Neurovascular Decompression in Cranial Nerves V, VII, IX, and X

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Chapter 125 Neurovascular Decompression in Cranial Nerves V, VII, IX, and X

The compression of specific cranial nerves at their entrance to or exit from the brain stem has been linked to a number of clinical conditions. Tic douloureux or trigeminal neuralgia is the most common, and perhaps the best described and investigated, of these cranial nerve disorders. Dandy was the first to observe, in 1932, that vascular compression of the trigeminal nerve in the posterior fossa might be the cause of tic douloureux.¹ Gardner and Sava later described vascular compression of the seventh cranial nerve in more than half of the patients they operated on via the posterior fossa for hemifacial spasm, the motor equivalent of trigeminal neuralgia.² However, it was not until Jannetta applied the operating microscope to the systematic study of these problems that the truly remarkable incidence of pathologic vascular compression of cranial nerves at their entry to or exit from the brain stem was appreciated.³ Based on his findings, Jannetta devised an operative technique (microvascular decompression) to displace these vessels from the affected nerve without sacrificing neural integrity.^3,⁴ This technique has been used to relieve the specific cranial nerve syndromes successfully in the majority of patients treated. This chapter discusses the individual cranial nerve vascular compressive syndromes and the decompression techniques that can be used in treating them.

Fifth Cranial Nerve

Clinical Presentation

Trigeminal neuralgia is characterized by a stereotypical clinical syndrome. Patients suffering from trigeminal neuralgia exhibit brief, intense paroxysms of pain confined to one or more divisions of the trigeminal nerve. These attacks are usually triggered by light cutaneous stimuli within the trigeminal territory. The pain typically is described as an intense stabbing or electrical shock sensation that patients frequently describe by rapidly flinging open their hands to indicate the paroxysmal nature of the jolts of pain. The pain is often more pronounced during the day, and many patients are pain free or have markedly fewer episodes at night. The most common areas of involvement are in the second and third trigeminal divisions, specifically anteriorly and in the region of the mouth. Because the mouth is a common site of symptoms, patients may undergo unnecessary dental surgery without achieving relief before the diagnosis of trigeminal neuralgia is made. Patients classically guard their faces, refuse to be touched, and avoid shaving, washing, applying makeup, chewing, and brushing their teeth, because any of these actions may provoke an attack. Over time, patients frequently report an increase in the number of attacks, a reduction of pain-free periods, and occasionally sensory disturbances in the involved trigeminal distribution or distributions.^4,⁵

Differential Diagnosis

Trigeminal neuralgia is occasionally the presenting complaint of a patient with multiple sclerosis. Trigeminal neuralgia occurs in 1% to 3% of patients afflicted with multiple sclerosis. Similarly, 2% to 4% patients with trigeminal neuralgia eventually are found to have multiple sclerosis.⁶ The clinical picture and site of the pathologic process (the root entry zone of the nerve) appear to be identical in idiopathic trigeminal neuralgia and multiple sclerosis patients. However, in multiple sclerosis, the cause of neuralgia is intrinsic demyelination of the nerve, which is not due to extrinsic vascular compression. Subsequently, microvascular decompression does not benefit multiple sclerosis patients, and a neural destructive procedure should be used to treat medically refractory cases.

A history of sustained facial pain that is not paroxysmal must be questioned carefully. Patients sometimes describe frequent repetitive jabs of pain as one prolonged attack. This does not preclude the diagnosis of trigeminal neuralgia. However, slowly developing pain that builds in intensity, lasts for variable periods (often hours to days), and then subsides is not characteristic of trigeminal neuralgia. The most common mistake in the diagnosis of trigeminal neuralgia, in our experience, has been mislabeling patients who suffer from chronic cluster syndrome. This and other atypical facial pain syndromes do not respond to surgical decompressive procedures.

Various other conditions must be considered in the differential diagnosis of trigeminal neuralgia. These include herpes zoster (postherpetic neuralgia), dental disease, orbital disease, temporomandibular dysfunction, and temporal arteritis, as well as post-traumatic neuralgias. None of these typically presents with the classic lancinating paroxysmal pain of trigeminal neuralgia. Once the clinical diagnosis of trigeminal neuralgia is made, magnetic resonance imaging (MRI) should be performed to rule out demyelinating disease, infection, inflammatory processes, vascular malformations, and neoplasms.

Medical Therapy

After the diagnosis of trigeminal neuralgia is made, a trial of 100 mg of carbamazepine given twice a day is initiated. The dose is increased by 100 mg every other day until pain control is achieved or toxicity develops. Patients are instructed to take this medication on a full stomach and to have monthly hematologic studies performed so that toxicity can be detected early. In this manner, good control of the pain can be achieved in the vast majority of patients.^7,⁸ Patients who are allergic or intolerant to carbamazepine can be treated with phenytoin, oxcarbazepine, clonazepam, and baclofen. Although gabapentin is frequently promoted for this indication, no studies have been published showing its efficacy, and it has rarely proved useful in our clinical experience. Surgery is reserved for patients whose pain is refractory to medical treatment or who develop medication-related side effects.

Indications

If the patient meets the typical clinical picture and fails medical therapy, surgical treatment options include microvascular decompression, selective percutaneous lesioning (with radiofrequency thermal coagulation or glycerol chemoneurolysis), or stereotactic radiosurgery of the trigeminal nerve. It is our practice to explain the relative benefits and risks of the surgical treatment options and assist the patient in choosing among these procedures (Table 125-1). We believe that microvascular decompression is the procedure of choice for the treatment of trigeminal neuralgia in otherwise healthy and relatively young (generally younger than 70 years) patients.⁹

Table 125-1 Relative Benefits of Percutaneous Trigeminal Neurolysis, Radiosurgical Trigeminal Neurolysis, and Microvascular Decompression of the Trigeminal Nerve for the Treatment of Trigeminal Neuralgia

Procedure	Benefits	Drawbacks
Percutaneous trigeminal neurolysis	• Safe, well tolerated despite age or infirmity • Brief or no hospitalization • Easily repeated if necessary

• Treats symptoms, not cause

• Destructive; permanently alters facial sensation

• Risk of corneal anesthesia

• Dysesthetic sequelae can be severe

• Increased recurrence with time

Stereotactic radiosurgery

• Safe, well tolerated despite age or infirmity

• No hospitalization

• Treats symptoms, not cause

• Delayed therapeutic response

• Risk of corneal anesthesia

• Increased recurrence with time

• Limited therapeutic data

Microvascular decompression

• Nondestructive; spares nerve

• No numbness

• No dysesthesia

• No corneal anesthesia

• Treats apparent cause; may be curative

• General anesthesia required

• Craniectomy required

• Increased risk of serious, lethal complications

• Potential increased risks with advancing age or comorbidities

Preoperative Considerations

We obtain high-resolution magnetic resonance images of the posterior fossa before treatment to reveal any unrecognized neoplasms, infectious causes, inflammatory processes, demyelinating plaques, or vascular malformations. We rarely obtain cerebral angiograms, because the information obtained by a routine angiogram is not helpful enough to warrant the small but inherent risk associated with arteriography.

