Translabyrinthine Approach

Patient Selection

Observation with serial imaging, stereotactic radiation treatment, and surgical resection are the three main management options for vestibular schwannomas. Tumor size, patient age, and residual hearing are principal factors that must be considered when selecting a treatment option. When surgical resection is considered, the translabyrinthine approach is used in most patients if the tumor is larger than 2.5 cm in the maximal dimension and in all cases of nonserviceable hearing in the involved ear regardless of tumor size. When tumors are confined to the IAC in an ear with serviceable hearing, the middle cranial fossa approach is typically preferred if the patient desires an attempt at hearing preservation. For patients with good hearing and a CPA-based tumor with minimal IAC extension, the retrosigmoid approach is ideal.

Hearing preservation surgery may be considered for patients with serviceable hearing, defined roughly as a pure tone average threshold of better than 50 dB and a speech discrimination score of greater than 50%. Exceptions exist if the hearing in the contralateral ear is poor or if bilateral tumors are present. In patients with serviceable hearing, one may attempt tumor removal through the middle fossa approach, even if the tumor extends up to 1 cm into the CPA. The retrosigmoid approach may be used in an attempt to preserve hearing if the tumor is smaller than 2.5 cm and does not extend to the fundus of the IAC. An auditory brainstem implant may be placed via the translabyrinthine or retrosigmoid approaches to rehabilitate hearing in patients with neurofibromatosis type 2 undergoing vestibular schwannoma resection.

Surgical Procedure

The procedure is performed under general endotracheal anesthesia. Three days prior to the procedure, the patient is started on famciclovir to reduce the risk of postoperative herpes reactivation along the facial nerve. Once in the operating room, muscle relaxants are used only for induction because longer-acting agents interfere with facial nerve monitoring. Invasive blood pressure monitoring is performed via an arterial line and a Foley catheter. Antibiotics with adequate cerebrospinal fluid (CSF) penetration are administered intravenously before skin incision. Third-generation cephalosporins are our antibiotic of choice in non–penicillin-allergic patients, and vancomycin is used in patients with penicillin allergy. These intravenous antibiotics are maintained for 24 hours postoperatively. Hair is clipped from the postauricular region. The skin is cleaned with povidone iodine (Betadine) and an iodine-impregnated adhesive drape (Ioban) is placed to cover the ear and postauricular scalp. Facial nerve monitoring is performed by a dedicated neurophysiologist, who monitors four channels throughout the procedure. Intraoperative auditory brainstem response monitoring is not performed for a translabyrinthine approach. The lower abdomen is also prepared and draped with Ioban to allow for the harvesting of abdominal fat; the navel and anterior superior iliac spine are prepared in the field for orientation.

Lidocaine 1% with epinephrine 1:100,000 is injected into the postauricular region. The incision is performed about two fingerbreadths, or 2 to 3 cm, posterior to the postauricular sulcus. The incision is C-shaped, curving anteriorly in both its superior and inferior extents to allow anterior retraction of the pinna and adequate exposure of deep structures within the craniotomy. The posterior aspect of the C-shaped incision allows for exposure of the cortex posterior to the sigmoid sinus. A scalp flap just superficial to the temporalis fascia and mastoid periosteum is developed anterior and posterior to the skin incision.

The incision through the next layer is brought down to the bone and is typically staggered either anterior or posterior to the skin incision to improve wound strength and decrease the risk of CSF leak through the wound. Subperiosteal flaps are created and elevated to expose the entire mastoid cortex. Care must be taken not to tear the skin of the external auditory canal. The soft tissue flaps are held forward with retention sutures, and self-retaining retractors are placed to expose the mastoid and cranium for bony dissection. To decrease the risk of pressure necrosis on the pinna, wet surgical gauze is placed as padding between the posterior aspect of the pinna and the retraction sutures and retractors. The temporalis muscle and, if desired, fascia are harvested for packing of the eustachian tube and epitympanic space.

A complete mastoidectomy is performed with a high-speed drill with various sizes of cutting and diamond burrs and a suction-irrigation system. It is our practice to perform this using a draped surgical microscope. Removing bone up to 2 cm posterior to the sigmoid sinus is crucial for adequate exposure of the dura of the posterior cranial fossa and to allow for gentle sigmoid compression if needed. Venous drainage should be preserved when possible. The Bill island, a small island of bone named for William Hitselberger, may be left over the otherwise uncovered sigmoid sinus ( Fig. 44.8 ), or the sigmoid sinus may be completely decompressed. The Bill island can protect the sigmoid sinus from the shaft of the burr as the drilling proceeds medially to remove the labyrinth, but injudicious manipulation of a sigmoid sinus with the Bill island present can lead to laceration of the sigmoid sinus. When bringing instruments in and out of the field, great care should be taken to avoid injury to the delicate outer layer of the sigmoid sinus. Mastoid emissary veins are occluded with bone wax or coagulated with bipolar cautery well away from their entry into the sigmoid sinus. Coagulation and ligation of these bridging veins allow for increased exposure and easier compression of the sigmoid and posterior fossa dura.

