Narrow duplicated or triplicated internal auditory canal (3 cases and review of literature): can we regard the separated narrow internal auditory canal as the presence of vestibulocochlear nerve fibers?

The narrow duplicated internal auditory canal (IAC) is a very rare malformation, and there is no report about the narrow triplicated IAC in the literature. It has been believed to be associated with congenital sensorineural hearing loss and to be a result of aplasia or hypoplasia of the vestibulocochlear nerve or the cochlear branch. We present 2 cases of unilateral narrow duplicated IAC and 1 case of unilateral narrow triplicated IAC with ipsilateral sensorineural hearing loss. The separated, accessory bony canals delineated on high-resolution computed tomography do not mean the presence of nerve fibers. In previously presented cases and in our case, the separated small canals were vacant and without a cochlear nerve fiber. We present new common radiological findings as follows: the bony canal to the cochlea is very thin and the connection with the modiolus of the cochlea is interrupted in narrow separated IAC.