Scala Tympani Versus Scala Vestibuli Cochlear Implantation in Incomplete Partition Type III Malformation

Incomplete partition type III (IP-III) is a congenital inner ear malformation characterized by a deficient separation between the cochlear modiolus and the internal auditory canal (IAC). In patients with IP-III and severe-to-profound sensorineural hearing loss, cochlear implantation (CI) remains the most effective therapeutic option. Its surgical placement is challenging. There is an increased risk of electrode array misplacement toward the IAC, and opening the cochlea always involves a gusher that must be addressed. Sequential CI was performed in a case with bilateral IP-III malformation due to a hemizygous pathogenic variant, c.84delG p.(Ser29Valfs*30), in the POU3F4 gene. The right ear went very swiftly with a correct placement in the scala tympani. Electrode insertion into the scala tympani of the left ear consistently resulted in the electrode ending up in the IAC during re-insertion attempts. The electrode placement was successful when a scala vestibuli insertion was chosen. The objective of this case report is to compare the surgical and audiological outcomes of cochlear implantation in the scala tympani versus the scala vestibuli in a patient with an IP-III malformation.