Intracochlear Schwannomas Confined to the Otic CapsuleIntracochlear Schwannomas Confined to the Otic CapsuleZi Yang Jiang, M.D., J. Walter Kutz, Jr. M.D., Peter S. Roland, M.D., Brandon Isaacson, M.D.

Department of Otolaryngology-Head and Neck Surgery, University of Texas Southwestern Medical Center, Dallas, TX 75390

AbstractObjective: To determine the natural history and treatment options for patients with intracochlear schwannomas.Methods: Seven patients with intracochlear schwannomas which where confined to the otic capsule were identified in a retrospective chart review at a tertiary referral center. Their histories were examined and the following characteristics were noted:1) presenting and associated symptoms, 2) initial MRI scan findings, 3) surgical interventions (if any), and 4) follow up MRI results. Results: All seven patients in our series presented with hearing loss. Tinnitus and vertigo were equally prevalent at 43%. Meanwhile, no patient presented with aural fullness or facial weakness. Of the seven patients, six had observational follow up MRIs with only one patient having any changes in MRI. Two out of the seven patients required surgical intervention for intractable vertigo which resulted in resolution of symptoms.Conclusions: Hearing loss is the most common presenting symptom in patients with intracochlear schwannomas, followed by tinnitus and vertigo. Aural fullness is seldom the presenting symptom in intracochlear schwannomas. High-resolution fast spin echo (FSE) T2-weighted MRI and traditional T1 gadolinium enhanced MRI are both sensitive in detecting vestibular schwannomas. Schwannomas will enhance on T1 images with gadolinium and will be hypo intense in a background of hyperintense cerebrospinal fluid on T2 images. The majority of intracochlear tumors in our series and other series show no significant size increase when followed with serial MRI scans.

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Intracochlear Schwannomas. Otology Neurotology. 2007:28;951-73. Daniels RL, Swallow C, Shelton C, Davison HC, Krejci CS, Harnsberger HR. Causes of unilateral sensorineural hearing loss

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4. Kennedy R, Shelton C, Salzman K, Davidson H, Harnsberger H. Otol Neurotol 2004;25:160-7 5. Hawke M, Kefne M, Robbins KT, Fredrickson JM, Sima A. Occult labyrinthine schwannoma. J Otolaryngol 1981;10:313-20.6. Hosino T, Ishii D. Intralabyrinthine neurilemoma. ORL J Otorhinolaryngol Relat Spec 1972;34:117-23 7. Jia H, Marzin A, Dubreuil C, Tringali S. Intralabyrinthine schwannomas: Symptoms and managements. Auris Nasus Larynx.

2008;35:131-68. Selesnick SH, Johnson G. Radiologic surveillance of acoustic neuromas. Am J Otol 1998;19:846-99. Charabi S, Tos M, Thomsen J. Vestibular schwannoma growth: the continuing controversy. Laryngoscope 2000;110:1720-5.

Conclusions• Hearing loss is the most common presenting symptom in intracochlear schwannomas, followed by

tinnitus and vertigo equally.

• Aural fullness is seldom the presenting symptoms in intracochlear schwannomas, whereas it can be in Meniere’s disease

• High-resolution fast spin echo (FSE) T2-weighted MRI and traditional T1 gadolinium enhanced MRI are both equally sensitive to detect vestibular schwannomas. The schwannoma will be enhancing on T1 and will be a lack of signal on T2.

• The majority intracochlear schwannomas followed with serial MRI scans in our series as well as other series shows no growth. In contrast, the majority of published reports on typical vestibular schwannomas progressively enlarge over time. Further investigation is needed to determine whether intracochlear schwannomas represent a special subgroup that differ in growth patterns.

IntroductionIntracochlear schwannomas are rare clinical entities that present with hearing loss vertigo, tinnitus, and rarely aural fullness. Historically, due to lack of specific investigational tools, cases of intracochlear and in general, intralabyrinthine schwannomas were often diagnosed as Meniere’s disease.1 Prior to the advent of magnetic resonance imaging (MRI), intracochlear schwannomas were only definitively found intra-operatively or during post-mortem autopsies.

