11 Cochlear Implantation in Cochlear Ossification Cochlear fibrosis and subsequently a partially or totally ossified cochlea may have several different causes. Apart from bacterial meningitis and otosclerosis, which are discussed in Chapters 12 and 13, a wide variety of other pathology can result in labyrinthitis ossificans (LO). LO is a pathologic process of intracochlear new bone formation in response to or as a result of inflammation. This can be tympanogenic, meningogenic, or hematogenic in origin,1 and can be caused by an infection, a systemic (autoimmune) or local (otosclerosis) disease, a destructive process or trauma, or can be caused by a lack of vascular supply.2 The most common conditions leading to labyrinthitis ossificans are3–7 • Bacterial meningitis • Autoimmune inner ear disease • Fracture of the labyrinth/intracochlear hemorrhage/persistent perilymphatic fistula • Chronic middle ear or cavity infection • Loss of labyrinthine blood supply (e g, after translabyrinthine surgery) • Otosclerosis Sporadic cases of LO presenting in patients with Usher syndrome,8 with sickle cell disease,9 with leukemia,10 after rubella vaccination,11 in Paget disease, in fibrous dysplasia, and after radiation therapy12 have been published, showing that this process seems to be a universal reaction of the cochlea. The presence of such pathology is challenging for CI surgeons because its management and follow-up need specific radiologic knowledge and sometimes quick handling; new drilling techniques need to be mastered and different surgical steps during a drill-out procedure of the cochlea might be needed. There are two important issues in the assessment of patients with a higher risk of cochlear ossification: • Evaluation of the presence and the phase of the intracochlear inflammation in the acute situation. This can only be evaluated by contrast-enhanced MRI. • Evaluation of the extent of the intracochlear obliteration (fibrosis and/or ossification). This can be necessary in the acute phase, but also years after the primary disease resulting in LO. This can be evaluated best by the combination of MRI and CT. The presence and phase of the intracochlear inflammation in relation to the onset of hearing loss and primary disease will influence the speed and method of management. It might necessitate urgent CI surgery, while the extent of the intracochlear disease will dictate the surgical technique, the surgical approach, and the type of auditory implant used. The outcome of cochlear implantation in this group is difficult to predict because the number of cases with this type of pathology per center is small and also because the original diseases leading to the ossification can induce central hearing loss or affect the peripheral neural tissues.11,13–16 The process of inflammation and ossification itself can also negatively affect the neural tissue in the cochlea, with damage to the remaining spiral ganglion cells or additional decrease in their number.16 Even the conditions for the spread of electrical current in the cochlea can be influenced by the LO process.11 As a rule, more extensive ossification is related to worse results in hearing outcome, sometimes because only partial insertion of the electrode array is possible.15 This has to be discussed with the patient or parents; support of lip-reading skills (level II, see Chapter 5) should be included in counseling as the most likely outcome of the procedure, although sometimes only signal function (level I) can be achieved. The process of intracochlear fibrosis and ossification seems to be a general reaction to stimuli of various origins.17–19 The time course can be variable. Otosclerosis can be considered as a separate, distinct entity because it presents not only with otosclerotic lesions in the cochlea (intracochlear ossification) but also with otospongiotic lesions around the cochlea. These are not found in LO. A certain chronological pattern in the progression of the LO process can be distinguished. Studies have been done in animals and humans on the pattern of ossification in relation to location and extent over time,2,18,20 showing that the area of the round window, close to the cochlear aqueduct, followed by the scala tympani of the basal turn are usually affected first and most severely. A relatively small proportion of cases do not follow this pattern and present with isolated patches of ossification only in the middle or apical turn of the cochlea.21 Total ossification of the cochlea is only rarely encountered.21 Different phases in the development of intracochlear fibrosis and ossification are described in the histopathologic literature.2,18,20,22 Four phases of cochlear fibrosis and ossification can be distinguished: 1. Acute phase: Inflammation of the intracochlear tissues: acute labyrinthitis: a purulent effusion fills the perilymphatic spaces, fibrin deposits, and granulation tissue are formed. 2. Middle phase: Start of fibrosis. Fibroblastic proliferation with collagen deposition followed by fibrosis. Angiogenesis is also present. 