Cochlear implantation (CI) is a well-known surgical procedure to rehabilitate patients with severe to profound sensorineural hearing loss. Indications for this surgery have expanded in the last 10 years including bilateral CI. Although CI has been described as a safe procedure with few major complications, it may have an adverse effect on the vestibular functions and produce dizziness. Prevalence of postoperative dizziness varies widely in the literature and is said to affect between 2% - 47%.

The structural and functional integrity of the vestibular system is necessary for maintenance of the complex postural system and adaptation to the environment. The absence of vestibular function is accompanied by poor prognosis and severe limitations in the activities of daily life, such as ambulating in low-light environments or on uneven ground, swimming, driving fast, etc.

The exact mechanisms responsible for the postoperative vestibular changes and/or symptoms, but several theories exist. Because of the very anatomic proximity between the auditory and vestibular systems, and their embryologic and physiologic alterations, they may be simultaneously involved in some bodily dysfunctions. This involvement is more frequent in peripheral alterations than in central ones.

The lateral wall and the fluid space are breached during cochleostomy. Insertion of electrode array may cause changes in the normal fluid homeostasis of the inner ear, damage to the basilar membrane, osseous spiral lamina and vestibular receptors; utricle, saccule and semicircular canals, surgery-induced inflammation resulting in fibrosis or loss of hair cells, foreign body reaction (labyrinthitis), produce perilymph leakage and alter the pressure in the inner ear. In addition, the electric stimulation of the cochlear implant may cause pathologic changes in the inner ear as a subsequent dysfunction of structures, resulting in vestibular alterations.

In previous research, the following vestibular assessments were utilized to determine vestibular injuries after CI: Caloric response, videonystagmography (VNG), vestibular-evoked myogenic potentials (VEMPs), video head impulse test (VHIT), rotatory chair and scleral search coil.

Knowledge of vestibular system function before and after CI surgery is important for the satisfactory management of each case. It also helps in the selection of which ear to implant to avoid bilateral vestibular areflexia and can assist in the management of any postoperative vestibular symptoms. So, there are two questions that should be raised when we consider the vestibular function of a patient who will submitted to CI: Is vestibular function present or not? and is the function symmetric?

Inclusion Criteria:

1. Children with bilateral severe to profound sensorineural hearing loss.
2. Age less than 6years at time of implantation.
3. Prelingual deafness.

Exclusion Criteria:

• Incomplete follow up.
• Other pathologies affecting balance as orthopedic problems before surgery.

Children with severe to profound hearing loss aged less than 6 years and candidate for cochlear implant with no motor problems before surgery.