6Post-Meningitic Deafness and the Ossified Cochlea

FA leading acquired cause

Bacterial meningitis is the most common cause of acquired severe sensorineural hearing loss in children; some degree of loss follows in roughly 5 to 35% of survivors, with frank deafness in about 2 to 11%. The deafness is usually severe-to-profound, permanent, and can affect one or both ears, with no consistent frequency pattern, so a meningitis history warrants prompt audiological assessment of both ears. Streptococcus pneumoniae, Haemophilus influenzae, and Neisseria meningitidis are the classic organisms; pneumococcus both drives a higher proportion of hearing loss and produces the most severe cochlear ossification. Haemophilus-related ossification tends to be less severe than pneumococcal, which is one reason the responsible organism is worth knowing when planning timing. Infection reaches the cochlea chiefly through the cochlear aqueduct adjacent to the round window, which explains why the basal turn bears the brunt of the damage.[2009][2014]

TThe clock: fibrosis then bone

Labyrinthitis ossificans begins as fibrosis within weeks of infection, as early as about 8 days, before maturing into new bone, so the window for an easy full insertion is short. New bone is most marked at the round window and proximal scala tympani of the basal turn, exactly where an array is normally introduced; the middle and apical turns are less often affected and the scala vestibuli is frequently spared. Some degree of cochlear neo-ossification is found at surgery in roughly 70% of patients deafened by meningitis, so it should be assumed and planned for rather than treated as a surprise. Total ossification of the cochlea is possible and is seen more often in children than adults, which raises the urgency for the youngest patients. The early fibro-ossific stage carries no preserved hearing to lose, so the timing argument is not about residual hearing preservation but about keeping the lumen open for a complete electrode insertion.[2014][2009]

TImaging surveillance and side selection

Because ossification can advance quickly, post-meningitic deafness is imaged early and may be re-imaged, with surveillance aimed at catching a still-patent cochlea before bone forms. High-resolution T2-weighted MRI of the canal and otic capsule is the modality of choice, showing fluid within the cochlea as a signal of patency; one study found MRI matched the operative findings in about 88% of patients. CT is less reliable for early fibro-ossific change, with reported accuracy ranging from about 53% to over 90%, and can miss fibrosis that has not yet calcified, with ossification detectable on CT from about two months post-infection. Ossification is commonly asymmetric within a patient, so imaging is used to choose the more patent ear for implantation, not merely to confirm candidacy. When imaging shows the basal turn obliterating, the practical message is to expedite surgery on the better ear rather than wait.[2014][2009]

COutcomes, bilateral implantation, and prevention

Ossification does not contraindicate implantation; outcomes with a partial insertion or fewer active electrodes are often still good, because residual neurons can support useful hearing. Temporal-bone counts in ossified ears found surviving neurons ranging from about 6,300 to 28,200 against roughly 35,500 in a normal infant cochlea, and benefit has been reported with as few as about 3,300 neurons, which underpins realistic optimism even after severe ossification. Because the basal turn ossifies first and the scala vestibuli is often spared, getting an array into a patent segment, even partially, can still deliver meaningful sound, and families should be counselled that fewer electrodes does not mean no benefit. Bilateral implantation deserves early consideration in meningitis, since both ears are at risk of progressive ossification and the more patent side today may not stay patent; implanting before the second ear closes off preserves the option of binaural hearing. Prevention frames the whole chapter: pneumococcal vaccination reduces the leading organism behind post-meningitic deafness and severe ossification, and vaccination is also part of standard implant-recipient care given the elevated meningitis risk in implanted ears.[2009][2014][2005]