Translabyrinthine Approach

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Chapter 49 Translabyrinthine Approach

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

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).

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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).

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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.

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FIGURE 49-8 Mastoidectomy with exposure of sigmoid sinus. Small bony island is left over sinus to protect it from shaft of burr.

FIGURE 49-9. Completed labyrinthectomy with ampullated ends of posterior and superior semicircular canals.

FIGURE 49-10. All bone has been removed, exposing dura of posterior fossa and internal auditory canal (IAC).

FIGURE 49-11. Bone has been removed from internal auditory canal and posterior fossa. Cochlear aqueduct can be seen inferior to internal auditory canal and superior to jugular bulb.

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.

The facial nerve is identified as it exits the lateral end of the IAC at the vertical crest of bone (Bill’s bar) with a sharp 3 mm hook. The facial nerve may be identified further in its proximal labyrinthine segment by additional bone removal. The hook is passed carefully along the inside of the superior distal IAC until Bill’s bar is palpated (Fig. 49-12). 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.

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Figure 49-12 Internal auditory canal (IAC) is skeletonized, and bone is removed to expose 180 to 240 degrees of canal. Facial nerve is identified as it exits IAC at Bill’s bar.

Figure 49-13. House-Urban dissector is used for intracapsular removal of tumor bulk.

Figure 49-14. Vestibular nerve and tumor are separated from facial nerve in internal auditory canal and dissected to porus acusticus and cerebellopontine angle.

All of the dissection so far has been extradural, and morbidity should be minimal. When the facial nerve has been positively identified, the dura of the posterior fossa over the midportion of the IAC is opened with 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 started closer to the sigmoid sinus. The incision extends to the IAC, and then curves superiorly and inferiorly around the porus acusticus. 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 the cerebellum. It is important to develop this plane accurately because doing so separates the major vessels of the CPA from the tumor.

With larger tumors, the size of the tumor is reduced by the use of the House-Urban (Fig. 49-13) or ultrasonic dissector. The surface of the tumor is carefully inspected first to identify nerves. Occasionally, the facial nerve is deflected posterior. The tumor capsule is incised, and the dissector is 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 collapsed toward its center, greatly facilitating its dissection from the CPA. 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 is usually anterior to the tumor, but may be draped over the top of it. 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 pulse rate or blood pressure. During this phase of the tumor removal, use of a fenestrated neurotologic suction tip helps avoid injury to surrounding structures.7

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. 49-14). Some tumors involve the lateral end of the IAC, complicating identification of the facial nerve in the canal. In these cases, bone is removed from the proximal fallopian canal to allow positive identification of the facial nerve where it is not involved with tumor. This maneuver greatly reduces injury to the facial nerve.

It may be necessary to identify the facial nerve at the brainstem and to begin to separate the tumor from the facial nerve medially to laterally. Careful, patient dissection results in complete separation of the facial nerve from the tumor as the tumor is dissected out of the posterior fossa. Continuous intraoperative facial nerve monitoring has greatly facilitated this process. It has been shown that use of scissors to free the nerve carefully from the tumor causes less trauma than the use of blunt dissection to establish this plane.

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 about 250 mL, our patients rarely require transfusions. We offer our patients the opportunity to withdraw 1 to 2 U of their own blood 1 month before the scheduled surgery.

During the drilling, the wound is periodically irrigated with a solution containing bacitracin to reduce the chance of infection. After the drilling has been completed, the bacitracin irrigant is attached to the suction-irrigator and used during the dissection of the tumor. This solution cannot be used during drilling because it tends to produce foam. We have reduced the rate of meningitis in our patients by using the bacitracin irrigation and administering perioperative antibiotics.

