Imaging of Temporal Bone

Nanodelivery of antioxidant Agents: A promising strategy for preventing sensorineural hearing loss

Sensorineural hearing loss (SNHL), often stemming from reactive oxygen species (ROS) generation due to various factors such as ototoxic drugs, acoustic trauma, and aging, remains a significant health concern. Oxidative stress-induced damage to the sensory cells of the inner ear, particularly the non-regenerating hair cells, is a critical pathologic mechanism leading to SNHL. Despite the proven efficacy of antioxidants in mitigating oxidative stress, their clinical application for otoprotection is hindered by the limitations of conventional drug delivery methods. This review highlights the challenges associated with systemic and intratympanic administration of antioxidants, including the blood-labyrinthine barrier, restricted permeability of the round window membrane, and inadequate blood flow to the inner ear. To overcome these hurdles, the application of nanoparticles as a delivery platform for antioxidants emerges as a promising solution. Nanocarriers facilitate indirect drug delivery to the cochlea through the round and oval window membrane, optimising drug absorption while reducing dosage, Eustachian tube clearance, and associated side effects. Furthermore, the development of nanoparticles carrying antioxidants tailored to the intracochlear environment holds immense potential. This literature research aimed to critically examine the root causes of SNHL and ROS overproduction in the inner ear, offering insights into the application of nanoparticle-based drug delivery systems for safeguarding sensorineural hair cells. By focusing on the intricate interplay between oxidative stress and hearing loss, this research aims to contribute to the advancement of innovative therapeutic strategies for the prevention of SNHL.

Microsurgical transcranial approaches to the posterior surface of petrosal portion of the temporal bone: quantitative analysis of surgical volumes and exposed areas

Different microsurgical transcranial approaches (MTAs) have been described to expose the posterior surface of the petrous bone (PPB). A quantitative, anatomical comparison of the most used MTAs, for specific areas of the PPB, is not available. Anatomical dissections were performed on five formalin-fixed, latex-injected cadaver heads (10 sides). Six MTAs were analyzed: Kawase approach (KWA), retrosigmoid approach (RSA), retrosigmoid approach with suprameatal extension (RSAS), retrolabyrinthine approach (RLA), translabyrinthine approach (TLA), and transcochlear approach (TCA). Surgical volumes and exposed areas of each approach were quantified with a dedicated neuronavigation system (ApproachViewer, part of GTx-Eyes II, University Health Network, Toronto, Canada) and adjuvant software (ITK-SNAP and Autodesk Meshmixer 3.5). Areas and volumes were compared using linear mixed models. TCA provided the best exposure of Trautmann's triangle and the retromeatal, suprameatal, meatal, and premeatal regions. RSAs provided the best exposure of the inframeatal region, with RSAS gaining significant exposure of the suprameatal region. KWA had the highest surgical volume, and RLA the lowest. Transpetrosal approaches offer the widest exposure of PPB proportionally to their invasiveness. Retrosigmoid approaches, which get to the studied region through a postero-lateral path, are paramount for the exposure of the inframeatal and suprameatal region and, given the adequate exposure of the remaining PPB, represent an effective approach for the cerebellopontine angle (CPA). These anatomical findings must be considered with approach-related morbidity and the pathological features in order to choose the most appropriate approach in clinical practice.

17O-labeled water distribution in the human inner ear: Insights into lymphatic dynamics and vestibular function

We evaluated the inner ear distribution of 17O-labeled saline administered to the human tympanic cavity. Magnetic resonance imaging was performed after intratympanic administration in five healthy volunteers and one patient with cochlear endolymphatic hydrops. In all volunteers, 17O-labeled water permeated the cochlear basal turn and vestibule at 30 min and disappeared gradually within 2–4 h. All participants experienced positional vertigo lasting a few hours to a few days. Visualization of 17O-labeled water distribution in the endolymphatic space of the posterior ampulla showed indistinct separation of endolymph and perilymph in the cochlea and most of the vestibule in all participants. Intralabyrinthine distribution of 17O-labeled water differed from that in previous reports of intratympanically administered gadolinium-based contrast agent. 17O-labeled water in the endolymphatic space may cause heavier endolymph and positional vertigo. These results of this study may add new insights for investigating the distribution and the effects of molecules in the inner ear after the intratympanic administration in living humans.

