

be attempted when the pure-tone average is

50 dB or less and the speech discrimination is

more than 70%. Tumor size also determines

whether hearing preservation is attempted, be-

cause a tumor R2 cm is rarely amenable to hear-

ing preservation despite initial hearing status.

Location also may play a role in hearing preserva-

tion because tumors far lateral in the IAC with

extension into the cochlea or vestibule may not

be amenable to hearing preservation.

All procedures are performed under general

anesthesia with neurophysiologic monitoring.

Facial EMG electrodes are inserted into the

obicularis oris and occuli muscles for continuous

facial nerve monitoring. Auditory brainstem re-

sponse is used in hearing preservation cases with

an acoustic ear insert in the external auditory

canal, a recording electrode placed at C0 on the

vertex, a reference in the ipsilateral ear lobule, and

a ground in the shoulder. Perioperative antibiotics

and steroids are used. Mannitol (1 g/kg) is given

just before opening the dura in all cases.

The translabyrinthine approach provides wide

access to the posterior fossa with little or no need

for brain retraction. The anatomy is familiar for

the neurotologist but often is unfamiliar to the

neurosurgeon. The facial nerve is identiﬁed early

in the case laterally at the fundus of the internal

IAC and medially at the brainstem. This lateral

surgical approach allows for the facial nerve to be

Radiation therapy

Although surgical resection has the goal of

complete tumor removal, radiation therapy has

the primary goal of tumor control. Leksell per-

formed the ﬁrst stereotactic radiosurgery for VS in

REMOVAL OF VESTIBULAR SCHWANNOMAS

333

Table 1

Advantages and disadvantages of surgical approaches for removal of vestibular schwannoma

Translabyrinthine

Middle fossa

Retrosigmoid

Advantages

Consistent facial nerve

identiﬁcation

No tumor size limitation

No intradural drilling

Wide exposure posterior

Fossa

Low recurrence rates

ABI placement possible

Low rate of headaches

Best hearing preservation

No intradural drilling

Low rate of headaches

No tumor size limitation

Hearing preservation possible

Wide exposure brainstem

ABI placement possible

Consistent facial

nerve identiﬁcation

Neurosurgeon familiarity

Disadvantages Complete hearing loss

Neurosurgeon

unfamiliarity

Abdominal fat graft

Limited tumor size

Temporal lobe retraction

Limited exposure

posterior Fossa

Increased risk of

recurrence of tumor

in an unfavorable

position related

to the facial nerve

Limited exposure

of lateral IAC

Intradural drilling

Postoperative headaches

Cerebellar retraction

Facial nerve identiﬁcation

is relatively late

in the dissection

Abbreviation: ABI, auditory brainstem implant.

in a favorable place deep in the IAC and places

the vestibular nerves laterally, where the surgeon

encounters the vestibular nerves initially on IAC

dissection. The main disadvantage of this ap-

proach is the lack of ability to preserve hearing.

TheMFCapproachwas seldomused for tumors

until recently because most tumors remained un-

diagnosed until they were too large to be removed

by MCF. Its popularity has increased recently as

imaging technology has allowed for detection of

small tumors and tumors with up to 1 cm in

the cerebellopontine angle are amenable to this

technique. Although this approach has the most

favorable hearing preservation rates, the tech-

nique is challenging because the facial nerve lies

between the surgeon and the tumor and the

principal anatomic landmarks for identiﬁcation

of the IAC are less reliable and may be

obscured. The superior approach to the IAC

makes the facial nerve and the superior nerve

the ﬁrst encountered by the surgeon on dissec-

tion through the temporal bone. Elevation and

retraction of the temporal lobe also carry the

risk of brain injury, including aphasia, seizures,

and stroke.

The retrosigmoid approach traditionally has

been the most widely used approach because of its

popularity among neurosurgeons and its wide

versatility. It aﬀords wide exposure of the posterior

fossa, can be used for excision of small and

large tumors, and oﬀers an opportunity for

hearing preservation. Intradural drilling of the

IAC is required. Like the translabyrinthine

approach, lateral surgical approach allows for

the facial nerve to be in a favorable position

deep in the IAC and places the vestibular nerves

laterally, where the surgeon encounters the

vestibular nerves initially on IAC dissection.

Surgical approaches

Retrosigmoid approach

The patient is positioned in a modiﬁed park

bench position, lying supine with the ipsilateral

shoulder and hip bumped with rolls and padding.

The patient’s head is ﬂexed and rotated toward

the opposite shoulder and secured with Mayﬁeld

pinions. This simple and straightforward position

enables excellent visualization of the contents of

the posterior fossa. Extreme rotation and ﬂexion

may cause venous occlusion and should be

avoided. Somatosensory evoked potentials are

monitored throughout the case. Potential changes

in the waveforms may indicate compromise of the

vascular system or spinal compression. Hair is

prepped with betadine solution and shaved for

four ﬁnger breadths behind the ear.

As shown in Fig. 1 , a curvilinear ‘‘C’’ incision

is made into the posterior scalp down onto the

neck. The incision is approximately 4 cm posterior

to the ear canal. The incision is carried through

334

BENNETT & HAYNES

Fig. 1. Skin incision for retrosigmoid approach.

and again at the end of the case. The dura is

then opened, as shown along the dashed lines in

Fig. 2 , and the dural ﬂaps are reﬂected laterally

and secured with sutures. The dural ﬂaps are

routinely irrigated throughout the case to avoid

desiccation. Moist cottonoid pledgets are placed

over the cerebellum to avoid intraoperative injury

and prevent desiccation throughout the case. The

cisterna magna is opened anteroinferiorly to the

cerebellum with a right angle pick to allow CSF

egression, which maximizes posterior fossa relaxa-

tion and minimizes the need to retract the cerebel-

lum during the case.