3. Late phase: Advanced fibrosis, start of ossification. Next to fibrosis new bone is formed, which usually starts in the scala tympani of the basal turn with deposition of osteoid. This is followed by neo-ossification/osteoid mineralization, and bone remodeling, which is the resorption of disorganized bone and replacement with new bone. This can last up to 6 to 12 months.18 4. Final phase or end stage of ossification: the process of inflammation and the bone remodeling phase have ceased. Animal and human studies have shown that the first signs of fibrosis and ossification can be present within 3 days after infection.20,23 The cochlea can be totally ossified in humans within 3 weeks up to 2 months; therefore, diagnostic and therapeutic interventions need to be performed urgently.6,18,24 The chances for good access to the cochlea are best when intracochlear fibrosis is not yet visible on MRI, leading to unforced electrode insertion and better hearing outcome during this (short) window of opportunity.18 Among the factors influencing the presence, pace, and extent of the LO process are the immunologic status of the patient, the type of primary pathology or the microorganism causing the primary disease, and also individual immunotypical patient factors in relation to the specific primary pathology or microorganism. These factors explain the large interindividual differences. It is important to remember that not every patient with these pathologies develops a sensorineural hearing loss, and that not all of the hearing losses found in these patients are combined with intracochlear obliteration. Two types of bone have been described in cochlear ossification: (1) metaplastic bone, highly cellular without osteoblasts or lamellar structure of bone, thought to be formed as a result of interference with the cochlear blood supply; and (2) osteoplastic bone, with low cellularity, presence of osteoblasts, and lamellar structure, and connected to the endosteal layer. The osteoplastic bone formation seems to be the result of damage to the endosteum, either surgical or through disease.1 According to these etio-logic concepts, both types of bone can be present in labyrinthitis ossificans. In cases with a risk of intracochlear obliteration, several steps in the diagnostic work-up are necessary. Generally two different work-ups apply. (1) A fast diagnostic work-up in cases with rapid loss of hearing (several days or less to 3 weeks) combined with a high risk of ossification: this can be the case in bacterial meningitis, autoimmune inner ear diseases, fractures, and hemorrhage. MRI and audiometric evaluation need to be performed urgently. (2) The extended diagnostic work-up will apply to all other cases with the pathology mentioned earlier and comprises additional T2-weighted (T2W) MRI. A management plan and surgical strategy can be developed based on the information gathered during the work-up. • Especially in bacterial meningitis, autoimmune inner ear diseases, fractures, and hemorrhage, the LO process can develop rapidly. Therefore, hearing evaluation has to be performed in all patients soon after diagnosis (within days to a maximum of 1.5 weeks or as soon as possible if these deadlines are missed) followed by urgent MRI evaluation in patients with severe or even moderate (>30 dB and progressive) hearing loss. These steps, the short time frame, and the follow-up are explained and discussed in Chapter 12. If the primary pathology developed more than a year previously, the work-up is similar to that for other pathology listed below in the extended diagnostic work-up. • Autoimmune inner ear diseases can develop as quickly as bacterial meningitis but are the only conditions that are reversible by treatment with corticosteroids. Urgent consultation with an immunologist or pediatrician is necessary for starting this treatment within 2 to 3 weeks. • In cases with head trauma, labyrinth fractures, hemorrhage, and bacterial cochleitis, the hearing deterioration can be very variable, ranging from immediate complete deafness to some hearing loss that remains stable or deteriorates slowly. It seems that the more severe the trauma/fracture/infection or hemorrhage the more likely the development of hearing loss and ossification, but the literature is only suggestive and not conclusive on this. No good guideline for hearing follow-up can be given, but it must be clear that hearing follow-up cannot be abandoned.25 We therefore advise audiometric follow-up at 1, 2, 3, 6, and 12 months in these cases. In all the other pathologies, acute and complete bilateral cochlear obliteration is much less likely; the primary pathology is a longer ongoing process. An extended diagnostic work-up, but in a less urgent time frame, is required in the following cases: • Persistent perilymphatic fistula • Chronic middle ear or cavity infection • Loss of labyrinthine blood supply • Otosclerosis The extended diagnostic work-up includes additional MRI scanning, most importantly T2W (heavily weighted) MRI. This will provide a blueprint of the scala tympani and scala vestibuli of the basal turn next to the middle and apical turns, and will show the presence or absence of intracochlear fluids. CT scanning can provide additional information about the cochlear ossification of the obliterated part of the cochlear lumen, although its sensitivity is low, especially for metaplastic bone. In autoimmune inner ear disease the location of fibrosis and ossification can be more