**5. Surgery**

Previous studies have concluded that there is no significant difference for audiologic outcomes between unilateral and bilateral cochlear implantation regarding surgical timing, as both ears can be implanted simultaneously or sequentially. Adult studies have shown that the second ear matches the first ear performance at 6 months [20]. The story has a difference when it comes to children, as it has been concluded that patients with simultaneous bilateral cochlear implantation have improved speech recognition and language when compared to

The cost-effectiveness of bilateral cochlear implantation has remained controversial despite evident advantages of binaural stimulation. A Canadian study has reported that cochlear implantation is cost-effective in adults compared to no implantation; however, sequential bilateral cochlear implantation has a slight superiority in comparison with unilateral implantation [22]. Other studies have approved cost effectiveness of bilateral simultaneous pediatric implantation and unilateral adult cochlear implantation, although they have not approved cost-effectiveness of bilateral sequential pediatric implantation and bilateral (sequential or

Selecting the right patient is the building block of a successful cochlear implantation. Therefore, a complete medical and audiologic workup is needed for evaluating candidacy of cochlear implantation and to make sure that the patient can tolerate anesthesia and surgical process. Patients are considered to take benefit from CI when they suffer from bilateral moderate to profound sensorineural hearing loss and when hearing aids cannot help them [24]. A combination of objective and subjective hearing tests is conducted to accurately identify the degree of hearing loss within audiometric frequencies. Currently available guidelines mention that children up to 2 years of age should have a bilateral profound sensorineural hearing loss, which is indicated by a pure tone audiometry (PTA) more than 90 dBHL for 500, 1000, and 2000 Hz frequencies, while patients older than 2 years of age should have bilateral sever to profound SNHL indicated by PTA more than 75 dBHL for 500, 1000, and 2000 Hz frequencies [25, 26]. Preoperative speech and language evaluation has the same importance for decision making regarding rehabilitation strategies and programs, as well as appropriateness of auditory performance, speech production, and mode of communication. Hearing loss is categorized to prelingual, postlingual, and perilingual types based on the time of onset. In prelingually deaf patients, hearing impairment occurs before gaining speaking skills, which is usually before 2 years of age, while it occurs after gaining complete speaking skills in postlingual patients which is usually after age of 5 years. In perilingual patients, hearing impairment occurs when some speaking skills are gained but are

In addition, preoperative imaging and auditory testing are needed. Imaging modalities such as computed tomography (CT) scan, for assessing temporal bone, and magnetic resonance imaging (MRI), for evaluating brain anatomy and ruling out abnormalities of cochlear nerve, are conducted [15]. After scheduling patient for surgery, pneumococcal vaccines are adminis-

children who were implanted sequentially [21].

140 An Excursus into Hearing Loss

simultaneous) adult implantation [23].

**4. Candidacy and patient selection**

not completed usually between 2 and 5 years of age [16].

tered according to FDA guidelines.

Cochlear implantation procedure is performed under general anesthesia associated with facial nerve monitoring. Surgeon needs to expose the mastoid, so a postauricular incision is made and soft tissue is dissected; latter, the surgeon makes a subperiosteal pocket for placement of implant magnet. A cortical mastoidectomy is performed associated with finding landmarks of temporal bone, such as incus, tegmen tympani, lateral semicircular canal, and sigmoid sinus. Then, the surgeon opens the facial recess, which is surrounded by chorda tympani, facial nerve, and incus buttress as its boundaries to identify the round window niche through the recess.

There are different methods for accessing scala tympani after finding the round window; in cochleostomy, the surgeon drills a separate hole and the anterior limit of the round window in extended cochleostomy. The implant is inserted into the cochlea, once the cochlea is opened. For making sure of the proper function of implant, an integrity test is performed by an audiologist at the end of the procedure. X-ray radiography is used to ensure proper location of cochlear implant by some surgeons. At the end, the patient is discharged the same day, and cochlear implant is usually activated 2–4 weeks postoperatively.
