Geniculate neuralgia: long-term results of surgical treatment. (Original Article).

Abstract

A rare cause of otalgia is geniculate neuralgia. In its most typical form, it is characterized by severe paroxysmal neuralgic pain centered directly in the ear. The pain can be of a gradual onset and of a dull, persistent nature, but occasionally it is sharp and stabbing. When the pain becomes intractable, an operation to surgically excise the nervus intermedius and geniculate ganglion via the middle cranial fossa approach is indicated. The purpose of this article is to review the long-term outcomes in 64 patients who were treated in this manner. Findings indicate that excision of the nervus intermedius and geniculate ganglion can be routinely performed without causing facial paralysis and that it is an effective definitive treatment for intractable geniculate neuralgia.

Introduction

A rare cause of severe intractable ear pain is geniculate neuralgia, which is also called tic douloureux of the nervus intermedius. In its most typical form, geniculate neuralgia is characterized by severe paroxysmal neuralgic pain centered directly in the ear. The pain can be of a gradual onset and of a dull, persistent nature, but occasionally it is sharp and stabbing. In 1976, the author described this condition in detail and proposed treatment by the excision of the nervus intermedius and excision of the geniculate ganglion via a middle cranial fossa approach. (1) Fifteen cases were reported.

It is the purpose of this article to review the long-term outcomes in 64 patients who were treated between 1966 and 1996 for geniculate neuralgia with excision of the nervus intermedius and geniculate ganglion. Findings indicate that excision of the nervus intermedius and geniculate ganglion can continue to be performed without causing facial paralysis and that it is an effective definitive treatment for intractable geniculate neuralgia.

Diagnosis

Sensation is supplied to the area of the ear by the Vth, VIIth, VIIIth, IXth, and Xth cranial nerves and the 2nd and 3rd cervical nerves. It is important to know the area of distribution served by each of these nerves so that an accurate diagnosis can be made. It is not uncommon to see an overlap, with involvement of more than one cranial nerve. The overriding characteristic of geniculate neuralgia described by the patient is "a severe paroxysmal neuralgic pain centered directly in the ear." The pain was described by one patient as that which would be caused by "an ice pick in the ear." The pain does not extend into the neck, into the face, or above the ear.

Before a diagnosis of geniculate ganglion neuralgia can be established, all other possible causes of otalgia must be eliminated. A thorough neuro-otologic examination must be performed; this examination should include an audiogram for pure tones and speech, auditory evoked response potentials, and vestibular tests, usually including alternate bilateral bithermal caloric testing. In order to exclude other causes of the pain, all test results must be normal. Likewise, findings on magnetic resonance imaging (MRI) with gadolinium enhancement of the entire brain, cerebellopontine angle, and facial nerve must also be normal. Finally, examinations of the nose, paranasal sinuses, mouth, teeth, nasopharynx, pharynx, and larynx must reveal no cause for the pain.

Surgical treatment

The specific surgical treatment for geniculate neuralgia is excision of the nervus intermedius and the geniculate ganglion via a middle cranial fossa surgical approach (figure 1). This procedure was devised in 1966, when it was found that excision of the nervus intermedius alone did not reliably eliminate pain from the facial nerve. It was clear that in some (if not most) patients, pain fibers passing from the geniculate ganglion to the brain did so through the motor trunk of the VIIth nerve, as well as the nervus intermedius. Anatomic dissections at that time suggested that most ganglion cells could be excised by slicing away the ganglion from the internal genu of the facial nerve.

The surgical technique involves exposure of the geniculate ganglion, the greater petrosal nerve, and the facial nerve from the cochleariform process to the cerebellopontine angle via the middle cranial fossa approach. The nervus intermedius is a clear-cut anatomic structure of approximately the same diameter as the chorda tympani nerve. It crosses over as a separate nerve from the superior vestibular nerve to the facial nerve. The nervus intermedius usually makes its exit from the inferior vestibular nerve at the porus acusticus, where it then crosses diagonally as an individual nerve for a length of 1/4 inch until it enters the facial nerve near the lateral end of the internal auditory canal. It is usually best to first open the internal auditory canal and excise a 5-mm segment of the nervus intermedius (figure 2).

