Trigeminal Neuralgia Due to an Acoustic Neuroma inthe Cerebellopontine Angle

Yoshizo Matsuka. DDS, PbDStaff Research AssociateDivision of Oral Biology and Medicine

Edward T, Fort, DDSLecturerDiagnostic Sciences of Orofacial Pain

Robert L. Merrill, DDS. MSAdjunct Associate ProfessorDiagnostic Sciences of Orofacial Pain

UCLA School of DentistryLos Angeles, California

Correspondence to:Dr Robert L. MerrillUCLA School of Dentistry10833 LeConte Ave./CHS Rm 43 009Box 951668Los Angeles, CA 90095-1668Fax: C310)206-5539E-mail rmerrill@ucla,edu

This case report first reviews the intracranial tumors associatedwith symptoms of trigémina! neuralgia (TN). Among patients withTN-like symptoms, 6 to 16% are variously reported to haveintracranial tumors. The most common cerebellopontine angle(CFA) tumor to cause TN-like symptoms is a benign tumor calledan acoustic neuroma. The reported clinical symptoms of theacoustic neuroma are hearmg deficits (60 to 97%), tinnitus (50 to66%), vestibular disturbances (46 to 59%), numbness or tinglingin the face (33%), headache (19 to 29%), dizziness (23%), facialparesis (17%). and trigeminal nerve disturbances (hypesthesia,paresthesia. and neuralgia) (Í2 to 45%). Magnetic resonanceimaging witb gadolinium enhancement or computed tomographywith contrast media are each reported to have excellent abilities todetect intracranial tumors (92 to 93%). Tbis article then reports arare case of a young female patient who was mistakenly diagnosedand treated for a temporomandibular disorder but was subse-quently found to bave an acoustic neuroma located in tbe CPA.J OROFAC PAIN 2000;14:147-151,

Key words: rrigeminal neuralgia, temporomandibular jointdisorders, acoustic neuroma, cerehellopontine angle,multiple sclerosis, neoplasms

Trigemmal neuralgia (TN) is one of the most debilitatingpain syndromes known to humans,' This condition is oftensecondary to central lesions, multiple sclerosis (MS), or vas-

cular compression, but almost 50% of cases are of unknown etiol-ogy (idiopathic). Although the exact cause of idiopathic TK is stillunknown, various conditions have heen reported to induce TN,mcluding tumors, '̂̂ iMS,* and vascular contact or compression ofthe trigeminal root.-''*^

Intracranial Tumors and Trigeminal Neuralgia

The percentage of intracranial tumors found in patients complain-ing of TN-like symptoms is not high. Yang and colleagues''assessed the value of magnetic resonance imaging (MRI) in evalu-ating TN in 51 patients who failed a trial of conservative treat-ment. They reported that 8 patients (16%) had cerebellopontmeangle (CPA) tumors, 5 patients (10%) were diagnosed with MS, 2had sphenoid or ethmoid sinusitis, 1 had menmgitis, 1 had

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trigeminal neuritis, and 27 (53%) had vascularcompression of the trigeminal root. Nomura andcolleagues* investigated 164 patients who pre-sented with TN as their Initial symptom. Theyreported that 14% of the patients had intracraniallesions and 35% had microvascular compression.Sindou et aF studied 350 consecutive TN patientsand reported that, in 6% of the cases, the cause ofthe TN was a tumor or a vascular malformation inthe CPA. Other investigators have also reportedthe prevalence of TN symptoms in hrain tumors.Puca et al^ reported that 7% of patients withextra-axial tumors of the posterior and middle cra-nial fossae presented with symptoms resemblingTN. Additionally, Matthies and Samii^ reportedthat 1 to 3% of patients with schwannoma (acous-tic neuroma) presented with TN-Íike symptoms.Earlier, Puca et al"^ described a group of patientsin which 10% of those with extra-axial tumors ofthe posterior and middle cranial fossae had TNsymptoms. Hence, TN symptoms are commonlyreported hy patients subsequently diagnosed withlntracranLal tumors. However, Selesnick et al"reported that in a group of 126 patients withacoustic neuroma, none had TN symptoms. Theincidence of subjective hearing loss reported inthat study is less than in other studies and may bedue to inclusion of a larger proportion of small(< 1 cm) tumors. Small acoustic neuroma tumorspresent with suhtle and more limited symptomsthan their larger counterparts.

In middle-aged patients with TN symptoms,intracranial tumors, MS, acoustic neuromas, andmeningiomas are frequently observed.''''^ Inpatients younger than 29 years of age with TNsymptoms, the prevalence of intracranial tumor orMS is reported to he virtually 100%.'' In the agegroup from 29 to 39 years of age with TN symp-toms, 45% had a tumor or MS. In the age groupfrom 40 to 59, the prevalence of tumors is 20%,and for those older than 60 it is 18%. Based onthe above percentages, imaging should be per-formed for all patients who have TN-like symp-toms, since all age groups have a risk of braintumors.

