12 Meningitis and Implantation Worldwide, vaccination against Haemophilus influenzae, Neisseria meningitidis, and Streptococcus pneumoniae has led to an absolute decline in numbers of patients suffering from bacterial meningitis. S. pneumoniae is nowadays the leading causative pathogen, accountable for ~68% of the bacterial meningitis infections in developed countries. In patients surviving bacterial meningitis, it is important to assess hearing in an early postmeningitic phase to identify patients who would benefit from cochlear implantation. Some of these patients are at risk for development of cochlear obliteration and delayed detection could lead to complicated cochlear implantation1,2 or diminished cochlear implant (CI) performance, or even preclude cochlear implantation at all3–5 (see also Chapter 11). Various audiologic tests and radiologic modalities are available to guide clinical decision making. A stepwise approach for the audiologic and radiologic evaluation and treatment of hearing loss in postmeningitis patients will be discussed. Furthermore, in cases with full obliteration the placement of an auditory brainstem implant (ABI) could be of benefit. Bacterial meningitis is the most common etiology for acquired hearing loss in children.6,7 Sensorineural hearing loss (SNHL) as a complication will occur in ~5 to 36% of bacterial meningitis patients. Severe to profound bilateral SNHL will occur in 3 to 9%, predominantly among pneumococcal meningitis survivors.8–11 Unfortunately, SNHL is not always noticeable or detected in the acute phase, leaving SNHL sometimes undetected for a long period, thereby postponing adequate follow-up and delaying treatment.6,11,12 A protocol for the follow-up of survivors of bacterial meningitis is important. Delayed audiologic assessment and/or delayed referral for cochlear implantation might lead to a worse hearing outcome. Especially in young children, hearing loss may be discovered only by formal assessment, and be delayed or missed without assessing the hearing, despite the fact that at this age it may critically affect the development of speech.13 A good evaluation of hearing, appropriate imaging as soon as possible, and CI counseling are crucial to obtaining the best rehabilitation options. A post-meningitis hearing evaluation protocol, such as proposed by Merkus et al,14 can lead to an accurate and swift assessment of all children (and adults) so that the severely hearing impaired can be implanted soon after their meningitis. The two key audiologic items of this protocol are: (1) hearing assessment before discharge or as soon as the patient is capable; (2) direct referral to an audiologic center/CI center if there is a hearing loss (>30 dB, in at least one ear). The first months are the most important in the follow-up of patients without hearing loss or with only mild hearing loss to confirm the stability of the hearing. When a (delayed) progression is noted, referral and further investigation are needed. In very young children (less than 12 months) it is preferable to have a specialized team to assess the hearing. Sensorineural hearing loss of 30 dB or more should lead to MRI scanning and follow-up. The hearing can deteriorate further and also late fibrosis/ossification (up to 6–12 months) is reported.15 Therefore, all cases with sensorineural hearing loss after meningitis, with or without the presence of labyrinthitis ossificans, need audiometric follow-up at 1, 2, 6, and 12 months after the first hearing test. Additional audiometric testing can be useful when there is doubt about the course of the hearing loss. When sensori-neural hearing deteriorates during the follow-up, MRI needs to be repeated to identify possible progression of intracochlear pathology such as labyrinthitis ossificans. Hearing deterioration to audiometric thresholds between 30 and 70 dB needs follow-up with audiometric testing and MRI scanning for evaluation.14 (See Figs. 12.1 and 12.2.) Hearing assessment should be done as soon as possible (preferably before discharge from the hospital) in all survivors of meningitis, children as well as adults, irrespective of the suspicion of hearing loss before the first audiologic tests. A protocolized follow-up scheme of formal hearing tests should be adopted in the following months, as the hearing loss can be progressive up to at least 6 months after the meningitis, with a check that the hearing is stable at 12 months. We have not seen any cases with postmeningitis hearing deterioration and development of cochlear fibrosis after 12 months of follow-up. If SNHL is present, immediate referral to a CI center is advocated for audiologic assessment and imaging of the cochlea; see part 2 of the flowchart (Fig. 12.2). With the introduction of