Incomplete Partition Type II Cochlear Malformations: Delineating the Three-Dimensional Structure from Digitized Human Histopathological Specimens

HYPOTHESIS

There are clinically relevant differences in scalae anatomy and spiral ganglion neuron (SGN) quantity between incomplete partition type II (IP-II) and normal cochleae.

BACKGROUND

IP-II is a commonly implanted cochlear malformation. Detailed knowledge of intracochlear three-dimensional (3D) morphology may assist with cochlear implant (CI) electrode selection/design and enable optimization of audiologic programming based on SGN maps.

METHODS

IP-II (n = 11) human temporal bone histological specimens were identified from the National Institute on Deafness and Other Communication Disorders National Temporal Bone Registry and digitized. The cochlear duct, scalae, and surgically relevant anatomy were reconstructed in 3D. A machine learning algorithm was applied to map the location and number of SGNs.

RESULTS

3D scalae morphology of the basal turn was normal. Scala tympani (ST) remained isolated for 540 degrees before fusing with scala vestibuli. Mean ST volume reduced below 1 mm 2 after the first 340 degrees. Scala media was a distinct endolymphatic compartment throughout; mean ± standard deviation cochlear duct length was 28 ± 3 mm. SGNs were reduced compared with age-matched norms (mean, 48%; range, 5-90%). In some cases, SGNs failed to ascend Rosenthal's canal, remaining in an abnormal basalward modiolar location. Two forms of IP-II were seen: type A and type B. A majority (98-100%) of SGNs were located in the basal modiolus in type B IP-II, compared with 76 to 85% in type A.

CONCLUSION

Hallmark features of IP-II cochleae include the following: 1) fusion of the ST and scala vestibuli at a mean of 540 degrees, 2) highly variable and overall reduced SGN quantity compared with normative controls, and 3) abnormal SGN distribution with cell bodies failing to ascend Rosenthal's canal.

The Cochlear Size Variations in Incomplete Partitions with Multiplanar Images on Pediatric Temporal Bone CT

Objectives

The purpose of the study was to evaluate cochlea dimensions by the multiplanar reconstruction of high-resolution computed tomography that could be useful in diagnosing incomplete partition (IP) malformations.

Methods

This study included 32 patients with 64 side cochleae diagnosed with IP defect and 38 cochleae as the control without any defect. Basal turn length (BL), cochlear height (CH), Mid-apical length (MAL), Mid-apical height, Cochlear length (A), and Cochlear width (B) were measured on reformat images.

Results

Twenty cochleae of these patients have been diagnosed with IP type I, 34 with IP type II, and 10 with IP type III. The MAL values are shorter than the control group in IP types I and III (p<0.001, p<0.001). BL values are shorter in IP type III cases (p<0.001). In IP II cases, BL and MAL values overlapped with the control group. CH did not differ significantly from the control group in any IP type. A and B values were significantly lower than the control group for IP I and III (p<0.01). There is a positive correlation between A and B values for all IP types (p<0.01).

Conclusion

Quantitative data about differences in the size and shape of the cochlea in IP cases would help differentiate them from the normal cochlea. Since A and B values showed a positive correlation, it is suggested that A and B values can be used to estimate CDL for IP types.

Speech Perception and Sound Localization Skills in Inner Ear Malformations: Children With Incomplete Partition Type-II

OBJECTIVE

The present study aimed to evaluate binaural auditory skills in bimodal and bilateral pediatric cochlear implant (CI) users with incomplete partition type-II (IP-II) and to reveal the effect of IP-II on performance by comparing the results to pediatric CI users with normal cochlear morphology.

STUDY DESIGN

Cross-sectional study.

SETTING

Tertiary referral center.

METHODS

Forty-one CI users (mean age 8.8 ± 1.9) were grouped as bimodal (BIM-IP) and bilateral (BIL-IP) users with IP-II; bimodal (BIM-N) and bilateral (BIL-N) users with normal cochlear anatomy. Speech perception in noise and sound localization skills were compared under 2 conditions; binaural (bilateral or bimodal) and monaural (first CI alone).

RESULTS

BIM-IP and BIL-IP showed no performance difference in binaural tasks. The BIM-N group showed remarkably poor performance in comparison to the groups of BIL-IP (p = .007), BIM-IP (p < .001), and BIL-N (p = .004) in terms of speech-in-noise skills. In sound localization abilities, similar significant differences were found between the group of BIM-N and the groups of BIL-IP (p = .001), BIM-IP (p < .001), and BIL-N (p = .004). All groups showed statistically significant improvements in binaural condition on both tasks (p < .05).

CONCLUSION

We revealed that bilateral and bimodal pediatric CI users with IP-II benefitted from implantation as much as bilateral users with normal anatomy. Differences in residual hearing between groups may explain the poor performance of bimodal users with normal cochlear morphology. To the best of our knowledge, it is the first study to unveil binaural performance characteristics in children diagnosed with a specific inner ear malformation subgroup.

High Riding Jugular Bulb Protruding Into Tympanic Cavity: Longitudinal Radiologic Study in a Deaf Child

BACKGROUND

High riding jugular bulb (HRJB) develops after 2 years and is rare at younger ages. High riding jugular bulb sometimes protrudes into the tympanic cavity, which can cause hemorrhagic complications during otologic surgery.