Next, the area of the geniculate ganglion is addressed. It is known from analysis of histologic sections and ganglion stains that the ganglion fibers lie anterior to the internal genu. (1) In addition, because the nerve is circular, the ganglion cells form a concave attachment so that they extend for a short distance over the superior edge of the motor trunk of the facial nerve and over the inferior edge of the facial nerve. (1) Grossly, these anatomic determinations are not visible. For this reason, it has been found effective to carefully identify surgically the posterior edge of the motor trunk of the facial nerve at the genu as well as peripheral and proximal to it for several millimeters. A very sharp knife is used to cut away the geniculate ganglion from the internal genu of the facial nerve. The greater petrosal nerve stump is cut away so that a 5-mm segment is excised. In order to remove an adequate number of ganglion cells, it has been found that 30% of the anterior portion of the internal genu of th e motor portion of the facial nerve can be excised along with the ganglion without causing a permanent facial paralysis (figure 3). As with any facial nerve surgery, the facial motor fibers must be handled delicately so that the remaining motor fibers function normally and do not become edematous.

Results

The study described in this article includes the 15 cases previously reported. (1) Between 1966 and 1996,64 patients were treated with excision of the nervus intermedius and geniculate ganglion. Forty-eight of these patients underwent excision of the nervus intermedius and geniculate ganglion alone, 13 had previously undergone a selective retrolabyrinthine Vth nerve section, and three had undergone a selective retrolabyrinthine Vth nerve section after excision of the nervus intermedius and geniculate ganglion. Patients who underwent the combination procedures had complicated cases of ear pain.

All patients, with the exception of one whose etiology was Lyme disease, experienced excellent results with respect to relief of ear pain. None experienced a sustained hearing loss following surgery, and none had a cerebrospinal fluid leak. Eleven patients experienced a partial temporary facial paralysis, and all recovered completely.

One patient had a prolonged temporary facial paralysis, but this patient eventually experienced an excellent recovery. This patient had sustained the palsy as a result of a surgical error. At the time of exposure of the greater petrosal nerve and geniculate ganglion, it was not recognized that there was no bone over this area, a finding that in seen in 5% of patients. (2) Consequently, excessive tension was placed on the greater petrosal nerve, which passed over to the internal genu and resulted in the facial palsy.

All 64 patients had a permanently non-crying eye on the involved side as a result of the excision of the greater petrosal nerve. This result is expected, and patients are apprised of it before surgery.

Case report

A white 47-year-old woman was referred for treatment of left ear pain of 2 years' duration. The pain had become increasingly more intense and more frequent. She reported that "the pain feels like an ice pick in the ear." The excruciating pain occurred two or three times each day and lasted for 3 minutes at a time. In addition, she described a feeling of spasms in her left eyelid, although none was visible upon examination at any time. Findings on computed tomography of the brain were normal. MRI with gadolinium studies of the brain and facial nerve showed no evidence of abnormality. Findings on physical examination of the ears, nose, and throat were completely normal. Vestibular and audiometric testing showed no evidence of neuro-otologic disease. Auditory evoked response and impedance audiometry were normal. A diagnosis of Left geniculate neuralgia was made.

On Sept. 7, 1994, a left middle cranial fossa surgical approach was used while the patient was under general anesthesia. A 3-inch temporal incision was made anterior and superior to the ear. A square of bone 1 1/2 inch on each side was removed. The temporal lobe dura was elevated, and bone was removed from the greater petrosal nerve, geniculate ganglion, internal genu, labyrinthine portion of the facial nerve, and upper portion of the internal auditory canal until a good view was obtained into the cerebellopontine angle. The nervus intermedius was dissected from the superior vestibular nerve at the porus acusticus and traced to its entry into the facial nerve near the lateral end of the internal auditory canal. A 3-mm segment of this nerve was excised with scissors. A small piece of temporalis muscle was placed over the dural defect in the internal auditory canal. Care was taken to identify the posterior edge of the motor portion of the facial nerve at the internal genu and for several millimeters proximal an d distal to this site. Using the posterior edge of the nerve as a guide, a sharp Beaver knife was used to excise the geniculate ganglion and 25% of the anterior portion of the motor part of the facial nerve at the internal genu.

The greater petrosal nerve was severed so that a 1-cm segment of this nerve was excised along with the geniculate ganglion. The dura was allowed to expand. The bone square was replaced, and the wound was closed in layers with interrupted subcutaneous chromic catgut sutures. Electron microscopy of the geniculate ganglion revealed minimal nonspecific myelin sheath delamination (figure 4).

The patient awoke from anesthesia and reported complete relief of her neuralgic pain. Her postoperative course was uneventful, and she was discharged on the third postoperative day. Follow-up examination 2 years later revealed a complete and permanent relief of then neuralgic pain, normal facial function, no vertigo, no hearing loss, and no tinnitus.