Closure involves the use of abdominal fat and, if the opening is large, a partial closure of the dura. Fat is obtained from the lower abdomen through a small transverse incision. The wound is closed in layers with polyglactin 910 (Vicryl) sutures, and a Penrose drain is inserted. Steri-Strips are used to reinforce the skin closure. Obliteration of “dead space” with deep sutures is important in reducing the risk of an abdominal wall hematoma. The fat is cut into strips and soaked in the bacitracin irrigant. The dura is closed with 4-0 silk along the posterior fossa incision. This closure may be reinforced with temporalis fascia or DuraGen dural graft matrix. The strips of fat are inserted through the dural opening and the IAC. These strips are tightly packed into the defect expanding on both sides of the dura to prevent leakage. Muscle is packed into the attic. The incus may be removed to pack the eustachian tube and the middle ear with muscle. The mastoid is also filled with fat.

Since 2003, we have begun performing a cranioplasty with titanium mesh overlying the fat. The wound is closed in layers with 0 chromic and 3-0 Vicryl. Steri-Strips are applied to the scalp incision. A head dressing and abdominal pressure dressings are applied.

Management of the Contracted Mastoid

There are few absolute contraindications to the use of the translabyrinthine approach in acoustic tumor removal. One absolute contraindication is active infection in the affected ear. In addition, there has been controversy regarding the use of this approach in anatomically constricted mastoids. A low-lying tegmen, an anterior sigmoid sinus, and a high jugular bulb are individually or collectively considered contraindications to this approach.

Using several crucial maneuvers, we have never altered our approach to the CPA based on anatomic variations.8 Wide removal of the bone of the temporal squama and presigmoid and postsigmoid posterior fossa dura overcomes the limitations imposed by a low-lying tegmen and anterior-placed sigmoid sinus. For a high jugular bulb, we recommend skeletonization along its anteromedial, medial, and posterior surfaces without compression. This skeletonization, combined with the ability to retract the widely exposed temporal lobe dura superiorly, provides an improved line of sight in the deep field of the CPA.

POSTOPERATIVE CARE

The abdominal drain is removed the following day. We no longer use a nasogastric tube and remove the orogastric tube at the time of extubation. In addition, the urinary catheter inserted at the beginning of the procedure is removed on postoperative day 1 or 2. The head dressing remains for 3 days, and the Steri-Strips remain for 1 week.

The patient stays in the intensive care unit usually for 1 day after surgery and stays in the hospital for 3 to 5 days. 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. We believe that early ambulation helps reduce complications and speeds recovery.

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 neurologic changes. If the patient has drainage from the nose, the nurses test it for glucose and alert the physician.

COMPLICATIONS

We performed a review of complications and facial nerve outcomes on 512 consecutive patients undergoing translabyrinthine craniotomy for unilateral, sporadic acoustic neuromas. In this section, we quantify many complication rates based on this review.

Facial Nerve

Facial nerve weakness or paralysis is not a complication, but a risk that cannot be entirely eliminated. The primary concern of most patients undergoing tumor removal is the ultimate facial nerve result. Continuous intraoperative facial nerve monitoring and meticulous dissection of the tumor from the facial nerve usually yield good facial nerve results. Eighty percent of our tumor patients are House-Brackmann grade I or II. Only about 5% of patients have a grade VI outcome. If the facial nerve is intimately involved with the tumor, or if the tumor is a facial neuroma, preservation of the anatomic continuity of the facial nerve may be impossible. We believe that repairing the nerve during the initial surgery is important. With the translabyrinthine approach, the nerve is identified in the labyrinthine segment, and exposed in the tympanic and mastoid portions, and either the nerve is rerouted or an interposed graft is sutured to the proximal and distal portions of the nerve. We currently use NeuraGen tubules to aid in our nerve anastomoses. Suturing the nerve in the CPA is difficult; if this is possible, usually only one suture can be placed. The result allows for normal facial tone and good emotional and voluntary motion. Mass action or synkinesis is always present. Grade III is the best result that can be expected.

When a primary anastomosis or nerve graft is impossible, or if facial nerve function does not return after 1 year, we perform a facial-hypoglossal (CN VII-XII) anastomosis. It gives good resting tone, fair voluntary motion with synkinesis, and usually a grade IV recovery. If the nerve has been paralyzed for several years, and the patient has poor tone, we combine the CN VII-XII anastomosis with a temporalis muscle transposition to the orbicularis oris. This procedure gives an immediate cosmetic improvement to the face at rest and gradual return of voluntary motion over 6 to 12 months.

