Translabyrinthine Approach

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Chapter 49 Translabyrinthine Approach

image Videos corresponding to this chapter are available online at www.expertconsult.com.

House1,2 first began removing acoustic tumors through the translabyrinthine approach in 1960. Physicians at the House Ear Clinic have been using this approach for most larger acoustic tumor removals. Since 1983, we have performed more than 2700 tumors using this approach. The translabyrinthine procedure allows excellent access to the cerebellopontine angle (CPA) and exposure of the entire facial nerve from the brainstem to the stylomastoid foramen. The approach is extradural through most of the surgery. The primary disadvantage is sacrifice of hearing.

Regardless of the size of the tumor, the translabyrinthine approach is ideal for acoustic neuromas when the hearing is poor. It is also ideal for facial nerve lesions, such as neuromas; trauma owing to operative injury; or head trauma. The approach has many advantages. It is the most direct route to the structures of the CPA (Figs. 49-1 and 49-2).3 The lateral end of the internal auditory canal (IAC) can be dissected to ensure complete tumor removal from this area, and to allow consistent anatomic identification of the facial nerve.4 The approach for facial nerve lesions offers exposure of the mastoid, tympanic, and labyrinthine portions of the facial nerve. Identification of the facial nerve in the mastoid is facilitated after removal of the semicircular canals (Fig. 49-3). Because the labyrinth has been removed, the labyrinthine segment of the nerve is readily followed into the IAC. The IAC and CPA can be exposed widely if the lesion involves the facial nerve in the posterior fossa. The facial nerve is readily accessible from the brainstem to the stylomastoid foramen and beyond into the parotid gland. In addition to vestibular schwannoma removal, the translabyrinthine craniotomy approach is used for other tumors (e.g., meningiomas, cholesteatomas involving the petrous bone and posterior fossa, cholesterol granulomas, glomus tumors, and adenomas), for decompression of the facial nerve, and for repair of the facial nerve by either direct end-to-end anastomoses or nerve grafting (Fig. 49-4).

For tumors involving the area anterior to the internal auditory nerve at the clivus, the standard translabyrinthine approach is modified to allow anterior exposure (Fig. 49-5). The facial nerve is removed from the fallopian canal in the tympanic and mastoid segments and is reflected anteriorly. The cochlea is removed to provide excellent exposure anterior to the IAC (see Chapter 52).

A major advantage of the translabyrinthine approach is that the patient is in the supine position with the head turned away from the surgeon (Figs. 49-6 and 49-7). This position eliminates some of the possible complications of the classic suboccipital approach to the CPA in which the sitting position is used, such as risks of air embolism and injury to the cerebellum from retraction. Quadriplegia has been reported in association with the sitting position.5 The translabyrinthine approach poses diminished danger of air embolism and requires less retraction of the cerebellum. Much of the surgery is extradural, lessening the chances of injury to the brain. The extradural dissection also greatly decreases the seeding of bone dust into the subarachnoid space.

SURGICAL PROCEDURE

The procedure is performed with general endotracheal anesthesia with inhalation agents. Muscle relaxants are used only for the induction because they may interfere with facial nerve monitoring. An orogastric tube and Foley catheter are placed. Antibiotics with good cerebrospinal fluid (CSF) penetration are given intravenously before skin incision. Cefuroxime is our antibiotic of choice in non–penicillin-allergic patients, whereas vancomycin is used in patients with penicillin allergy. These intravenous antibiotics are maintained for 24 hours perioperatively. A generous amount of hair is shaved from the postauricular and temporal areas. The skin is cleaned with povidone-iodine (Betadine), and a sheet of Ioban is placed to cover the entire area. Because facial nerve monitoring is routine during all of our translabyrinthine procedures, needle electrodes are inserted into the orbicularis oris muscles before the drape is applied. The lower abdomen is also prepared and draped with Ioban to allow for the harvesting of fat; the navel is prepared in the field for orientation.

Lidocaine 1% (Xylocaine) with epinephrine 1:100,000 is injected into the postauricular region. The epinephrine assists with homeostasis. The incision is performed about 2 to 4 cm posterior to the postauricular sulcus. Generally, the larger the tumor, the more posterior an incision is required, to allow for extended decompression of the dura posterior to the sigmoid sinus. The incision is curved anteriorly to allow anterior retraction of the pinna. The posterior curve of the incision allows exposure of the area posterior to the sigmoid sinus. This exposure is important to allow access to the CPA. 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 decrease risk of CSF wound leak after closure. The Lempert elevator is used to elevate the periosteum off the bone of the mastoid. Soft tissue must be removed from the posterior edge of the external auditory canal to an area far posterior to the sigmoid sinus. Care must be taken not to tear the skin of the external auditory canal; otherwise, CSF otorrhea may develop postoperatively. Self-retaining retractors are placed to expose the mastoid and cranium for extensive bony dissection. At this point, muscle may be harvested for packing of the eustachian tube and epitympanic space. Temporalis fascia may also be taken for support of the dural closure.