Consensus on MR Imaging of Endolymphatic Hydrops in Patients With Suspected Hydropic Ear Disease (Meniere)

Endolymphatic hydrops (EH) is considered the histological hallmark of Meniere's disease. Visualization of EH has been achieved by special sequences of inner ear magnetic resonance imaging (MRI) with a gadolinium-based contrast agent via intravenous or intratympanic administration. Although it has been applied for more than 10 years since 2007, a unified view on this technique has not yet been achieved. This paper presents an expert consensus on MRI of endolymphatic hydrops in the following aspects: indications and contra-indications for patient selection, methods of contrast-agent administration (intravenous or intratympanic), MRI sequence selection, the specific scanning parameter settings, and standard image evaluation methods and their advantages and disadvantages. For each part of this consensus, a comment is attached to elucidate the reasons for the recommendation.

MR Imaging of Cochlear Modiolus and Endolymphatic Hydrops in Patients With Menière's Disease

Background: Menière's disease (MD) is an inner ear disorder characterized by recurrent episodes of spontaneous vertigo, unilateral low-frequency sensorineural hearing loss, tinnitus, and aural fullness. Current diagnosis still often has to rely on subjective and audiometric criteria only, although endolymphatic hydrops is recognized as the pathophysiological substrate of the disease, having been demonstrated in anatomical pathological studies and by magnetic resonance (MRI). The modiolus has a close functional and anatomical relationship with the cochlear nerve and membranous labyrinth and can be evaluated with MRI but no data exist on the modiolar size in MD.

Purpose: Our purpose is to examine the following hypothesis. Is cochlear modiolus smaller in symptomatic ears in MD?

Methods: We used a retrospective 3 Tesla MR study (heavily T2-weighted 3D fast asymmetric spin-echo images and 0.5 mm slice thickness) comparing the mean modiolar area (MMA) in the index and best ears of eight patients with definite MD based on audiometric data. The obtained MMA values were compared against the audiometric data and the presence of vestibular endolymphatic hydrops.

Results: No differences were seen in MMA between best and worst ears. Ears with a pure tone average (PTA) ≥25 dB and more pronounced endolymphatic hydrops showed lower MMA (not statistically significant). Two patients with extreme endolymphatic hydrops showed a noteworthy ipsilateral decrease in the cochlear modiolus area.

Conclusion: No differences were seen in MMA between best and worst ears in definite MD. Worse hearing function (PTA ≥ 25dB) and more pronounced endolymphatic hydrops seem to be associated with lower MMA. This might be related to bone remodeling as a consequence of endolymphatic hydrops. Further research is needed to corroborate and explore these findings.

Imaging of inner ear malformations: a primer for radiologists

In the multidisciplinary management of patients with inner ear malformations (IEMs), the correct diagnosis makes the differences in terms of clinical and surgical treatment. The complex anatomical landscape of the inner ear, comprising several small structures, makes imaging of this region particularly challenging for general radiologists. Imaging techniques are important for identifying the presence and defining the type of IEM and the cochlear nerve condition. High-resolution magnetic resonance imaging (MRI) sequences and high-resolution computed tomography (HRCT) are the mainstay imaging techniques in this area. Dedicated MRI and HRCT protocols play an important role in the diagnosis and treatment of patients with inner ear disease. The most suitable technique should be selected depending on the clinical setting. However, in cases of congenital malformation of the inner ear, these techniques should be considered complementary. Since prompt intervention has a positive impact on the treatment outcomes, early diagnosis of IEMs is very important in the management of deaf patients. This article reviews the key concepts of IEMs for clinical radiologists by focusing on recent literature updates, discusses the principal imaging findings and clinical implications for every IEM subgroup, thus providing a practical diagnostic approach.

