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Classification of Inner Ear Malformations
Abstract
Inner ear malformations (IEM) of the inner ear roughly represent 20% of congenital sensorineural hearing loss. There are eight different categories. IEMs were grouped into categories and subgroups according to their radiological appearance. Within a group, they usually demonstrate similar clinical features. Certain anomalies can be diagnosed by visual observation of the image. In the present system cochlear dimensions necessary for the distinction between the certain abnormalities are also described. It is very important to classify IEMs properly and have a universally accepted system so that we can understand each other better. This is similar to using a common language. In this chapter after description of normal cochlea, each malformation is described in detail.KeywordsInner ear malformationsCochleovestibular malformationsClassificationRadiologyImaging
... Cochlear implant surgery has been performed for more than 60 years in the world [2]. Cochlear implant surgery has been done for many years at our institution with nearly 3,000 patients both with normal and abnormal cochlear anatomies [3]. As these patients transition from infancy to adulthood, they are expected to lead normal and healthy lives. ...
A cochlear implant is a life-changing operation that significantly improves the lives of patients. Those with cochlear implants require ongoing measures to ensure the longevity of both their devices and their well-being. One concerning issue is the potential device failure due to the use of surgical instruments during procedures. In this report, we present a successful case of utilizing an ultrasonic osteotome for a primary septorhinoplasty in a 22-year-old patient who had undergone cochlear implant surgery 17 years prior. To our knowledge, this is the first recorded instance of applying a piezoelectric tool on a patient with a cochlear implant. Our findings support the safety of using a piezo osteotome in cochlear implant recipients.
Objectives
The objectives of this study were to assess auditory perception and speech intelligibility outcomes in children with cochlear nerve (CN) hypoplasia who received cochlear implants (CIs) using Categories of Auditory Performance II (CAP II) and Speech Intelligibility Rating (SIR) scales.
Methods
In total, 40 children who received CI and who were aged between 3 and 18 years were included in this study. The study group included 20 children with CN hypoplasia at least one ear, while the control group included 20 children with normal cochleas and cochlear nerve structures. All children in the study and control groups who participated were evaluated using the CAP II and the SIR scale. Demographic data were collected.
Results
Significant differences were found between the study and control groups’ CAP II and SIR scores (p < 0.001). It was found that CAP II scores were positively correlated with SIR scores in the study (r = 0.743, p < 0.001) and control (r = 0.601, p < 0.001) groups. In the study group, significant negative correlations were found between SIR scores and age at implantation (r = −0.674, p = 0.004) and between CAP II scores and age at implantation (r = 0.751, p = 0.003). In the control group, a significant negative correlation was found between age at implantation and CAP II scores (r = −0.805, p = 0.001). Similarly, a significant negative correlation was found between age at implantation and SIR scores (r = −0.702, p = 0.007).
Conclusion
Even for children with severe inner ear malformation and CN hypoplasia, CI is an effective treatment modality for auditory perception and speech production. However, it should be noted that CN hypoplasia affects auditory performance negatively in children with CI.
Introduction
The preoperative determination of suitable electrode array lengths for cochlear implantation in inner ear malformations is a matter of debate. The choice is usually based on individual experience and the use of intraoperative probe electrodes. The purpose of this case series was to evaluate the applicability and precision of an angular insertion depth (AID) prediction method, based on a single measurement of the cochlear base length (CBL).
Methods
We retrospectively measured the CBL in preoperative computed tomography (CT) images in 10 ears (8 patients) with incomplete partition type 2 malformation. With the known electrode length (linear insertion depth, LID) the AID at full insertion was retrospectively predicted for each ear with a heuristic equation derived from non-malformed cochleae. Using the intra- or post-implantation cone beam CT images, the actual AID was assessed and compared. The deviations of the predicted from the actual insertion angles were quantified (clinical prediction error) to assess the precision of this single-measure estimation.
Results
Electrode arrays with 15 mm (n = 3), 19 mm (n = 2), 24 mm (n = 3), and 26 mm (n = 2) length were implanted. Postoperative AIDs ranged from 211° to 625°. Clinical AID prediction errors from −64° to 62° were observed with a mean of 0° (SD of 44°). In two ears with partial insertion of the electrode, the predicted AID was overestimated. The probe electrode was intraoperatively used in 9/10 cases.
