Both computed tomography (CT) and magnetic resonance imaging (MRI) render complementary information in the preoperative assessment of cochlear implant candidates. CT is an excellent modality to identify anomalies of the bony labyrinth, vestibular aqueduct, otic capsule, and eventual concomitant middle ear anomalies or anatomic variations that may complicate surgery. MRI is superior in the assessment of the membranous labyrinth, internal auditory canal (IAC), cerebellopontine angle (CPA) cistern, and auditory pathway. Contrast administration will increase the detection of infectious, inflammatory, or autoimmune diseases of the inner ear and of meningeal pathology as a cause of hearing loss. These findings may directly impact patient management (Hegarty et al. 2002). If only one imaging modality is chosen, one should bear in mind that abnormalities detected with MRI are more likely to influence the implantation process (e.g., asymmetric nerve hypo- or aplasia, cochlear obstruction) (Parry et al. 2005).

Congenital hearing loss or profound hearing loss in early childhood may be the result of developmental abnormalities of the cochleovestibular system. They may be part of a syndrome or due to sporadic chromosomal abnormalities, which may be linked to gestational infections or ototoxic drugs. As described in Congenital Malformations of the Temporal Bone, arrested or aberrant development of the labyrinth will lead to a myriad of malformations.

Labyrinthine or cochlear aplasias are absolute contraindications for CI. In other dysplasia CI may be considered, but decision-making should be taking into account the neural function of the auditory nerve and—particularly in syndromic cases—cognitive function. Prior documentation of hearing or proven auditory nerve function is considered beneficial. Surgery may be technically challenging, especially in syndromic cases with associated middle ear anomalies where normal anatomical landmarks such as the facial recess, stapes, or round window are distorted or absent. A precise description of the middle and inner ear status on imaging will render a roadmap for the surgeon. Moreover, imaging will identify anomalies which predispose to perilymph gusher or perilymph oozing. “Gushing” of cerebrospinal fluid (CSF) during cochleostomy is the result of perilymphatic hydrops due to a broad communication between the subarachnoid space and the perilymph in the cochlea as can be seen in X-linked hearing loss (Friedman et al. 1997). Preoperative perilymph oozing or slow, persistent flow of CSF may occur in patients with enlarged vestibular aqueducts and modiolar deficiency. In case of asymmetric developmental abnormalities, imaging might influence the choice of side of operation (Fig. 2).

Labyrinthitis due to bacterial meningitis is the most common cause of postnatally acquired hearing loss. Other causes of labyrinthitis are viral infections, inflammatory conditions, trauma, and autoimmune diseases. (see also Inner Ear Pathology). In both infectious and noninfectious labyrinthitis, the labyrinth will become inflamed—leading to degeneration of sensory structures in the organ of Corti and of spiral ganglion cells. (Merchant and Gopen 1996; Rappaport et al. 1999; Klein et al. 2003). Eventually, labyrinthitis ossificans may develop with replacement of intralabyrinthine fluid by fibrous tissue or bone formation. This will increase the risk for complications during cochlear implantation or may even preclude implantation. Fibrous tissue may be removed preoperatively relatively easily with a little hook. Proximal bony obliteration may be drilled out increasing the surgical risk of damaging neural structures. Once the obliteration exceeds to the second half of the basal turn of the cochlea, surgical access to the scala tympani is precluded. In such cases, implantation of a double array may be considered. (Lenarz et al. 2001; Bredberg et al. 1997). If the ossificiation is limited to the scala tympani, a full insertion of the implant may be achieved into the scala vestibuli (Lin 2006) (Fig. 3e, f).

Labyrinthitis may progress rapidly to a fibro-osseous stage. Therefore, early audiometric testing and imaging are recommended and early intervention may be appropriate to improve the outcome in terms of hearing restoration. Bilateral implantation has been advocated by some groups. (Merkus et al. 2010).

Imaging findings will play a major role in treatment planning. Since MRI is sensitive to soft tissue changes in the early phase of labyrinthitis, it is the modality of choice in suspected acute labyrinthitis. In the acute phase of labyrinthitis, MRI will first show enhancement within the labyrinth without any signs of obliteration on T2 weighted images. As soon as fibroblastic proliferation occurs, T2 weighted images will show signal loss within the labyrinth. This fibrous tissue may or may not be enhancing. CT will frequently be normal in acute labyrinthitis or in case of purely fibrous replacement. Once neo-ossification occurs, CT will show osseous obliteration. The combination of MRI- and CT-findings will allow for differentiation between fibrous tissue and ossification (Fig 4).

The precise description of presence, location, and extent of obliteration of the cochlea will guide surgical planning as well as the choice of cochlear implant (single array, double array).