the protocol, a crucial step is taken toward better awareness among pediatricians and neurologists/intensivists of the risk of SNHL after meningitis and the need for a swift evaluation. They are the “gatekeepers” of this protocol, as they see these patients at admission and during the clinical phase of the meningitis treatment. A close collaboration with pediatricians and neurologists/intensivists in the region is therefore of utmost importance for every CI team. Fig. 12.1 Postmeningitis hearing evaluation and treatment flowchart part 1. ABR in children. “Urgent” is within 2 weeks ENT, ear, nose, throat; OAE, otoacoustic emission; SNHL, sensorineural hearing loss.. (This flowchart is adapted from Merkus et al 2010,11 for explanation see text.) Fig. 12.2 Postmeningitis hearing evaluation and treatment flowchart part 2. “Urgent” is within 2 weeks CI, cochlear implant; MRI, magnetic resonance imaging; SNHL, sensorineural hearing loss. (This flowchart is adapted from Merkus et al 2010,11 for explanation see text.) Bacterial meningitis is found more frequently in children before the age of 2 years. In this group especially, objective hearing evaluation using otoacoustic emissions (OAE)16 and auditory brainstem response (ABR) is necessary. In case of a passed OAE follow-up should be frequent, since hearing deterioration is possible and if it occurs it is most likely soon after the meningitis. Follow-up should be done in an audiologic center, but if this is not feasible, at least OAE should be done followed by a quick referral in case of progression. In case of a failed OAE the referral should be immediate and objective measurements should be done within 2 weeks. This consensus protocol was intended to provide easily accessible and usable guidance for all the professionals involved in every hospital. Moreover, due to the vaccination programs for H. influenzae and S. pneumoniae, the number of meningitis cases is decreasing, making the routine of hearing follow-up in every meningitis case less frequent and correspondingly more vulnerable to being overlooked. Administration of dexamethasone prior to antibiotic treatment in meningitis in adults and children will reduce the neurologic complications and the risk of hearing loss.17–21 We therefore advocate in children dexamethasone 0.6 mg/kg/day in 4 doses for 4 days starting prior to the first antibiotic infusion, and in adults 10 mg every 6 hours for 4 days (40 mg/day), especially if a pneumococcal infection is present. As the lysis of bacteria in the cochlea is supposedly one of the triggers leading to the intracochlear immune response, it seems important to start with the dexamethasone therapy at least 10 to 30 minutes prior to the first antibiotic administration.18,20 An unresolved question is how quickly the obliteration of the cochlea can become manifest. According to animal experiments, case reports, and the experience in our group it seems to be a matter of weeks.1,2,22 It is recommended that if the OAE test at discharge is failed, a decision whether cochlear implantation is needed should be made within 2 to 3 weeks. A cascade of actions needs to be completed to enable such a decision to be made. First of all prompt referral to a cochlear implant center is essential. Referral to a cochlear implant center is especially important in these cases as counseling, diagnosis, and expertise are needed in a timely manner within a multidisciplinary approach. This is particularly so because the hearing loss does not appear to be an emergency case to the parents or even the doctors around them in a sometimes otherwise healthy child or adult. The cochlear implant center will evaluate all patients with a sensorineural hearing loss of 30 dB or more and screen postmeningitic patients with < 30 dB loss or still normal hearing. In our experience this is a safe and valuable cut-off point for deciding between non-affected ears and affected ears. Thus, children or adults with a > 30 dB hearing loss should be considered “at risk” for developing irreversible SNHL; moreover, children are prone to develop a problem in speech and language development. See flowchart part 2 (Fig. 12.2). Although 30 dB hearing loss alone is not enough for cochlear implantation, signs of fibrosis on MRI and a 30 to 70 dB hearing loss should be very closely monitored via frequent hearing tests and MR imaging. In case of progression of hearing loss or fibrosis on the MRI scan, cochlear implantation is inevitable. More than 70 dB hearing loss and signs of labyrinthitis or fibrosis on the MRI (see next section) are reason to perform an urgent cochlear implantation. Below 30 dB loss a “follow-up policy” is adequate: in this “at risk” group, repeated hearing assessment and, when indicated, MRI are the