Conclusion
The analyzed method provides good predictions of the AID based on LID and CBL. It does not account for incomplete insertions, which lead to an overestimation of the AID. The probe electrode is useful and well established in clinical practice. The investigated method could be used for patient-specific electrode length selection in future patients.
Morphologically congenital sensorineural hearing loss can be investigated under two categories. Majority of the congenital hearing loss (80%) are membranous malformations. Here the pathology involves inner ear hair cells. There is no gross bony abnormality and therefore, in these cases, high resolution computerized tomography and MRI of the temporal bone reveal normal findings. Remaining 20% have various malformations involving the bony labyrinth and therefore, can be radiologically demonstrated by CT and MRI. The latter group involves surgical challenges as well as problems in decision making. Some cases may be managed by hearing aid, some need cochlear implantation while some cases are candidates for an auditory brainstem implantation. During cochlear implantation, there may be facial nerve abnormalities, cerebrospinal fluid leakage, electrode misplacement or difficulty in finding the cochlea itself. During the surgery for inner ear malformations, surgeon must be ready to modify the surgical approach or choose special electrodes for surgery. In the present review article inner ear malformations are classified according to the differences observed in the cochlea. Hearing and language outcome after various implantation methods is closely related to the status of cochlear nerve and a practical classification of the cochlear nerve deficiency is also provided.
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Complete labyrinthine aplasia (CLA), also referred to as Michel aplasia, is a severe congenital anomaly of the inner ear, defined by the complete absence of inner ear structures. The purpose of this study was to document the imaging findings in a series of patients with CLA, with review of the literature, to better understand this anomaly.
The CT and MR imaging findings of 9 patients (14 ears with CLA) were retrospectively evaluated. The audiologic tests and patient charts were also retrospectively reviewed.
CLA was bilateral in 5 and unilateral in 4 patients. The petrous bone was hypoplastic in all 14 ears, but the otic capsule was aplastic in only 5. The middle ear and mastoid volumes were decreased in most of the ears. The stapes was aplastic in 1 ear and was dysplastic in 5 ears. The internal acoustic canal was aplastic in 4 ears and markedly narrowed in 10 ears. The facial nerve canal showed a variety of anomalies and aberrant courses in 11/14 ears. The bony covering of the jugular bulb was defective in 9 ears. Tegmen tympani defects were seen in 3 patients, and there were several accompanying skull base and posterior fossa anomalies.
Although CLA is a rare developmental anomaly, its accurate diagnosis and its differential diagnosis from labyrinthine ossificans is crucial. Proper guidance of these patients for brain stem implantation in the critical period of brain development depends on the recognition of the characteristic imaging findings of CLA.
To report the surgical aspects of cochlear implantation in malformed cochlea.
Tertiary care center.
Retrospective case review.
Between November 1997 and October 2004, 20 patients with inner ear malformations were implanted in our department. The age range was between 2 and 37 years (average, 8.8 yr). The anomalies were classified according to Sennaroglu and Saatci classification. There were two patients with common cavity deformity, four cases of incomplete partition (IP) type I (cystic cochleovestibular malformation), four cases of IP type II (classical Mondini's deformity), nine patients with large vestibular aqueduct (LVA) syndrome, and one patient with X-linked deafness.
Standard transmastoid facial recess approach was used in 17 patients (three patients with IP I, four patients with IP II, and nine patients with LVA syndrome). In the remaining patient with IP I, because of the dehiscent and anteriorly located facial nerve, the surgical approach had to be modified, and an anteroposterior approach was used. After elevating the tympanomeatal flap, the electrode was inserted through the ear canal and then transferred to the mastoid through a full-length cut produced in the ear canal. The flap then returned to its place. In the patients with common cavity deformity, the electrode was inserted by the transmastoid labyrinthotomy approach. Facial nerve had an abnormal course in four patients, but no patient had facial weakness postoperatively. Cerebrospinal fluid gusher was encountered in four patients, whereas oozing was present in five patients. It seems that a slightly larger cochleostomy may reduce postoperative rhinorrhea. The patient with common cavity deformity showed abnormal vestibular stimulation which decreased and was totally abolished during a 3-month period.
