HISTORICAL BACKGROUND

The first vestibulocochlear nerve section was performed in 1898 by Krause,² and the first posterior fossa vestibulocochlear nerve section for the treatment of vertigo in a patient with Meniere’s disease was performed by Frazier in 1904.³ McKenzie⁴ was the first to perform selective division of the superior half of the vestibulocochlear nerve in 1931. This procedure was popularized by Dandy, who first sectioned the vestibulocochlear nerve in 1925, and later began performing selective vestibular neurectomies in 1932. Dandy eventually performed 624 vestibular neurectomies; half of these patients underwent selective vestibular neurectomy.⁵ This series of patients is impressive not only because of the large number of patients, but also because the procedures were performed without microscopic assistance and modern antibiotics. With Dandy’s death in 1946, vestibular neurectomy was largely replaced by peripherally destructive procedures. Although highly successful in treating vertigo, residual hearing was compromised with these procedures.

The first microsurgical division of the vestibular nerve was performed in 1961 by House⁶ through a middle cranial fossa approach; this approach was modified further by Fisch⁷ and Glasscock.⁸ The middle cranial fossa approach allows the surgeon to identify and section selectively the vestibular nerve within the internal auditory canal (IAC). The procedure is technically challenging, however, and has a high incidence of postoperative facial nerve weakness and deafness.

The retrolabyrinthine approach for division of the trigeminal nerve was described by Hitselberger and Pulec in 1972,⁹ and in 1978, Brackmann and Hitselberger reported treatment of vertigo and tic douloureux by selective division of the vestibular and trigeminal nerves via a retrolabyrinthine approach.¹⁰ Silverstein and Norrell¹¹ noted a clear cleavage plane between the cochlear and vestibular nerve fibers while resecting a ninth cranial nerve neurilemmoma via a retrolabyrinthine approach, and suggested that selective vestibular neurectomy was feasible in this fashion. Silverstein’s subsequent reports^12,13 on the success of retrolabyrinthine vestibular nerve section in eliminating vertigo, while avoiding facial nerve damage and hearing loss, ushered in a new era for selective vestibular neurectomy.

The success and increasing popularity of the retrolabyrinthine approach to vestibular neurectomy in the 1980s led to efforts to improve the technique further. In an effort to prevent cerebrospinal fluid leak, which was caused by difficulty reapproximating the dura anterior to the sigmoid sinus, many surgeons adopted a retrosigmoid approach for vestibular neurectomy. This approach also allows division of the nerve more laterally in the cerebellopontine angle cistern, where identification of the vestibulocochlear cleavage plane may be easier. The retrosigmoid procedure can be extended in some cases to include drilling of the posterior IAC, allowing visualization of the intracanalicular portion of the nerve; this may be helpful in cases where the nerve bundles cannot be distinguished within the posterior fossa. In an effort to avoid problems with postoperative headache, which was a common complication after retrosigmoid vestibular neurectomy, Silverstein and colleagues^14–16 subsequently proposed a combined retrosigmoid-retrolabyrinthine approach.

PREOPERATIVE EVALUATION

Important preoperative considerations include the etiology of vertigo; the degree of disability; previous therapies; and the patient’s age, overall health, hearing status, and motivation. Surgical intervention for vertigo should be considered only in patients with incapacitating vertigo who have failed maximal medical therapy and are believed to be able to compensate centrally for the expected postoperative unilateral vestibular deficit. In addition, reliable identification of the offending ear is a crucial component of the preoperative evaluation. This identification is accomplished by audiometry, vestibular testing, and, most importantly, the patient’s history. Historical clues to diagnosis of laterality in vestibular disease include ipsilateral hearing loss, aural fullness, and tinnitus associated with the vertigo spells. If the patient has auditory symptoms in the contralateral ear, one must suspect that the disease may have become bilateral, and surgery on the poorer ear is relatively contraindicated in this setting.

