s1042368008000090.pdf

Neurosurg Clin N Am 19 (2008) 265–278

Transotic Approach to the Cerebellopontine Angle

J. Dale Browne, MD a , * , Ugo Fisch, MD b

a Department of Otolaryngology, Wake Forest University School of Medicine, Winston-Salem, NC, USA

b Department of Otolaryngology, University of Zurich, Zurich, Switzerland

The development by House in the early 1960s

of the translabyrinthine approach to lesions in

the cerebellopontine angle revolutionized their

treatment. Until the late 1970s, this was the

primary approach used in the University of

Zurich Department of Otolaryngology for the

treatment of acoustic neuromas. At that time, an

extension in the degree of temporal bone dissec-

tion was introduced to provide improved facial

nerve identiﬁcation and tumor visualization in

larger lesions [1] . This new approach featured

the complete exenteration of all pneumatic cell

tracts of the temporal bone, total removal of

the otic capsule with transposition of the facial

nerve, and obliteratior of the middle ear cleft.

The procedure was described as the transotic ap-

proach to distinguish it more clearly from the

less extensive transcochlear approach introduced

by House et al for the resection of skull base tu-

mors [2] .

The original transotic approach eliminated

many exposure problems encountered with the

translabyrinthine procedure, yet introduced

a temporary postoperative facial paralysis from

transposition of the facial nerve. To address this

problem, a modiﬁcation was developed that

involved preservation of the facial nerve within

the fallopian canal, thereby eliminating the

temporary paralysis of permanent transposition

while maintaining improved exposure [3,4] .As

a result of the success of this procedure for the

removal of larger tumors, the transotic approach

has replaced the translabyrinthine approach in

the treatment of virtually all acoustic neuromas

treated in the Department of Otolaryngology.

The purpose of this article is to present a detailed

summary of the advantages, disadvantages, and

technical aspects of this method as it relates to

the surgical therapy of acoustic neuromas.

Surgical technique

The principal objective of the transotic ap-

proach is the direct lateral exposure of the

cerebellopontine angle via the medial wall of the

temporal bone. No cerebellar retraction is re-

quired, with the limits of dissection along the

medial wall extending from the superior petrosal

sinus to the jugular bulb and from the internal

carotid artery to the sigmoid sinus. The facial

nerve is left undisturbed within the tympanic and

mastoid segments of the fallopian canal. The

component steps in the transotic approach consist

of (1) a subtotal petrosectomy with preservation

of the tympanic and mastoid segments of the

fallopian canal, (2) total removal of the otic

capsule with wide exposure of posterior fossa

dura along the medial temporal bone, (3) tumor

removal with maximal facial nerve exposure, and

(4) dural reconstruction with cavity obliteration.

Subtotal petrosectomy

The foundation of the transotic approach is

the successful completion of a subtotal petrosec-

tomy before advancing to otic capsule removal

and tumor exposure ( Figs. 1, 2, and 3 ). This in-

volves the obliteration of the eustachian tube isth-

mus, closure of the external auditory canal, and

complete exenteration of all air cell tracts to

This article is originally appeared in Otolaryngologic

Clinics of NA: Vol 25, issue 2, April 1992; p. 331–346.

* Corresponding author. Department of Otolaryn-

gology, Wake Forest University Medical School, Medi-

cal Center Boulevard, Winston-Salem, NC 27157.

doi:10.1016/j.nec.2008.02.008

neurosurgery.theclinics.com

266

BROWNE & FISCH

Fig. 1. (A) An S-shaped incision is made from the temporal region to 2 cm below the mastoid tip (A-B), with the su-

perior portion (A-C) made at the conclusion of the procedure if needed for the temporalis muscle ﬂap. (B) The postaur-

icular skin is anteriorly reﬂected superﬁcial to the temporalis muscle. An anteriorly based ﬂap is created for mastoid

periosteum and soft tissues. (C) The external auditory canal is transected at the level of the bony-cartilaginous junction.

(D) The skin edges of the cartilaginous canal are separated slightly from underlying cartilage, everted laterally, and

closed. The preserved periosteal ﬂap is folded over the closed meatus and sutured to the cartilage for a two-layered clo-

sure. (Adapted from Fisch U, Mattox D. Microsurgery of the Skull Base. Stuttgart, Germany, Georg Thieme Verlag;

1988; with permission.)

include the retrosigmoid, retrofacial, antral, retro-

labyrinthine, supralabyrinthine, infralabyrinthine,

peritubal, and pericarotid cells. At the end of this

initial dissection, the internal carotid artery, jugu-

lar bulb, and mastoid segment of the fallopian ca-

nal have been skeletonized.