Based on these findings, cochlear implantation is surgically feasible in patients with common cavity, IP types I and II, and LVA. The surgeon should be ready to make modifications in the surgical approach because of the abnormal course of the facial nerve and be ready to produce special precautions to cerebrospinal fluid gusher.
Objective: To investigate the histopathology of inner ear malformations (IEMs) in order to explain their pathophysiology.
Method: Light microscopy was used to study 33 specimens exhibiting various IEMs in the collection of the Otopathology Laboratory at Harvard University's Massachusetts Eye and Ear Infirmary.
Results: The investigation found 18 incidences of cochlear hypoplasia (CH) (3 CH-I, 10 CH-II, 5 CH-III), 11 incomplete partitions (IPs) (5 IP-I, 6 IP-II), 2 vestibular dilatations, and 2 cases of cochlear nerve aplasia. The IP-I cases had characteristic defective endosteums, while the IP-II cases showed hydropic changes in the scala vestibuli. The CH cases were small in size externally, with normal or defective internal architecture.
Conclusion: In combination with embryological data, these findings suggest that cases of CH-III and CH-IV are most probably genetically predetermined to be small in size, and that development of the membranous labyrinth stops at a point earlier than normal, so that it is shorter. At the time of complete ossification, this results in a cochlea with small external dimensions and normal internal architecture. In CH-I and CH-II cases, there is arrested development of the internal architecture, in addition to a small cochlea; it is most likely that in these cases, there is a severely defective vascular supply from the internal auditory canal (IAC).
IP-I may be the result of a defective vascular supply from the blood vessels of the IAC.
In IP-II, an enlarged endolymphatic sac (EES) appears to be the genetic abnormality that causes the other abnormalities, as it allows high pressure to be transmitted into the cochlea and vestibule.
In IP-III, the pathophysiology appears to be an abnormal vascular supply from the middle ear mucosa, caused by a genetic abnormality and resulting in a thinner otic capsule and the absence of the modiolus.
To examine the association between cochlear nerve canal (CNC) dimensions and sensorineural hearing loss (SNHL).
Retrospective review.
Tertiary pediatric hospital.
Children with SNHL and CNC stenosis.
The CNCs measured in axial and 45° oblique planes on temporal bone computed tomography (TBCT) in children with SNHL were compared with TBCT from children with normal hearing and 100 normal temporal bone specimens. Additional inner ear abnormalities were recorded. Hearing was measured using 4 frequency pure-tone averages (PTAs).
The degree of CNC stenosis related to the degree of SNHL.
Fifty-three patients (32 female) with SNHL had CNC stenosis in 85 ears (32 bilateral, 21 unilateral). The mean (SD) axial CNC measurement for 85 ears was 0.98 (0.57) mm (range, 0-1.75 mm). The mean (SD) Poschl CNC measurement was 1.30 (0.69) mm (range, 0-2.80 mm). Of 85 ears, 64 had at least 1 additional inner ear abnormality. The mean (SD) PTA was 56.2 (40.8) dB. For each ear separately axial and Poschl plane CNC measurements were highly correlated (P < .001). The degree of CNC stenosis was significantly (P = .02) related to degree of hearing loss, and PTA decreased in the CNC stenosis population by 1.4 dB per year (P = .054). In addition, PTA and additional inner ear abnormalities were found to be significantly correlated (P = .002).
Cochlear nerve canal stenosis is associated with SNHL, and the degree of stenosis predicted the degree of SNHL. In addition, the presence of CNC stenosis with additional inner ear abnormalities may affect the severity of SNHL.
Inner ear malformations constitute about 20% of congenital sensorineural hearing loss. In this review article an updated classification of cochlear malformations is provided. Incomplete partition and cochlear hypoplasia cases are each divided further into three groups. There are two main difficulties in the surgery of inner ear malformations; gusher and facial nerve abnormalities. Radiological features of malformations necessary to identify these problems preoperatively are discussed. Facial nerve abnormalities that may occur are described. Two different types of cerebrospinal fluid leakage are defined and necessary measures to prevent leakage are described. Standard and modified surgical approaches to overcome the described problems are described with literature findings. Finally meningitis which may occur with and without cochlear implantation in this special group of patients is emphasized. This is common in incomplete partition type I patients and is usually due to a fistula in one of the windows (usually oval window) which occurs as a result of cerebrospinal fluid pressure. This is a medical emergency leading to potential meningitis and measures that should be taken to stop the leak as soon as possible are described.
The association of X-linked mixed deafness with stapes gusher has been recognized for 20 years, and imaging studies by polytomography have shown dilatation of the lateral end of the internal auditory meatus (IAM) in some cases. We have made genetic linkage studies in 7 pedigrees in whom deafness was inherited in an X-linked manner. All patients had a full range of audiometric and vestibular function tests. Thin section high resolution CT in two planes was used to assess the state of the middle and inner ears. We found a distinctive inner ear deformity in some of the deaf males characterised not only by a wide bulbous IAM but more importantly, by deficient or absent bone between the lateral end of the IAM and the basal turn of the cochlea. We believe that this results in a communication between the subarachnoid space in the IAM and the perilymph in the cochlea, leading to perilymphatic hydrops and a "gusher" if the stapes is disturbed. Moreover, some of the obligate female carriers seem to have a milder form of the same anomaly associated with slight hearing loss. Genetic studies on some of the deaf males with apparently normal inner ear anatomy suggest a different locus on the X chromosome and hence a different pathogenesis for the deafness.
Approximately 20% of patients with congenital sensorineural hearing loss have radiographic abnormalities of the inner ear. A broad spectrum of anomalous patterns have been described, most of which have been lumped together under the term "Mondini's dysplasia." We feel that this grouping of many dissimilar entities under a single umbrella term is unwarranted. Based on a review of 63 patients with 98 congenitally malformed ears, we have been able to recognize a number of distinct anatomic patterns from their radiographic appearance. A remarkable similarity between these morphologies and the appearance of the inner ear at various stages of embryogenesis was found. This led us to propose a classification system based upon the theory that these deformities result from an arrest of development during varying stages of inner ear organogenesis.
An X-linked syndrome characterized in males by profound mixed deafness, vestibular abnormalities, congenital fixation of the stapes and perilymphatic otorrhea on attempted stapedectomy has been documented in a large Caucasian kindred. Female heterozygotes have similar but milder audiologic abnormalities. The syndrome of congenital fixation of the stapes with perilymphatic gusher may be a relatively common form of X-linked deafness and is an important clinical entity because affected males may be significantly benefited by sound amplification.
Congenital dysplasias of the labyrinth of the inner ear are associated with varying degrees of hearing loss. There is a risk of a fistulous communication between the subarachnoid space and the middle ear cavity in some cases that present either as cerebrospinal fluid otorhinorrhea or as recurrent attacks of meningitis. The types of deformity where such a fistula is likely have not been clearly defined. The authors correlated the hearing state with the imaging assessment in 20 patients with congenital malformation of the labyrinth and, in particular, the cochlea. In addition the postmortem histologic findings from one patient with severe cochlear dysplasia who died from otogenic meningitis are described. The key to the assessment is the basal turn of the cochlea. If the basal turn is present and of normal caliber then some hearing is possible and there is no risk of a major fistula. However, if the basal turn is wider than normal or replaced by an undeveloped sac then there is anacusis and very real risk of fistula. In such cases the deformed labyrinth needs to be packed with fibrofatty tissues after just one attack of meningitis.
To introduce aplasia or hypoplasia of the vestibulocochlear nerve (VCN) as a possible cause of hearing loss and to identify the magnetic resonance (MR) imaging characteristics of this entity.
In seven patients with congenital deafness or unexplained sensorineural hearing loss, MR imaging enabled diagnosis of aplasia or hypoplasia of the VCN. Axial (0.7-mm) three-dimensional Fourier transformation-constructive interference in steady state (3DFT-CISS) images and parasagittal reconstruction images perpendicular on the course of the VCN were obtained. Twenty normal inner ears were also studied; their findings were compared with those of the patients.
