Partitioned Versus Duplicated Internal Auditory Canal

Abstract

A double internal auditory canal (IAC) is an uncommon 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 features and differences between the 2 forms. All 3 patients underwent high-resolution computed tomography and magnetic resonance imaging. 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 incomplete bony septum. Conversely, in the PTCD-associated form, neuroimaging revealed the presence of 2 separated and anomalously coursing canals for the facial and vestibulocochlear nerve. The aforementioned different radiologic findings probably reflect a more complex spectrum of etiopathogenetic mechanisms affecting the facioacoustic primordium and leading 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 otherwise normal in size and location; conversely, "duplication" should be reserved for IAC anomalies encountered in patients with PTCD or other hindbrain malformations.