Operative Positioning

While we frequently use the sitting position for microvascular decompression procedures (as described in detail later), others often use a lateral or park bench position (Fig. 125-1).¹⁰ Briefly, for lateral or park bench positioning, the patient is induced, intubated, and placed under general anesthesia, and the head is secured in three-point pin fixation. The patient is then placed in the lateral decubitus position with the unaffected side down. A gel roll is placed in the axilla of the dependent side, all pressure points are padded, and the nondependent arm is supported by a padded armrest. The neck is then secured in a slightly flexed position, and the head is turned 10 to 20 degrees from the affected side to provide optimal exposure and a clear line of sight to the pathology during surgery. The vertex of the head is then positioned based on the site of vascular compression.¹⁰ For decompression of the fifth cranial nerve, the vertex of the head is maintained parallel to the floor. For decompression of the lower cranial nerves, the vertex of the head is turned 10 to 20 degrees toward the floor. The patient is secured to the operative table with 3-inch tape and/or Velcro straps, and the shoulder of the affected side can be gently taped caudally to provide additional working space. The remaining portions of the operation are similar to those described later, including incision, dural opening, intradural dissection/decompression, and closure.

FIGURE 125-1 View of patient positioning laterally on the operating table for left-sided trigeminal neuralgia. The inset demonstrates the incision position for left-sided microvascular decompression for trigeminal neuralgia.

(Adapted from McLaughlin MR, Jannetta PJ, Clyde BL, et al. Microvascular decompression of cranial nerves: lessons learned after 4400 operations. J Neurosurg 90:1-8, 1999.)

Anesthetic Considerations

During the operation in the sitting position, the patient should be chemically paralyzed and under controlled ventilation for two reasons: (1) this minimizes motion in the field, which is greatly magnified by the operating microscope, and (2) it prevents the patient from developing a gasp reflex should a small amount of air embolization occur. This reflex occurs with only a tiny entrainment of air and can rapidly result in a massive air embolism.

To detect air embolization, a Doppler precordial detector and an end-tidal carbon dioxide monitor are used because they can detect even minute amounts of air. This detection allows the anesthesiologist to raise the venous pressure and prevent further entrainment of air, avoiding massive air embolization. The effectiveness of these methods of intravenous air detection is such that we abandoned the use of central venous pressure catheters for this type of surgery. The central venous pressure catheter was originally inserted to allow the aspiration of air trapped in the right atrium. Small amounts of air, however, do not sequester in the atrium but pass through the heart into the pulmonary circulation. If detected at its earliest stages, raising the venous pressure to prevent further entrainment is sufficient.

When the patient is positioned in a sitting position, positive end-expiratory pressure, although not routinely employed, can be used to raise the venous pressure almost to the level of the head, creating the physiologic equivalent of having the patient supine. This approach should prevent any air entrainment and add a further margin of safety. The level of venous pressure can be adjusted to avoid significantly raising intracranial venous pressure, with its associated increase in intracranial pressure.

If the patient is placed in a lateral decubitus position, the risk of air embolism is less but not fully obviated, so similar monitoring is probably warranted. As with all neurosurgical anesthesia, it is desirable for the patient to have as smooth an induction as possible; it is even more important that anesthesia be terminated so that the patient is allowed to awaken gradually and does not buck on the endotracheal tube.

Positioning Preferences

Although the patient can be positioned in either a sitting position or the lateral decubitus position for microvascular decompressive procedures, we use the sitting position for such procedures because it can be easily achieved in patients of any physiognomy and produces a relaxed operative field with the intracranial structures in their normal anatomic relationships. Moreover, it offers advantages for the anesthesiologist in that it avoids chest compression, allows good ventilation, and provides good access to the patient. In this position, cerebrospinal fluid and irrigant do not pool but flow out of the wound. Bleeding can be irrigated from the wound minimizing the use of suction during the operation. This aspect is critical because of the potential risk of inadvertent injury to cranial nerves, other neural structures, or small blood vessels with suctioning.

We achieve the sitting position using a pin-fixation head holder for rigid fixation of the skull. The patient’s head is rotated 15 to 30 degrees to the ipsilateral side. The head is flexed gently to provide ample room for placing one or two fingers beneath the patient’s chin (Fig. 125-2). The elevation (or angle) of the back of the table is such that the patient is actually in a semisitting or slouched position, although higher elevation of the backrest may be necessary in the older patient with a less flexible neck.

FIGURE 125-2 Lateral view of patient positioning on the operating table.

(Adapted from Apfelbaum RI: Microvascular decompression of the trigeminal nerve. In Wilson CB [ed]. Neurosurgical Procedures: Personal Approaches to Classic Operations. Baltimore: Williams & Wilkins, 1992, pp 137-155.)

Operative Procedure

After the patient is satisfactorily anesthetized and positioned, the operative table is angled an additional 15 to 20 degrees to the ipsilateral side so that the surgeon approaches the patient at an angle of approximately 45 degrees from the midline. The hair is shaved only from the posterior quadrant of the head on the affected side, and sterile preparation and draping are performed. The incision is vertical and located 3 to 5 mm medial to the mastoid notch (Fig. 125-3). We use a linear incision approximately 8 cm long that is centered two thirds above and one third below the mastoid notch.

FIGURE 125-3 Placement of the incision for microvascular decompression of the fifth, seventh, and ninth cranial nerves. For decompression of the fifth cranial nerve, the incision (dotted line) is positioned as shown so that two thirds of the length is above the level of the mastoid notch. For decompression of cranial nerves VII and IX, the incision is placed slightly lower so that half of the length is above the level of the mastoid notch.

To reduce scalp bleeding, the scalp is routinely infiltrated with 0.5% lidocaine with epinephrine (1:200,000). After incision of the skin, hemostasis is achieved with Dandy clamps secured to the drapes with elastic bands. Electrocautery is used to divide the occipital muscle mass down to the occipital bone. The anastomosis between the occipital and the posterior auricular branches of the external carotid artery is often encountered with this exposure and divided. The muscle mass is then stripped from the posterior surface of the occipital bone. Care must be taken not to strip too far laterally, because this determines the exposure once the self-retaining retractor is placed. Bridging emissary veins are coagulated, and their openings in the bone are sealed with bone wax. A Valsalva maneuver at this point can confirm hemostasis.