Discussion

In cases of primary geniculate neuralgia uncomplicated by other types of pain, excision of the geniculate ganglion and nervus intermedius via the middle cranial fossa approach has provided reliable and precise results. In cases where initially there are overlapping pains from more than one nerve, the patient must be apprised that more than one procedure might be required. (3) The author has found that the two major nerves involved in ear pain are the Vth and VIIth nerves. The nerve that seems to cause the major pain is usually attacked first. If necessary, surgery can be performed on the second nerve to relieve residual pain. One patient who sustained a severe disabling blast injury to the ear initially complained of pain right in the ear; excision of the geniculate ganglion and nervus intermedius was successful in relieving this pain. As the patient began to feel better, however, he complained of diffuse pain around the ear; this pain was completely relieved 1 year later by selective retrolabyrinthine Vth ne rve section.

One elderly woman was referred by a neurosurgeon after she had had what was believed to be a complete suboccipital Vth nerve section. Even though she had complete anesthesia of the right side of her face, she still complained of right ear pain. She had total loss of right hearing and vestibular function and partial facial palsy with synkinesis. Excision of the geniculate ganglion and nervus intermedius was successful in significantly alleviating her pain, although it did not eliminate it. The author subsequently used a translabyrinthine surgical approach to the cerebellopontine angle and found that the sensory root of the Vth nerve, although somewhat disturbed, was grossly intact. Total incision of the sensory branch of the nerve provided the patient with significant relief. She is not listed as having hearing loss, vestibular loss, or partial facial weakness because she experienced no change following surgery on the geniculate ganglion and all her findings were pre-existing.

One of the most perplexing cases occurred in a man 38 years of age who had a documented history of seropositive Lyme disease, after which he developed left ear pain that had persisted for 6 years. The nature and distribution of the pain were similar to those of geniculate neuralgia. The patient had been taking heavy doses of narcotics and was in a pain-management program. Excision of the geniculate ganglion and nervus intermedius provided what seemed to be a 25% relief of pain. Selective retrolabyrinthine Vth nerve section provided another 50% improvement, allowing the patient to get along on two hydrocodone tablets per day.

To the author's knowledge, this treatment has been utilized by only one other physician group. Dudley Weider, MD, at The Mary Hitchcock Clinic in Hanover, N.H., and colleagues have performed 23 procedures of this type (personal communication, December 1996). A report of their experience treating patients with ear pain was published in 1991. (4)

One important question concerns the anatomic site of the ganglion cells. I originally studied 100 temporal bones and found a consistent anatomic distribution of the ganglion cells within the geniculate ganglion attached to the anterior edge of the internal genu of the motor branch of the facial nerve conforming to the tubular shape of the nerve. I found that some of the ganglion cells extended both superiorly and inferiorly to the anterior edge of the motor root. I reasoned that by excising a portion of the motor root, we would in turn remove the ganglion cells on this concave surface.

Rupa et al reported a study of the dissection of 11 human temporal bones and the distribution of ganglion cells at the internal genu. (5) In one of their specimens, they found extension of cell bodies into the labyrinthine segment of the facial nerve. In another specimen, they found a single ganglion cell in the area of the genu, which led them to postulate that the removal of the geniculate ganglion might not be effective in all patients. Although this might be a potential problem, from a practical standpoint the 64 patients treated in this series (with the exception of the one patient with Lyme disease) have in fact achieved exemplary results. Additional anatomic studies are required to clarify the nature of this anatomic variation.

In conclusion, physicians who deal with pain in the ear and the head must be aware of the characteristics of all neuralgic pains and the anatomic distribution of the nerves innervating the area. Sometimes multiple nerves must be excised. These procedures can be performed without causing permanent facial paralysis, hearing loss, or vestibular loss. These methods offer relief for patients with intractable ear pain.

From the Pulec Ear Clinic, Ear International, and the University of Southern California School of Medicine, Los Angeles.

References

(1.) Pulec JL. Geniculate neuralgia: Diagnosis and surgical management. Laryngoscope 1976;56:955-64.

(2.) Rhoton AL, Jr., Pulec JL, Hall GM, Boyd AS, Jr. Absence of bone over the geniculate ganglion. J Neurosurg l968;28:48-53.

(3.) Pulec JL. Retrolabyrinthine selective posterior root section of the trigeminal nerve for the treatment of trigeminal neuralgia. Ear Nose Throat J 1996;75:601-6.

(4.) Rupa V, Saunders RL, Weider DJ. Geniculate neuralgia: The surgical management of primary otalgia. J Neurosurg 1991;75:505-11.

(5.) Rupa V, Weider DJ, Glasner S, Saunders RL, Geniculate ganglion: Anatomic study with surgical implications. Am J Otol 1992;13:470-3.