keystones in the follow-up. When considering placement of a CI, it is wise also to scan the complete brain as the CI magnet will hamper visualization of the brain post implantation (see Chapter 3). (See Fig. 12.3.) Different Phases of Postmeningitic Cochlear Inflammation as Seen on MRI and HRCT Normal • No cochlear enhancement on gadolinium-enhanced T1W MRI (GdMRI) • No loss of fluid on heavily T2-weighted MRI (T2W MRI) • No calcification on high-resolution CT (HRCT) Acute phase • Cochlear enhancement on GdMRI (yellow arrow) • No loss of fluid on T2W MRI. Intermediate phase • Cochlear enhancement on GdMRI • Loss of fluid on T2W MRI (red arrow) Final phase • No cochlear enhancement is present, fairly significant loss of fluid is seen on T2W MRI. To distinguish whether cochlear obliteration is caused by either fibrosis or ossification, the combination of T2W MRI and HRCT (blue arrow) is needed. Fig. 12.3a–l Radiologic phases of inflammation, fibrosis, and ossification. First column GdMR images, second column T2W MR images, and third column HRCT images. (Adapted from references14, 23, 24 with permission of Otology & Neurotology.) Relatively recently it has been recognized that there is a strong correlation between the development of hearing loss and enhancement on T1W images.23 One can expect deterioration of the hearing in a postmeningitis child with enhancement on the T1W image. The quality of the image and the slice thickness is important if there is any doubt about candidacy for a CI. The imaging will indicate location of the most inflamed area within the cochlea and accordingly the outcome of hearing loss. See Figs. 12.4 and 12.5, illustrating cases in which the decision not to implant was based on the MR image in combination with the hearing result. Fig. 12.4a–c Unilateral hearing loss and enhancement. Fig. 12.5a–d Asymmetric hearing loss; a tailored approach. Abnormalities on postmeningitis T2W images will appear later than on the contrast-enhanced T1W images. T1W images will show the inflammation in the acute phase and T2W images will show loss of fluid, which is due to obliteration with either fibrosis or calcified (fibrous) tissue. Patients should be considered as CI candidates as soon as there is any loss of fluid in the weeks following onset of meningitis. Only when there is a single side affected (unilateral hearing loss and MRI abnormalities) and stable normal hearing remaining on the contralateral side, can unilateral implantation or no implantation be considered. The hearing of the normal hearing side must be monitored closely in the following months. If only one cochlea is enhanced it is very likely that the normal hearing of the unenhanced cochlea will be preserved.23 A good hearing follow-up is needed in this patient group, as explained in earlier sections. There is no routine need for MRI, but if there is deterioration of the hearing then referral to a CI team and urgent MRI are necessary. This is the most difficult group when it comes to decision making. The hearing is too good for placement of a CI, but is definitely deteriorated. Further deterioration might become apparent in time. With the help of audiometric follow-up and T1W MRI, certain assumptions can be made that help in the decision process. Reimbursement policies may also influence decisions in this group as well as differences in hearing thresholds between the ears. It is wise is to follow up closely with appropriate hearing evaluation (ABR in young children) and when in doubt perform a second MRI. If obliteration, as seen on T2W MRI, sets in there is no time to waste. This is the group often referred to in discussion of simultaneous bilateral cochlear implantation.25 Fortunately, it seems to involve a minority of patients with postmeningitis hearing loss, but it is the most demanding one. These are the patients in whom there is no time to lose and in whom rapid bilateral cochlear implantation should be performed. MRI can inform the surgeons whether the stage is still acute or in case of obliteration is already intermediate or even final. In the acute phase, cochlear implantation should not present a problem. In the intermediate phase, it depends strongly on the amount of obliteration and the time between the scan and the operation. In the final phase, no enhancement can any longer be seen. In addition, obliteration will be seen on T2W MRI in this phase, but it is unknown whether (a part of) the obliterated intracochlear area is calcified. Combination imaging with HRCT is needed. One must remember that obliteration can be both fibrosis and/or calcification23 and that these imaging modalities are complementary. The calcification process is thought to start within weeks, but as yet it is unknown when this period ends. Bacterial