A modified Weitlaner retractor (Apfelbaum retractor) that serves as the base for a self-retaining brain retractor (Codman & Shurtleff, Raynham, MA) is then placed within the wound (Fig. 125-4). The retractor is secured by placing a gauze sponge through the loops of the handle and clipping it to the drape above the patient’s head to provide good three-point fixation and achieve adequate stability for the retractor arm. Several bur holes are made and enlarged into a circular craniectomy (2.5-3 cm) (Fig. 125-5). The craniectomy should extend superiorly to the transverse sinus and laterally to expose the sigmoid sinus. The lateral extension of the bony opening often carries the craniectomy over mastoid air cells, which are thoroughly waxed at the completion of the craniectomy. Care is taken to displace the dura as the rongeuring proceeds to avoid entering the dura or venous sinuses. Bridging veins may also be encountered and have to be coagulated.

FIGURE 125-4 Position of the self-retaining retractor. Fixation of the retractor base to the drapes via an encircling gauze sponge provides firm, three-point fixation. The notched blade of the retractor protects cranial nerves VII and VIII.

FIGURE 125-5 A, Placement of initial bur holes and rongeuring of the base to create a circular craniectomy. B, Dural incision for a left-sided approach showing the L-shaped dural incision. The exposure afforded by the dural opening can be expanded in a T shape at the corner of the opening. The transverse and sigmoid sinuses are exposed by the craniectomy.

The dura then is opened in an inverted L-shaped manner 3 to 5 mm parallel to the sigmoid and transverse sinuses (Fig. 125-5). The dura can be further opened in a T shape at the superior corner if increased exposure is needed. The dura is then secured with tenting sutures superiorly and laterally to retract the sinuses slightly and complete the exposure.

Occasionally, adhesions or bridging vessels are encountered along the superior posterior margin of the cerebellum along the transverse sinus. These must be divided sharply to free the cerebellum. A flexible retractor arm is then placed on the retractor base. This retractor arm should be positioned so that a gentle arch is formed and sharp kinks and bends are avoided (Fig. 125-4). Its tension is adjusted so that it remains in any position in which it is placed but can be readily moved without undue force. A specially shaped retractor blade that has an elongated finger at its superior margin (Codman & Shurtleff) is used (Fig. 125-4). The purpose of the finger is to allow deeper retraction in the vicinity of the trigeminal nerve while avoiding deep retraction and potential injury to the seventh and eighth cranial nerves. A narrow retractor blade could achieve the same depth of exposure superiorly but might penetrate into the cerebellum. Once the retractor blade is in place, the superior lateral margin of the cerebellum is retracted in a medial-to-inferomedial direction, and the operating microscope is brought into use.

Before the microscope is placed, an armrest is brought into position. This is a Mayo stand, modified as suggested by Malis, with the top removed and replaced with a 6 × 18–inch piece of metal. This metal sheet is padded, covered with a plastic sheet, and then covered with sterile drapes. Its height can be independently adjusted from the operating table to provide adequate support for the surgeon’s arms.

Our standard procedure is to set up the operating microscope with the left-sided stereoscopic binocular observer tube for the surgical assistant. The scrub nurse is positioned on the surgeon’s right. This positioning is used for all cases regardless of whether the exposure is on the right or left side of the patient. It allows for a standardized operative setup with excellent access between the surgeon and the nurse.

With the microscope in place, the cerebellum is gently retracted further medially. The approach should be angled as sharply as necessary to visualize the cerebellar surface. Adhesions and small bridging vessels are lysed as the cerebellum is retracted. Once the lateral extent of the cerebellum is visualized, the angle of approach is changed to follow the petrous bone anteriorly. McLaughlin et al.¹⁰ refer to this change as “turning the corner” and emphasize the necessity of doing this under direct vision. At this point, the petrosal vein can be identified. This vein frequently is encountered two thirds of the way from the dura to the trigeminal nerve, but great variability exists, and it may be absent or positioned close to the nerve. It often consists of two channels that form a Y-shaped bifurcation just before entering the dura. To permit adequate retraction and deeper dissection, the petrosal vein may need to be coagulated and divided sharply.

Once the petrosal vein has been identified and addressed, the retractor blade can be advanced. This is done while keeping the retractor blade close to the tentorium, which should be relatively horizontal in the operative field (variations in this view can be corrected with the use of the Trendelenburg control of the operating table). By advancing over the superior surface of the cerebellum, the surgeon can avoid the seventh and eighth nerves. It is not necessary to open the arachnoid around them. This approach exposes the arachnoid overlying the trigeminal nerve. If any bleeding is encountered while retracting the cerebellum, a dorsal bridging vein from the cerebellum to the tentorium may have been torn. Removing the retractor and depressing the cerebellum slightly allows inspection of this area and control of this problem before proceeding. This tear is an infrequent occurrence, but the surgeon must be aware of its possibility. When possible, we first open the arachnoid about the petrosal vein to inspect the trigeminal nerve. This approach allows detection of compressing veins whose removal by petrosal vein resection would lead to the erroneous assumption of a negative exploration. Such inspection also provides the possibility of preserving a portion of the petrosal system while still allowing adequate access to the trigeminal nerve. Preservation of part or all of the petrosal venous system is desirable in terms of reducing risk of venous cerebellar infarction.

The arachnoid overlying the fifth nerve is then opened sharply and widely to expose this area. This opening may be difficult because of the depth at which the work is being done and because of the narrow exposure. In some cases, the arachnoid is quite thin and translucent and can be easily punctured and teased free; in other cases, it is thick and opaque and must be sharply dissected. A great deal of care must be taken to avoid tugging on underlying structures. The trigeminal nerve is usually easily identified at this point, and the neurovascular relationships at the brain stem then can be identified.

The site of pathology is typically at the brain stem, and vessels impinging distally on the nerve are not usually the cause of the problem. The typical situation involves the superior cerebellar artery looping down in front of the nerve and emerging from the nerve dorsally at the point where the nerve exits the brain stem (Fig. 125-6). Opening the arachnoid widely allows full inspection of the entire circumference of the nerve at the brain stem. The first vessel seen may not be the only vascular channel involved in the neurovascular compression, because in a significant number of cases, multiple vessels have been encountered. It is also necessary to open the arachnoid anterior to the nerve to allow proper placement of the prosthesis.

FIGURE 125-6 A, Schematic view of a left trigeminal nerve decompression. The superior cerebellar artery is compressing the superior edge of the trigeminal nerve. B, Elevation of the superior cerebellar artery reveals indentation and grooving by the artery. C, Shredded Teflon felt is gently worked in between the nerve and the compressing artery. D, The shredded Teflon felt is placed between the artery and the nerve so that the thrust of the arterial force is now directed away from the underlying nerve.

The fourth nerve is a thin, delicate structure in the arachnoid above the fifth nerve and usually just below the tentorium. One of the reasons that sharp rather than blunt dissection of the arachnoid is recommended is that great care must be taken to avoid injuring this nerve. In addition, care must be taken in the dissection of this arachnoid to avoid injuring small vascular channels traversing the subarachnoid space.