Patients are often desperate for relief of debilitating symptoms, and are anxious to try any treatment that offers a chance at cure. Patients should be counseled that there is no promise of a cure with any treatment, and that often the best course is a conservative one. This is especially true for patients with vertigo that is not due to Meniere’s disease because surgery for these patients is much less likely to succeed.¹

If maximal medical therapy has failed, especially in classic unilateral Meniere’s disease, the patient may be a suitable candidate for surgery. Patients considering vestibular neurectomy should be counseled that this form of treatment does not address the underlying disease, but simply endeavors to eliminate one major symptom of the disease. The Meniere’s disease process continues to affect the inner ear even after surgery, and further hearing loss is anticipated, unless remission occurs. In addition, patients should know that they are trading a partial unilateral vestibular lesion for a total loss of vestibular function on that side, and that postoperative vestibular rehabilitation is crucial to the central nervous system compensation process.

Preoperative documentation of hearing with audiometric testing is obtained in all patients. Because the audiogram measures only the patient’s current hearing ability, however, the utility of the patient’s future hearing should also be considered. Because the disease process may cause a continued deterioration in hearing postoperatively, a practical approach to determining surgical candidacy takes this future hearing loss into consideration. If residual hearing is of borderline usefulness to the patient, and future hearing loss is anticipated, a procedure that is less risky than vestibular neurectomy, such as labyrinthectomy or intratympanic gentamicin treatments, may be a wiser choice.

Radiographic evaluation to exclude retrocochlear pathology is mandatory before considering vestibular surgery. Generally, magnetic resonance imaging (MRI) of CN VIII with administration of paramagnetic contrast material is preferred. Computed tomography (CT) scanning may also be useful to evaluate the bony anatomy of the temporal bone, but is not routinely required preoperatively.

When a patient has been determined to be a candidate for surgery from an otologic standpoint, the patient must be determined to be medically fit for intracranial surgery. Any procedure performed for vertigo is elective, and every effort should be made to optimize the patient’s medical condition before surgery. Before proceeding with surgical intervention, the patient should understand the risks and benefits of the procedure. Providing patients with reasonable expectations regarding their postoperative outcome is also important.

PERTINENT NEUROANATOMY

Within the IAC lie the superior and inferior vestibular nerves, the cochlear nerve, the facial nerve, the singular (posterior ampullary) nerve, and the nervus intermedius. The anatomy of these nerves and their relationships with each other are described in this section for the right ear as if the patient is supine with the head turned away from the surgeon (Fig. 36-1).

FIGURE 36-1 Anatomy of CN VII and VIII from the brainstem to the internal auditory canal as viewed from a position posterior to the nerves. The facial nerve begins posteroinferior to the cochleovestibular nerve and rotates around the cochleovestibular nerve until it reaches the anterosuperior quadrant of the internal auditory canal. The cochlear nerve fibers begin to separate from the vestibular nerve fibers in the cerebellar cistern. The cross sections show the rotation of the nerves. The superior vestibular nerve is divided to show the facial nerve anteriorly. Co, cochlear nerve; F, facial nerve; IV, inferior vestibular nerve; PAN, posterior ampullary nerve; PSCC, posterior semicircular canal; SV, superior vestibular nerve; VN, vestibular nerve.

The transverse (falciform) crest divides the lateral IAC into superior and inferior halves. The superior half is divided into anterior and posterior quadrants by Bill’s bar. The facial nerve and nervus intermedius occupy the anterosuperior quadrant, and the superior vestibular nerve, which innervates the superior semicircular canal, the horizontal semicircular canal, the utricle, and a portion of the saccule, occupies the posterosuperior quadrant. The inferior half of the IAC is occupied by the cochlear nerve anteriorly and the inferior vestibular nerve posteriorly. The inferior vestibular innervates the saccule, and is joined by the singular nerve, which innervates the posterior semicircular canal. This junction occurs where the singular canal emerges from its canal into the posteroinferior quadrant of the IAC approximately 2 mm medial to the transverse crest.

