HYPOTHESIS:Congenital unilateral conductive hearing impairment alters auditory white matter tract connections of the brain. BACKGROUND:Unilateral conductive hearing loss has negative effects on speech perception in noise and sound localization ability. This study examines auditory white matter tracts in a rat model with surgically induced unilateral ear canal atresia, compared with controls. MATERIALS AND METHODS:Twelve-month euthanized rats, 7 with left-sided surgically created ear canal atresia (UCA) and 4 controls, were scanned in a 9.4 T MRI scanner for animal research purposes. Diffusion-weighted images were acquired. Two different methods for probabilistic fiber tracking were used. Fractional anisotropy (FA) was calculated from whole brains and from tracts between defined auditory regions of interest. RESULTS:Both methods of fiber tracking show significantly higher global FA in rats with UCA. Within-group comparisons in UCA show higher FA on the hearing side between the cochlear nucleus and inferior colliculus, compared with the side of hearing loss, while in controls, there was no asymmetry. Lower FA was also found between the medial geniculate complex and the auditory cortex on the left side than on the right in UCA, in contrast to controls, where there was no difference between the hemispheres. CONCLUSION:The asymmetry found in UCA indicates alterations of auditory white matter tracts as a response to asymmetric hearing, partly confirming previous findings in experiments on ferrets.

Hypothesis Unilateral congenital conductive hearing impairment in ear canal atresia leads to atrophy of the gray matter of the contralateral primary auditory cortex or changes in asymmetry pattern if left untreated in childhood. Background Unilateral ear canal atresia with associated severe conductive hearing loss results in deteriorated sound localization and difficulties in understanding of speech in a noisy environment. Cortical atrophy in the Heschl’s gyrus has been reported in acquired sensorineural hearing loss but has not been studied in unilateral conductive hearing loss. Methods We obtained T1w and T2w FLAIR MRI data from 17 subjects with unilateral congenital ear canal atresia and 17 matched controls. Gray matter volume and thickness were measured in the Heschl's gyrus using Freesurfer. Results In unilateral congenital ear canal atresia, Heschl's gyrus exhibited cortical thickness asymmetry (right thicker than left, corrected p = 0.0012, mean difference 0.25 mm), while controls had symmetric findings. Gray matter volume and total thickness did not differ from controls with normal hearing. Conclusion We observed cortical thickness asymmetry in congenital unilateral ear canal atresia but no evidence of contralateral cortex atrophy. Further research is needed to understand the implications of this asymmetry on central auditory processing deficits.

IntroductionAcoustic radiation is one of the most important white matter fiber bundles of the human auditory system. However, segmenting the acoustic radiation is challenging due to its small size and proximity to several larger fiber bundles. TractSeg is a method that uses a neural network to segment some of the major fiber bundles in the brain. This study aims to train TractSeg to segment the core of acoustic radiation. MethodsWe propose a methodology to automatically extract the acoustic radiation from human connectome data, which is both of high quality and high resolution. The segmentation masks generated by TractSeg of nearby fiber bundles are used to steer the generation of valid streamlines through tractography. Only streamlines connecting the Heschl's gyrus and the medial geniculate nucleus were considered. These streamlines are then used to create masks of the core of the acoustic radiation that is used to train the neural network of TractSeg. The trained network is used to automatically segment the acoustic radiation from unseen images. ResultsThe trained neural network successfully extracted anatomically plausible masks of the core of the acoustic radiation in human connectome data. We also applied the method to a dataset of 17 patients with unilateral congenital ear canal atresia and 17 age- and gender-paired controls acquired in a clinical setting. The method was able to extract 53/68 acoustic radiation in the dataset acquired with clinical settings. In 14/68 cases, the method generated fragments of the acoustic radiation and completely failed in a single case. The performance of the method on patients and controls was similar. DiscussionIn most cases, it is possible to segment the core of the acoustic radiations even in images acquired with clinical settings in a few seconds using a pre-trained neural network.

Background Individuals with unilateral hearing loss show poor spatial hearing, but individual variability is high. Aims/objectives To investigate if the degree of hearing loss in unilateral ear canal atresia affects horizontal sound localization and speech recognition. Materials and methods Twelve subjects with unilateral ear canal atresia without childhood hearing intervention. Previously published data from eight normal-hearing subjects in normal binaural as well as experimentally induced unilateral hearing loss served as a reference. Horizontal sound localization and recognition of speech in spatially separate competing speech were assessed. Results Linear regression analysis demonstrated a relationship between sound localization accuracy (SLA) and the air conduction pure tone average of the atretic ear (r = 0.85, p=.007). The large proportion of variability in SLA (72%) explained by the degree of hearing loss of the atretic ear indicates that binaural processing is possible. SLA was worse than for normal hearing individuals (p<.0001), and comparable to moderate simulated unilateral hearing loss (p=.13). Speech discrimination was significantly worse than normal (p<.0001) and not dependent on degree of hearing loss of the atretic ear. Conclusions and significance Individuals with congenital unilateral ear canal atresia show impaired horizontal SLA and recognition of speech in competing speech.

ObjectivesThe objective is to investigate if unilateral conductive hearing loss in ear canal atresia without hearing treatment in childhood leads to cortical reorganization in functional connectivi ...

Conclusions: Even though sound perception may be limited after treatment with an auditory brainstem implant (ABI), it provides benefits and should be selectively offered to patients. Importantly the patients must be motivated, given reasonable expectations of outcome and offered long-term rehabilitation with a considerable 'learn to listen' period with the implant device. Objectives: To describe the clinical experiences and results of 24 ABI surgeries performed in Uppsala University Hospital between 1993 and 2013. Methods: Most patients (n = 20) suffered from neurofibromatosis type 2 (NF2); a few patients (n = 4) were paediatric non-NF2 patients. The files were searched for information on the presurgery size of the vestibular schwannoma, whether the patient had undergone gamma knife treatment, the surgical approach, the side effects of the surgery and of the use of the implant, the electrode activation pattern and implant use, and categories of auditory performance (CAP) score. Results: Our results show that many patients greatly benefited from an ABI, and most of the patients used their implants even though the hearing improvements usually consisted of awareness of surrounding sounds and improved lip-reading. No severe side effects were observed from implant stimulation.