13Choosing the Array, Setting Expectations: Electrodes and Outcomes
A malformed cochlea changes both what you put in and what you promise afterwards. Matching the electrode to the anomaly minimises misplacement, while the anomaly and the cochlear nerve together set the outcome range you must counsel honestly.
CMatch the array to the anatomy
Lateral-wall (straight) arrays are the default for common cavity and many malformed cochleae: they hug the outer neural wall, distribute contacts along an irregular lumen and reduce the risk of fold-over or extracochlear/intra-vestibular misplacement. Perimodiolar arrays are generally avoided when the modiolus is deficient or absent, because there is no central column for the curling array to wrap around and electrodes may sit against bone or empty cavity. Hypoplastic cochleae need shorter or custom (compressed, slim) arrays so that contacts stay within the limited lumen rather than buckling or protruding; full-length insertion is neither possible nor desirable. In a common cavity the goal is to place contacts circumferentially against the wall where neural tissue is most likely, often with a straight array advanced under direct or image guidance rather than blind full insertion.[2017][2005][2020]
CConfirm placement on the table
Intraoperative imaging (cone-beam CT, rotational fluoroscopy or plain transorbital/Stenvers views) confirms the array lies within the cochlear lumen and not in the IAC, vestibule or cranial cavity - a real hazard in malformed ears. Electrically evoked compound action potentials (ECAP/NRT-type telemetry) and stapedial reflex thresholds give an on-table signal that the array is exciting neural tissue, not just impedance through fluid. Impedance and integrity testing distinguish a well-seated array from one in a CSF-filled cavity, where unusually low or uniform impedances can flag malposition. A documented gusher (see the gusher map) demands a strategy ready before incision - lumbar drain, head-up positioning, a sealing array and soft-tissue packing at the cochleostomy.[2017][2009][2020]
TOutcomes scale with severity and nerve
Malformed but nerve-bearing cochleae can achieve open-set speech: IP-II (Mondini) and EVA frequently approach the results of normal-anatomy implantees. Common cavity and severe hypoplasia give more variable outcomes - some children develop useful open-set hearing, others remain at detection/pattern levels, reflecting how much and where neural tissue survives. Cochlear nerve deficiency is the single strongest negative predictor: nerve hypoplasia can still give worthwhile gains, but nerve aplasia generally cannot support a cochlear implant and points to ABI. Outcome is determined far more by the neural substrate and time-to-implant than by the elegance of the electrode itself; the array prevents harm and ensures contact, but the nerve writes the ceiling.[2005][2016][2017]
TCounsel the range, not a point
Honest counselling presents a range tied to the specific anomaly and nerve status, never a single promised result, because malformation outcomes are inherently more variable than typical-anatomy CI. Families should understand that EVA and IP-II generally carry an optimistic prognosis, while common cavity and severe hypoplasia carry guarded, individualised expectations. Where the nerve is borderline, families are counselled that the implant is a reasonable attempt with a defined fallback (ABI) if response is poor, and that early benefit may be limited. Expectation-setting is revisited after activation: ECAP responses, behavioural detection and early progress refine the prognosis given before surgery.[2016][2005][2020]
Which array choice and counselling message best fit this child?
Why are perimodiolar arrays generally avoided in cochleae with a deficient modiolus?
Which finding is the single strongest negative predictor of cochlear implant outcome in a malformed ear?
Which malformations most often approach normal-anatomy open-set speech results after implantation?