Abstract
Objective
To demonstrate the added value of magnetic resonance imaging (MRI) over computed tomography (CT) during adult cochlear implant evaluation.
Patients
Two adult patients are discussed in whom MRI studies diagnosed bilateral vestibular schwannomas during cochlear implant candidacy evaluation.
Interventions
Temporal bone CT and MRI.
Main outcome measure
Diagnosis of NF2.
Results
Two adult patients, ages 67 and 68 years, were evaluated for cochlear implant candidacy. Both patients experienced slowly progressive, bilateral hearing loss without complaints of vertigo, and neither patient had a family history of hearing loss or neurogenic tumors. Both patients had near-symmetric pure tone thresholds on audiometric testing. An MRI and a CT scan were performed on both patients, and bilateral vestibular schwannomas were identified on MRI.
Conclusions
Though MRI is not routinely utilized in adult cochlear implant evaluation, it may be of greater clinical value than CT in the setting of adult-onset hearing loss. MRI allows for sensitive evaluation of cochlear patency and architecture, and cochlear nerve status. As demonstrated in the two index cases, MRI also provides the added benefit of evaluating for causes of retrocochlear hearing loss. These two patients would have likely experienced a significant delay in diagnosis of NF2 without preoperative MRI, particularly given the limitations of scanning following CI magnet placement.
1
Introduction
There is not a clear consensus on the most efficient preoperative radiographic evaluation for cochlear implant (CI) candidates with post-lingual deafness. Both high-resolution computed tomography (CT) of the temporal bone and magnetic resonance imaging (MRI) offer unique benefits . A CT scan is an accurate predictor of operative bony anatomy, and it is generally a quicker and less expensive study. However, MRI may be more sensitive to pathology relevant to implantation . For cochlear implant candidates with congenital hearing loss and those with a complicated otologic history, performing both studies may be prudent. In candidates with previously normal hearing and no significant otologic history, an MRI alone may be sufficient.
Neurofibromatosis type-2 (NF2), in which an upward of 95% of patients develop bilateral vestibular schwannomas, can lead to an insidiously progressive bilateral sensorineural hearing loss . We present two cases where NF2 was diagnosed by contrast-enhanced MRI after a CT scan did not clearly identify bilateral vestibular schwannomas. These findings demonstrate the added value of MRI for the workup of CI candidates with previously normal hearing and no prior otologic disease.
2
Case 1
A 67-year-old man with no family history of hearing loss presented for CI evaluation in the setting of slowly progressive bilateral sensorineural hearing loss without tinnitus, aural fullness or vertigo. At the time of presentation, he reported that his right ear was his better hearing ear, but he experienced minimal benefit with amplification on either side.
His neurotologic exam was unremarkable aside from bilateral hearing loss. Audiometric evaluation confirmed a pure tone average of 90 dB on the right and 85 dB on the left; word recognition scores were 30% on the right and 0% on the left. Non-contrast CT of the temporal bones revealed asymmetric widening of the left internal auditory canal (IAC). A subsequent contrast-enhanced MRI revealed bilateral IAC lesions consistent with vestibular schwannomas. The left-sided lesion measured 14 × 7 mm and the right-sided lesion measured 3 × 3 mm ( Fig. 1 ). A diagnosis of NF2 was made, and the patient elected to defer cochlear implantation until repeat imaging better characterized the growth pattern of the tumors. A 1-year follow-up MRI demonstrated no tumor growth, and an audiogram revealed stable hearing. At that point, the patient elected to not pursue cochlear implantation given his diagnosis and the need for continued MRI surveillance. Given his age and relatively small tumor sizes, he continues to be followed with a “wait-and-scan” strategy.
2
Case 1
A 67-year-old man with no family history of hearing loss presented for CI evaluation in the setting of slowly progressive bilateral sensorineural hearing loss without tinnitus, aural fullness or vertigo. At the time of presentation, he reported that his right ear was his better hearing ear, but he experienced minimal benefit with amplification on either side.
His neurotologic exam was unremarkable aside from bilateral hearing loss. Audiometric evaluation confirmed a pure tone average of 90 dB on the right and 85 dB on the left; word recognition scores were 30% on the right and 0% on the left. Non-contrast CT of the temporal bones revealed asymmetric widening of the left internal auditory canal (IAC). A subsequent contrast-enhanced MRI revealed bilateral IAC lesions consistent with vestibular schwannomas. The left-sided lesion measured 14 × 7 mm and the right-sided lesion measured 3 × 3 mm ( Fig. 1 ). A diagnosis of NF2 was made, and the patient elected to defer cochlear implantation until repeat imaging better characterized the growth pattern of the tumors. A 1-year follow-up MRI demonstrated no tumor growth, and an audiogram revealed stable hearing. At that point, the patient elected to not pursue cochlear implantation given his diagnosis and the need for continued MRI surveillance. Given his age and relatively small tumor sizes, he continues to be followed with a “wait-and-scan” strategy.
3
Case 2
A 68-year-old man with a history of occupational noise exposure presented for CI evaluation in the setting of slowly progressive bilateral sensorineural hearing loss. He reported that his hearing deterioration always seemed symmetric and was associated with bilateral tinnitus. He denied symptoms of dizziness.
His neurotologic exam was unremarkable except for binaural hearing loss. Audiometric testing revealed a pure tone average of 65 dB on the right and 57 dB on the left, with word recognition scores of 52% on the right and 30% on the left. A non-contrast CT scan of the temporal bones demonstrated widening of the left internal auditory canal while gadolinium-enhanced MRI revealed bilateral IAC lesions measuring 15 × 12 mm on the left and 7 × 7 mm on the right ( Fig. 2 ). A diagnosis of NF2 was made, and the patient elected to delay cochlear implantation until repeat imaging better characterized the growth pattern of the tumors. At the time of writing, a follow-up MRI has not yet been performed.