meningitis can occur at all ages, but young children and even infants are more prone due to their immunologic status. This age group needs extra expertise in the assessment and rehabilitation phase. Difficulties in the audiologic and radiologic assessment are discussed here, along with sequelae and the counseling of the parents. The method of hearing evaluation in young CI candidates depends on the developmental age and cooperation of the child.26 Especially in the age group from birth to approximately 5 or 6 months, behavioral measurements cannot be used to obtain reliable thresholds; objective methods are needed in this age group. Measurement of auditory brainstem responses (ABR) is well-established for predicting the hearing threshold around 3 kHz. In some cases, more frequency-specific information is needed. For instance, children with moderate to severe hearing losses in the lower and middle frequencies and hearing losses larger than 100 dB in the higher frequencies may show an absent click ABR.27 These children could benefit greatly from hearing aids and are not cochlear implant candidates per se.28 Other objective measurements such as auditory steady-state responses (ASSR), tone burst ABR, and electrocochleography (ECochG) may provide better frequency-specific information. A hearing aid trial is considered standard procedure in most cochlear implant centers, though the necessity of a hearing aid trial prior to cochlear implantation has been questioned recently because it may delay cochlear implantation in some children. We consider it an important part of the diagnostic protocol in most infants, especially because it enables behavioral assessment at this stage. Furthermore, amplification prior to cochlear implantation is important because it could improve the outcomes of the procedure, as it activates the auditory pathway. Also the wearing of hearing aids facilitates the use of the behind-the-ear CI processor. The preoperative evaluation of young children with hearing loss after meningitis differs from that of other hearing-impaired children in many respects. The interval between establishing hearing loss and implantation of the cochlear implant can be as short as one week. In this short period the parents need to be informed about hearing loss and about the possibility of cochlear implantation, and counseled in the decision making. It is a difficult period in which to expect parents to take well thought-out decisions since they are naturally in a stressful situation as their child has just recovered from a life-threatening disease. It is important that parents fully realize the fact that the child has a permanent and profound damage of the inner ears and is suffering from subsequent hearing loss. In this process, behavioral observation audiometry may be helpful. A hearing aid trial is omitted for reasons of urgency when bilateral severe to profound hearing loss is confirmed in combination with signs of fibrosis on MRI. The interval between establishing hearing loss and implantation is often too short for parents to absorb and appreciate all the consequences of the hearing loss, cochlear implantation, and possible long-term effects of meningitis. However, the time between implantation and first fitting of the implant can be used for this purpose, including the process of setting realistic expectations of the cochlear implant. The expectations may be lower for these children than for other children with cochlear implants because of long-term effects of meningitis that cannot be fully predicted at the time of implantation. Especially in the postmeningitis population it is of importance that the diagnostic process is embedded in a multidisciplinary approach, which comprises surgical, audiologic, communicative, and psychosocial disciplines. The preferred imaging modality in postmeningitis patients is MRI. The preferred scanning sequences are T1W, gadolinium-enhanced T1W, T2W, heavily weighted T2 (CISS/Fiesta C), and general brain scan sequence. All these sequences together will take at least 45 minutes to perform. The small slice thickness and the duration will make the scan vulnerable to movement and therefore unsuitable for young children without general anesthesia. Up to an age of at least 5 years general anesthesia is required in order to obtain the necessary images as soon as possible. A positive side effect is that in some hospitals this general anesthesia can also be used in performing an ABR. The cochlear implant team is focused on the rehabilitation of hearing but should not forget that meningitis can be devastating in many ways. First of all, parents and patients are relieved the child is still alive and hearing is sometimes not the key issue in their lives. Numerous sequelae