Our review of patients from 2000 to 2004 revealed anatomic preservation of the facial nerve in 97.5%. Twelve of the 512 patients had a severed facial nerve; the average tumor size in those patients was 3.7 cm. Six of these patients underwent primary anastomosis of the nerve, whereas three patients underwent greater auricular nerve grafting at the time of tumor removal. Of the six patients who underwent primary anastomosis, five obtained a House-Brackmann grade of III or IV, whereas the remaining one patient retained a grade of VI. Only one of the patients who underwent cable-grafting obtained a House-Brackmann grade of III, whereas one remained completely paralyzed, and the third was lost to follow-up. Of the remaining three patients who did not undergo immediate facial nerve reconstruction, two underwent hypoglossal-facial anastomosis in the early postoperative period, and one elected for no reconstruction. One patient who underwent hypoglossal-facial anastomosis achieved a grade IV, and the other patient was lost to follow-up.

Bleeding

The most dramatic and potentially fatal complication is an early postoperative hematoma in the CPA. This complication is manifested by signs of increased central nervous system pressure, such as loss of consciousness and nonreactive pupils. It is managed by immediate opening of the wound and removal of the fat while the patient is in the intensive care unit. An advantage of the translabyrinthine approach is that the angle may be rapidly decompressed for this uncommon complication. The patient is taken back to surgery, and the bleeder is identified and controlled. In the 512 patients reviewed from 2000-2004, there were four subdural hematomas (0.8%) and three CPA clots (0.6%).

Bleeding is part of the procedure. The most dramatic bleeding occurs if the sigmoid sinus is entered. Opening of the sinus produces profuse bleeding; because the bleeding is venous, it is easy to stop with light pressure over the sinus. Bleeding is controlled with extraluminal packing with absorbable knitted fabric (Surgicel), thrombin-soaked absorbable gelatin sponge (Gelfoam), or microfibrillar collagen (Avitene). Great care is taken to prevent the packing from entering the lumen of the sinus. If this occurs, the packing then enters the pulmonary circulation, resulting in a pulmonary embolism.

If the lumen of the jugular bulb is opened, the jugular vein is ligated in the neck, and the bulb is packed to control bleeding. This complication is extremely rare.

Arterial bleeding is seldom a problem. Great care is taken to identify and avoid the anterior cerebellar artery because thrombosis or injury to this artery can be fatal. This injury is extremely rare with modern microsurgical techniques.

Cerebrospinal Fluid Leak

Before 1974, we used temporalis muscle to close the dura, and our incidence of CSF leak was 20%.2 Since we began using abdominal fat instead, this incidence has been reduced to less than 7% in translabyrinthine acoustic tumor removals.9 Since we began using titanium mesh for cranioplasty in mid-2003, our incidence of CSF rhinorrhea has been reduced to 3.3%.

Most leaks can be stopped with a pressure head dressing and bed rest with the patient’s head elevated. Typically, we leave the dressing in place for 3 days. If the CSF leak continues with the dressing in place, or if it recurs when the dressing is removed, a lumbar spinal drain is inserted, and the patient is placed at bed rest for 3 to 4 days. This conservative management controls CSF rhinorrhea in two thirds of patients. In the remaining one third of cases with persistent leak through the nose, the patient is taken back to surgery, and the wound is reopened. The ear canal is oversewn, and the epithelium medial to the overclosure is removed completely followed by wide canalplasty and packing of the eustachian tube. In cases of wound leak, the wound may be oversewn in addition to pressure dressing. If this fails, the wound is reopened and reclosed in layers occasionally with additional fat placement. A wound exploration typically requires harvesting of additional fat.