Jannetta microsurgical instruments (V. Mueller & Co., Chicago, IL), Rhoton dissectors (V. Mueller & Co.), or Apfelbaum dissectors (Integra Life Sciences, Plainsboro, NJ) are of sufficient length and properly fashioned to allow adequate vision throughout the operation. Various microsurgical scissors, including the Kurze left and right pistol-grip scissors (V. Mueller & Co.) and straight and angled bayoneted microscissors, are also employed. Once the arachnoid has been opened fully and the area has been inspected completely, the exact nature of the compression can be determined. A microdental mirror (warmed in hot saline to reduce fogging) may be useful in inspecting the region anterior to the nerve. This trigeminal nerve exposure is carried out directly over the seventh and eighth nerves (Fig. 125-6). The presence of these nerves must be kept in mind to avoid traumatizing them during the dissection or while inserting or removing instruments. The arterial loops that are found are then carefully dissected free of the trigeminal nerve.

When the superior cerebellar artery is the problem, the intent is to elevate it to a horizontal rather than vertical orientation and to displace it upward and away from the nerve (Fig. 125-6). This elongated vessel may have small branches going to the brain stem. Normally, these branches do not present a problem in the elevation of the vessel, as long as their position is kept in mind. Venous channels above or below the nerve are dissected away from the nerve and are coagulated and divided. The coagulation of these vessels is facilitated by the use of small up-and-down–angled bipolar forceps that prevent the spread of current to the adjacent neural structures. In the case of vessels compressing the nerve inferiorly, they must be displaced further inferiorly away from the nerve. In all cases, it is important to avoid kinking the arterial channels as they are repositioned.

To secure these vessels free of the nerve, a small prosthesis is inserted between the artery and the nerve (Fig. 125-6). For this purpose, we use either Ivalon or shredded Teflon felt. Ivalon, a synthetic polyvinyl formyl alcohol foam sponge material (Unipoint Industries, High Point, NC) has been safely used as a biologic implant for more than 30 years. This material comes packed in formalin and must be washed carefully to remove all traces of preservative. It can then be cut into small blocks and autoclaved. Before its use, Ivalon must be soaked for about 10 minutes in a saline solution to rehydrate it and allow it to become soft and pliable. A small block of the material is then carved to fit between the artery and the nerve. We usually fashion the block into a saddle-shaped structure so that it fits completely over the nerve. This structure effectively alters the arterial force vectors and creates a satisfactory decompression. In the case of a vessel inferior to the nerve, a similar type of sponge with a longer posterior element is fashioned, and this posterior element is inserted inferior to the nerve between the artery and the vein.

Shredded polytetrafluoroethylene (Teflon) felt is another suitable prosthetic material and is particularly useful when the perineural subarachnoid space is narrow. The felt is shredded by grasping and tearing it with two hemostats to create a soft prosthesis resembling a cotton ball. It is gently interposed between the nerve and the artery in a large-enough quantity to ensure decent decompression. The Teflon felt is somewhat easier to place than Ivalon. A slightly higher risk of an aseptic meningeal reaction (headache and sterile cerebrospinal fluid pleocytosis) may occur with Teflon; the reaction is self-limited but may nevertheless prolong recovery time.

On several occasions, we created a sling using a partial thickness of the tentorium that was looped down around the vessel and reattached to the tentorium with a small suture. This was effective when the subarachnoid space was too cramped to place Ivalon without adding compression to the nerve but was technically much more difficult than inserting the sponge prosthesis. If venous channels alone are encountered, no prosthesis is required and the channels are coagulated and divided. Coagulation alone shrinks them, which increases the tension on the nerve and allows for potential recanalization, so the coagulated vessels should always be divided. Tumors can also be the sole cause of neural compression or found displacing a vessel against the nerve.

After decompression, if visible spasm is produced in vessels by the surgical manipulation, topical papaverine placed on a very small piece of Gelfoam is placed on the vessel for a few minutes to reverse the spasm. The operative field is then irrigated, and the retractor is removed. The cerebellum should be inspected at this point to be sure that there is no surface bleeding. We routinely place a piece of Gelfoam over the surface of the cerebellum and then effect a water-tight dural closure using continuous and interrupted 4-0 braided sutures. A watertight closure minimizes the chance of a subsequent cerebrospinal fluid leak. We then place the rongeured bone fragments and drilling slurry wrapped in Gelfoam sponge into the craniectomy defect to provide a matrix for new bone formation and improved cosmesis. The wound is then closed in layers using various grades of resorbable sutures followed by a running nylon skin suture. A small light surgical dressing is then applied.

Postoperative Considerations

Patients are nursed in the semisitting position for the first 24 hours and are observed carefully for any alterations in neural function or signs of pressure in the posterior fossa resulting from cerebellar swelling or hematoma. Patients are allowed out of bed and begin oral intake on the first postoperative day. The urinary catheter is removed at that time, and intravenous fluids are discontinued as soon as the patient is able to achieve adequate oral intake. The surgical dressing is removed on the second postoperative day.

Many patients have a postoperative headache. We routinely prescribe mild narcotic analgesics (codeine). The headache usually subsides within the first 2 days but may occasionally persist for several weeks. Most patients recover rapidly from this procedure and are ready for discharge by the third to fifth postoperative day. The majority of patients prefer a week at home for additional convalescence. During that time, their activities are not restricted, and they are encouraged to increase their activity gradually.

Operative Results

We analyzed our data in a consecutive series of 559 patients treated with microvascular decompression between November 1975 and June 2009. Some data points were not recorded in every case. Compression of the trigeminal nerve was found in 527 of 544 patients (97%) (Table 125-2). In 435 patients (78%), an artery was found compressing the nerve, most frequently the superior cerebellar artery (80%) (Table 125-3). In 6 cases (1%), an artery associated with a cerebellopontine angle tumor was found compressing the fifth cranial nerve, and in another 6 cases, the tumor itself was thought to be the compressing agent (Table 125-2). No compression of the nerve was identified in 17 patients (3%).

Table 125-2 Operative Findings in 559 Consecutive Patients Who Underwent Microvascular Decompression for Trigeminal Neuralgia

Operative Finding	Patients
Arterial channels (alone, with veins, or AVM)	435 (78%)
Venous channels alone	80 (14%)
Tumor (6 with artery, 6 without artery)	12 (2%)
No nerve compression	17 (3%)
Not recorded	15 (3%)
Total patients	559 (100%)

AVM, arteriovenous malformation.

Table 125-3 Compressing Artery Found at Surgery in 441 Patients ^∗ Who Underwent Microvascular Decompression for Trigeminal Neuralgia

Artery Found	Patients
SCA	351 (79.6%)
SCA and AICA	39 (8.8%)
AICA	39 (8.8%)
Basilar artery	7 (1.6%)
Trigeminal nerve	1 (<0.2%)
Vertebral artery	1 (<0.2%)
Unnamed	3 (<0.7%)
Total patients	441 (<99.9%)

SCA, superior cerebellar artery; AICA, anterior inferior cerebellar artery.