diffuse, whereas in otosclerosis it is predominantly in the scala tympani of the basal turn (see Chapter 13). In fractures or hemorrhage it also depends on the location of the lesion. Audiometric evaluation is as important in this group of patients as in “normal” CI candidates, but in the LO group audiometric testing can also reveal a still limited but progressive hearing loss while LO is developing. This means that moderate loss (>30 dB and progressive) requires MRI evaluation to identify the presence and phase of intracochlear inflammation. Audiometric evaluation can also be used as a screening tool to keep track of possible development of intracochlear disease (post meningitis, autoimmune conditions, fracture, hemorrhage). Both aspects are more important during the fast diagnostic work-up. After the first assessment of sensorineural hearing loss (30 dB and progressive) leading to imaging, the hearing can deteriorate further and late fibrosis/ossification (up to 6–12 months) is also reported.26 Therefore, all cases with sensorineural hearing loss related to the diseases mentioned (especially the more acute ones), with and without presence of LO as found on MRI, need audiometric follow-up at 1, 2, 3, 6, and 12 months after the primary disease to check for late LO development when urgent cochlear implantation has not already been carried out. Of course, additional audiometric testing can be useful when there is doubt about the course of the hearing loss. If the sensorineural hearing deteriorates during the follow-up, MRI needs to be repeated to document possible progression of intracochlear pathology. More information on audiometric evaluation and management in the acute phase (of bacterial meningitis) can be found in Chapter 12. The four phases of intracochlear fibrosis and ossification as seen histopathologically can also be detected on imaging (see also Chapter 12): 1. Acute phase. Inflammation causing labyrinthitis is visible on T1W MRI by contrast enhancement of the cochlea and labyrinth; on T2W imaging there is no sign of loss of intracochlear/intralabyrinthine fluid. On T1W imaging without contrast, the cochlea and labyrinth can be more hyperintense than in the normal situation. 2. Middle phase. Start of fibrosis, with contrast enhancement on T1W MRI of the cochlea and labyrinth (caused by inflammation and angiogenesis) and also loss of fluid in the cochlea/labyrinth on T2W MRI (caused by fibrosis). On T1W images without contrast, the cochlea and labyrinth may be more hyperintense. 3. Late phase. Advanced fibrosis and start of ossification with no sign or few signs of enhancement remaining on T1W MRI with contrast. Mild hyperintensity of the cochlear turns may be present; on T2W MRI clear loss of intracochlear/intralabyrinthine fluid. Differentiation between fibrosis or ossification as the cause of the loss of fluid might be possible by combining the information found on MRI imaging with that found on CT imaging. 4. Final phase or end stage of ossification. No signs of active inflammation remain: no enhancement on T1W imaging with contrast. Loss of fluid on T2W imaging. The ossification can usually be visualized with CT (but beware of low sensitivity) and can be graded (for classification see later). This final stage of ossification is reached after 6 to 12 months of the start of the primary pathology or may not be attained in case of a chronic ongoing infection (e.g., chronic infection in radical cavity). Magnetic resonance (T2W) imaging is superior to CT scanning for detection of the loss of intralabyrinthine fluid.12,14,23,27 However, ossification in the third and fourth histopathological phases might be visible on CT, whereas this cannot be differentiated from fibrosis on MRI. The literature reports that metaplastic bone is more difficult to detect on CT than osteoplastic bone, due to its low mineralization.12 For this reason, cochlear ossification can be found incidentally, demonstrating that CT does not identify all ossification cases; its sensitivity is found to be low.3,28 The time interval between imaging and the surgical procedure might be a contributing factor when the remodeling of bone is still ongoing. Limitations of imaging techniques might also be factors. Fibrous tissue that is present during or after LO without further transformation into ossification cannot be seen on CT, but the combination of loss of fluid on T2W MRI and absence of ossification on CT suggests (noncalcified) fibrosis or undetected ossification. CT and MRI therefore are complementary modalities for the evaluation of this kind of pathology.3,12 The intracochlear neo-osteogenesis as well as the fibrotic tissue can usually also be clearly recognized during surgery. Information on the patency of the scala vestibuli is provided by T2W MRI. • Presence of acute labyrinthitis: – MRI T1W with gadolinium enhancement • Presence of fibrosis or ossification: – MRI T2W: loss of intralabyrinthine fluid • Presence of intracochlear ossification: – CT scanning: limited sensitivity (62–95%) Besides the cochlea, the lateral semicircular canal (LSCC) can provide information on patency; it can show signs of ossification before the cochlea does and therefore can serve as a screening tool, especially on CT imaging.14,26,29,30 If calcification