Intravenous Delayed Gadolinium-Enhanced MR Imaging of the Endolymphatic Space: A Methodological Comparative Study

In-vivo non-invasive verification of endolymphatic hydrops (ELH) by means of intravenous delayed gadolinium (Gd) enhanced magnetic resonance imaging of the inner ear (iMRI) is rapidly developing into a standard clinical tool to investigate peripheral vestibulo-cochlear syndromes. In this context, methodological comparative studies providing standardization and comparability between labs seem even more important, but so far very few are available. One hundred eight participants [75 patients with Meniere's disease (MD; 55.2 ± 14.9 years) and 33 vestibular healthy controls (HC; 46.4 ± 15.6 years)] were examined. The aim was to understand (i) how variations in acquisition protocols influence endolymphatic space (ELS) MR-signals; (ii) how ELS quantification methods correlate to each other or clinical data; and finally, (iii) how ELS extent influences MR-signals. Diagnostics included neuro-otological assessment, video-oculography during caloric stimulation, head-impulse test, audiometry, and iMRI. Data analysis provided semi-quantitative (SQ) visual grading and automatic algorithmic quantitative segmentation of ELS area [2D, mm²] and volume [3D, mm³] using deep learning-based segmentation and volumetric local thresholding. Within the range of 0.1-0.2 mmol/kg Gd dosage and a 4 h ± 30 min time delay, SQ grading and 2D- or 3D-quantifications were independent of signal intensity (SI) and signal-to-noise ratio (SNR; FWE corrected, p < 0.05). The ELS quantification methods used were highly reproducible across raters or thresholds and correlated strongly (0.3-0.8). However, 3D-quantifications showed the least variability. Asymmetry indices and normalized ELH proved the most useful for predicting quantitative clinical data. ELH size influenced SI (cochlear basal turn p < 0.001), but not SNR. SI could not predict the presence of ELH. In conclusion, (1) Gd dosage of 0.1-0.2 mmol/kg after 4 h ± 30 min time delay suffices for ELS quantification. (2) A consensus is needed on a clinical SQ grading classification including a standardized level of evaluation reconstructed to anatomical fixpoints. (3) 3D-quantification methods of the ELS are best suited for correlations with clinical variables and should include both ears and ELS values reported relative or normalized to size. (4) The presence of ELH increases signal intensity in the basal cochlear turn weakly, but cannot predict the presence of ELH.

Clinical high-resolution imaging and grading of endolymphatic hydrops in Hydropic Ear Disease at 1.5 T using the two-slice grading for vestibular endolymphatic hydrops in less than 10 min

BACKGROUND

Hydropic Ear Disease (Menière) is one of the most common inner ear disorders and one of the most common causes of vertigo attacks. The underlying pathology is a distension of the endolymphatic space of the inner ear, termed endolymphatic hydrops. However, the unequivocal morphologic confirmation of ELH has been restricted to post-mortem histologic analysis until 2007, when the first clinical MR imaging report demonstrated ELH in living patients with Menière's disease at 3 T combined with intratympanic application of contrast. Imaging techniques have since then evolved further. However, a high magnetic field strength of 3 T has consistently been mandatory for reliable clinical imaging of ELH. This limitation has significantly prevented ELH imaging from being widely available across different health care systems around the world. With the aim of filling this gap, in the present study, we aim to describe the feasibility of ELH imaging at 1.5 T in clinical practice and to develop a dedicated grading system for cochlear and vestibular ELH for MR imaging at 1.5 T.

METHODS

In this retrospective study, we examined 30 patients with suspected hydropic ear disease undergoing diagnostic MR imaging. Contrast agent was diluted eightfold in saline solution and unilaterally applied by intratympanic injection as described previously. MRI scanning was performed using a 16-channel head coil on a 1.5 T Achieva Philips Medical Systems Scanner using a 3D FLAIR sequence. For the cochlea, a 3-stage grading was developed. For the vestibulum, a 4-stage grading based on two axial slices was developed by analysing both the superior and the inferior part of the vestibulum. The presence of hydropic herniation of the endolymphatic space into the posterior crus of the horizontal semicircular canal was evaluated.

RESULTS

In all 30 patients, the perilymphatic fluid spaces of the inner ear showed clear and high signal intensity, while the endolymphatic space was not enhanced. In all patients, the vestibular endolymphatic space could be clearly delineated and differentiated from the perilymphatic space. Analysis of the cochlear endolymphatic space revealed no evidence of ELH in 7 patients, a grade 1 cochlear ELH in 11 patients and a grade 2 cochlear ELH in 12 patients. Analysis of the vestibular endoylmphatic space revealed no evidence of ELH in 8 patients, a grade 1 vestibular ELH in 5 patients, a grade 2 vestibular ELH in 9 patients and a grade 3 vestibular ELH in 8 patients. Three patients showed a clear hydropic herniation of the vestibular endolymphatic space into the posterior non-ampullated crus of the horizontal SCC.

