4Who Already Has Vestibular Loss: Etiology and Baseline
Many of the insults that cause profound deafness also injure the labyrinth, so a large share of candidates arrive already vestibularly impaired. The etiology of the hearing loss predicts the pattern of vestibular risk, and roughly half of candidates have some bilateral weakness before any surgery — the clinical baseline against which any surgical loss must be judged.
FHow common is baseline weakness
About 50% of candidates tested by caloric have bilateral vestibular hypofunction to some degree, and 40% have it by quantitative head-impulse testing 23% of 43 candidates showed at least 20% caloric asymmetry between ears, and ice-water caloric identified unilateral profound loss in 11% of 47 candidates Up to 72% of children and adults with significant sensorineural hearing loss have some level of vestibular dysfunction.[1982][2005]
TEtiology predicts the pattern
Post-meningitis hearing loss generally shows abnormal semicircular-canal function in essentially all cases, though otolith responses vary Connexin 26 (GJB2) loss tends toward otolith dysfunction more than canal impairment In congenital sensorineural loss, canal dysfunction is seen in ~41% and otolith dysfunction in ~42%, roughly split between bilateral and unilateral.[2013][2013]
TSyndromic and genetic associations
Vestibular hypofunction commonly accompanies hearing loss from Usher type IB / DFNA11, in-utero rubella, Waardenburg, Wildervanck, Goldenhar, Pendred, and possibly Jervell-Lange-Nielsen syndromes CHARGE-association children may have complete semicircular-canal aplasia in one or both labyrinths while retaining otolith/saccular function — directly relevant to VEMP-based ear selection Combined hearing-and-vestibular loss is also seen with Cogan and BOR syndromes, enlarged vestibular aqueduct, otosclerosis, CMV, ototoxicity, trauma, aging and prematurity.[2002][1983]
FWhy baseline testing matters
Because most candidates present with unknown hearing-loss etiology, baseline vestibular status is often unknown, a strong argument for routine pre-op testing Roughly half of candidates already have measurable bilateral weakness, so implanting blindly risks removing the better-functioning labyrinth Pre-op vestibular testing is a low-cost, high-value addition that guides ear selection and informed consent.[1982][2004]
What does the etiology predict about this child's vestibular status?
Approximately what fraction of CI candidates have some degree of bilateral vestibular hypofunction on caloric testing?
In CHARGE association, the typical vestibular finding relevant to ear selection is: