Radiological Characterization of Malformations of the Internal Auditory Canal

Malformations of the internal auditory canal (IAC) are rare. They can present as a narrowing of the canal due to aplasia or hypoplasia of the vestibulocochlear nerve, complete atresia, or even a doubling of the IAC. The aim of our study is to provide a comprehensive overview of the different types of IAC anomalies and to provide a classification based on radiological findings and their relation to syndromes and/or inner/middle ear anomalies. In addition, IAC malformations will be explained in a putative phylogenetic context.

All patients who underwent pre-interventional imaging between 1995 to 2024 for evaluation of a hearing implant in domo with an inner ear malformation were included in the present retrospective study. The available imaging data, i.e. high resolution computed tomography (HRCT) or cone beam CT (CBCT) of the temporal bone and supplementary MR of the temporal bone, were reviewed independently by two neuroradiologists. Malformations of the IAC and concomitant malformations of the middle and inner ear were recorded. Demographic and clinical data were also collected. Based on the data and information obtained, a radiological classification of the different IAC malformations was provided.

A total of 36 patients (55 affected ears) were included in the analysis. The majority of the patients were female (75%). The mean age was 6.3 ± 9.4 years (mean ± std). A syndromic disease was present in 28% of the patients. Due to severe hearing loss, a total of 48% of patients received a hearing system. Based on the radiological findings, we performed the following typing: Type I - Narrow IAC; Type II - Atresia with isolated facial nerve canal; Type III - Double IAC with/without atresia, Type IV - Complete atresia. In descending order, the frequency of these malformations of the IAC in our cohort was distributed as follows: Type III - Double (n= 29, 52.7%), Type I - Narrow (n=15, 27.3%), Type IV - Complete atresia (n=4, 7.3%), Type II - Atresia with isolated facial nerve canal (n=7, 12.7%).

Since hypoplastic IAC may be associated with hypoplastic or absent cochlear nerve and sensorineural hearing loss, radiological assessment of the IAC is of critical importance in the evaluation of patients with severe sensorineural hearing loss undergoing cochlear implantation. Accurate analysis of the imaging data and understanding the complexity of the malformations are of great importance in assessing the expected benefits prior to cochlear implantation.

· IAC malformations can be classified into four different groups based on recurring patterns.. · IAC malformations are often associated with hypo-/aplasia of the vestibulocochlear nerve.. · The facial nerve is usually present, but may have an aberrant course..

· Döring K, Salcher R, Lanfermann H et al. Radiological Characterization of Malformations of the Internal Auditory Canal. Rofo 2025; DOI 10.1055/a-2699-9904.