Radiological Characterization of Malformations of the Internal Auditory Canal

Abstract

Purpose

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.

Material and Methods

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.

Results

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%).

Conclusion

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.

Key Points

• 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.

Citation Format

• 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

Zusammenfassung

Ziel

Fehlbildungen des inneren Gehörgangs (IAC) sind selten: Sie können sich als Verengung des Gehörgangs aufgrund einer Aplasie, als vollständige Atresie oder sogar als Verdopplung des IAC präsentieren. Ziel dieser Studie ist es, einen umfassenden Überblick über die verschiedenen Arten von IAC-Malformationen zu geben und eine Klassifizierung auf Basis radiologischer Befunde und ihrer Assoziation mit Syndromen und/oder Innen- bzw. Mittelohrfehlbildungen zu erstellen. Darüber hinaus werden IAC-Fehlbildungen in einem phylogenetischen Kontext erläutert.

Materialien und Methoden

In die vorliegende retrospektive Studie wurden alle Patienten aufgenommen, die zwischen 1995 und 2024 zur Beurteilung eines Hörimplantats bei einer Innenohrfehlbildung einer präinterventionellen Bildgebung durchlaufen haben. Die verfügbaren Bildgebungsdaten, hochauflösende Computertomografie (HRCT) oder digitale Volumentomografie (DVT) des Felsenbeins sowie ergänzende MRT-Aufnahmen des Felsenbeins, wurden von zwei Neuroradiologen unabhängig voneinander ausgewertet. Dabei wurden Fehlbildungen der IAC und begleitende Fehlbildungen des Mittel- und Innenohrs dokumentiert. Zudem wurden demografische und klinische Daten erhoben. Auf der Grundlage der gewonnenen Daten und Informationen wurde eine radiologische Klassifizierung der verschiedenen IAC-Fehlbildungen vorgenommen.

Ergebnisse

Insgesamt wurden 36 Patienten (55 betroffene Ohren) in die Analyse einbezogen. Die Mehrheit der Patienten war weiblich (75%). Das Durchschnittsalter betrug 6,3 ± 9,4 Jahre (Mittelwert ± Standardabweichung). Bei 28% der Patienten lag eine syndromale Erkrankung vor. Aufgrund eines schweren Hörverlusts erhielten 48% der Patienten ein Hörsystem. Auf der Grundlage der radiologischen Befunde erfolgte folgende Typisierung: Typ I: enge IAC; Typ II: Atresie mit isoliertem Facialiskanal; Typ III: doppelter IAC mit/ohne Atresie; Typ IV: vollständige Atresie. In absteigender Reihenfolge verteilte sich die Häufigkeit dieser Fehlbildungen der IAC in unserer Kohorte wie folgt: Typ III (doppelter innerer Gehörgang): n = 29 (52,7%), Typ I (enger innerer Gehörgang): n = 15 (27,3%), Typ IV (vollständige Atresie): n = 4 (7,3%), Typ II (Atresie mit isoliertem Fazialiskanal): n = 7 (12,7%).

Kernaussagen

• IAC-Fehlbildungen lassen sich anhand wiederkehrender Muster in vier verschiedene Gruppen einteilen.

• IAC-Fehlbildungen gehen häufig mit einer Hypo-/Aplasie des Nervus vestibulocochlearis einher.

• Der N. facialis ist in der Regel vorhanden, kann aber einen abberranten Verlauf aufweisen.

Keywords

Internal auditory canal - Temporal bone - Cochlear implant - Atresia - HRCT - CBCT

Publication History

Received: 16 June 2025

Accepted after revision: 10 September 2025

Article published online:
29 September 2025

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