A purely intracanalicular cochlear schwannoma presenting with progressive hearing loss.
Schwannomas arising from the cochlear nerve and confined to the internal auditory canal are rare. Clinically, a cochlear schwannoma can cause a progressive hearing loss. We report the case of a 56-year-old woman with a cochlear schwannoma that manifested as a slowly progressive hearingloss. The lesion was diagnosed by gadolinium-enhanced 3-Tesla magnetic resonance imaging.
Schwannomas in the internal auditory canal usually arise from the vestibular segment of the VIIIth cranial nerve. It was once thought that most vestibular schwannomas originate in the superior vestibular nerve, (1,2) but later studies found that the superior and inferior divisions are equally involved. (3,4) Recent reviews of the histology and surgery literature have demonstrated that most schwannomas arise from the covering cells (Schwann cells) of the inferior vestibular nerve (5,6) Schwannomas that arise from the cochlear nerve and are limited to the internal auditory canal are rare. (7) We describe an intracanalicular schwannoma that involved only the cochlear nerve and presented as deafness.
A 56-year-old woman presented with a slowly progressive hearing loss in the right ear. Her hearing loss was associated with fullness and nonfluctuating tinnitus. Her history was unremarkable. An otolaryngologic examination revealed a normal-appearing tympanic membrane on both sides. Audiologic evaluations included pure-tone air- and bone-conduction audiometry and speech discrimination testing. Pure-tone average scores at 500, 1,000, and 2,000 Hz revealed a 95-dB hearing loss on the right and a 15-dB loss on the left. Her speech discrimination score was 10% on the right and 90% on the left. A complete vestibular examination was performed--including oculomotor tests (smooth pursuit, saccades, optokinesis, and gaze-evoked nystagmus), examination of the cranial nerves, vestibulo-ocular reflex testing (head-shaking test, etc.), a fistula test, and a Dix-Hallpike test--and findings were unremarkable.
Gadolinium-enhanced 3-Tesla Tl-weighted (figures 1 and 2) and T2-weighted (figure 3) magnetic resonance imaging (MRI) detected a 3-mm enhancing mass. The mass involved the cochlear nerve in the fund us of the right internal auditory canal, which was occupying the inferior portion of the canal.
The patient was advised on the risks and consequences of leaving without surgery or radiotherapy, as well as the possible complications of these treatments. She was informed of the three options available: (1) close observation with serial MRI, (2) gamma-knife radiosurgery, and (3) open surgical excision of the tumor. Although we recommended open surgery via a translabyrinthine approach, the patient refused it and refused gamma-knife treatment, as well. Therefore, she was followed with close observation and imaging.
Acoustic neuroma, which is a misnomer for vestibulocochlear schwannoma, originates in the lateral aspect of the junction between the glial cells and the Schwann cells of the VIIIth cranial nerve; it accounts for about 8% of all intracranial tumors. (8) Vestibulocochlear schwannomas usually originate in the vestibular nerve, but in some cases they arise from the cochlear nerve, as did the lesion in our patient. The vestibular nerve tends to have a more disordered arrangement of sheath cells at the glial cell-Schwann cell junction. (9)
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Before imaging techniques attained their current level of sophistication, most cochlear schwannomas were detected during surgery for severe vertigo, during cochleostomy for cochlear implantation, and at autopsy. Advances in imaging have led to an increase in the number of reported cases. (8,10) We diagnosed our patient by 3-Tesla MRI, which identified the lesion very clearly even though it was quite small.
[FIGURE 2 OMITTED]
[FIGURE 3 OMITTED]
Cochlear schwannomas can be divided into three categories according to whether they are confined to the cochlea, confined to the internal auditory canal, or if they extend to both. Only about 20 cases of a cochlear schwannoma located in both the cochlea and internal auditory canal have been reported in the literature. (8,11,12) In our patient, the schwannoma was confined to the internal auditory canal.
Management choices for tumors located in the cochlear nerve and internal auditory canal depend on several factors, including the age and medical status of the patient and the hearing levels in the involved and uninvolved ears. For patients who are older or whose hearing in the other ear is poor, simple observation will allow the patient the opportunity to use the hearing in the involved ear for as long as possible. Observation may be the appropriate choice even for older patients whose hearing in the involved ear is poor, provided that periodic imaging is performed to evaluate tumor growth.
For younger patients, observation until hearing is no longer functional should be discussed. In younger patients whose hearing is already poor, the tumor can be observed until it demonstrates increased growth or it can be removed via a translabyrinthine approach. Surgery is indicated when patients experience non-serviceable hearing and intractable vertigo. (13) We managed our patient with close observation because she refused other treatments; fortunately, she had no symptoms other than hearing loss.
In conclusion, cochlear schwannomas are extremely rare. A slowly progressive unilateral hearing loss without any vestibular findings should prompt consideration of a cochlear schwannoma. Imaging with 3-Tesla MRI can detect small cochlear schwannomas in the internal auditory canal, and it helps differentiate between a cochlear schwannoma and a vestibular schwannoma. When a cochlear schwannoma is present, surgery can be postponed until hearing is no longer functional or until tumor growth makes removal imperative.
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Corresponding author: Huseyin Isildak, MD, Delaware Otologic Medicine and Surgery Fellowship Program, Christiana Care Health Systems, 1941 Limestone Rd., Suite 210, Wilmington, DE 19808. Email: firstname.lastname@example.org
From the Delaware Otologic Medicine and Surgery Fellowship Program, Christiana Care Health Systems, Wilmington (Dr. Isildak); and the Department of Otorhinolaryngology (Dr. Ibrahimov, Dr. Yilmaz, and Prof. Enver) and the Department of Radiology (Prof. Albayram), Cerrahpasa Faculty of Medicine, istanbul University, istanbul, Turkey. The case described in this article occurred when all the authors were with the Cerrahpasa Faculty of Medicine.
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|Title Annotation:||ORIGINAL ARTICLE|
|Author:||Isildak, Huseyin; Ibrahimov, Metin; Yilmaz, Mehmet; Enver, Ozgun; Albayram, Sait|
|Publication:||Ear, Nose and Throat Journal|
|Article Type:||Case study|
|Date:||Oct 1, 2011|
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