A complete mastoidectomy is performed with a high-speed drill with various sizes of cutting and diamond burrs. Removing bone 2 cm posterior to the sigmoid sinus is crucial for adequate exposure of the dura of the posterior cranial fossa. A small island of bone (Bill’s island—named for William F. House, who first suggested it) is left over the otherwise exposed sigmoid sinus (Fig. 49-8). This bony cover protects the sigmoid sinus from the shaft of the burr as the drilling proceeds medially to remove the labyrinth. 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 over the sinal dural angle and a small amount of bone over the middle fossa dura adjacent to the angle. In larger tumors or contracted mastoids, we recommend removal of 2 to 3 cm of bone from temporal squama. We prefer to perform all of the lateral bone work before beginning the labyrinthectomy to obtain better exposure of the deep structures.

After the complete mastoidectomy is performed, and the bone is removed from posterior fossa dura, sigmoid sinus, and some of the middle fossa dura, the deepest point of dissection shifts to the sinal-dural angle. The labyrinthectomy begins with the removal of the lateral semicircular canal and extends posterior to the posterior canal. The bone removal is continued inferior and anterior toward the ampullated end of this canal (Fig. 49-9). The ampulla of the posterior canal is the landmark for the inferior border of the IAC. The inferior extent of bony removal is the jugular bulb. The posterior semicircular canal is opened inferiorly to the vestibule and superiorly to the common crus. The facial nerve is identified in its descending portion in the mastoid and skeletonized to just proximal to the stylomastoid foramen.

We prefer to identify the facial nerve after the posterior semicircular canal has been removed to use the side of the diamond burr rather than the end of it; this helps reduce the possibility of injury to the nerve. The mastoid segment of the facial nerve serves as the anterior limit of dissection, and it is important to remove as much of its overlying bone as possible to maximize exposure for tumor dissection. With this portion of the facial nerve identified, the remainder of the bone of the inferior IAC is removed to the vestibule. After opening the vestibule widely, the removal of the superior portion (nonampullated end) of the posterior canal is carried to the common crus, which is composed of the nonampullated ends of the posterior and superior semicircular canal.

The common crus is opened to the vestibule. The superior canal is now opened and removed to its ampullated end in the vestibule. This portion 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. Similarly, the singular nerve exits the IAC at the posterior semicircular canal ampulla, and the inferior vestibular nerve exits the canal at the saccule and the spherical recess. Identification of these structures delineates the superior and inferior extent of the IAC. As the bone posterior to the IAC is removed, the vestibular aqueduct and the beginning of the endolymphatic sac are removed. An eggshell thickness of bone is left over the dura of the IAC to avoid injury to the underlying structures until all of the bony dissection is completed (Fig. 49-10).

The IAC is not entered at this time because bone must be removed medially to the porus acusticus. The IAC runs deep from the vestibule and away from the surgeon. A great deal of bone must be removed to expose the contents of the IAC and the CPA properly. Bone is removed around the canal superiorly and inferiorly to expose at least 270 degrees in circumference. The inferior limit of bone removal is the cochlear aqueduct and the jugular bulb. The cochlear aqueduct enters the posterior fossa directly inferior to the midportion of the IAC, superior to the jugular bulb (Fig. 49-11).6 It identifies the location of the neural compartment of the jugular foramen anterior to the jugular bulb. By not removing bone from anterior and deep to the cochlear aqueduct, injury to CN IX, X, and XI is avoided. Bone is removed from the inferior portion of the IAC and particularly the inferior lip, affording access to the inferior poll of the tumor in the CPA.

The bone is removed from the superolateral IAC last because of its close proximity to the facial nerve. Bone should be removed from the superior lip of the IAC. This dissection is tedious because the facial nerve often underlies the dura along the anterosuperior aspect of the IAC. The surgeon must be careful not to allow the burr to drop into the canal and possibly injure the nerve. As with the inferior lip, all of the bone must be removed from the superior lip to allow access to the superior pole of the tumor. With the superior lip, the facial nerve may be close to the surface, making this part of the removal laborious.

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