Meningitis

The incidence of meningitis has been declining with the use of bacitracin irrigation and reduced surgical time. The review of 512 patients operated on from 2000-2004 revealed postoperative meningitis in 3 patients (0.6%). A spinal tap is performed when the patient has a fever, elevated white blood cell count, and a stiff neck. If the CSF white blood cell count is greater than 100 wbc’s/ml, we use high doses of intravenous antibiotics. In addition to the cell count, the spinal fluid is cultured for anaerobic and aerobic bacteria, and total protein and glucose levels are measured. In typical patients with meningitis, the CSF protein level is elevated, and the glucose level is reduced. Antibiotics are altered if the cultures so indicate. The usual response to treatment is reduction in fever, decrease in white blood cell count, and reduction in headache. The spinal tap is repeated on the 4th or 5th treatment day. Treatment is continued until the CSF white blood cell count is less than 100 wbc’s/ml, and the CSF is composed mostly of monocytes.

RESULTS

Greater than 5000 acoustic neuromas have been removed at the House Ear Clinic. With experience and refinements of technique, the results have progressively improved. A review from our database of acoustic tumor cases provides data from 1302 patients who underwent a translabyrinthine acoustic tumor removal between 1982 and 1993. The mean age of patients was 50 years; 46% were men, and 54% were women. Tumor size ranged from 0.5 to 6.5 cm, with a mean size of 2.4 cm. Operating time averaged 3.3 hours. Three (0.2%) deaths occurred in this series.

Previously acquired data on long-term (6 month) facial nerve function as determined by the House-Brackmann scale were available on 889 cases, with a mean follow-up time of 2.1 years. Of these, 58.2% had a grade I function; 12.6%, grade II; 13.2%, grade III; 7.8%, grade IV; 3.3%, grade V; and 5.1%, grade VI. For cases undergoing surgery since the advent of facial nerve monitoring in 1988 and with at least 1 year follow-up, 59% of the 312 patients had grade I facial nerve function; 15.4%, grade II; 9.3%, grade III; 7.7%, grade IV; 4.2%, grade V; and 4.5%, grade VI.

In our review of 512 patients who underwent translabyrinthine removal of unilateral, sporadic acoustic neuromas between 2000-2004, the mean age was 49 years; 49% were men, and 51% were women. The average tumor size was 2.4 cm with a range of 0.5 to 5 cm. Of these 512 patients, 392 (77%) were examined at 1 year or returned a validated facial nerve questionnaire. Of these patients, 67.6% had grade I facial nerve function at 1 year; 13.3%, grade II; 8.2%, grade III; 7.1%, grade IV; 0.8%, grade V; and 3.1%, grade VI. This study also detected a decrease in facial outcome with larger acoustic neuromas, particularly greater than 3.5 cm in size. For these patients with “giant” vestibular schwannomas, a House-Brackmann grade of I or II at 1 year postoperatively could be achieved in only about 50%.

Postoperative Follow-up

In our experience, vestibular schwannomas rarely recur after translabyrinthine removal. Our recurrence rate for unilateral tumors removed through the translabyrinthine approach treated between 1961 and 1995 was 0.3%.10 The average interval to recurrence was 10 years. Based on these findings, we have recommended a single gadolinium-enhanced magnetic resonance imaging (MRI) study 5 years postoperatively.

SUMMARY

The translabyrinthine approach to tumors involving the temporal bone and CPA offers excellent and safe exposure. We have used this approach for more than 40 years to remove greater than 3000 tumors. Our experience has yielded many refinements of the original procedure, and we continue to seek improvements to reduce the morbidity. Mortality now approaches 0%. We continue to believe that the translabyrinthine approach is the approach of choice for most large acoustic neuromas and all tumors when preoperative hearing is poor or unlikely to be preserved.

EDITORIAL COMMENT

Neurotologic approaches to cranial base tumors are a team endeavor in which the neurotologist and the neurosurgeon must be fully familiar with the other members’ techniques. A frequent comment by former clinical fellows after completing training at the House Ear Clinic is that differences exist in the removal of acoustic tumors, especially larger tumors, between neurosurgeons familiar with the translabyrinthine approach and surgeons who are adjusting to this anterior exposure.

The editors have invited William E. Hitselberger and Marc Schwartz to provide the following neurosurgical perspective on tumor removal through the translabyrinthine approach. With a personal experience of more than 6000 acoustic tumors removed with this technique, Dr. Hitselberger has insights that are particularly relevant for neurotologic teams in the early phases of collaboration.