The cochlear nerve, which was initially directly anterior to the inferior vestibular nerve in the fundus of the internal canal, rotates 90 degrees inferiorly so that it is directly inferior to the superior and inferior vestibular nerves at the level of the porus acusticus. The superior and inferior vestibular nerve fibers begin to merge just medial to the transverse crest. A gross separation of the cochlear and vestibular nerve fibers usually exists medial to the porus acusticus¹⁷; however, in 25% of cases, the separation is evident only histologically. Even in cases of a visible cleavage plane, there can be a high degree of nerve fiber overlap (Fig. 36-2).¹⁸ The cochlear nerve fibers enter the brainstem slightly inferior and posterior to the vestibular nerve fibers.

FIGURE 36-2 A-F, Variability in the separation of the cochlear and vestibular fibers. The presence of a cleavage plane does not correspond to a complete segregation of cochlear and vestibular fibers.

Rights were not granted to include this figure in electronic media. Please refer to the printed book.

(Modified from Rasmussen A: Studies of the VIIIth cranial nerve of man. Laryngoscope 50:667, 1940. Used by permission from Wolters-Kluwer.)

A landmark that may be useful in identification of the cochleovestibular cleavage plane is the nervus intermedius. This nerve contains the afferent and parasympathetic fibers of the facial nerve, and runs between the facial and cochleovestibular nerves along their entire length. It is often located on the anterior portion of the cochleovestibular cleavage plane. It enters the brainstem near the cochleovestibular nerve, and its fibers terminate in the salivatory and glossopharyngeal nuclei.

The facial nerve runs proximally from its anterosuperior position in the lateral IAC to a position that is inferior and slightly anterior to the cochleovestibular nerve at the brainstem. Because of its ventral position, it is hidden by the cochleovestibular nerve along most of its intracisternal course; however, it may be visualized by gentle retraction of the cochleovestibular nerve or with the use of an endoscope. It is slightly grayer in color than the cochleovestibular nerve.

CN V is located superior to the facial and cochleovestibular nerves and can often be identified by its characteristic striations that are perpendicular to its course. CN IX, X, and XI are located inferior to the facial and cochleovestibular nerves (Fig. 36-3).

FIGURE 36-3 Anatomy of the cerebellopontine angle as viewed through a large retrosigmoid craniectomy showing CN V, VII, VIII, IX, and X. SS, sigmoid sinus; ce, cerebellum; 5, cranial nerve V; 6, cranial nerve VI; 7, cranial nerve VII; 8, cranial nerve VIII; 9, cranial nerve IX; 10, cranial nerve X; 11, cranial nerve XI.

RETROLABYRINTHINE APPROACH

The patient is positioned in the standard fashion for mastoidectomy after removing approximately 3 to 5 cm of hair. The planned surgical site is marked and injected with a mixture of local anesthetic and epinephrine, and the scalp is prepared and draped in the standard fashion (Fig. 36-4A). The facial nerve is monitored electromyographically throughout the procedure. Auditory function is generally monitored by recording intraoperative auditory brainstem responses, although near-field CN VIII electrodes are preferred by some surgeons after the nerve is exposed. A wide postauricular scalp flap is elevated and turned forward, exposing the temporal bone. The authors prefer distinct scalp and musculoperiosteal incisions, each of which can be individually closed at the end of the case.

FIGURE 36-4 Retrolabyrinthine approach. A, Skin incision. B, Drilling the mastoid cavity with exposure of sigmoid sinus. C, Retraction of the dura and sigmoid sinus to identify facial and vestibulocochlear nerves. D, CN V, VII, VIII, and XI exposed. Note the relationship of the branch of the anterior inferior cerebellar artery to CN VII and VIII. This relationship is highly variable, and the vessel does not always run between the nerves as illustrated here. E, Division of the vestibular nerve after separation from the cochlear nerve fibers.

