الفهرس 
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Abstract
This study aimed to : Imaging of the inner ear and internal auditory canals has become an integral tool in the clinical evaluation of patients with severe to profound SNHL. Those patients benefit a little from hearing aids and so, the cochlear implantation become the most helpful and successful treatment. The decision on whether cochlear implant is indicated was made in a multidisciplinary setting and relies on clinical, audiological and radiological evaluation. Accordingly the purpose of the current work was to establish the patients’ candidacy for the operation and choose the appropriate ear for unilateral implantation. This study enrolled 46 patients with severe to profound SNHL referred from ENT Department at Mansoura University Hospital for radiological assessment before undergoing surgery of cochlear implantation. Forty five patient underwent HRCT study, while 43 one underwent MRI examination. The patients were screened for having absolute contraindication, relative contraindication and other incidental complicating anatomical variations. According to these radiological findings, three cases were entirely not fit for the surgery as having absolute contraindications; the first had bilateral cochlear nerve aplasia and the other two had labyrinthitis ossificans and bilateral otospongiosis with complete obstruction of cochlear lumen. Three patients had unilateral CND, so, implantation of the opposite side was considered. One patient with haematogenic labyrinthitis ossificans after congenital infection had unilateral affection, so contralateral implantation was considered. Detection of unilateral dilated VA, high jugular bulb and anteriorly protruded sigmoid sinus played a major role in determination of the side of implantation. Detection of middle ear abnormalities had postponed the decision of the surgery in 5 patients. 3 D gradient echo MRI pulse sequences was very valuable and conclusive imaging tool by its great capability in detection of the cochlear patency. It was indispensable in detection of cochlear nerve integrity considering the fact that normal CT morphology of IAC and BCNC does not mean presence of normal cochlear nerve. The consequences of missing either isolated cochlear nerve deficiency or unsuspected retro cochlear/brain pathology might ultimately result in inappropriate decision by the surgeon. Thus, MR imaging ensured the essential requirements for implantation surgery. Also, MR imaging had the advantages of avoiding high risks of ionizing radiation especially with children. MRI was better in detection in abnormalities of enlarged ELD and sac. The tradition limitations of MRI are the cost and need for sedation in children population.