NEUROSURGICAL TECHNIQUES IN ACOUSTIC TUMOR SURGERY

The strategy for the removal of an acoustic neuroma depends on whether the tumor is large or small. The techniques used in each of these situations, although similar, vary enough in important details that differences are described and emphasized here. The slight variation in technique is necessary because of the variation in the difficulty in preserving neurologic structures in each of these situations. Although variations exist in the technique used, the size of an acoustic neuroma is not a limiting factor in the choice of the translabyrinthine approach. In 30 years and more than 3000 acoustic neuromas, I Units have never found a tumor that was too large to take out through this approach.

Removal of Small Acoustic Tumor

In the removal of a small or a large acoustic neuroma through the translabyrinthine approach, the importance of exposure cannot be overemphasized. Adequate exposure of the tumor is the sine qua non of the procedure. Bone removal should include the bone over the middle fossa dura, the sigmoid sinus should be skeletonized so that it can be easily compressed, and bone removal should extend down to the jugular bulb. The posterior fossa dura should be cleared and easily retractable. The IAC should be skeletonized for at least 180 degrees from the posterior presentation. The labyrinthine portion of the facial nerve should be identified and uncovered.

During the drill-out of the IAC, the rotation of the drill is important because the facial nerve is near the surface of the canal and exposed to a greater degree when the tumor is small than when it is larger. In a larger tumor, the tumor usually acts as a buffer between the facial nerve and the drill. If the drill is rotating into the IAC, the bit can catch on the bony edge, and the fast-moving burr may injure the nerve.

The dura should be opened over the end of the IAC, and the facial nerve should be positively identified visually and with the facial nerve stimulator. The nerve at the end of the canal is anterior and superior to the superior vestibular nerve. The plane between these nerves can be readily developed if the bony dissection of the IAC has been completed at its lateral extent. After division of the facial-vestibular anastomosis, the plane between the superior vestibular nerve and the facial nerve leads the surgeon into the plane between the facial nerve and the tumor. This latter plane is carried medially down to the porus acusticus.

At this point, the nerve may be bound down in adhesions and tumor. High magnification (×40) may be necessary to keep the facial nerve plane delineated from the adhesions and tumor. Facial nerve dissection may be facilitated if the nerve is identified at the brainstem. The facial nerve arises anterior and medial to the cochleovestibular nerve. The anterior inferior cerebellar artery usually crosses between CN VII and VIII near the brainstem. The facial nerve is generally quite distinct and has a whiter color than CN VIII because of a heavier concentration of myelin.

Developing the facial nerve plane from medial to lateral leads to the medial extent of the tumor. Sometimes, the tumor “shells out” from the bed of CN VIII. More important, the continuing plane of the facial nerve can be developed back to the porus. The facial nerve plane is developed from the medial brainstem side and the lateral IAC side. Usually, when the facial nerve has been cleared from the surface, the tumor can be easily delivered. The importance of facial nerve dissection lies in the preservation of the facial nerve and in the delineation and ultimate removal of the tumor.

Blood vessels lying on the surface of the tumor should be dissected free without coagulation, if possible. This method preserves the blood supply to the adjacent brainstem and the facial nerve. A very fine bayonet forceps and scissors can be used to free the vessels from the surface of the tumor without coagulation.

After the tumor has been removed, the tumor bed is carefully evaluated for any small bleeders. Bipolar coagulation set at a low level and oxidized cellulose are generally sufficient to treat such bleeding.

Removal of Large Acoustic Neuroma

The bony removal for a large acoustic neuroma, although similar to that for a small neuroma, varies enough that important variations should be mentioned. Wide, adequate exposure is the key, and is accomplished by thorough removal of bone over the middle fossa, posterior fossa, and IAC. Additionally, bone should be removed for at least 1 cm posterior to the sigmoid sinus over the subocciput. Even with a contracted mastoid, adequate exposure can be obtained for removal of any-sized neuroma if the bone removal has been exploited to the maximum. Another key for removal of a large acoustic neuroma from the cerebellopontine angle is extradural retraction. If the bone removal is inadequate, this retraction against the residual bone is impossible. Bony overhangs at the external genu of the facial nerve and the overhang of the posterior external auditory canal should also be removed.