During the initial drilling, a fragment of bone is acquired for later use in wound closure. A large temporalis fascia graft should be harvested and set aside to dry. A complete mastoidectomy is performed, and the sigmoid sinus is carefully outlined and skeletonized (Fig. 36-4B). Posterior fossa dura is decompressed at least 1.5 cm behind the sigmoid sinus. Some surgeons leave an island of bone over the sinus, whereas others prefer to remove all bone. Regardless, enough bone overlying the sigmoid sinus should be removed to allow retraction of the sinus into the posterior aspect of the surgical defect so that the CN VIII complex can be easily visualized in the cerebellopontine angle cistern. The antrum is opened, but care should be taken not to dissect too far anteriorly to protect the epitympanum and ossicle heads. All presigmoid bone and air cells are removed posterior to the posterior semicircular canal, including the perilabyrinthine air cells, retrolabyrinthine air cells, and retrofacial tract air cells, which overlie the endolymphatic sac. The superior margin of dissection is the superior petrosal sinus, and the inferior margin is the jugular bulb. When this bone is all removed, the posterior fossa dura has been exposed. All retrofacial, facial recess, and zygomatic root air cells should be obliterated with bone wax. The wound is copiously rinsed to remove bone dust.

The dura is incised parallel to the sigmoid sinus margin, and the cerebellum is lightly retracted. When some cerebrospinal fluid is evacuated, the tentorium cerebelli and the trigeminal nerve are identified superiorly. The vestibulocochlear nerve can be visualized with gentle retraction of the cerebellum, medial to the bone of the posterior semicircular canal (Fig. 36-4C). The facial nerve is identified positively by electric stimulation after gentle retraction of the CN VIII complex. If a cleavage plane is evident in CN VIII, this is developed by blunt dissection with a microscopic instrument (Fig. 36-4D). If no cleavage plane is present, the surgeon must create an arbitrary plane by sharp dissection (Fig. 36-4E). The superior portion of the nerve, containing the vestibular fibers, is divided sharply, taking care not to injure the facial nerve or the nervus intermedius. When the nerve section is complete, the cut ends of the nerve physically separate. It is unnecessary to resect a portion of the nerve. Functional integrity of the facial nerve is confirmed by proximal stimulation after the vestibular nerve section. Care is also taken to preserve the nervus intermedius fibers, which run between CN VII and VIII.

The wound is irrigated with bacitracin solution and is ready to be closed. An autogenous graft of abdominal fat is harvested to obliterate the temporal bone defect. The bone graft harvested previously is trimmed to size and placed over the aditus ad antrum to prevent prolapse of fat into the epitympanum. The temporalis fascia is placed anteriorly to isolate the retrolabyrinthine defect from the anterior temporal bone; this prevents the outflow of cerebrospinal fluid into the eustachian tube. Rarely, a watertight closure of the presigmoid dura is possible. Fat is placed into the defect, and the scalp wound is closed in two or three layers. The retrolabyrinthine procedure is shown in the video accompanying this chapter.

RETROSIGMOID OR SUBOCCIPITAL APPROACH

The patient is positioned in the standard fashion for mastoidectomy or in the lateral “park-bench” position, at the discretion of the surgeon. The head is rotated contralaterally with the neck slightly flexed. A lumbar drain is placed electively by some surgeons to allow for posterior fossa decompression. Electrodes for intraoperative brainstem auditory evoked response and facial nerve monitoring are placed. The planned surgical site parallel to the hairline is marked and injected with local anesthetic containing 1:100,000 epinephrine (Fig. 36-5A). Placement of the incision avoiding the greater and lesser occipital nerves can be accomplished by using a curvilinear or sigmoidal incision along the hairline. This incision should extend from the top of the auricle down to the upper neck, just posteroinferior to the mastoid tip. The surgical site is prepared and draped in the standard fashion. Some surgeons routinely employ a lumbar drain for these cases. If this drain has been placed, 60 to 90 mL of cerebrospinal fluid is drained at the time of skin incision; this decompresses the posterior fossa and minimizes the need for cerebellar retraction.¹⁹ The skull is exposed, and a 2 cm diameter retrosigmoid craniectomy is made. Any posterior mastoid air cells entered in this process must be obliterated.