MRI allowed schwannomas to be found at earlier stages. T1 images with gadolinium will show enhancement within the cochlea. Whereas, T2 images will show cut off or amputation of the cochlear signal when a schwannoma is present.2 Labyrinthitis, hemorrhage, and ossification can also cause loss of signal on T2, therefore, T1 imaging may be used to exclude certain competing diagnoses. High-resolution fast spin echo (FSE) T2-weighted MRI and traditional T1 gadolinium enhanced MRI are both equally sensitive to detect vestibular schwannomas.3

Due to its location, intracochlear schwannomas typically present with sensorineural hearing loss. Hearing loss is usually progressive but approximately 15-32% of cases can present with sudden hearing loss.2,4 Occasionally, a mixed type hearing loss can occur, presumably due to blockage of inner ear fluid by the tumor. This may dampen the stapes footplate.4 Furthermore, the tumor may cause secondary endolymphatic hydrops which may result in disequilibrium and vertigo.5,6

Table 1 Summary of Presenting Symptoms

MethodsSeven patients with intracochlear schwannomas with no extension into the vestibule or internal auditory canal were identified in a retrospective chart review at a tertiary referral center. Their histories were examined and the following characteristics were noted:1) presenting and associated symptoms, 2) initial MRI scan findings, 3) surgical interventions (if any), and 4) follow up MRI results.

ResultsAll the patients in this series presented with hearing loss (see table 1). In all cases except one in which the hearing loss was “severe to profound”, hearing loss was profound. Tinnitus and vertigo were both equally prevalent at 43%. Meanwhile, no patients in our series presented with any aural fullness or facial weakness.

Out of the seven patients in our series, six of the patients had follow up MRI scans. Only one patient definitively had any change in the tumor size (case 2). The patient in case 5 had a previous scan in 1999 that we did not have access to, therefore it is indeterminate was to whether the intracochlear schwannoma was simply not noticed on previous scans or whether it is a new finding.

Case Presentations

Case #2: A 58 year old male presented with severe to profound sensorineural hearing loss in 2005. The patient denied any dizziness or tinnitus. A focal enhancing mass was found in the basal turn of the left cochlea. A follow up MRI in 2006 showed an increase in contrast enhancement, however yearly follow up MRI scans in 2007 and 2008 were all stable with no evidence of change.

Case #3: A 45 year old female presenting with sudden profound hearing loss that started in 1992. She has had no intervention and was referred to our center in 2006. She denied any tinnitus or vertigo but complained of some unsteadiness over the years. An MRI scan in 2006 showed an abnormal enhancement in the right cochlea. A repeat MRI in September 2007 demonstrated no interval change. However, clinically the patient developed severe vertigo in May 2007. A translabyrinthine resection of the right cochlear mass was completed in 2008. The tumor was identified to be a schwannoma 8 x 7 x 2 mm.Case #4: A 52 year old male presented with left sided hearing loss that began in 2006. The patient had tinnitus but denied vertigo. An MRI showed a mass in the basal to ascending turn of the cochlea in 2008. There was no previous MRI for comparison. The patient’s speech discrimination score dropped from 92% in 2006 to 36% in 2008.

Case #1: A 67 year old male presented with gradual hearing loss in his left ear in 1990. He denied any vertigo but complained of tinnitus. MRI done in 1990 and 1996 was reported to be normal. He was referred to our center in June 2005 where he was found to have profound hearing loss in his left ear. A 2 x 3 mm lesion was reported on MRI in the basilar turn of the left cochlea in January 2007. A repeat scan in October 2007 and in August 2008 revealed no changes.