fallopian canal as a bridge of bone from the

geniculate ganglion to the stylomastoid foramen

( Figs. 4 and 5 ). Posterior exposure is achieved

through removal of the semicircular canals and

vestibule. The inferior and anterior exposure in-

herent to this technique follows removal of the co-

chlea by drilling under and anterior to the

fallopian canal bridge. Special care is taken to ex-

pose all dura between the jugular bulb, internal

carotid artery, and semicanal of the tensor tym-

pani muscle. Before completion of the superior ex-

posure, the remaining bone over the posterior

Otic capsule removal

Exposure of the internal auditory canal con-

tents requires a complete removal of the otic

capsule with continued preservation of the

267

TRANSOTIC APPROACH TO THE CEREBELLOPONTINE ANGLE

268

BROWNE & FISCH

Fig. 3. (A) The bony eustachian tube is removed as far as the isthmus with diamond burs, taking care to avoid injury to

the carotid artery. (B) After bipolar coagulation of the mucosa of the bony-cartilaginous junction, the eustachian tube is

obliterated with bone wax. (Adapted from Fisch U, Mattox D. Microsurgery of the Skull Base. Stuttgart, Germany,

Georg Thieme Verlag; 1988; with permission.)

fossa dura is removed between the superior petro-

sal sinus, sigmoid sinus, and posterior internal au-

ditory canal.

Completion of the important superior expo-

sure follows identiﬁcation of the labyrinthine

segment of the facial nerve at the meatal foramen

by careful removal of the anterior-superior

bone overlying the internal auditory canal. This

identiﬁcation is enhanced through the use of facial

nerve monitoring. Subsequently exposure of pos-

terior fossa dura is completed along the superior

petrosal sinus and the posterior-superior acoustic

porus. The completed exposure is diagrammati-

cally illustrated in Fig. 5 .

medially, the intracanalicular portion of the tu-

mor is freed from the facial nerve. As it is sepa-

rated from the nerve, the tumor is displaced into

the space created by removal of the otic capsule.

Once the porus is reached, the mobilized portion

of tumor can be excised and the remaining intra-

dural tumor debulked by intracapsular removal.

After complete hemostasis, removal of the

intradural portion may then proceed with a pos-

terior fossa incision, which begins between the

sinodural angle and the posterior edge of the

porus and is subsequently extended anteriorly

below the porus. By retraction of the dural edges

with 4–0 Vicryl sutures, the complete circumfer-

ence of the tumor can be uncovered. Removal of

the neuroma is accomplished by additional intra-

capsular removal, in conjunction with meticulous

dissection of the tumor capsule from feeding

vessels and the facial nerve. Identiﬁcation and

Tumor removal

Tumor removal begins with separation of the

neuroma from the facial nerve at the meatal

foramen ( Figs. 6, 7, and 8 ). Working laterally to

Fig. 2. (A) The mastoid cortex is widely exposed. The remaining skin of the external auditory canal is removed, as well

as the tympanic membrane, ossicles and posterior canal wall. All pneumatic cell tracts associated with the middle ear

are thoroughly removed, the mastoid tip is removed to facilitate cavity obliteration. The tympanic and mastoid seg-

ments of the facial nerve are identiﬁed, leaving only a thin covering of bone over the nerve. The air cells are removed

in the following order: retrosigmoid, retrofacial, retrolabyrinthine, supralabyrinthine, infralabyrinthine, pericarotid,

and supratubal. (B) The surgical site following removal of all air cell tracts: ET, eustachian tube; ICA, internal carotid

artery; JB, jugular bulb; SS, sigmoid sinus; LSC, lateral semicircular canal; PSC, posterior semicircular canal; SSC,

superior semicircular canal; MCF Dura, middle cranial fossa dura. All middle ear mucosa has been removed. (Adapted

from Fisch U, Mattox D. Microsurgery of the Skull Base. Stuttgart, Germany, Georg Thieme Verlag; 1988; with

permission.)

TRANSOTIC APPROACH TO THE CEREBELLOPONTINE ANGLE

269

Fig. 4. (A) Posterior exposure. As in the translabyrinthine approach, the semicircular canals are removed and vestibule

opened. The meatal dura is exposed from the posterior fundus of the canal to the porus. The bone removal is extended

interiorly around the enlarged internal auditory canal and under the preserved fallopian canal. The endolymphatic sac is

exposed. (B) Inferior and anterior exposure. The cochlea is drilled away and the posterior fossa dura is gradually exposed

by working under and anterior to the fallopian canal, preserved as a bridge of bone. The dura is exposed between the

jugular bulb, internal carotid artery, and the semicanal of the tensor tympani muscle. With this exposure, the cochlear

aqueduct is encountered. Arachnoid within the aqueduct may be opened to allow decompression of the posterior fossa

before the dura is incised. (From Fisch U, Mattox D. Microsurgery of the Skull Base. Stuttgart, Germany, Georg Thieme

Verlag; 1988; with permission.)

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