FIGURE 36-5 Retrosigmoid approach. A, Skin incision is designed to avoid injury to greater or lesser occipital nerves. B, View of nerves after craniectomy. C, Closer view of nerves with removal of a portion of the internal auditory canal (IAC). Co N, cochlear nerve; ES, endolymphatic sac; FN, facial nerve; PAN, posterior ampullary nerve; SVN, superior vestibular nerve; VN, vestibular nerve; 9, cranial nerve IX; 10, cranial nerve X; 11, cranial nerve XI.

All drilling is completed before opening the dura to minimize entry of bone dust into the subarachnoid space. Emissary veins are a potential source of bleeding that can be controlled with cautery or bone wax. The dural incision may be either curvilinear or trifurcate. After opening the dura to expose the posterior fossa, the cerebellopontine angle is approached by gentle retraction of the cerebellum, preferably from the lower portion of the wound (Fig. 36-5B). Medial traction of CN VIII is dangerous to the hearing and is frequently associated with cerebellar retraction. Auditory brainstem responses should be monitored closely during this portion of the procedure. This is particularly true if a cerebellar retractor is used. The cerebellum is elevated superiorly, separating it from the temporal bone. The operculum and the endolymphatic sac can be helpful landmarks because the endolymphatic duct exits the temporal bone at the level of the IAC and is only a few millimeters posterior to the IAC.

The cranial nerves in this region are exposed by separating the arachnoid mater and the vessels. CN V and VII-XI can be visualized, with CN V being superior to the facial and vestibulocochlear nerve complex, and CN IX-XI exiting inferiorly (see Fig. 36-3). CN V can be identified by its characteristic striations, which are perpendicular to the long axis of the nerve. Identification of CN IX-XI is confirmed with identification of the jugulodural fold, a condensation of dura that extends across the sigmoid sinus from the posterior aspect of the temporal bone. Approximately 1 cm anterior to the fold, the cochleovestibular nerve enters the IAC. The facial nerve is located anteroinferior to the vestibulocochlear nerve medially along the brainstem, and continues to move superiorly and anterior to CN VIII until it enters its location in the anterosuperior portion of the IAC (see Fig. 36-1). Identification of the facial nerve can be confirmed with use of the facial nerve stimulator.

At the level of the porus, the cochlear and vestibular fibers are usually separated by a cleavage plane, allowing for sharp dissection of the cleavage plane and selective transection of the vestibular fibers. The vestibular nerve is slightly grayer in appearance than the cochlear nerve because of the more dense arrangement of the cochlear fibers. The nervus intermedius runs along the anterior aspect of the cleavage plane and may be identified with endoscopic assistance. There is also a small arteriole that frequently runs along the posterior cleavage plane. In cases where a definite cleavage plane cannot be identified, which occurs in approximately 25% of cases,²⁰ the nerve may be arbitrarily divided as described previously, or drilling of the posterior portion of the IAC may be performed (see Fig. 36-5C).

If drilling of the posterior IAC is required, the drilling extends no further laterally than the singular canal, which carries the posterior ampullary nerve and enters the IAC approximately 2 mm medial to the falciform crest in the posteroinferior quadrant.²¹ When adequate exposure has been obtained, the superior vestibular and the singular nerves are sectioned. The inferior vestibular nerve should not be sectioned laterally because of its close relationship to CN VIII and the cochlear blood supply.

Careful irrigation is performed, and the dura is reapproximated. Because this approach is associated with a higher incidence of postoperative headache, many authors recommend performing a cranioplasty after the retrosigmoid approach to repair the craniectomy defect.^22–24 An alternative technique described by Silverman and coworkers,¹⁹ using a sandwich of absorbable gelatin sponge (Gelfoam), absorbable gelatin film (Gelfilm), and Gelfoam in the craniectomy defect, may prevent adhesion of cervical musculature to the dura. This Gelfoam-Gelfilm-Gelfoam sandwich has been shown to minimize the incidence of postoperative headache, and may decrease reactive chemical meningitis related to foreign cranioplasty materials. The muscle, fascia, and skin are closed in layers.