is visible on CT (LSCC or intracochlear), MRI should determine unambiguously the patency or non-patency of the cochlea. MRI and CT images help in the decision-making process and show the patency of the cochlear lumen and thus the extent of the LO. A surgical plan can now be made with the proper imaging and with the assistance of the following classification and guideline. Labyrinthitis ossificans seems to be a universal process in reaction to a specific inflammatory stimulus; however, in different patients and even in different cochlea, differences in the location and extent of the ossification can be found. The following classification is a guide to the appropriate surgical strategy with best hearing outcomes and possibly smallest damage to the intracochlear structures (see Table 11.1 and Fig. 11.1–Fig. 11.6). Fig. 11.1 Schematic presentation of Grade I (IA) ossification: only the area of the round window is affected. Fig. 11.2 Grade I (IB) ossification: up to half of the scala tympani of the basal turn is affected. Fig. 11.4 Grade II: the scala tympani of the basal turn is completely ossified; the scala vestibuli is less than half ossified, also grade II. Fig. 11.5 Grade III: both the scala tympani and scala vestibuli of the basal turn are ossified, while the middle and apical turns are patent. This can occur with the ascending part of the basal turn being accessible (IIIA) or inaccessible (IIIB). Fig. 11.6 Grade IV: totally ossified cochlea. Usually the first location of ossification is the area of the round window, close to the entrance of the cochlear aqueduct, grade IA. The ossification will then spread to the first third to half of the scala tympani in the basal turn (grade IB). Both classify as grade I. The second grade represents ossification of the basal turn involving more than half to the whole of the scala tympani (grade II), while the scala vestibuli of the basal turn remains at least partially accessible. Grade II also represents a total ossification of the scala tympani of the basal turn, while the scala vestibuli is ossified for less than half of the basal turn. The ascending part of the basal turn, the middle turn, and the apical turn are patent. Grade III represents the situation in which both the scala tympani and the scala vestibuli of the basal turn are totally ossified. Finally grade IV represents total ossification of the cochlea. The group of autoimmune inner ear diseases (AIED; primary or secondary/systemic) is the only pathology with intracochlear inflammation that has been proven to be reversible when treated promptly (within 14–30 days), and therefore demands a different approach regarding cochlear implantation and follow-up.4,5,12,31 This condition presents with a sudden onset of hearing loss bilaterally in days to weeks. It differs from ISSHL (idiopathic sudden sensorineural hearing loss), which presents unilaterally and within 24 to 48 hours. A history of weight loss, uveitis, keratitis, joint disease, bowel complaints, or skin rashes points in the direction of systemic disease. These patients need to be seen urgently by an immunologist/pediatric immunologist; treatment with immunosuppressive medication has to be started quickly and will prove to be a diagnostic tool, but only after further diagnostic evaluation by nasendoscopy (with biopsy), a consultation by internal medicine, and blood tests (e.g., ESR, ANA, ANCA, RF) have been performed.32,33 Follow-up on the hearing thresholds and presence of labyrinthine enhancement with repeated T1W MRI with gadolinium enhancement will demonstrate the effect of the medical treatment.31 Some of these patients will not react to the medication, others might need stronger immunosuppressive (methotrexate, azathioprine) or even cytostatic medication (cyclophosphamide) with negative side effects or unwanted side effects (loss of fertility, loss of hair, induction of bladder cancer), making cochlear implantation sometimes the preferable option compared with the continuation of this kind of medication.33 This group of patients can present with acute loss of vestibular function in addition to the hearing loss. • Primary autoimmune inner ear disease (AIED) is characterized by bilateral perceptive sensorineural hearing loss that presents in days to weeks, without an underlying systemic disease present. Patients can react well on immune suppressive medication (“prednisolone-responsive disease”). • Secondary autoimmune inner ear disease can be due to Wegener disease, Cogan disease, rheumatoid arthritis, systemic lupus erythematosus, Sjögren syndrome, polyarthritis nodosa, relapsing polychondritis, sarcoidosis, inflammatory bowel diseases (colitis ulcerosa, Crohn disease), Hashimoto disease, Churg–Strauss syndrome, or Behçet syndrome.
11.1 Fibrosis and Ossification Process
11.2 Management Work-up
11.2.1 Fast Diagnostic Work-up
11.2.2 Extended Diagnostic Work-up
11.3 Audiometric Evaluation
11.4 CT and MRI
11.4.1 Fibrosis and Ossification on Imaging
Best imaging modalities according to histopathological phase of labyrinthitis ossificans
11.5 Surgical Planning
11.5.1 Classification of Ossification and Surgical Strategy
Grade I
Grade II
Grade III
Grade IV
11.5.2 Autoimmune Inner Ear Disease
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