∗ Arterial compression either alone or in combination with veins, arteriovenous malformations, or tumors was noted in 441 patients. No such compression was noted in 118 of the 559 patients treated in the series.

Generally, our clinical results of this procedure correspond well with those of Jannetta as reported by Barker et al.⁴ Most patients awakened from anesthesia without tic pain, but some continued to postoperative pain for a few days or weeks (Table 125-4). This pain was less than that present immediately before surgery and gradually tapered off. Carbamazepine or phenytoin may be restarted for tic pain relief, if necessary, and then slowly tapered over a few weeks. In long-term follow-up (mean 75 months) of 501 consecutive patients who underwent microvascular decompression for refractory trigeminal neuralgia over more than 33 years (Table 125-5), the pain was controlled with or without medication in 416 (84%) patients. Of these patients, 22 (4%) had an occasional jab of pain but did not required any medication. An additional group of 68 patients (14%) required medication for full pain control after surgery. Before surgery, all of these patients had pain that was uncontrolled with maximal medical therapy. Although they did not experienced a perfect result, this group of patients greatly benefitted from the procedure. During this long follow-up period, 80 patients (16%) experienced severe recurrences that were refractory to medical therapy. These instances were failures of the procedure and necessitated an additional, usually destructive procedure to achieve relief.

Table 125-4 Initial Results Recorded in 523 Patients ^∗ Treated with Microvascular Decompression for Trigeminal Neuralgia

Result	Patients
Complete relief	474 (91%)
Immediate	415 (79%)
At discharge	27 (5%)
After discharge	32 (6%)
Pain reduced	32 (6%)
With medication	23 (4%)
With additional surgery	9 (2%)
Pain not relieved	12 (2%)
Died	5 (1%)
Total patients	523 (100%)

∗ Initial results were not available in 36 of the 559 patients treated in the series.

Table 125-5 Long-Term Results in 501 Patients ^∗ Treated with Microvascular Decompression for Trigeminal Neuralgia

Result	Patients
No recurrence	326 (65%)
Mild pain, no medication required	22 (4%)
Pain medically controlled	68 (14%)
Severe pain not controlled medically	80 (16%)
Died	5 (1%)
Total patients	501 (100%)

∗ Long-term results were not available in 58 of the 559 patients treated in the series.

Complications

The complications in our series are presented in Table 125-6. Five deaths occurred in this series, emphasizing the need for careful patient selection and screening. Cerebellar hemorrhagic infarction resulted in three deaths. We believe that this potentially lethal complication can be limited by minimizing the number of veins sacrificed at surgery. Although this may not be the only factor, since we have taken pains to spare the veins we have not had a death in the last 17 years. The most common type of complication is cranial nerve palsy. Transient facial numbness, which occurred in 19 patients (3%), and fourth nerve palsy, which occurred in 18 patients (3%), represent the most frequent of these. In all cases of fourth nerve palsy, the diplopia subsided over time (a few weeks to several months). Facial nerve palsy occurred in 8 patients (1%), and hearing loss occurred in 14 patients (3%). The facial nerve palsies that were severe were associated with cerebellopontine angle tumors in 4 of the 5 cases. The milder palsies were self-limited and resulted in good to satisfactory recovery. Hearing loss or disequilibrium may be caused by eighth nerve dysfunction. This was mild in 27 patients (5%) and severe in 14 patients (3%). Patients who develop hearing loss from eighth nerve dysfunction usually do not recover their hearing, although 1 of our patients did. This type of hearing loss must be distinguished from modest decreases in hearing that many patients experience immediately postoperatively because of fluid behind the eardrum (presumably tracking in through the mastoid area). This is a benign, self-limited process that clears spontaneously within a few weeks. Because we could not retrospectively distinguish these two, all are grouped under eighth nerve dysfunction.

Table 125-6 Complications in 559 Patients Treated with Microvascular Decompression for Trigeminal Neuralgia

Complication	Patients
Death^∗	5 (0.9%)
Cerebellar infarction^∗	6 (1.1%)
Supratentorial infarction^∗	3 (0.5%)
Brain stem infarction^∗	1 (0.2%)
Focal seizures	5 (0.9%)
Cranial nerve dysfunction
Fourth nerve palsy (transient)	18 (3.2%)
Sixth nerve palsy (transient)	2 (<0.4%)
Seventh nerve palsy (permanent)	5 (0.9%)
Seventh nerve palsy (transient)	3 (0.5%)
Eighth nerve dysfunction	21 (3.8%)
Facial numbness	19 (3.4%)
Dizziness, disequilibrium, ataxia	20 (3.6%)

∗ Three deaths were from cerebellar infarction, and one each occurred from supratentorial infarction and brain stem infarction; these patients were included in the totals of the infarctions.

Occasionally, patients experience nonpainful, twinge-like feelings in the face that are often described as a zippy sensation. It is not painful but often produces great anxiety in the patient, who fears that it portends the return of pain. These feelings are frequent in our experience. They usually subside with time and do not appear to indicate a potential return to pain.

Conclusions

The Jannetta microvascular procedure, as detailed here, has proved effective in treating trigeminal neuralgia in most patients by treating the apparent cause of the problem rather than merely the symptoms. It offers the major advantage of sparing neural function and avoiding anesthesia dolorosa, other dysesthetic sensations, or facial sensory losses such as corneal anesthesia, but it carries with it a small risk of serious sequelae, including death.^4,^9,¹¹ Although small but not insignificant risks are associated with this procedure, we believe that microvascular decompression remains the treatment of choice for trigeminal neuralgia.

Seventh Cranial Nerve

Clinical Presentation

The motor analogue of trigeminal neuralgia is hemifacial spasm, which is caused by vascular compression of the seventh cranial nerve. This disorder is less frequent than trigeminal neuralgia. We typically see five cases of trigeminal neuralgia for each case of hemifacial spasm. Females are more frequently affected than males (3:2 ratio). Although rare reports of this disorder in children exist, it is typically an adult disorder with a mean age of onset of 45 years.¹²

Patients with this condition suffer from repetitive, painless paroxysmal twitching of the facial muscles. Classically, this disorder starts with the muscles around the eyes and progresses slowly and insidiously to involve the middle and lower facial musculature. In severe cases, the spasm spreads to involve both the corrugator of the forehead and the platysma muscle on the anterior neck. At times, severe sustained contractures lasting for several seconds, the so-called tonus phenomenon, occur. The patient cannot voluntarily relax, so the contractures result in a grotesque disfigurement with a forced closure of the eye and a tight grimace of the mouth.

Hemifacial spasm is often misdiagnosed as an emotional problem, because like many neurologic problems it becomes worse during periods of emotional stress. The symptoms can have a profound influence on an individual’s life by altering self-image, affecting relationships with others, and seriously altering career potential. Later, as the disease progresses, the repetitive frequent eye closures may alter an individual’s ability to read or drive a car safely. Moreover, mild facial motor weakness may be noted between spasms and hearing may be moderately impaired.