The dissection continues with the removal of all bone covering the posterior fossa dura medial to the sigmoid sinus and down to the labyrinth. It is important to remove all bone in the sinodural angle in addition to the bone over the middle fossa dura adjacent to the angle. In larger tumors or contracted mastoids, 2 to 3 cm of bone should be removed from the temporal squama, allowing for more adequate compression and, ultimately, better exposure during tumor resection. The lateral bony ledges of the temporal squama should not restrict the placement of instruments; rather, the temporal lobe and dura should be the limiting factor. In general, much of the lateral bone work is completed before beginning the labyrinthectomy; this facilitates exposure of the deep structures. However, some surgeons advocate for leaving a thin plate of bone over the middle and posterior fossa surfaces to allow for natural retraction as drilling proceeds more medially. These thin plates of bone can then be removed rapidly after medial exposure is accomplished and the CSF space is decompressed.

After a complete mastoidectomy is performed and the bone is removed from the posterior fossa dura, sigmoid sinus, and middle fossa dura, the deepest point of dissection shifts to the labyrinth. Labyrinthectomy may be accomplished in any order, but often begins with the removal of the lateral semicircular canal, extending posteriorly and inferiorly to the posterior canal, and finally medially to the superior canal. Alternatively, labyrinthectomy can start at the sinodural angle, focusing on the posterosuperior aspect of the labyrinth and proceeding anteriorly. If the lateral canal is addressed first, the labyrinthine bone is removed until the ampullated end of the canal is drilled ( Fig. 44.9 ). The posterior canal is then drilled, with its ampulla as the landmark for the inferior border of the IAC. The inferior extent of bony removal is the jugular bulb or cochlear aqueduct, whichever lies more superior; both can be quite variable in terms of their positions relative to the IAC and may be encountered even as the posterior canal is drilled away. As the posterior semicircular canal is opened inferiorly and then medially, the vestibule is reached. While drilling the ampulla of the posterior canal, care must be taken as the second genu and vertical segment of the facial nerve lie just lateral to the vestibule in this region. Further drilling of bone inferior to the posterior canal is necessary for full exposure, and can be performed at this time. This drilling often exposes the endolymphatic duct and sac, and the duct is often transected during drilling.

Superiorly, the common crus is noted and drilled, leading to the superior canal. The subarcuate artery is often encountered running through the bone within the arch of the superior semicircular canal and serves as a landmark for the superior aspect of the IAC. Although the subarcuate artery may yield bothersome bleeding, occasionally enough to obscure the surgical view, continued drilling in the medial direction usually leads to obliteration of the artery and abatement of bleeding.

The labyrinthectomy is completed as the superior canal is opened toward its ampullated end, leading to the vestibule. The ampulla of the superior canal identifies the area where the superior vestibular nerve exits the lateral end of the IAC and is in close proximity to the labyrinthine segment of the facial nerve. In similar fashion, the singular nerve exits the IAC at the posterior semicircular canal ampulla, and the inferior vestibular nerve exits the IAC at the saccule and the spherical recess. The identification of these structures helps delineate the superior and inferior extent of the IAC. At this point, the dura of the posterior fossa is nearly completely exposed ( Fig. 44.10 ).

One may identify the mastoid segment of the facial nerve after the posterior semicircular canal has been exenterated using the side, rather than the tip, of the diamond burr to remove bone from the posterior aspect of the nerve. However, some surgeons advocate for identification of the facial nerve in its vertical segment before labyrinthectomy. Slow, long strokes of a diamond burr in the direction of the vertical segment of facial nerve with copious irrigation and moderate magnification are required during this dissection to minimize the chance of injury to the facial nerve. The vertical segment of the facial nerve serves as the anterior limit of bony dissection at this level, and it is important to remove as much bone as possible from the posterior aspect of the nerve to maximize exposure for tumor dissection.

After labyrinthectomy and positive identification of the facial nerve, the IAC is identified. A fenestrated Brackmann suction-irrigator is often used at this point. Broad strokes within the petrous bone with a diamond burr allow for exposure of the IAC, which is often noticed as a faint pink structure running parallel to the external auditory canal. After the IAC is positively identified, troughs superior and inferior to the IAC are drilled, exposing at least 180, and preferably 270, degrees of IAC dura.

