Brief Answer:
Possible complications listed below.

Detailed Answer:
Hello and welcome to " Ask a Doctor" service.

I have read your query and here is my advice.

Complications of cochlear implant surgery, since the mastoid bone is resected, include postoperative infection of the surgery site, meningitis, facial nerve paralysis, leakage of cerebrospinal fluid.

In most cases, the results of the cochlear implantation are excellent.

In case of a complication, it should be treated with standard techniques in a hospital setting.

To avoid complications it is necessary to be followed up for two or three weeks postoperatively with the treating Doctor and to avoid strenuous physical activity for a couple of months after implant activation.

Hope this helps.

Feel free to ask if you have further questions.

---