Hearing deficits (60 to 97%) are the most com-monly reported clinical symptom of the acousticneuroma, followed by tinnitus (50 to 66%),vestibular disturbances (46 to 59%), numbness ortingling in the face (33%), headache (19 to 29%),dizziness (23%), facia! paresis (17%), and trigemi-nal nerve disturbances (hypesthesia, paresthesia,and neuralgia) (12 to 45%)."-'-' The most com-monly reported symptoms associated with othertypes of inttacranial tumors are hyperesthesia.

reduced or absent corneal reflex, facial palsy, mas-ticatory weakness, hearing loss, and/or ataxia. •

Computed tomography (CT) and MRI arereported to have excellent detection ability forintracranial tumor. A CT scan without contrast isreportedly able to detect a lesion in 73 to 76% ofpatients. If a contrast medium is used, this rateincreases to 93%.^''^ Magnetic resonance imaging,with its better soft tissue resolution and muitipla-nar capability, is able to depict the intracraniaicourse of the trigeminal nerve''' and has detectedthe mass in 92% of patients with known lesions.^Furthermore, MRI provides superior definition ofthe tumor's boundary and of its relationship withadjacent structures.^*

The treatment outcome and prognosis for acous-tic neuroma with TN symptoms are very favor-able. In one study, 89% of patients with extra-axial tumors of the posterior and middle cranialfossae experienced postoperative pain relief fromsurgery,^ and gamma knife for acoustic neuromapatients has also provided pain relief postopera-tively.̂ ^ Otber researchers have reported that thegamma knife'^ and stereotactic radiosurgery (X-knife) are effective in tbe treatment of acousticneuroma.^^

Some investigators have reported on the morbid-ity from surgery for acoustic neuroma. Harner etaP* performed surgery for acoustic neuromathrough a retrosigmoid suhoccipital craniectomy.They reported tbat the facial nerve was preservedin 86% of patients and that delayed or partialparesis developed in 50% of the patients. Foote etaP^ reported that 72% of patients who receivedgamma knife surgery developed a new or progres-sive facial or trigeminal neuropathy (or both).Andrews and associates reported on posttreatmentmorhidity after stereotactic radiotherapy. In theirstudy, trigeminal neuropathy was seen in 3% ofpatients, vestibulocochlear neuropathy in 29% ofpatients, scalp pain or tic pain in 27% of patients,and dizziness in 23% of patients.'^

Case Report

A 27-year-old woman visited the UCLA GraduateOrofacial Pain Clinic with a complaint of pain inthe right masseter muscle that radiated upward tothe cheek and forehead. Tbe pain was triggered byswallowing and licking of the lips.

One year prior to the initial visit, the patienthad developed pain after a dental procedure thatradiated to tbe right ear and chin. Her pain wasexacerbated by eating. She was giyen 400 mg

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Fig 1 'ri-weighted sagittal MBJ showing 2,0-cm massat die cerebellopontine angle.

Fig 2 Axial gadolinium-enhanced MRIshows a mass suggestive oí an acoustic neu-roma or menjngioma at the right cerebellci-pontine angle.

ibuprofen oti the assumptioti that she was havingan inflatnmatoty response to the dental treatment.However, she returned 1 month later, indicatingthat the pain was worsening. At that point, shewas referred to a tetnporomandihular disorder(TMD] specialist for evaluation. She apparentlybecatne pain-free for 5 months after treatment forTMD, rhen returned to her physician, indicatingthat the pam had returned again 3 days prior. Thephysician referred her back to the dentist to have anightgnard made.

When the patient came to the UCLA OrofacialPain Clinic, she complained of the same pam thatshe had reported to her physician. She indicatedthat the pain was continuous (24 hours/day) andwas variahle in intensity, withont a tetnporal pat-tern. It was exacerbated by brushing her teeth andwashing her face, pushing on her teeth, talking,licking her lips, and totiching the right face or rightpalate. The pain occasionally awakened her duringthe night. She described it as electrical shock-like,with occasional soreness in the right temporo-mandibular joint (TMJ) and the angle of themandible. There were no associated autonomiesymptoms.

Neurologic and stomatognathic examinationsrevealed no abnormalities. The range of ¡awmotion was unrestricted and pain-free. No painwas elicited during examination of the TMJ. Sometenderness was noted in the masticatory muscles,but the pain complaint was not duplicated oraggravated by the muscle assessment. Because ofthe lack of abnormal mtisculoskeletal findings, itwas the authors' impression that the patient didnot have a TMJ problem and would require fur-rher assessment, including brain MRI, Since tbepatient was in pain at the time of the examinationand the pain had a neuropathic quality and presen-tation, gabapentin was initially prescribed for her,and arrangements were made for further assess-ment. When she increased the gabapentin to 900mg per day, the pain decreased significantly. Shewas subsequently referred for a neurologic evalua-tion and MRI to rule out an intracranial tumor orMS. The MRI showed a large 2,0-cm mass at theright CPA, suggestive of an acoustic neuroma (Figs1 and 2), and the patient was scheduled forsurgery to remove the tumor.