Inferior trough drilling is carried out inferiorly until the jugular bulb is identified and anteriorly until the cochlear aqueduct is broached. The cochlear aqueduct enters the posterior fossa directly inferior to the midportion of the IAC, superior to the jugular bulb ( Fig. 44.11 ). It can be indistinct in certain patients, particularly when the tumor is large. It identifies the location of the neural compartment of the jugular foramen anterior to the jugular bulb. It is important to note that a jugular bulb that lies in close proximity to the cochlear aqueduct may preclude adequate exposure of the cochlear aqueduct when drilling in this area. Avoidance of further dissection anterior and deep to the cochlear aqueduct allows for preservation of CN IX, X, and XI. Once the cochlear aqueduct is identified, the bone between the jugular bulb and the inferior aspect of the IAC, along the posterior fossa dura, should be removed anteriorly to the plane of the cochlear aqueduct. This provides the greatest amount of exposure of the inferior pole of the tumor. In a well-aerated mastoid, extended length burrs, if available, may facilitate drilling of the inferior trough. All the bone along the inferior aspect of the IAC is removed.

Once the cochlear aqueduct is broached, CSF egress is often noted. If the aqueduct is identified but has not been opened, teasing the dura away with a Rosen needle can lead to egress of CSF. The release of CSF at this point allows for decompression of the middle fossa, posterior fossa, and IAC, facilitating further drilling, particularly of the superior trough. As more CSF is released, the natural dural pulsations of the middle and posterior fossae are amplified.

With the inferior trough drilled to expose the jugular bulb and cochlear aqueduct, and the inferior aspect of the IAC exposed, attention is turned to the superior trough. Drilling superiorly requires significant care to ensure that the dura along the superior aspect of the IAC is not violated, as the facial nerve may run adjacent to this dura. This drilling is carried out from a posterior to anterior fashion until the remnant of the vestibule and ampullated end of the superior semicircular canal are reached. The facial nerve stimulator may be used to probe the dura around the IAC during bone dissection to help identify the expected location of the facial nerve. The surgeon must be careful not to allow the burr to drop or spin into the canal and possibly injure the nerve. As with the inferior trough, all of the bone must be removed from the superior aspect of the IAC to allow access to the superior surface of the tumor. Drilling further laterally, the labyrinthine segment of the facial nerve can be identified, which further confirms the location of the fundus of the IAC. However, the labyrinthine segment is not routinely decompressed.

With superior and inferior troughs drilled, gentle drilling is then performed to ensure that all bone along the posterior aspect of the IAC is removed. In addition, if not already performed, the angles of the petrous bone superior and inferior to the IAC at the porus acusticus are drilled deeply with a small diamond burr to ensure adequate mobility of the superior and inferior dural flaps. Inadequate drilling in these two angles significantly impairs intradural visualization of the tumor and mobility for microdissection.

With the drilling completed, the middle ear is addressed. The incus is removed and the facial recess is optionally drilled for maximum exposure of the eustachian tube. The tensor tympani tendon is sectioned with Bellucci scissors. Small pieces of bone wax pressed onto woven oxidized regenerated cellulose (Surgicel Nu-Knit) are introduced using a gimmick elevator, alternating with small pieces of muscle, to obliterate the eustachian tube. Occasionally, fascia is placed in the eustachian tube before this packing is performed. Alternatively, if desired, the incus may also be used to obliterate the eustachian tube.

Remnant muscle is used to fill the middle ear space in its entirety, with care taken to pack the inferior aspect of the middle ear and hypotympanic air cell tracts in addition to the mesotympanum. A broad, flat disc of bone wax is then placed to isolate the epitympanum from the mastoidectomy and craniotomy cavity. Some surgeons advocate for no middle ear packing, instead walling off the epitympanum from the mastoidectomy and craniotomy cavity with fascia, bone wax, or both, and leaving the eustachian tube open. Yet other surgeons pack the eustachian tube without removing the incus, approaching the middle ear from its superior aspect and sectioning the tensor tympani tendon; this is typically only possible if enough middle fossa decompression has been performed. Bone wax is widely placed throughout the remnant mastoid air cells, including at the mastoid tip, to minimize the risk of CSF egress through these air cells and the hypotympanum.

Once the middle ear has been addressed, the facial nerve is identified as it exits the lateral end of the IAC at the vertical crest of bone (Bill’s bar). A sharp 3-mm hook is passed carefully along the inside of the superior distal IAC until the Bill’s bar is palpated ( Fig. 44.12 ). It is not unusual for the facial nerve monitor to sound a warning as the hook passes along the nerve at the proximal portion of the fallopian canal. The hook can then be reflected posteriorly to avulse the superior vestibular nerve, hence identifying the most lateral extent of the plane between the tumor and facial nerve.

