Chapter 49 Translabyrinthine Approach

John W. House, James Lin, Rick A. Friedman, Robert D. Cullen

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House ^1,² 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).

FIGURE 49-1 MR image of large acoustic neuroma, illustrating direct route to cerebellopontine angle through mastoid and labyrinth.

FIGURE 49-2. Postoperative CT scan of patient shown in Figure 49-1. Note extent of removal of bone from mastoid and labyrinth.

FIGURE 49-3. Facial nerve identified in mastoid portion after removal of semicircular canals. Note island of bone over sigmoid sinus.

FIGURE 49-4. Facial nerve graft through translabyrinthine approach. Greater auricular nerve graft has been placed from internal auditory canal (IAC) to proximal mastoid facial nerve.

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).

FIGURE 49-5 Meningioma involving internal auditory canal and extending anterior to clivus can be removed through translabyrinthine/transcochlear approach.

FIGURE 49-6. Patient placed in supine position with head turned away from surgeon. Anesthesiologist is at foot of table.

FIGURE 49-7. Surgeon is seated with operating microscope. Nurse is across table. Facial nerve monitor is at lower left.

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.

PATIENT SELECTION

Tumor size and residual hearing are the principal factors influencing the choice of the translabyrinthine approach. We use the translabyrinthine approach in most cases if the tumor is larger than 2.5 cm in maximal dimension, and in all cases of nonserviceable hearing in the involved ear. When tumors are confined to the IAC in an ear with serviceable hearing, we use the middle cranial fossa approach in an attempt to save hearing. For patients with good hearing and tumors primarily based in the CPA with minimal extension into the IAC, the retrosigmoid approach is chosen.

Our definition of serviceable hearing is a pure tone average threshold better than 50 dB, a speech discrimination score of greater than 50%, or both. This definition is referred to as the 50/50 rule. Exceptions exist if the hearing in the contralateral ear is poor, or if bilateral tumors are present. In such cases, we may attempt tumor removal through the middle fossa approach, even if the tumor extends 1 cm into the CPA. We may use the retrosigmoid approach in an attempt to save hearing if the tumor is smaller than 1.5 to 2 cm and does not extend into the lateral half of the IAC.

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.