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Discussion

Acoustic neuromas are generally slow-growing,and patients are reported to experience clinicalsymptoms for long periods of time before seekingmedical treatment (0.6 to 5 years).''•""'-'' Tbetumor discussed in this report was undouhtedlypresent during the time the patient was being seenby the physician and dentist, who assumed she hada TMJ problem, although her developing symp-toms at that time wete consistent with neuropathyand not with a TMD,

This case suggests several important points forconsideration regarding orofacia! pain patients.First, the doctor should understand the signs andsymptoms of the various orofacial pain conditions,mcluding TMD and TN, since this is critical forappropriate diagnosis and management. It hasbeen our experience that often, when an orofacialpain condition is not clearly understood, thepatient is referred for TMJ evaluation and treat-ment. In such a case, TMD treatment may beundertaken unnecessarily, and the condition caus-ing the pain is not addressed.' Based on the find-ings of our examination, the patient did not have aTMD, but TN. The fact that she did not fit the ageprofile for TN was of great concern; hence she wassent for further evaluation to rule out a centrallesion or a demyelinating disease.

To evaluate an orofacial pain condition, it is nec-essary to undertake a complete assessment, includ-ing a neurologic examination. However, knowl-edge of the various condirions that can causeorofacial pain is imperative, and data from anexamination will be useless without this knowl-edge. This patient presented to the physician, thedentist, and to the authors witb the same com-plaints, Musculoskeleta! problems such as TMD donot usually show the temporal pattern that is char-acteristic of TN, with alternating complete remis-sion and exacerbation. It was our concern with thisyoung patient who presented with neuralgia-likesymptoms that she had a tumor or MS, smce thisrisk is high in young patients who present withsimilar symptoms.'' A thorough neurologic assess-ment should he conducted routinely to assess forhearing loss, vestibular disturbances, numbness ortingling of the face, or trigeminal disturbances thatare characteristic of acoustic neuromas.""'^ Othertypes of intracranial tumors may also show someclinicai symptoms, including hypesthesia, reducedor absent corneal reflex, facial palsy, masticatoryweakness, hearing loss, or ataxia,'"'"' Interestingly,in this case, the patient did not show any abnotmalfindings in neurologic examinations by either the

orofacial pain specialist or the neurologist. Anadditional and obligatory part of the evaluation forTN, therefore, is the MRI or CT scan with con-trast, since these modalities have high sensitivityfor the detection of intracranial tumors.^'^Magnetic resonance imaging is reported to heslightly more sensitive than the CT scan with con-trast for detection of intracranial lesions.'̂ -^^

Tumors in the posterior fossa are more hkely tocause TN-likc symptoms than are tumors in anyother location. This area encompasses the trigemi-nal nerve path as it emerges from the pons, runsanteriorly and superiorly through the prepontinecistern and finally over the petrous ridge to thetrigeminal ganglion in Meckel's cave.̂

The neoplasm most hkely to produce TN is abenign, slowly growing, extra-axial tumor thatcompresses the trigeminal root.^-' The increasingpressure on the trigeminal root or ganglion mayinduce loss of myelination in the trigeminal sen-sory root.'' It has been proposed tbat this loss ofmyelination results in ephaptic short-circuitingwithin the nerve toot, resulting in facial pain andsensory deficits,^' Acoustic tumors represent themost common type of tumor associated withTN.^''' Some authors helieve that tumors push thetrigeminal nerve root against the superior cerebel-lar artery, producing a neurovascular conflict simi-lar to the vascular compression theory proposedfor classic TN.'

Bullitt and coworkers^ reported that carba-mazepine is an effective drug in the temporarytreatment of TN with intracranial tumors. Thepatients in the study tended to respond to the drugat least temporarily, with improvement of symp-toms; however, no patient was relieved of pain formore than 1 year. Importantly, the authors con-cluded that an initial response to carbamazepinecannot be used to exclude the diagnosis of tumor.Gabapentin has also been reported to be effectivefor TN.̂ '̂̂ -' In the present case, gabapentin (900mg) decreased the pain while the patient was in theprocess of receiving a more thorough evaluationfor her neuralgia-like symptoms.

Fortunately, the prognosis for acoustic neuromaor benign tumor surgery is good, although all ofthe surgical procedures are associated with somerisk of morbidity.'^"'^

Conclusions

Tbis case report describes a 27-year-old femalewho presented to rbe UCLA Orofacial Pain Chnicwith a condition previously diagnosed and treated

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as a TMD by her primary care physician and sub-sequent TMD specialist. Tbe patient described thesame symptoms tbat she had reported to the previ-ous doctors. These symptoms included sharp,shooting, episodic pain that seemed to resolve tem-porarily with TMJ treatment. A carefnl examma-tion excluded any TMJ component to her paincomplaint and she was given a preliminary diagno-sis of TN, with an intracranial tumor or MS left aspossible causes of her symptoms. Subsequent eval-uation with MRI found a 2-cm tumor in the CPA.This case emphasizes the need for careful evalua-tion of orofacial pain, taking into account thedescription of the pain as well as its temporal pat-terns.

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