Electromyography can be used to help establish the diagnosis of hemifacial spasm. Electromyographic studies in cases of hemifacial spasm characteristically reveal 5 to 20 rhythmically occurring burst discharges per second, along with individual discharges and longer-lasting bursts. The rate of discharge of the latter may be as high as 150 to 250 bursts per second.¹³ These findings are pathognomic for hemifacial spasm and can help resolve any uncertainty about the diagnosis.

Differential Diagnosis

The differential diagnosis of the hemifacial spasm condition includes several entities. Emotional and nervous tics differ from hemifacial spasm in their multifocal presentation, involving multiple muscles that are innervated by various nervous territories rather than being confined solely to the territory of a unilateral facial nerve. Blepharospasm is a bilateral forced contracture of the musculature about the eye. It differs from hemifacial spasm in its bilateral nature and involvement of only the musculature about the eye rather than a steady progression down the face. It appears to have a different cause and is not thought to respond to this type of surgery.

More closely mimicking hemifacial spasm are the synkinetic movements that may occur following aberrant regeneration of the facial nerve after Bell palsy. A history of antecedent Bell palsy with these movements developing upon regeneration of the nerve is most helpful in excluding it. Synkinetic movements develop with regeneration of the nerve and not as a late finding after adequate recovery from Bell palsy. Facial myokymia also must be considered in the differential. These undulating, worm-like movements associated with intrinsic brain stem pathology have a distinct and diagnostic electromyographic pattern. The association of other cranial nerve defects may also help clarify this diagnosis.

Medical Therapy

In contrast to trigeminal neuralgia, no medical treatment has been effective in relieving hemifacial spasm permanently. Some success has been obtained with the injection of botulinum toxin into affected muscles. The effect is frequently limited and requires repeated injections. Concern also exists about the cumulative toxicity of repeated botulinum injections.

Indications

Hemifacial spasm patients who are in reasonably good health and are generally younger than 70 years are potential surgical candidates. Alternative options that have been used for the treatment of hemifacial spasm include (1) selective neurotomy, (2) distal nerve avulsion, and (3) facial nerve sectioning with or without anastomosis to the hypoglossal or spinal accessory nerve. Selective neurotomy and distal nerve avulsion result in incomplete improvement and are associated with recurrence and facial nerve palsy. Partial division of the facial nerve, although immediately effective, frequently results in recurrence of symptoms that coincides with regeneration of the sectioned facial nerve. Repeated sectioning of the facial nerve after progression or recurrence results in additional neural destruction that eventually causes a permanent facial palsy. In an attempt to avoid recurrence after sectioning, some authors have attempted seventh nerve sectioning with subsequent anastomosis to either the spinal accessory or the hypoglossal nerve in an effort to prevent distal facial nerve regeneration. This technique does not always prevent distal regeneration and recurrence and can result in tongue atrophy and facial paralysis. Because of these problems, we believe the treatment of choice for hemifacial spasm is microvascular decompression the seventh cranial nerve.

Preoperative Considerations

Once the diagnosis of hemifacial spasm is established by clinical and electrical evaluation, high-resolution MRI of the posterior fossa with and without contrast material should be obtained. Neoplasm, inflammation, infection, and non-neoplastic structural lesions that are revealed by thin-cut MRI studies should be treated accordingly. As in trigeminal neuralgia, the absence of a visualizable vascular loop on imaging does not rule out such a lesion. Preoperative and anesthetic considerations, as well as patient positioning, are identical to those described previously for trigeminal neuralgia. Intraoperative monitoring of the seventh (electromyography) and eighth (brain stem auditory evoked responses) cranial nerves is useful during this procedure.^14,¹⁵

Operative Procedure

The incision is positioned so that half of the incision length is above the level of the mastoid notch (Fig. 125-3). The exposure of the occipital bone and the craniectomy are then performed as detailed previously. Similar to trigeminal nerve microvascular decompression, the craniectomy is extended laterally to expose the sigmoid sinus. Vertically, the craniectomy (Fig. 125-5) is extended superiorly to just below the transverse sinus and inferiorly to the floor of the posterior fossa. At this point, the bone is usually fairly thin and curves to extend almost straight away from the surgeon. It is important to not leave a lip on this area that will prevent the free egress of cerebrospinal fluid. The dura is opened in an L shape or reverse L shape 3 to 5 mm parallel to the sigmoid sinus and the floor of the posterior fossa, fairly close to these structures; if necessary, it can be further opened in a T shape. The dural edges are then secured with tenting sutures to widen the exposure.

The same type of self-retaining retractor system is used, but the retractor blade is arced from side to side and tapers in width (Aesculap, Center Valley, PA). This retractor is placed beneath the cerebellum, and the cerebellum is elevated at its inferior lateral margin. The operating microscope, configured exactly as previously, is brought into use at this juncture. Under magnified vision, the cerebellum is gently elevated. It is important that the cerebellum is elevated by retracting upward on it rather than retracting it from lateral to medial. The latter may cause traction injuries to the seventh and eighth nerves. A Cottonoid strip is then placed along the medial inferior edge of the exposure to act as a wick that facilitates drainage of cerebrospinal fluid and prevents it from welling up in the operative field. With elevation of the cerebellum, the retractor can be advanced anteriorly under direct vision until the spinal part of cranial nerve XI comes into view. The arachnoid at this area is opened sharply, which allows further elevation of the cerebellum and exposure of the remaining nerves of the jugular foramen (Fig. 125-7). Occasionally, minute bridging veins have to be coagulated and divided to cause this exposure. Once the ninth cranial nerve, which is usually slightly separated from nerves X and XI, is identified, the exposure is carried medially by sequentially dividing the arachnoid (using sharp dissection) between the ninth nerve and the cerebellum.

FIGURE 125-7 Microvascular decompression for hemifacial spasm. The retractor is elevating the cerebellum, exposing the posterior inferior cerebellar artery (PICA), which compresses the root exit zone of the facial nerve (VII). The inset shows the vessel displaced posteriorly and inferiorly away from the nerve by shredded Teflon felt.

No attempt is made at this point to identify the seventh and eighth nerves at the porus acusticus (although they often may be in view). They are not followed from the porus acusticus medially to the brain stem, because this increases the risk of injury to the eighth nerve. Rather, the dissection is carried out just above the ninth nerve, and by sharply dividing the arachnoid, the cerebellum is gently elevated. Proceeding laterally to medially in this manner, the choroid plexus emanating from the lateral recess of the fourth ventricle soon comes into view. Its elevation exposes the root entry zone of the seventh and eighth nerves at the brain stem.