Case #5: A 54 year old male who presented with gradual decrease in hearing in his left year in 2006. The patient’s medical history is complicated by a intracanalicular schwannoma that was irradiated with gamma knife in 1999 in his right ear. A repeat MRI in 2006 found a mass in the left basal turn of the cochlea. No surgical intervention was suggested.Case #6: A 37 year old male presenting with gradual hearing loss in his right ear. Although the patient denied vertigo, he complained of tinnitus. A MRI in 2006 showed 2 small foci of enhancement, one in the basal turn of the right cochlea and another in the modiolus. A repeat MRI in May 2009 showed no interval change. However, at the same time, the patient complained of a 2-3 week course of vertigo that resolved. Case #7: 35 year old female presenting with sudden hearing loss in her right ear. The audiometric findings revealed a pure tone audiometric threshold of 60dB at 2000 Hz and a 20-40dB threshold at other frequencies. An initial MRI showed an enhancing mass in the middle turn of the cochlea. A repeat MRI scan completed 9 months later, after the patient developed vertigo, revealed no interval change. She underwent surgical resection of her tumor and her vertiginous symptoms resolved.

Presenting Symptom Number (Percentage)

Hearing Loss 7 (100%)

Tinnitus 3 (43%)

Aural Fullness 0 (0%)

Vertigo 3 (43%)

Facial Weakness 0 (0%)

Figure 1 Case 1 Coronal T1 MRI with fat suppression and gadolinium shows enhancement in the middle turn of the left cochlea. The two distinct areas of enhancement above the tumor represent the tympanic and labyrinthine facial nerve.

DiscussionHearing loss was the most prevalent presenting symptom, followed by tinnitus and vertigo equally in our series. This mirrors a previous report of 68 cases where hearing loss was the presenting symptom in 93% of cases, and tinnitus (50%) and vertigo (51%).7

Indications for surgical intervention in a patient with a intracochlear schwannoma include: 1) intolerable vertigo, 2) extension of the tumor into the CPA or middle ear, 3) evidence of tumor growth, or 4) concern for pathologic diagnosis. Based on these indications, it was found that tumors that involve the IAC required surgery more often than tumors confined to the labyrinth (46% vs. 7%)4

The surgical approach selected for removal of intracochlear schwannomas depends entirely on the location of the tumor and whether extension into the internal auditory canal is present. Tumors confined to the cochlea can be removed using a post auricular transcanal transotic approach. Care must be taken not to injure petrous carotid artery. The first genu of the petrous carotid artery can be as close as 1 mm from the inferior and ascending junction of the basal turn of the cochlea. Limiting the dissection inferior to the cochleariform process will prevent a facial nerve injury when opening the middle turn of the cochlea. The traditional transmastoid transotic approach will be necessary in tumors that extend into the internal auditory canal. Entering the modiolus will result in egress of CSF from the posterior fossa into the middle ear. The middle ear and Eustachian tube will then need to be obliterated to prevent a CSF leak.

Hearing preservation has not been reported in patients undergoing resection of intracochlear schwannomas. Anacusis often occurs as a result of the natural history of the tumor or after surgical removal. A BAHA, while not allowing for sound localization, can improve the head shadow effect and some measures of hearing in noise in patients with single sided deafness.7

Non-operative management with annual MRI scans is an option when the patient still has residual hearing or if the patient is asymptomatic. In a recent study, it was found that in a series of 20 patients for which observation was the management, only 15% of the patients had any growth identified on subsequent MRI scans.4 Even then, the tumors that grew were all transmodiolar (involving both the cochlea and the IAC), rather than pure intracochlear tumors. Indeed, in our study, only one of six patients on follow up had any noticeable change in tumor size. It is interesting to note that tumor growth is not necessarily associated with changes in symptoms. For example in case 3, the patient developed vertigo despite an unchanged MRI. Similarly in case 2, the tumor size increased but the patient had no symptomatic change. The reported average growth of vestibular schwannomas is 1.8-2.4mm/year.8,9 Published reports of tumor growth with observation range from 53% to 82%, although these represents schwannomas in general, rather than those restricted to the cochlea.8,9

Figure 2 Case 3 axial T1 MRI with gadolinium shows enhancement in the ascending basal turn, middle turn and apex of the right cochlea. of enhancement above the tumor represent the tympanic and labyrinthine facial nerve.

Figure 3 Case 6 axial T1 MRI with gadolinium shows enhancement in modiolus of the right cochlea as well as in the ascending basal turn.