The facial nerve is identified at the end of the IAC, as in a smaller tumor. This dissection can be more difficult if the end of the canal is distorted by an impacted tumor, which is occasionally invasive into the otic capsule. After identification of the facial nerve at the end of the IAC, the dura is opened over the posterior fossa anterior to the sigmoid sinus. The tumor may bulge into the dural opening. A rapid decompression of the interior of the tumor can be carried out with the House-Urban rotary dissector, starting from the posterosuperior compartment of the tumor adjacent to the tentorium. At this point, who am not concerned with moderate venous bleeding; rather, the goal is rapid debulking of the tumor. Coagulating small bleeding vessels is unnecessary; these stop bleeding when the tumor is removed.

After the tumor has been decompressed, the cisterna lateralis is emptied of CSF. This step adds further to the available space and allows greater room for retraction. The position of the facial nerve should be ascertained with the facial nerve monitor before radical resection of the tumor is undertaken. Usually, the facial nerve is anterior to the tumor, but it may be superiorly placed. Rarely, it can even be in a posterior position, which is an especially dangerous position for the facial nerve because the surgeon must operate past the facial nerve to remove the tumor, subjecting it to increased risk.

After decompression of the tumor, the facial nerve dissection can be started. High magnification (×40) and sharp dissection are best suited for this process. The nerve is usually stretched and attenuated by the tumor. The facial nerve monitor is invaluable in delineating the nerve when it has been thinned out over the surface of the tumor. The facial nerve dissection proceeds from the medial and lateral ends of the tumor.

Vascular radicles are removed from the surface of the tumor, avoiding coagulation whenever possible. A large branch of the petrosal vein is usually positioned on the posterior medial surface of the tumor and should be sought after, identified, and dealt with, either with preservation, if easily accomplished, or with bipolar coagulation.

After tumor removal, all bleeding points in the tumor bed should be controlled with bipolar coagulation. The smallest bipolar coagulating tips possible should be used to avoid excessive heat and facial nerve injury.

REFERENCES

1. House W.F. Acoustic neuroma [Monograph]. Arch Otolaryngol Head Neck Surg. 1964;80:598-757.

2. House W.F. Translabyrinthine approach. In: House W.F., Luetje C.M., editors. Acoustic Tumors Management. Baltimore: University Park Press; 1979:43-87. vol. 2

3. Brackmann D.E. Translabyrinthine removal of acoustic neurinomas. In: Brackmann D.E., editor. Neurological Surgery of the Ear and Skull Base. New York: Raven Press; 1982:235-241.

4. House W.F., Leutje C.M., editors. Acoustic Tumors Management. Baltimore: University Park Press, 1979. vol. 1

5. Hitselberger W.E., House W.F.. A warning regarding the sitting position for acoustic tumor surgery. [Editorial]. Arch Otolaryngol Head Neck Surg. 106, 1980, 69.

6. Brackmann D.E., Green D. Translabyrinthine approach for acoustic tumor removal. Otolaryngol Clin North Am. 1992;25:311-329.

7. Brackmann D.E. Fenestrated suction for neuro-otologic surgery. Trans Am Acad Ophthalmol Otolaryngol. 1977;84:975.

8. Friedman R.A., Brackmann D.E., van Loveren H.R., Hitselberger W.E. Management of the contracted mastoid in the translabyrinthine removal of acoustic neuroma. Arch Otolaryngol Head Neck Surg. 1997;123:342-344.

9. Rodgers G.K., Luxford W.M. Factors affecting the development of cerebrospinal fluid leak and meningitis after translabyrinthine acoustic tumor surgery. Laryngoscope. 1993;103:959-962.

10. Shelton C. Unilateral acoustic tumors: How often do they recur after translabyrinthine removal? Laryngoscope. 1995;105:958-966.

11. Brackmann D.E., Cullen R.D., Fisher L.M. Facial nerve function after translabyrinthine vestibular schwannoma surgery. Otolaryngol Head Neck Surg. 2007;136:773-777.

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