Two techniques are helpful at this point: (1) the operating table is rotated forward using the Trendelenburg control to increase the exposure superiorly toward the seventh and eighth nerves, and to minimize the retraction that is necessary, and (2) the retractor blade is replaced with a blade that has an elongated process in its center (Codman & Shurtleff). This finger-like protrusion can be advanced up under the choroid plexus to elevate it and improve the visualization. This is a difficult area in which to work comfortably. With the patient’s head flexed and the table tilted forward, the facial nerve is visible in front of the eighth nerve with its origin slightly inferior. We use a facial nerve stimulator to confirm localization. The facial nerve usually has a slightly gray coloration compared with the pure white appearance of the eighth nerve. The individual components of the eighth nerve normally are not appreciated as separate nerves but rather run together as a compact bundle.

The site of cross-compression is found in this region where the seventh nerve leaves the brain stem. Several vessels have been encountered in our experience (Table 125-7). The anterior inferior cerebellar artery may loop up against the nerve and then continue either laterally or inferiorly. The posterior inferior cerebellar artery likewise can loop up to compress this area before taking a more inferior course. An ectatic vertebral artery can sometimes cause the same problem. On one occasion, an indentation of the nerve was noted, but no definite vascular channel was found. On closer inspection, an exostotic protuberance from the floor of the posterior fossa was noted, and when the retractor was released, it could be seen that this protuberance mated with the indentation on the nerve. In this instance, the protuberance was removed with a high-speed diamond drill to bring about relief.

Table 125-7 Operative Findings in 73 Consecutive Patients Who Underwent Microvascular Decompression for Treatment of Hemifacial Spasm

Cause of Seventh Nerve Compression	Patients
Loop of AICA	29 (39.7%)
Loop of PICA	22 (30.1%)
Vertebral artery at AICA origin	7 (9.6%)
Vertebral artery at PICA origin	4 (5.5%)
Vertebral artery exclusively	4 (5.5%)
AICA and PICA	3 (4.1%)
Vein	2 (2.7%)
Aneurysm	1 (1.4%)
Bone exostosis	1 (1.4%)
Total patients	73 (99%)

AICA, anterior inferior cerebellar artery; PICA, posterior inferior cerebellar artery.

When a vessel is encountered, it must be carefully dissected free of the nerve and placed in such a way that relieves the pressure on the nerve, while not kinking or compromising the vessel. Small tethering branches to the brain stem often limit the degree of displacement that can be achieved. The surgeon must always be aware of the possible presence of small branches along the medial side of the vessel going to the brain stem, especially at the apex of loops. After carefully dissecting the vessel free of the nerve and using the utmost care not to manipulate either the seventh or the eighth nerve, an Ivalon sponge prosthesis is fashioned to fit between the two. This sponge often takes on a complicated shape because of the limited access in this area and the necessity of accommodating various structures. We try to interdigitate the prosthesis between the vessels and often fashion protuberances on it to fit within the loops of the vessel to help anchor it in place. Alternatively, shredded Teflon felt can be used; it is softer and easier to manipulate. It may be less likely to compress the adjacent nerves and less likely to compromise the vessel and its branches. The Teflon felt should be shredded to a cotton ball–like consistency (Fig. 125-7), because it provides inadequate cushioning and is easily displaced when employed in sheet form. Absorbable materials, such as a Gelfoam sponge, should be avoided because the vessel may return to its compressive position against the nerve upon absorption. Similarly, muscle, which is attractive because it is easy to insert, has led to recurrences as the muscle atrophied under the continued arterial pulsations and allowed the artery and nerve to come into contact again.

Once a satisfactory decompression of the nerve is achieved, spasm is lysed with topical papaverine, the area is irrigated, and the retractor is removed, while the effects of these maneuvers on the vascular anatomy are carefully observed. Closure and postoperative care are identical to those used in treating patients with trigeminal neuralgia nerve decompression.

Operative Results

In 73 consecutive cases, a cause of compression was identified in each situation. No negative explorations were encountered (Table 125-7). The most common cause of arterial compression was the anterior inferior cerebellar artery (40%), followed by the posterior inferior cerebellar artery (30%) (Table 125-7).

Generally, our clinical results are similar to those of Barker et al.¹⁶ and Samii et al.¹⁷ In our series, hemifacial spasm was relieved in all patients after microvascular decompression (Table 125-8). Of 67 patients (92% of the total in the series), 6 patients (8%) had good relief and 61 patients (84%) had complete relief of spasm in long-term follow-up (mean follow-up 8.8 years). All patients who had long-term follow-up, 70 patients (96%) from the series, had a greater than 50% reduction in twitches.

Table 125-8 Long-Term Results (Mean Follow-Up 8.8 Years) in 73 Consecutive Patients Who Underwent Microvascular Decompression for Treatment of Hemifacial Spasm

Result	Patients
Excellent (complete resolution of symptoms)	61 (84%)
Good (rare residual twitches)	6 (8%)
Fair (50% reduction in twitches)	3 (4%)
Poor (return of preoperative symptoms)	0 (0%)
Unavailable	3 (4%)
Total patients	73 (100%)

We found that 18 patients (25%) had recurrence of symptoms. Of these, 12 patients had mild recurrences (less than 50% of preoperative level), and 10 of these patients resolved spontaneously. Another 3 patients had moderate recurrences (50% of preoperative symptom level); 1 patient resolved spontaneously, but the others worsened significantly. Finally, 3 patients had a significant (equivalent to preoperative symptom level) return of symptoms, and 1 of these patients resolved spontaneously. We reoperated on 1 of the patients who suffered a significant return of symptoms at 5 months. Re-exploration revealed an unsatisfactory positioning of the prosthesis. The prosthesis was replaced, resulting in full resolution of facial spasm after surgery.

Complications

Most complications resulted in transient neurologic deficits or dysfunction (Table 125-9). Transient problems included facial weakness (11 patients), focal seizures (2 patients), and supratentorial stroke (1 patient). The transient facial weakness began in 6 patients 1 week after surgery. Of these patients, 3 had trace weakness that could only be detected with careful examination. The other 3 patients developed moderate (1 patient) or severe facial weakness (2 patients) that resolved over 2 to 6 months. In addition, 2 patients had new onset focal seizures at 1 and 6 months postoperatively. One patient had a supratentorial stroke and recovered completely. Three complications resulted in permanent deficits (Table 125-9), including quadriplegia secondary to a brain stem infarct (1 patient) and moderate hearing loss (2 patients).

Table 125-9 Complications in 73 Consecutive Patients Who Underwent Microvascular Decompression of the Seventh Cranial Nerve for Treatment of Hemifacial Spasm

Complication	Patients
Permanent
Brain stem stroke (quadriplegia)	1 (2%)
Unilateral hearing loss	2 (3%)
Transient
Facial weakness
Trace	8 (11%)
Moderate	1 (1%)
Severe	2 (3%)
Focal seizure	2 (3%)
Supratentorial stroke	1 (1%)

Conclusions

Microvascular decompression as applied to the treatment of hemifacial spasm offers even more convincing results than those obtained in the treatment of trigeminal neuralgia both because of the lack of efficacious alternative forms of therapy and because of the visible and graphic effects of the surgical procedure. This procedure carries a small but significant risk of serious sequelae. It is a more difficult procedure than the decompression of the trigeminal nerve, and its potential benefits must be weighed carefully in this nonlethal, painless condition.

