17Special Arrays for the Difficult Cochlea

TThe ossified basal turn

Cochlear ossification (labyrinthitis ossificans), most often after pneumococcal meningitis or otosclerosis, usually confines new bone to the basal turn near the round window, so a 1 mm bur can extend the basal-turn opening anteriorly until a patent lumen is found. The drill-out must NOT exceed ~8 mm: beyond that the dissection risks the internal carotid artery, and bleeding from the vasa vasorum signals the surgeon to stop (cross-ref Ch.15 Surgery).[2002]

CEscalating the drill-out

When scala tympani is obliterated, the strategy escalates: extend superiorly to insert into scala vestibuli, then a circummodiolar drill-out (working between the anterior carotid, superior tympanic facial nerve and labyrinthine facial segment), and finally split/double arrays — two short bundles in separate cochleostomies into the basal and middle/upper turns — or compressed arrays for a short patent segment.[2012]

TThe Sennaroglu spectrum

Inner-ear malformations are classified by the Sennaroglu & Saatci (2002) system: Michel deformity, cochlear aplasia (~3–7%), common cavity, cochlear hypoplasia (~7–15%), incomplete partition I (absent modiolus, cystic), IP-II (classic Mondini, 1.5 turns, dilated vestibule, enlarged vestibular aqueduct) and IP-III (X-linked). Deformities are bilateral in ~65% of cases and similar in ~93% of those.[2014]

CArray choice without a modiolus

Array choice follows the anatomy: when no modiolus exists (IP-I, common cavity), perimodiolar arrays are contraindicated and a straight lateral-wall or custom cavity/ring electrode is used, positioned against the OUTER wall of the cavity where surviving neuroepithelium lies; a transmastoid labyrinthotomy or transcanal approach helps avoid the aberrant facial nerve (cross-ref Ch.12 Imaging).[2009]

TThe auditory brainstem implant

The auditory brainstem implant (ABI) bypasses cochlea and cochlear nerve entirely, laying a flat silicone surface paddle (typically ~12–21 contacts) on the cochlear nucleus in the lateral recess of the fourth ventricle via a translabyrinthine or retrosigmoid approach — for NF2 after schwannoma resection and increasingly children with cochlear-nerve aplasia or complete labyrinthine aplasia.

CABI outcomes

ABI place-coding is crude, so outcomes generally fall below cochlear-implant performance — often sound awareness and lip-reading support rather than open-set speech — and non-tumour/pediatric recipients generally do better than NF2 patients. Penetrating-microelectrode ABI variants were trialled for finer selectivity but showed no clear benefit.