COMBINED RETROLABYRINTHINE/RETROSIGMOID APPROACH

Silverstein¹⁴ proposed a modification of the above-described techniques, termed the combined retrolabyrinthine-retrosigmoid approach. This approach involves a limited mastoidectomy with exposure of the sigmoid sinus and posterior fossa dura. A dural incision is made approximately 2 to 3 mm posterior to the sigmoid sinus, and the sinus and dura are retracted anteriorly (Fig. 36-6) to allow evaluation of the cerebellopontine angle to determine whether an identifiable cleavage plane exists between the cochlear and vestibular nerve fibers. If not, dura is reflected off the temporal bone, and the IAC is opened. The superior vestibular and posterior ampullary nerves are divided within the IAC, as in the retrosigmoid approach. This division allows performance of the neurectomy with less bone removal and less cerebellar retraction.

FIGURE 36-6 Dural incision used in combined retrolabyrinthine/retrosigmoid approach. PFD, posterior fossa dura; SS, sigmoid sinus.

ENDOSCOPIC-ASSISTED VESTIBULAR NEURECTOMY

Several authors have reported on the use of endoscopic assistance for vestibular neurectomy procedures.^25–27 The potential advantages include a magnified view of relevant structures, and the ability to use angled or flexible scopes to allow visualization of structures not seen well with the microscope, such as the cleavage plane between the cochlear and vestibular nerves, the nervus intermedius, the facial nerve, and branches of the anterior inferior cerebellar artery. Potential disadvantages include difficulty in visualization because of fluids on the scope, thermal injury to important structures from the heat of the endoscope, lack of instruments specifically designed for endoscopic neurotology, and difficulty because of lack of depth perception when viewing images in two dimensions.²⁷ Any of these factors could lead to injury of structures not generally at risk when performing the procedure with binocular microscopy. The primary advantage of an endoscope may be to allow visualization of any mastoid air cells violated while drilling the IAC, so that these can be properly obliterated to prevent cerebrospinal fluid leak.

POSTOPERATIVE COURSE

A mastoid dressing is applied postoperatively. Patients are typically monitored overnight in the neurosurgical intensive care unit, and the urinary catheter is removed on postoperative day 1. If a fat graft was taken from the abdomen, an abdominal drain is placed in the donor site, and is removed when it produces less than 30 mL over a 24 hour period. Routine use of sequential compression devices is necessary to assist in preventing deep venous thrombosis while the patient is immobile. Patients at high risk for thrombosis may receive subcutaneous heparin postoperatively. Vestibular rehabilitation activities are begun on postoperative day 1, and physical therapy is often consulted to encourage patient activity and an early return to independent ambulation. Postoperative antibiotics are not given routinely. Patients are typically hospitalized for 3 to 5 days. A postoperative audiogram is obtained at 1 month.

EFFICACY

The gold standard for the surgical control of vertigo is the transmastoid labyrinthectomy. Assuming the offending ear is properly lateralized and the operation is completed successfully, the success rate for control of episodic vertigo with labyrinthectomy should be 100%. Series report success rates of greater than 95%; poor outcomes are most likely secondary to incomplete vestibular compensation.²⁸ A review of the available literature (Table 36-1) shows that the results for the retrolabyrinthine and retrosigmoid techniques are favorable, with vertigo being improved in 91% to 100% of patients with Meniere’s disease, and 68% to 100% of patients with vertigo from etiologies not related to Meniere’s disease. The combined retrolabyrinthine and retrosigmoid approach is reported to have a success rate of 92% to 95% for patients with Meniere’s disease. No data are available for patients with other causes of vertigo. A challenge in interpretation of these data is the natural course of Meniere’s disease, which is often a progression to spontaneous complete relief of vertigo even if no treatment is provided.^29–32