CASE PRESENTATION

We describe a congenitally deaf child with bilateral inner ear malformations and a right-sided HRJB on CT at 9 months. This child had undergone left cochlear implantation (CI) at 19 months, and right CI was planned at 6 years. However, we decided not to perform the right CI because preoperative CT images revealed that the right jugular bulb (JB) was enlarged and protruded into the tympanic cavity, completely covering the round window (RW).

CONCLUSION

This is the first pediatric case in which a longitudinal CT scan proves that HRJB develops and protrudes over time. These findings suggest that the earlier the HRJB forms, the larger it may grow. We must keep in mind the possibility of the enlargement and protrusion of HRJB.

Genetics of Inner Ear Malformations: A Review

Inner ear malformations are present in 20% of patients with sensorineural hearing loss. Although the first descriptions date to the 18th century, in recent years the knowledge about these conditions has experienced terrific improvement. Currently, most of these conditions have a rehabilitative option. Much less is known about the etiology of these anomalies. In particular, the evolution of genetics has provided new data about the possible relationship between inner ear malformations and genetic anomalies. In addition, in syndromic condition, the well-known presence of sensorineural hearing loss can now be attributed to the presence of an inner ear anomaly. In some cases, the presence of these abnormalities should be considered as a characteristic feature of the syndrome. The present paper aims to summarize the available knowledge about the possible relationships between inner ear malformations and genetic mutations.

Special electrodes for demanding cochlear conditions

Optimal matching of an electrode array to the cochlear anatomy plays a key role in bringing the best benefit of CI technology to the users. Even within the category of normal anatomy cochlea, the size variation is huge justifying MED-EL's FLEX electrode array to be available in five different lengths. Within the malformed inner-ear category the anatomical variation is huge, convincing MED-EL to custom-design the electrode array as per the request from the operating surgeons. Thanks to G. Bredberg, M. Beltrame, L. Sennaroglu, J. Gavilan, S. Plontke, T. Lenarz, J. Müller, and few others for their valuable suggestions on unique electrode designs satisfying various needs. Translational research efforts at MED-EL in cooperation with CI surgeons from across the world led to the implantation of a variety of electrode array designs in patients with special cochlear needs.

Recurrent Meningitis in Congenital Inner Ear Malformation

Spontaneous cerebrospinal fluid otorrhea is very rare. Because of nonspecific symptoms, it is usually diagnosed when complications such as meningitis occur. Cerebrospinal fluid leak may be caused by cochlea malformation, which permits nonphysiological communication between subarachnoid space and tympanomastoid cavity. Nearly 20% of congenital sensorineural hearing loss is connected with inner ear bone malformation. We present a case of 40-year-old man suffering since early childhood from recurrent meningitis and right ear deafness, caused by congenital internal ear malformation. For many years, patient with sensorineural hearing loss had not undergone diagnostic radiology; computed tomography scans of the temporal bone had not been performed. Developing meningitis in early childhood was regarded as the reason for deafness.

Classification and Current Management of Inner Ear Malformations

Morphologically congenital sensorineural hearing loss can be investigated under two categories. The majority of congenital hearing loss causes (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 magnetic resonance imaging of the temporal bone reveal normal findings. The remaining 20% have various malformations involving the bony labyrinth and, therefore, can be radiologically demonstrated by computerized tomography and magnetic resonance imaging. The latter group involves surgical challenges as well as problems in decision-making. Some cases may be managed by a hearing aid, others need cochlear implantation, and some cases are candidates for an auditory brainstem implantation (ABI). During cochlear implantation, there may be facial nerve abnormalities, cerebrospinal fluid leakage, electrode misplacement or difficulty in finding the cochlea itself. During surgery for inner ear malformations, the 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 outcomes after various implantation methods are closely related to the status of the cochlear nerve, and a practical classification of the cochlear nerve deficiency is also provided.

Usefulness of measuring electrically evoked auditory brainstem responses in children with inner ear malformations during cochlear implantation

CONCLUSIONS

EABR is a reliable and effective way of objectively confirming device function and implant-responsiveness of the peripheral auditory neurons up to the level of the brainstem in cases of inner ear malformation.

OBJECTIVE

To investigate the usefulness of measuring the intra-operative electrically evoked compound action potential (ECAP) and electrically evoked auditory brainstem response (EABR) in patients with and without congenital inner ear anomalies during cochlear implantation.

METHOD

Thirty-eight consecutive children (40 ears) aged 5 or younger with congenital profound hearing loss. Twenty-four (25 ears) lacked congenital inner ear anomalies. The 14 patients (15 ears) with a malformation had common cavities (four ears), incomplete partition type I (three ears), cochlea hypoplasia type III (three ears), enlarged vestibular aqueduct (four ears), and cochlear nerve canal stenosis (one ear). Main outcome measures are ECAP and EABR responses.

RESULTS

Of the 25 ears lacking any malformation, 21, three, and one showed 'Good', 'Variable', and 'No' ECAP responses, respectively, and 24 and one showed 'Good' and 'Variable' intra-cochlear responses, respectively. Of the 15 ears with a malformation, two showed 'Good' ECAP responses, nine had 'Variable' ECAP responses, and four showed 'No' ECAP responses. Moreover, five showed 'Good' EABR responses and 10 showed 'Variable' EABR responses.