Fifth and Seventh Cranial Nerves

Cushing ¹⁸ described a few patients suffering from the combined clinical picture of trigeminal neuralgia and hemifacial spasm, a condition that he termed tic convulsif. In patients who appear to have features of both trigeminal neuralgia and hemifacial spasm, it is appropriate to explore the root entry zone of both the fifth and the seventh cranial nerves.¹⁹ Although vascular channels compressing on both nerves should be anticipated, it is conceivable that only one nerve will be affected because of anomalous innervation. It is always the safest course to explore both nerves.

Ninth Cranial Nerve

Clinical Presentation

Glossopharyngeal neuralgia is a condition that is analogous to trigeminal neuralgia occurring in the ninth cranial nerve territory. The incidence of these two disorders differs greatly, with glossopharyngeal neuralgia being much less common than trigeminal neuralgia. Females are more commonly affected than males (2:1).²⁰ The onset of symptoms is typically between 40 and 60 years of age, with a peak incidence in the fifth decade.²⁰

This disorder has been classified into two groups based on the origin of pain. Patients with the tympanic form have pain that starts in the region of the ear and radiates to the throat, whereas patients with the oropharyngeal form have pain that begins in the throat and radiates to the ear. Despite differences in the origin of pain, patients classically describe the pain as a paroxysmal shooting, stabbing, or lancinating. Both sides of the face and throat are equally affected.²⁰ Consistent with the close anatomic proximity of the vagal system, cases in which paroxysms have been associated with bradycardia, syncope, and occasionally asystole have been reported. The paroxysms are frequently triggered swallowing cold beverages but can be precipitated by yawning, talking, chewing, coughing, sneezing, or touching in the region of the tragus. These episodic attacks often occur in clusters that last from days to months and frequently relapse.

The diagnosis of glossopharyngeal neuralgia can be confirmed by the application of topical cocaine (10%) to the patient’s trigger zone. Patients with glossopharyngeal neuralgia typically report immediate relief from the painful paroxysms, as well as prevention of retriggering with stimulation for 1 to 2 hours after the administration of the anesthetic.

Differential Diagnosis

A classic history and topical cocaine testing frequently make diagnosis of glossopharyngeal neuralgia straightforward. In some instances, the diagnosis is not clear and other disorders must be considered. Trigeminal neuralgia (particularly involving the third division) can mimic many of the symptoms of glossopharyngeal neuralgia or occur concurrently with it. The paroxysmal nature of cluster headaches can sometimes be confused with glossopharyngeal neuralgia. The pain from superior laryngeal nerve neuralgia can also be mistaken for glossopharyngeal neuralgia.

Medical Therapy

Medical therapy for glossopharyngeal neuralgia is similar to that of trigeminal neuralgia. Initially, control of symptoms should be attempted with carbamazepine with appropriate laboratory and clinical monitoring (see the Medical Therapy section under the Fifth Cranial Nerve section). Failure of carbamazepine therapy should prompt trials with other agents (as outlined in the same section).

Indications

Once the diagnosis of glossopharyngeal neuralgia is established and other underlying structural or inflammatory causes are ruled out, medical therapy should be instituted as outlined previously. Microvascular decompression is indicated in patients whose pain is refractory to medical therapy. Patients selected for surgery should be in good medical condition and are generally younger than 70 years of age.

Preoperative Considerations

Following a diagnosis of glossopharyngeal neuralgia, the underlying cause of the condition should be sought. High-resolution MRI with and without contrast material through the posterior fossa is used to determine whether the neuralgia is the result of neoplasm, infection, inflammation, vascular malformation, or another lesion. Each lesion should be treated accordingly.

Surgical options other than microvascular decompression for the treatment of glossopharyngeal neuralgia include (1) percutaneous thermal rhizotomy of the glossopharyngeal at the jugular foramen, (2) extracranial sectioning of branches of the glossopharyngeal nerve, (3) intracranial sectioning of the glossopharyngeal nerve, and (4) sectioning of the upper vagal nerve rootlets. The nonspecific nature of percutaneous rhizotomy of the glossopharyngeal nerve can provide relief from pain but not infrequently results in permanent dysphagia and hoarseness. Extracranial sectioning of the glossopharyngeal or vagal nerve for neuralgia may provide immediate relief but is associated with recurrence of symptoms. Intracranial sectioning of the glossopharyngeal nerve and at times the upper fibers of the vagus nerve has been successful at relieving glossopharyngeal neuralgia. It is usually well tolerated but can result in vocal cord paralysis, diminished gag reflex, and dysphagia. Microvascular decompression can be used to avoid these difficulties and provide a permanent solution to the symptoms associated with glossopharyngeal neuralgia.

The anesthesia and positioning for microvascular decompression of the ninth cranial nerve are the same as for seventh nerve decompression.

Operative Procedure

As in surgery on the seventh cranial nerve, the incision of the ninth cranial nerve is positioned so that half of the incision length is above the level of the mastoid notch. The operative exposure is the same as the one detailed for the seventh cranial nerve but with the modification that the root entry zone of the ninth cranial nerve is inspected and decompressed. This exposure is accomplished by following the superior surface of the ninth nerve back to the brain stem and then visualizing this area, working between the seventh and the eighth nerves above and the ninth nerve below or between nerve IX and nerve X. When decompression cannot be achieved, sectioning of cranial nerve IX and the upper fascicles of cranial nerve X can provide good relief.

Operative Results

Because of the rare occurrence of glossopharyngeal neuralgia, few large series with long-term follow-up have evaluated the efficacy of microvascular decompression for this disorder.²⁰^–²² In 2002, Patel et al.²⁰ reported the efficacy of microvascular decompression for glossopharyngeal neuralgia in 217 patients. This study found that immediately after surgery 67% of patients had complete relief and an additional 25% had partial relief, for an immediate postoperative success rate of 92%. Of the 50 patients with long-term follow-up (mean follow-up 4 years), 58% had complete relief of symptoms, 18% had partial relief (minimum of four-point improvement on a continuous pain scale, with or without medications), and 24% had a lack of substantial improvement. Moreover, this study found that isolated throat pain was a positive predictor of operative success.

Complications

In the series reported by Patel et al.,²⁰ the rates of various complications were broken down into quartiles of approximately 50 patients over the period extending from 1973 to 2000. Various complications, including intracranial hematoma (rate of 0%-5.8% over quartiles), brain stem infarction (0%-4.1%), cranial nerve IX/X palsy (0%-4.2%), eighth/other cranial nerve palsy (0%-4.2%), cerebrospinal fluid leak (1.5%-5.8%), operative-related death (0%-5.8%), and dysphagia (0%-4.2%), were observed.