Combined Diagnostic Value of Both CT and MRI in Pre-Operative Evaluation of Cochlear Implant Patients

Abstract
Background: Cochlear implantation is considered an acceptable treatment for severe to profound sensorineural hearing loss with normal cochlea and cochlear nerve. CT is the best modality for evaluation of bony labyrinth and MRI is the best modality to evaluate membranous labyrinth so combined CT and MRI is mandatory for preoperative evalu-ation for cochlear implantation, radiologist should be familial with absolute and relative contraindication of cochlear im-plantation.
Aim of Study: The aim of this study is to evaluate the role of HRCT and MRI in pre-operative assessment of cochlear implantation candidates.
Patients and Methods: Our study included 60 patients (120 ears) 39 of them were males while 21 were females. The age of our selected patents ranged from 2 to 60 years with a mean of 15.8 years most of them were in pediatric age group 2-10 years representing 60%. The present study included patients with bilateral profound sensory neural hearing loss, minimum age of eligibility is 1 year, both sexes will be included. We excluded pediatric age group >1 year. All patients were subjected to the clinical evaluation. Computed Tomog-raphy (CT), all CT studies (60 figs) were obtained using a 320-row multidetector CT scanner (Aquilion One Toshiba Medical Systems, Otawara, Japan) installed in Tanta University Educational Hospital.Magnetic Resonance Imaging (MRI), all MRI studies (60 figs) were obtained using a closed MRI machine (General Electric SIGNA) HS (high speed) with magnets of intensity field 1.5T.
Results: Combined HRCT and MRI revealed a normal appearance of the labyrinth and internal auditory canal in 44 (88 ears) patients (73%). In 16 (32 ears) patients (26%) had abnormalities of the labyrinth; 10 patients (16%) of them had congenital anomalies and 6 patients (10%) had acquired Sensoneural Hearing Loss (SNHL). Ten patients (16%) had congenital abnormalities of inner ear bilaterally; absent cochlea (n=3) represented 5%, IP type I (n=2) represented 3%, IP type II (n=4) represented 6%, common cavity (n=1) represent about 2%, absent vestibule (n=3) represented 5%, dilated vestibule (n=6) represented 10%, dilated vestibular aqueduct (n=5) represented 8% and dysplastic semicircular canals (n=4) represented 7%. The cochlear nerve was normal in 57 figs (95%), while two patients (3%) had absent nerve, and one patient (2%) presented with atrophied cochlear nerve. Nar-rowed internal auditory canal (n=3) represented 5%. Six patients (10%) had acquired sensoneural hearing loss after meningitis, labyrinthitis, otitis media, trauma and sequalae of old age. Calcifications within the cochlea and in the semicircular canals caused by labyrinthitis ossificans (n=3) represented 5% and otosclerosis (n=1) represented about 2%. In current study, we found 4 ears with narrow IAC and absent vestibulocochlear nerve, 2 ears with narrowed IAC and atro-phied small sized vestibulocochlear nerve. In all of them the assessment of VCN were done using 3D MRI.
Conclusion: Combined HRCT and MRI studies are man-datory for evaluation of inner ear, the radiologist must be familiar with imaging findings that absolutely contraindicate implantation (Cochlear aplasia, cochlear nerve aplasia and labyrinthine aplasia), and with those that relatively contrain-dicate implantation (labyrinthitis ossificans, other inner ear dysplasia) and with other findings that could significantly alter or complicate surgery (hypoplastic mastoid process, facial nerve dehiscence, oto-mastoiditis).