An implantable electrode is described for a cochlear implant patient with a malformed common cavity cochlea having a single internal cavity defined by an outer cavity wall or patients having an incomplete partition or conventional spiral-shaped cochlea. An intra-cochlear electrode array is configured to be inserted into the cochlea through a single cochleostomy opening. Outer array branches are closable about a center axis and the electrode array is configured to be closed into a single tube including the array branches for insertion through the single cochleostomy opening into the internal chamber of the cochlea. The electrode array opens within the internal cavity after insertion into the cochlea so that the array branches move away from the center axis to lie with their outer surfaces against the outer cavity wall to deliver the electrical stimulation signals through the stimulation contacts to adjacent neural tissue for auditory perception by the patient.