All of the dissection so far has been extradural, and morbidity should be minimal. The dura of the posterior fossa is now opened with a microscopic scalpel and/or sharp scissors. The length of the incision depends on the size of the tumor. For smaller tumors and nerve sections, the incision is made close to the IAC. For larger tumors, it is initiated closer to the sigmoid sinus. The incision extends to the IAC and may curve superiorly and inferiorly around the porus acusticus, and additional relaxing incisions may be performed as necessary. The surgeon must take care to avoid blood vessels on the surface of the tumor and adjacent to the dura. Posteriorly, the petrosal vein lies close to the dura. The IAC is opened over the inferior vestibular nerve and reflected superiorly to avoid injury to the facial nerve. Cottonoids are placed posteriorly between the tumor and cerebellum. It is important to develop this plane accurately because doing so separates the major vessels of the CPA from the tumor. During this phase of the surgery, the use of a fenestrated suction tip helps avoid injury to the surrounding structures.

With larger tumors, debulking is often accomplished with an ultrasonic surgical aspirator ( Fig. 44.13 ). The surface of the tumor is carefully inspected first to identify the nerves, because the facial nerve very occasionally passes posterior to the tumor. The tumor capsule is incised and the aspirator inserted to begin the intracapsular removal of the bulk of the tumor. Excessive manipulation of the tumor must be avoided to prevent traction of the facial nerve. The capsule of the tumor is then gradually collapsed toward its center, facilitating its dissection from the CPA and facial nerve.

The tumor is followed medially to the brainstem. The plane between the tumor and the brainstem is developed with sharp and blunt dissection. Cottonoids are placed between the brainstem and the tumor to protect the underlying structures. At this point, attempts are made to identify the facial nerve superiorly; it usually lies anterior to the tumor but may occasionally be draped over the superior aspect. CN IX is identified inferiorly; in large tumors, CN IX, X, and XI may be stretched over the inferior surface of the tumor. Manipulation of the tumor may cause a change in the heart rate or blood pressure, particularly as CN V is approached near the brainstem.

The vestibular nerve and tumor are separated from the facial nerve in the IAC and carefully dissected medially to the porus acusticus and into the CPA ( Fig. 44.14 ). Some tumors involve the lateral end of the IAC, complicating identification of the facial nerve in the canal. In these patients, it becomes imperative to remove bone from the proximal fallopian canal to allow positive identification of the facial nerve where it is not involved with the tumor. This maneuver greatly reduces the risk of injury to the facial nerve.

It is often necessary to identify the facial nerve at the brainstem and separate the tumor from the facial nerve from medial to lateral. Careful, patient dissection often results in complete separation of the facial nerve from the tumor as the tumor is dissected out of the posterior fossa.

As the tumor is dissected free, bleeding is controlled with bipolar cautery. Only the vessels that enter the tumor capsule are coagulated. The other vessels are freed from the tumor capsule. A small blood vessel may accompany CN VIII. As the nerve is cut, control of bleeding with bipolar cautery may be necessary. Careful control of bleeding produces minimal blood loss. With an average blood loss of between 200 and 400 mL, patients rarely require transfusions.

Closure involves the use of abdominal fat and partial or complete closure of the dura. Fat is obtained from the lower abdomen through a small transverse incision. Hemostasis with electrocautery and obliteration of dead space with deep sutures help reduce the risk of an abdominal wall hematoma. The wound is closed in layers, typically with absorbable sutures only, and a Penrose drain may be inserted. The fat is cut into strips of various sizes in preparation for packing the craniotomy site.

The dura is closed with sutures along the posterior fossa incision; complete approximation of the dural edges is rarely possible. This closure may be reinforced with temporalis fascia or DuraGen dural graft matrix, if desired. Strips of abdominal fat are then inserted through any remaining gaps in the dura. Additional fat is used to pack the mastoid cavity in its entirety.

A titanium mesh cranioplasty plate is then placed over the fat and secured to the cortex with self-drilling screws. The wound is closed in layers with absorbable sutures, and the skin is typically sutured with nylon suture. Mastoid and abdominal dressings are applied.

Postoperative Care

If placed, the abdominal drain is removed on postoperative day 1. The urinary catheter is removed on postoperative day 1 or 2. The mastoid dressing remains for 3 days and scalp sutures are removed between 1 and 2 weeks postoperatively.

The patient usually stays in the intensive care unit for 1 day after surgery and in the hospital for 2 to 4 days thereafter. Progressive ambulation begins the day after surgery. The patient sits on the side of the bed, stands by the bed, and is encouraged to sit in a chair with the assistance of physical and/or occupational therapists. Activity is gradually increased. Early ambulation helps reduce complications, including deep venous thrombosis, and speeds recovery.

The vital signs and temperature are monitored frequently during the first 2 to 3 days after surgery. In addition, the nurses are instructed to observe the patient for possible CSF leak and neurological changes. Rhinorrhea or egress of fluid along the scalp surgical site are investigated immediately.

Complications