The facial nerve and inferior and superior vestibular and cochlear branches of the VCN were identified on the MR images in the 20 normal inner ears. Aplasia of the VCN was detected in two patients with normal labyrinths but with a severe stenosis of the internal auditory canal. A common VCN with absence of the cochlear branch was found bilaterally in two patients with a congenital malformation of the labyrinth. A common VCN with absence or hypoplasia of the cochlear branch was found in three patients with normal internal auditory canals and labyrinths.
Submillimetric gradient-echo images (eg, 3DFT-CISS) should always be used to exclude aplasia or hypoplasia of the cochlear branch of the VCN in all cochlear implant candidates and patients with congenital deafness. This entity, which can occur with or without associated labyrinthine malformation, should be confirmed in two planes.
To determine the computed tomographic (CT) appearance of the normal modiolus and the pathologic alteration in patients with a large vestibular aqueduct and an otherwise normal-appearing cochlea.
Temporal bone CT studies obtained before and after a major upgrade of CT capability in 1992 were reviewed in four groups: Group A (1.5-mm section thickness) comprised 50 normal ears in 43 patients, group B (1-mm section thickness) comprised 75 normal ears in 50 patients, group C (1.5-mm section thickness) comprised 16 ears with a large vestibular aqueduct in 10 patients, and group D (1-mm section thickness) comprised 23 ears with a large vestibular aqueduct in 12 patients. All groups comprised adult and pediatric patients.
In groups A and B, the normal modiolus was visualized in 90% and 100% of ears, respectively. In groups C and D, with a total of 39 ears with a large vestibular aqueduct and an otherwise normal cochlea, modiolar deficiency was demonstrated in 100% of ears.
CT is an excellent technique for depicting the cochlear modiolus. Results suggest that all ears with a large vestibular aqueduct have associated cochlear modiolar deficiencies. Thus, a large vestibular aqueduct may be only occasionally, if ever, an isolated developmental anomaly of the inner ear.
The report proposes a new classification system for inner ear malformations, based on radiological features of inner ear malformations reviewed in 23 patients.
The investigation took the form of a retrospective review of computerized tomography findings relating to the temporal bone in 23 patients (13 male and 10 female patients) with inner ear malformations. The subjects were patients with profound bilateral sensorineural hearing loss who had all had high-resolution computed tomography (CT) with contiguous 1-mm-thick images obtained through the petrous bone in axial sections.
The CT results were reviewed for malformations of bony otic capsule under the following subgroups: cochlear, vestibular, semicircular canal, internal auditory canal (IAC), and vestibular and cochlear aqueduct malformations. Cochlear malformations were classified as Michel deformity, common cavity deformity, cochlear aplasia, hypoplastic cochlea, incomplete partition types I (IP-I) and II (IP-II) (Mondini deformity). Incomplete partition type I (cystic cochleovestibular malformation) is defined as a malformation in which the cochlea lacks the entire modiolus and cribriform area, resulting in a cystic appearance, and there is an accompanying large cystic vestibule. In IP-II (the Mondini deformity), there is a cochlea consisting of 1.5 turns (in which the middle and apical turns coalesce to form a cystic apex) accompanied by a dilated vestibule and enlarged vestibular aqueduct.
Four patients demonstrated anomalies involving only one inner ear component. All the remaining patients had diseases or conditions affecting more than one inner ear component. Eight ears had IP-I, and 10 patients had IP-II. Ears with IP-I had large cystic vestibules, whereas the amount of dilation was minimal in patients with IP-II. The majority of the semicircular canals (67%) were normal. Semicircular canal aplasia accompanied cases of Michel deformity, cochlear hypoplasia, and common cavity. In 14 ears, the IAC had a defective fundus at the lateral end. In two ears the IAC was absent. In all seven cases of common cavity malformations, there was a bony defect at the lateral end of the IAC. In five of them the IAC was enlarged, whereas in two the IAC was narrow. All patients with IP-I had an enlarged IAC, whereas in patients with type II disease, four had a normal IAC and 10 had an enlarged IAC. All cases of IP-II had an enlarged vestibular aqueduct, whereas this finding was not present in any of the cases of IP-I. In all cases, the vestibular aqueduct findings were symmetrical on both sides (simultaneously normal or enlarged). No patient demonstrated enlargement or any other abnormalities involving the cochlear aqueduct.
