CI Atlas · Preoperative Imaging · Module 06

6Cochleovestibular malformations — the classifications

A malformed inner ear is development frozen at a moment in time, and reading it is the art of recognising which moment. The further back the arrest, the more is missing: arrest at the placode leaves the Michel deformity with no labyrinth at all; a little later, a single common cavity; later still, a small or incompletely partitioned cochlea that is entirely implantable. A succession of classifications — Mondini's eighteenth-century description, Jackler's embryogenesis-based scheme, and the worldwide-accepted Sennaroglu system — turns this spectrum into named categories that predict candidacy, electrode choice and the risk of a perilymph gusher. The crucial fork is between the few forms with no implantable cochlea or nerve, which mean an auditory brainstem implant, and the many that simply change the surgical plan. This module covers the map of malformations.

Imaging note

Representative CT and MRI images for this chapter are being added soon. The interactive figures here are original schematic teaching diagrams; to respect copyright we do not reproduce third-party radiographs.

TMalformation as arrest

Malformations are graded by the embryologic timing of arrest— the earlier development stops, the more severe the deformity (Module 5's embryology made visible). Reading the morphology backward to its arrest point is how the class is assigned.

CFrom Mondini to Sennaroglu

The lineage runs from Mondini (1791) through Jackler, Luxford & House (1987, embryogenesis-based, with CT correlate and arrest week) and Phelps to the worldwide-accepted Sennaroglu–Saatci (2002) scheme: complete labyrinthine aplasia → rudimentary otocyst → cochlear aplasia (± dilated vestibule) → common cavity → cochlear hypoplasia 1–4 → incomplete partition I–III, plus EVA.[1987][2002]

The worldwide-accepted Sennaroglu–Saatci scheme grades cochleovestibular malformations by the embryologic timing of arrest — the earlier the arrest, the more severe. The crucial fork is between forms with no implantable cochlea or nerve (Michel, rudimentary otocyst, cochlear aplasia → auditory brainstem implant) and the implantable ones (common cavity, hypoplasia, incomplete partition), where imaging shifts from a yes/no gate to surgical planning — array choice, gusher and facial-nerve anticipation. Malformations are bilateral ~65% of the time. Schematic, after Sennaroglu & Saatci.

CThe forms that mean ABI

A minority have no implantable cochlea or nerve and redirect to an auditory brainstem implant: complete labyrinthine aplasia (Michel), the rudimentary otocyst, and cochlear aplasia (absent cochlea and cochlear nerve). The key distinction is cochlear aplasia with a dilated vestibule (CADV, no neural elements → no CI benefit) versus the common cavity, which does contain neural elements lining its periphery and is implantable.

CFrom gate to surgical planning

For the implantable forms — common cavity, hypoplasia, incomplete partition — imaging shifts from a yes/no gate to surgical planning. A common cavity is implanted via a banana-shaped labyrinthotomy with a straight lateral-wall array (avoid modiolar-hugging arrays — the neural elements line the wall), watching for inadvertent IAC insertion. Malformed ears predict a CSF gusher and an aberrant facial nerve, so imaging forewarns the surgeon (Surgery chapter). Malformations are bilateral ~65% of the time. The detail of incomplete partition and EVA is the next module.

Case 12.6 · Which malformations preclude a CI?

Imaging shows complete absence of the labyrinth in one child and a common cavity in another. The team must decide CI vs ABI.

How do these differ?

Self-assessment — Module 52 questions

Question 1 · Trainee

Which classification is the worldwide-accepted scheme?

Question 2 · Clinician

How does a common cavity differ from cochlear aplasia with a dilated vestibule (CADV)?

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