The advantage of selective vestibular neurectomy over destructive labyrinthine procedures is division of the vestibular fibers with preservation of the cochlear fibers. The ability of the procedure to preserve hearing is an important consideration. As mentioned earlier, vestibular neurectomy does not change the course of the hearing loss, but is designed only to treat the immediately debilitating symptom of vertigo. In addition, vestibular neurectomy itself introduces a risk of hearing loss secondary to the surgery. Lack of a distinct cleavage plane between the vestibular and cochlear nerve fibers is the primary cause of damage to auditory fibers. This risk may be theoretically decreased using the retrosigmoid approach, owing to surgical division of the vestibular nerve more laterally, where the cleavage plane becomes more distinct. Medial retraction of the auditory nerve may also lead to a sensorineural hearing loss. In addition, a conductive hearing loss may occur later from fixation of the ossicular chain caused by bone dust that accumulates in the oval window during the procedure.^33,34 A study by Teixido and Wiet³⁴ showed that the most common audiometric abnormality after retrolabyrinthine vestibular neurectomy is low-frequency conductive hearing loss thought to be due to ossicular fixation from this mechanism.

As shown in Table 36-2, reports of hearing loss after vestibular neurectomy state that retrolabyrinthine patients have a 7% to 58% incidence of hearing loss, whereas retrosigmoid patients have a 7% to 45% incidence of hearing loss. These data must be interpreted with caution because the postoperative time points at which the hearing losses were evaluated vary among studies, and are no doubt contaminated by the continued decline of hearing because of the natural progression of Meniere’s disease. A study by Wazen and coworkers³⁵ showed that serviceable hearing decreased from 81% to 43% of patients at an average of 4 years after vestibular neurectomy. A reasonable conclusion may be drawn that hearing loss continues after vestibular neurectomy, just as it does with untreated Meniere’s disease,^29–31 but perhaps at a slightly slower rate.

The other classic symptoms of Meniere’s disease, tinnitus and aural fullness, also occasionally improve after vestibular neurectomy. As shown in Table 36-2, tinnitus was reduced in half of patients, and aural fullness was reduced in two thirds of patients after the retrolabyrinthine approach.

COMPLICATIONS

Table 36-3 summarizes the complications encountered with posterior fossa vestibular neurectomy. For the retrolabyrinthine approach, the most common complication is cerebrospinal fluid leak, which occurs in up to 12% of patients. Wound infection and meningitis are also common complications, occurring in up to 6% and 4% of patients. The most commonly cited complication with retrosigmoid vestibular neurectomy is significant postoperative headache, sometimes disabling, which can persist for years after surgery. The reported incidence of cerebrospinal leak and wound infection are much lower than for the retrolabyrinthine approach at 4%, and the wound infection rate is similar at 5%. Although facial nerve paresis is a risk, this occurs rarely with the posterior fossa approaches and is not generally reported in the literature. Other complications reported in the literature for these operations include hydrocephalus, continued imbalance, tinnitus, aseptic meningitis, and abdominal hematoma if an abdominal fat graft is used.

Review of the literature shows that the incidence of headache after retrosigmoid vestibular neurectomy approaches 1 in 10. The etiology for such headache syndromes is still a matter of debate in the otology and neurosurgery literature. Numerous explanations have been proposed, and many strategies have been presented in an effort to reduce this problem. Adhesion of cervical musculature to the dura that is exposed during the craniectomy can subsequently result in traction on the dura with head movement. Injury to the greater and lesser occipital nerves during the procedure, either by retraction or during the incision itself, has been frequently cited as a possible contributing factor. A third explanation may be that bone dust can be trapped in the subarachnoid space, which can cause chemical meningitis or interfere with cerebrospinal fluid resorption and cause increased intracranial pressure. Other factors including dural tension, cerebellar retraction, and aseptic meningitis have been posited as contributing to postoperative headache.

Efforts to prevent the attachment of the deep neck musculature to exposed dura, designing skin incisions to avoid the occipital nerves, and the avoidance or minimization of intradural bone drilling all have been shown to decrease the incidence of postoperative headache.¹⁹ The prevention of cervical muscle adherence to dura has been described using cranioplasty and wound closure modifications. Cranioplasty to replace missing bone volume was initially advocated to decrease the incidence of postoperative headache. Cranioplasty increases operative time, however, and more recent studies have shown that the foreign materials such as methylmethacrylate may lead to a higher incidence of headache, owing to increased local tissue reaction.³⁶ In addition, the data suggest that there is no decrease in the frequency of postoperative headache in cranioplasty patients.^36,37