can follow meningitis. Fortunately, many problems improve over time. • Paresis/weakness of one or more limbs • Cognitive impairment, which will interfere with the assessment of learning ability and rehabilitation • Memory loss/lack of concentration, which will interfere with rehabilitation • Loss of balance/dizziness • Clumsiness • Residual headaches • Epilepsy/seizures • Loss of sight Bacterial meningitis is potentially lethal and parents naturally relieved that their son or daughter has survived this devastating disease. They are sometimes taken aback that there is then a new emerging dilemma apparent: the hearing loss or even deafness of their child. The cochlear implant team has to make a special effort to give the parents time to adjust to the new situation while still emphasizing the importance of a swift diagnostic follow-up. Some parents feel it a real burden to have to decide whether a cochlear implant will be the best for their child’s future. Parents want their child to hear very well after the surgery and rehabilitation. This is not a realistic prospect, as only in some of the children will the hearing be perfect with the use of a CI (categories of auditory performance [CAP] = 5–6; speech intelligibility rating [SIR] = 5), whereas others will perform poorly after meningitis (CAP = 3; SIR = 0).29 The variability of outcomes is due to sequelae other than hearing loss, which are not always visible at a young age, and arise from the unknown extent of neural damage. It is still uncertain whether a complete electrode insertion is possible. These uncertainties should be discussed and any predictions about the final result should be tempered accordingly. Luckily, recent research has shown that in case of no loss of fluid on T2W MRI the likelihood of an unsuccessful insertion is nil,23 so it is possible to offer some hopeful statements about success. Anesthesiologic concerns are stated in Chapter 6, Section 6.6.30,31,32 When a patient is assessed for cochlear implantation and the (possible) cause of deafness is meningitis, this patient should be assessed and counseled with care. The meningitis could have been years ago and the history is not always very clear, especially with adult patients who experienced their hearing loss and had the meningitis at a young age. The status of cochlear ossification should be clear before any prognosis of the result of cochlear implantation can be discussed with the patient. After a couple of months the sequelae of meningitis are mostly well-known and at a final stage. Depending on the age of the patient, sometimes the hearing loss and the cognitive disabilities are the last to be discovered. If a CI is not considered in the direct postmeningitis phase, it is usually several years before the question arises again. In these patients the urgency to perform an implantation before the cochlea is obliterated no longer applies. They should be assessed like any other CI implant candidate, except for an additional MRI scan. Counseling should be done with care, considering the expectations and surgical results. In the diagnostic work-up the assessment of the cochlear patency via MRI is essential. If obliteration is seen it is correlated with less favorable outcomes.23 In case of fibrosis or ossification in (a part of) the cochlea, certain surgical options are available. A partial basal turn drill-out, a scala vestibuli insertion, a complete basal turn drill-out in a canal wall down procedure, and a double array placement are options. A guideline and the surgical techniques are described in Chapter 11. When there is no possibility for cochlear implantation within the obliterated cochlea, an ABI should be considered. The literature is not clear about the primary advice in case of a fully obliterated cochlea. Should placement of a CI be attempted, followed by ABI placement if the CI placement is unsuccessful? Or should a direct decision for an ABI be made? Or should sign language alone be advised? The best chances of regaining some hearing are with a CI, but in individual cases an ABI can be successful. Substantial case series to support any of the strategies are lacking. In our opinion an attempt to find an opening within the cochlea in a canal wall down procedure is the best way to confirm the possibility of CI insertion. If this is unsuccessful, an ABI and/or use of sign language are both still possible. Fig. 12.1.1 An infant girl of 3 months had pneumococcal meningitis and received dexamethasone and 14 days of antibiotics in the intensive care unit. She recovered well but did not move her left leg adequately. There were some doubts about her hearing. At ABR testing she was shown to be deaf. Imaging followed swiftly and the CT scan showed no abnormalities, as shown here.