The tumor and the seventh to eighth nerve

complexes are identiﬁed at the brainstem and

dissection is performed in a cooperative fashion

between the neurosurgeon and neuro-otologist.

The lateral surface of the tumor is examined for

a rare lateral displacement of the facial nerve or

major vascular structure. Visual inspection of the

IAC is often dicult until large tumors are

internally debulked. If still dicult to visualize,

the IAC can be palpated with blunt instrumenta-

tion. The dura above the IAC is coagulated with

bipolar cautery in an arc several centimeters

above the posterior lip of the IAC before making

a similar incision. The dura is then elevated down

to the porus acousticus of the IAC and reﬂected

over the tumor. Several cotton balls are placed

medially to the IAC to prevent bone dust from

accumulating in the cerebellopontine angle.

Dissection begins with an otologic drill and

medium-sized cutting burs until the IAC is ap-

proached. Diamond burs are then used to create

superior and inferior troughs closer to the IAC

until nearly 180 to 270 of bone is removed

around the posterior IAC ( Fig. 3 ). Exposure of

the IAC continues laterally until the IAC appears

normal and the end of the tumor is encountered.

For hearing preservation to be accomplished, the

common crus of the bony labyrinth and the

vestibule must not be injured during dissection.

Drilling continues until a thin layer of bone re-

mains over the IAC dura. This bone is removed

with careful dissection and the IAC dura is then

opened. It is preferred to gain exposure of the

IAC lateral to the tumor before opening the

dura. Keeping the dura intact provides a protec-

tive layer to the contents of the IAC during dril-

ling. Opening the dura too early requires further

drilling laterally to gain tumor control with an

open IAC. The superior vestibular nerve, inferior

vestibular nerve, and tumor are identiﬁed in the

posterior aspect of the canal. Gentle retraction

the skin and subcutaneous tissues and an anterior

ﬂap is dissected for nearly 1 cm. Electrocautery is

used to incise the musculoperiosteum down to the

bone. Oﬀset incisions allow for overlapped closure

and a reduced incidence of incisional cerebrospi-

nal ﬂuid (CSF) leaks.

As shown in Fig. 2 ,a4 4 cm craniectomy is

performed. The anterior and superior limits of the

craniotomy are the sigmoid and transverse si-

nuses, respectively. As a general rule, the external

ear canal approximates the level of the transverse

sinus. Laterally exposed mastoid air cells near the

sigmoid sinus are occluded with bone wax to

prevent transgression of CSF at initial opening

Fig. 2. Craniotomy for retrosigmoid approach.

REMOVAL OF VESTIBULAR SCHWANNOMAS

335

Fig. 3. IAC dissection in retrosigmoid approach.

solution and four ﬁngerbreadths of hair are

shaved above and behind the auricle. As shown

in Fig. 4 , a C-shaped incision is made extending

from one ﬁnger breadth above the ear and two ﬁn-

ger breadths behind the postauricular crease down

to one ﬁnger breadth posteroinferiorly to the mas-

toid tip. The incision is made through the skin and

a skin ﬂap is elevated for 1 cm toward the ear

through the entire incision. The stepped incision

allows for easier closure and prevention of CSF

leak. A large superﬁcial temporal fascial graft is

harvested and placed on a block. As shown in

Fig. 4 , a C-shaped musculoperiosteal incision is

made with electrocautery from just above the tem-

poral line to the mastoid tip. This incision is oﬀset

from the cutaneous incision by 1 cm throughout

the incision. The periosteum is elevated to the

external auditory canal and retracted with dura

hooks. Several large pieces of digastric or sterno-

cleidomastoid muscle are harvested for later use

in packing the middle ear.

The bony exposure is performed in three

stages: complete mastoidectomy, labyrinthec-

tomy, and IAC dissection. Most of the drilling is

performed with cutting burs; however, diamond

burs are used when dissection is around critical

areas. A complete mastoidectomy is performed,

skeletonizing the bone overlying the sigmoid sinus

and the tegmen. As shown in Fig. 5 , the facial

nerve is identiﬁed throughout its mastoid course

with a large diamond bur. In previous reports

the facial recess was opened, the incudostapedial

of the superior vestibular nerve reveals the facial

nerve, which is identiﬁed physiologically with

a stimulator at minimal settings (0.05 mA). The

vestibular nerves are sectioned laterally, and tu-

mor dissection is performed in the plane between

the tumor and the facial and cochlear nerves in

a lateral to medial fashion. Endoscopic assistance

with a 30 endoscope also may be valuable to

inspect the lateral IAC and reduce the risk of

residual disease.

Once the tumor dissection is complete, the

operative ﬁeld is copiously irrigated and hemo-

stasis is achieved with bipolar cautery. The entire

bone surrounding the IAC is sealed with bone wax

applied with a cotton pledget. Gelfoam is then

placed over the remaining seventh and eighth

nerve complex and ﬁbrin glue is used to reinforce

the seal of the IAC. The dura is then closed with

running 3-0 nylon closure. Fibrin glue is placed

over the closure of dura. The subcutaneous tissues

and skin are closed in several layers with absorb-

able 2-0 and 3-0 vicryl sutures and staples are

placed in the skin. A compressive dressing is

placed over the wound to apply pressure in the

postoperative period. The patient is kept in the

neurointensive care unit for 24 to 48 hours and

kept on steroids and antibiotics.

Translabyrinthine approach

The patient is placed in the supine position and

the head is turned away from the operative side.

The initial positioning is much simpler with this

approach than with the retrosigmoid approachd

no pins, head holders, or park bench positioning

is required. The hair is prepped with betadine

Fig. 4. Skin and periosteal incisions for translabyrinthine

approach.

Plik z chomika:

Inne pliki z tego folderu:

Inne foldery tego chomika: