Partitioned Versus Duplicated Internal Auditory Canal: When Appropriate Terminology Matters

Objective: A double internal auditory canal (IAC) is an un- common malformation among temporal bone anomalies related to sensorineural hearing loss. This anomaly has been described as an isolated finding in otherwise normal patients, as well as a frequent feature in pontine tegmental cap dysplasia (PTCD). In both circumstances, the term duplication is currently used to describe this malformation. We conducted a retrospective study on 3 cases of IAC duplication (2 isolated and 1 PTCD-associated form) and reviewed the literature to evaluate both imaging fea- tures and differences between the 2 forms. Intervention(s): All 3 patients underwent high-resolution com- puted tomography and magnetic resonance imaging. Results: Neuroimaging documented different radiologic features between isolated and PTCD-associated IAC duplication. In the isolated form, the IAC seemed to have normal position and size, but it was partitioned in 2 portions by a complete or incompletebony septum. Conversely, in the PTCD-associated form, neuro- imaging revealed the presence of 2 separated and anomalously coursing canals for the facial and vestibulocochlear nerve. Conclusion: The aforementioned different radiologic findings probably reflect a more complex spectrum of etiopathogenetic mechanisms affecting the facioacoustic primordium and lead- ing to overlapping anomalies of the IAC. We speculate on the appropriate terminology in describing this entity and propose that ‘‘partition’’ should be used to describe a double IAC oth- erwise normal in size and location; conversely, ‘‘duplication’’ should be reserved for IAC anomalies encountered in patients with PTCD or other hindbrain malformations.