12.1 Introduction
12.2 Hearing Loss after Bacterial Meningitis
12.3 Audiologic Follow-up after Meningitis
12.4 Postmeningitis Hearing Evaluation and Treatment Flowchart
12.4.1 First Hearing Evaluation
12.4.2 Dexamethasone
12.4.3 Obliteration
12.4.4 Hearing Loss of 30 dB or More
12.4.5 Radiologic Phases of Inflammation, Fibrosis, and Ossification14,23,24
12.5 Early Postmeningitis Radiology and Decision Making
a In this case of an 11-month-old infant, hearing evaluation was performed 2 weeks after start of the meningitis. The ABR showed a deafened right ear and a normal functioning left ear. On contrast-enhanced T1W MR images, the right deaf ear (yellow arrow) showed an enhancement, whereas no enhancement was present in the left ear (green arrow).
b The heavily weighted T2W MR images showed a decrease in fluid filling of the cochlea on the inflamed right side (yellow arrow). On the other side a normal fluid distribution was seen within the complete labyrinth. (The left side lateral canal was completely fluid filled, adjacent image not shown here.) The decision for unilateral cochlear implantation or no implantation is debatable in this case.
c The hearing of the unaffected left ear was followed during the next 12 months by audiometric testing at 1, 2, 6, and 12 months and remained stable over years.
a In this case we encountered slight enhancement on contrast-enhanced T1W MR imaging, only in the left basal turn (scala tympani, white arrow), as shown here. The other ear (red arrow) had become deaf directly post meningitis and the cochlea showed contrast-enhancement. Hearing on the left remained stable during three sequential ABRs (3000 Hz) over 3 weeks, showing a stable high-frequency hearing loss of 60 dB.
b The T2W MR image showed a normal fluid-filled cochlea on the left side, and hypointense “fluid loss” on the right side. Because of the unenhanced lower frequency area at the middle and apical turn on the left side and the stable results of the ABRs we scheduled this child for a CI in the deafened right ear and a hearing aid rehabilitation for the high-frequency hearing loss in the left ear.
c The left side had some enhancement at the region of the round window in the week directly post meningitis. CT investigation was done one year and several years later. A closer view of the round window region (yellow arrows) showed calcification of the round window area. It appears that MRI enhancement in the acute phase and obliteration/ossification in the end stage are closely related.
d The hearing remained stable over several years and the hearing aid in the left ear is used daily. Notable is the mixed-type hearing loss, which suggests that the calcified round window (yellow arrow in [c]) is causing a conductive low-frequency component in addition to the postmeningitis SNHL.
12.5.1 Unilateral Hearing Loss and Radiology
12.5.2 Bilateral 0–30 dB Loss and Radiology
12.5.3 Bilateral 30–70 dB Loss and Radiology
12.5.4 Bilateral > 70 dB Loss and Radiology
12.6 Difficulties in the Assessment Phase
12.6.1 Audiologic Assessment in Infants
12.6.2 Imaging in Infants
12.6.3 Other Sequelae of Meningitis
Sequelae after meningitis
12.6.4 Counseling Parents
12.7 Decision Making
12.7.1 Hearing and MRI Assessment
12.7.2 Ossification
12.7.3 ABI in Postmeningitis Cases
Case 12.1 Bilateral CI in a Young Patient with Active Postmeningitis Enhancement of the Cochlea (Fig. 12.1.1–Fig. 12.1.7)
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