CONCLUSION

In summary, the findings presented in this study offer an easy, reliable and universally available technique of ELH imaging for diagnostic management of patients with suspected Hydropic Ear Disease.

Deep learning for the fully automated segmentation of the inner ear on MRI

Segmentation of anatomical structures is valuable in a variety of tasks, including 3D visualization, surgical planning, and quantitative image analysis. Manual segmentation is time-consuming and deals with intra and inter-observer variability. To develop a deep-learning approach for the fully automated segmentation of the inner ear in MRI, a 3D U-net was trained on 944 MRI scans with manually segmented inner ears as reference standard. The model was validated on an independent, multicentric dataset consisting of 177 MRI scans from three different centers. The model was also evaluated on a clinical validation set containing eight MRI scans with severe changes in the morphology of the labyrinth. The 3D U-net model showed precise Dice Similarity Coefficient scores (mean DSC-0.8790) with a high True Positive Rate (91.5%) and low False Discovery Rate and False Negative Rates (14.8% and 8.49% respectively) across images from three different centers. The model proved to perform well with a DSC of 0.8768 on the clinical validation dataset. The proposed auto-segmentation model is equivalent to human readers and is a reliable, consistent, and efficient method for inner ear segmentation, which can be used in a variety of clinical applications such as surgical planning and quantitative image analysis.

Correlation between High-Resolution Computed Tomography Scan Findings and Histological Findings in Human Vestibular End Organs and Surgical Implications

BACKGROUND

Histological study of vestibular end organs has been challenging due to the difficulty in preserving their structures for histological analysis and due to their complex geometry. Recently, radiology advances have allowed to deepen the study of the membranous labyrinth.

SUMMARY

A review and analysis of surgical implications related to the anatomy of the vestibular end organ is performed. Radiological advances are key in the advancement of the knowledge of the anatomy and pathology of the vestibule. Thus, application of such knowledge in the development or improvement of surgical procedures may facilitate the development of novel techniques. Key Messages: During the last few decades, the knowledge of the anatomy of the auditory system through histology and radiology had improved. Technological advances in this field may lead to a better diagnosis and therapeutic approach of most common and important diseases affecting the inner ear.

A probabilistic atlas of the human inner ear's bony labyrinth enables reliable atlas-based segmentation of the total fluid space

Intravenous contrast agent-enhanced magnetic resonance imaging of the endolymphatic space (ELS) of the inner ear permits direct, in-vivo, non-invasive visualization of labyrinthine structures and thus verification of endolymphatic hydrops (ELH). However, current volumetric assessment approaches lack normalization. The aim of this study was to develop a probabilistic atlas of the inner ear's bony labyrinth as a first step towards an automated and reproducible volume-based quantification of the ELS. The study included three different datasets: a source dataset (D1) to build the probabilistic atlas and two testing sets (D2, D3). D1 included 24 right-handed patients (12 females; mean age 51.5 ± 3.9 years) and D2 5 patients (3 female; mean age 48.8 ± 5.01 years) with vestibular migraine without ELH or any measurable vestibular deficits. D3 consisted of five patients (one female; mean age 46 ± 5.2 years) suffering from unilateral Menière's disease and ELH. Data processing comprised three steps: preprocessing using an affine and deformable fusion registration pipeline, computation of an atlas for the left and right inner ear using a label-assisted approach, and validation of the atlas based on localizing and segmenting previously unseen ears. The three-dimensional probabilistic atlas of the inner ear's bony labyrinth consisted of the internal acoustic meatus and inner ears (including cochlea, otoliths, and semicircular canals) for both sides separately. The analyses showed a high level of agreement between the atlas-based segmentation and the manual gold standard with an overlap of 89% for the right ear and 86% for the left ear (measured by dice scores). This probabilistic in vivo atlas of the human inner ear's bony labyrinth and thus of the inner ear's total fluid space for both ears represents a necessary step towards a normalized, easily reproducible and reliable volumetric quantification of the perilymphatic and endolymphatic space in view of MR volumetric assessment of ELH. The proposed atlas lays the groundwork for state-of-the-art approaches (e.g., deep learning) and will be provided to the scientific community.