Radiological findings of congenital malformations in the present study suggested two different types of incomplete partition. Cystic cochleovestibular malformation (IP-I) and the classic Mondini deformity (IP-II). The type I malformation is less differentiated than the type II malformation. Classic Mondini deformity has three components (a cystic apex, dilated vestibule, and large vestibular aqueduct), whereas type I malformation has an empty, cystic cochlea and vestibule without an enlarged vestibular aqueduct. Mondini deformity represents a later malformation, so the amount of dysplasia is much less than in type II. Therefore, it is more accurate and useful for clinical purposes to classify these malformations (in descending order of severity) as follows: Michel deformity, cochlear aplasia, common cavity, IP-I (cystic cochleovestibular malformation), cochlear hypoplasia, and IP-II (Mondini deformity). Only in this way can these complex malformations be grouped precisely and the results of cochlear implantation compared.
In the process of evaluating our patients, we realized that the term "Mondini deformity" was being used to describe two different types of incomplete partition of the cochlea. THE First one consisted of an unpartitioned, completely empty cochlea where the interscalar septum and entire modiolus were absent, giving the cochlea a cystic appearance; a grossly dilated vestibule accompanied this lesion. The second pathology fitted the classic description of Mondini deformity, consisting of a normal basal turn and cystic apex (where the middle and apical turns form a cystic cavity), dilated vestibule, and enlarged vestibular aqueduct. This study was planned to investigate the differences between the two types of incomplete partition for inner ear malformations based on radiologic features.
We conducted a retrospective review of temporal bone computed tomography (CT) findings.
The subjects were 18 patients with profound bilateral sensorineural hearing loss who had high-resolution CT with contiguous 1-mm thick images obtained through the petrous bone in axial sections. The CT results were reviewed as incomplete partition type I (IP-I) and type II (IP-II). Incomplete partition type I (unpartitioned cochlea, cystic cochleovestibular malformation) is defined as a malformation in which the cochlea lacks the entire modiolus and interscalar septa, resulting in a cystic appearance and there is an accompanying grossly dilated vestibule. In incomplete partition type II (incompletely partitioned cochlea, the Mondini deformity), there is a cochlea comprised of a normal basal turn and cystic apex accompanied by a minimally dilated vestibule and enlarged vestibular aqueduct (VA). Measurements involving the cochlea, vestibule, vestibular aqueduct, and internal auditory canal (IAC) were done to determine the characteristic features of these pathologies.
: Thirteen ears had IP-I and 18 ears had IP-II anomaly. The size of the cochleae in both anomalies showed no significant difference from the normal findings. Only the internal architecture was different. All ears with IP-I had grossly dilated vestibules. Although both anomalies demonstrated vestibular dilatation, the degree of that was minimal in patients with IP-II. In IP-I anomalies, the IAC was larger than that in IP-II anomalies. An enlarged VA accompanied all cases of IP-II, whereas only one of the patients with IP-I had VA that could be demonstrated on CT. In all cases, the VA findings were symmetric on both sides: normal or enlarged.
Inner ear measurements on radiologic findings in this study confirmed the presence of two different types of incomplete partition: IP-I (unpartitioned cochlea, cystic cochleovestibular malformation) and IP-II (incompletely partitioned cochlea, the classic Mondini deformity). The type I malformation is less differentiated than the type II malformation. Classic Mondini deformity has three components (a cystic apex, dilated vestibule, and large vestibular aqueduct), whereas type I malformation has an empty, unpartitioned cochlea and dilated vestibule without an enlarged VA. Mondini deformity represents a later malformation, so the degree of dysplasia is milder than that in type I. Not only the appearance, but also the measurements of the inner ear structures would be helpful in determining the type of malformation.
X-linked mixed deafness with congenital fixation of the stapedial footplate and perilymphatic gusher
- W E Nance
- WE Nance
Sataloff’s comprehensive textbook of otolaryngology
- L Sennaroglu
- G Sennaroglu
- B Ozgen