IntroductionThe rate of cochlear implants at King Abdulaziz University Hospital has increased significantly over the years. Because of this, the purpose of this study is to examine outcomes of post-operative cochlear implantation. This study will aim to determine if there is a correlation between MRI and CT scans including calcification and the outcomes of the cochlear implantation procedure. Additionally, there is a lack of literature regarding the outcomes of cochlear implants as a choice of hearing rehabilitation in such patients showing a “gap” in literature. This study will assess demographic information, pathological and surgical findings, and the results from such assessments to include imaging, audiological assessments, rehabilitation services, cochlear implant device and types of surgery. Success and complication rates will be determined and the type of cochlear implant will be examined to determine if it had an effect on the outcome of the surgery.
Sensorineural hearing loss (SNHL) is a common complication resulting from bacterial meningitis. Almost 33% of children who are diagnosed with meningitis will develop SNHL at some point post-meningitis (Ahmed & Quraishi, 2006). “SMHL in meningitis is attributed to cochlear involvement through various routes of spread including through the internal auditory canal (IAC), hematogenously, or through the cochlear aqueduct” (Reeck & Lalwani, 2003, p. 576). IAC inflammation has been found although it is not nearly as significantly seen as in cochlear aqueduct. Reversible SNHL occurs in a large amount of meningitis cases however the exact pathophysiology is not clear (Ahmed & Quraishi, 2006).
Reeck and Lalwani (2003) conducted a retrospective case study using a sample of three patient participants who had significant SNHL. The patients had a normal cochlear although an ossified vestibular labyrinth. The researchers reviewed the patients’ histories, operative intervention, imaging finding, and operative findings to gather data. Outcome measures used include imaging findings, clinical history, and operative intervention and findings (Reeck & Lalwani, 2003). What they found was that two of the three patients went through cochlear implantation procedure with full insertion of electrodes. The other patient had an isolated tympani ossification therefore the electrode was implanted in the scala vestibuli. Patterns of isolated ossification and SNHL can be seen in patients post-meningitis without radiographic evidence of cochlea (Reeck & Lalwani, 2003).
Ahmed & Quraisi (2006) discussed the aetiological causes of SNHL in meningitis cases. The specific aetiologies examined include ototoxicity, anesthesia (general, spinal), infective (bacterial, fungal, mycoplasma, viral), autoimmune (Cogan’s Syndrome, Wegener’s Granulomatosis, polyarteritis nodosa, Kawasaki Disease), metabolic, haematolgical, neoplasms, vestibular, neurological, traumatic, and miscellaneous. All of these aetiologies have specific conditions associated with them that would contribute to SNHL in meningitis patients. Knowing the background of all possible aetiologies of SNHL could lead to further investigation into specific diseases such as meningitis. This could give a better understanding of how hearing loss occurs and the impact duration of meningitis before treatment has on whether or not hearing loss is reversible or can be treated.
Durisin, Bartling, Arnoldner, Ende, Prokein et al (2010) conducted a retrospective clinical study at an academic referral center of the Medical University of Hannover. The participants of the study included 126 patients who were significantly deafened by meningitis over a twenty year span. Of these 126 patients, 31 were adults and 95 were children. Children were defined as those patients being 12 years of age and under at the onset of meningitis. All patients showed no bilateral auditory brainstem response (Durisin et al, 2010). The interventions used in this study include surgical findings, patient history, and imaging results. These findings were analyzed by experienced neuroradiologists and surgeons. What they found was that 30 of the 95 children showed symptoms of labyrinthitis ossificans and 11 of the 31 adults showed changes in bony structure of the cochlea (Durisin et al, 2010). Indications from high resolution computed tomography (HRCT) showed that ossification was detected more often if the time interval was longer between onset of meningitis and HRCT evaluations. In 67% of children and 55% of adults with obliteration, bilateral ossification was observed. The earliest onset of labyrinthitis ossificans were seen HRCT scans as soon as four weeks post-onset. It was concluded that cochlear implants should be done bilaterally as soon as possible following onset of meningitis.
Richardson, Reid, Tarlow, & Rudd (1997) conducted a multicenter prospective study to determine the pathogenesis and natural history of hearing loss in children who suffered acute bacterial meningitis. Location for the settings included 21 hospitals throughout South Wales and England. Participants included 124 children ages 4 weeks old to 16 years old that were recently diagnosed with bacterial meningitis. Participants had undergone extensive audiological assessments with the first tests being conducted within only six hours of being diagnosed. The differences between neural, cochlear, and conductive defects were identified through using a combination of auditory brainstem responses, optoacoustic emissions, and tympanometry (Richardson et al, 1997). All participants showed hearing loss at the first sign of contracting meningitis. Approximately 10% of children had reversible hearing loss that was resolved with 48 hours after initial diagnosis and was more prevalent in those children who had been ill for 24 hours or more. The researchers concluded that hearing loss began in early onset of meningitis and reversed itself on its own. If the meningitis was not treated promptly permanent hearing loss could have occurred (Richardson et al, 1997).
Several other research studies were conducted related to the outcome of cochlear implantation surgery in post-meningitic patients. All showed that there were positive outcomes from the surgery across all age groups from infancy through the elderly. Comparison studies were done in post-meningitic and non-meningitic patients post-surgery to determine if there were better results in one group over the other (Mosnier, Felice, Esquia, Borel, Bouccara et al, 2013; Roukema, Van Loon, Smits, Smit, Goverts et al, 2011; Bille & Ovesen, 2014). Additionally, some studies specifically looked at the ossified cochleae and comparison studies were conducted to examine differences in ossified cochleae and non-ossified cochleae in implantation surgeries (El-Kashlan, Ashbaugh, Zwolan, & Telian, 2003; Nichani, Green, Hans, Bruce, Henderson, & Ramsden, 2011; Kemink, Zimmerman-Phillips, Kileny, Firszt, & Novack, 1992). Electronically evoked brainstem responses were also examined determining that electrode mapping is an effective method to determine the outcomes of cochlear implantation surgery (Lambert, Ruth & Hodges, 1991; Guiscafre, Martinez, Benitez-Diaz & Munoz, 1984).
Research has found that cochlear implants in post-meningitis patients of all ages were successful in the recovery of language skills and as a successful intervention for hearing loss (Reeck and Lalwani 2003; Durisin, Bartling, Arnoldner, Ende, Prokein et al 2010; El-Kashlan, Ashbaugh, Zwolan, & Telian, 2003; Nichani, Green, Hans, Bruce, Henderson, & Ramsden, 2011; Kemink, Zimmerman-Phillips, Kileny, Firszt, & Novack, 1992). Specific themes were identified to include demographics (age, race, gender), audiological assessment outcomes, imaging, cochlear implant devices and the type of surgery, and rehabilitation. In addition, a correlation will be examined between CT scans an MRI which will include calcification and cochlear implantation procedure outcomes. The “gap” in literature suggests that more research needs to be done that focuses on the outcomes of cochlear implants for hearing rehabilitation as there is not much recent relevant literature. By determining the success and complication rates of cochlear implantation surgeries, it could potentially provide a greater understanding as to whether or not the type of cochlear implant effects the outcome of surgery.
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