Blockage pattern of longitudinal flow in Meniere's disease

3D Real IR MR Findings in Acoustic Neuromas: Altered Perilymph Metabolism

OBJECTIVES

This study aimed to investigate the perilymph metabolism by analyzing the 3D real IR MR findings in acoustic neuroma (AN) after intravenous administration of gadolinium (Gd).

METHODS

Eleven patients (6 men and 5 women) diagnosed with AN were included, and 3D real IR MRI was performed 4 hours after intravenous Gd injection. The signal intensity and details of inner ear, tumor, and internal auditory canal (IAC) by MRI were analyzed.

RESULTS

Four patients had tumors confined to the IAC, and 5 had tumors that extended to the cerebellopontine angle cistern. The signal intensity of the cochlea, vestibule, and IAC fundus was conspicuously enhanced in 3D real IR images than the control side. One patient had a tumor in the cochlea, in which the signal intensity of the semicircular canal and vestibule was increased. One patient had an intravestibular tumor in which the signal intensity of the semicircular canal was increased and the cochlea had endolymphatic hydrops in the affected ear.

CONCLUSIONS

The synchronously increased signal intensity in the inner ear and IAC may indicate that IAC may serve as a channel for removal of the perilymph in the inner ear; the blockage by the tumor may have changed the hydrodynamics of the perilymph to cause a longer retention of Gd in the inner ear.

Finite Element Modeling of Residual Hearing after Cochlear Implant Surgery in Chinchillas

Cochlear implant (CI) surgery is one of the most utilized treatments for severe hearing loss. However, the effects of a successful scala tympani insertion on the mechanics of hearing are not yet fully understood. This paper presents a finite element (FE) model of the chinchilla inner ear for studying the interrelationship between the mechanical function and the insertion angle of a CI electrode. This FE model includes a three-chambered cochlea and full vestibular system, accomplished using µ-MRI and µ-CT scanning technologies. This model's first application found minimal loss of residual hearing due to insertion angle after CI surgery, and this indicates that it is a reliable and helpful tool for future applications in CI design, surgical planning, and stimuli setup.

Endolymphatic Hydrops in Patients With Intralabyrinthine Schwannomas

Purpose: The presence of endolymphatic hydrops (EH) in patients with intralabyrinthine schwannomas (ILSs) is poorly understood. This study aims to determine whether there is a correlation between endolymphatic hydrops and clinical presentations of ILS.

Methods: Data from nine patients with ILSs were retrospectively reviewed between 2007 and 2020. Temporal bone MRI with intratympanic or intravenous injection of gadolinium was applied to detect ILSs and EH.

Results: 3D real inversion recovery (IR) sequence MRI of the temporal bone confirmed ipsilateral EH in four patients (4/6). All four patients with EH on MRI presented with vertigo similar to Meniere's disease. Among these patients with EH, one patient with EH in the cochlea showed moderate sensorineural hearing loss, while three patients with EH in both the vestibule and cochlea showed profound hearing loss. MRI demonstrated a transmacular tumor (TMA) in one patient, intravestibular (IV) in four patients, and vestibulocochlear (VC) in four patients. Two IV cases showed moderated hearing loss, while the TMA and VC cases showed profound hearing loss. Transotic resection of the tumor was applied in five patients; translabyrinthine resection was applied in one patient; two patients were under observation; and one patient was given intratympanic injection of gentamicin (ITG). During follow-up, all of the treated patients reported relief of vertigo, and postoperative MRI was performed in two patients, which showed no tumor recurrence. The two patients under observation showed no deterioration of hearing loss or vertigo. One patient was lost to follow-up.

Conclusion: EH concurrent with ILSs has been underestimated previously. With the extensive application of temporal bone MRI paradigms, such as 3D-real IR sequence MRI, more cases of potential EH in patients with ILS will be identified. The severity of hearing loss may be associated with the location of the tumor and the degree of EH.

Otoconia: Mimicking a calcite-based functional material of the human body. From basic research to medical aspects

Otoconia (calcite-based biominerals) are part of the sensory system in the inner ear of vertebrates, acting as gravity receptors responding to linear accelerations. Biomimetic otoconia are grown by double-diffusion into gelatine-gel matrices, and represent the first example of successful imitation of a biomineral, not only in outer shape but also in composite structure and hierarchical inner architecture. Biomimetic and biogenic (human) otoconia are investigated by X-ray methods, chemical analytics, ESEM, and TEM. Shape development (morphogenesis) as well as (partial) dissolution of the calcite component of the composite underline the hierarchical inner architecture built of more dense rhombohedral branches (with plane end-faces) and a rounded, more porous belly area. Atomistic simulations are performed in order to get insight into very first nucleation steps. Based on the detailed observations made up to now, first assumptions for the function of otoconia are developed, including the questions of density distribution within the volume of the specimen, the surrounding endolymph, as well as anchoring and interconnections of otoconia. A final point concerns the degeneration of otoconia which is caused by complexing agents and/or changes in ion concentrations (and pH) of the endolymph.

Principles of calcite dissolution in human and artificial otoconia

Human otoconia provide mechanical stimuli to deflect hair cells of the vestibular sensory epithelium for purposes of detecting linear acceleration and head tilts. During lifetime, the volume and number of otoconia are gradually reduced. In a process of degeneration morphological changes occur. Structural changes in human otoconia are assumed to cause vertigo and balance disorders such as benign paroxysmal positional vertigo (BPPV). The aim of this study was to investigate the main principles of morphological changes in human otoconia in dissolution experiments by exposure to hydrochloric acid, EDTA, demineralized water and completely purified water respectively. For comparison reasons artificial (biomimetic) otoconia (calcite gelatin nanocomposits) and natural calcite were used. Morphological changes were detected in time steps by the use of environmental scanning electron microscopy (ESEM). Under in vitro conditions three main dissolution mechanisms were identified as causing characteristic morphological changes of the specimen under consideration: pH drops in the acidic range, complex formation with calcium ions and changes of ion concentrations in the vicinity of otoconia. Shifts in pH cause a more uniform reduction of otoconia size (isotropic dissolution) whereas complexation reactions and changes of the ionic concentrations within the surrounding medium bring about preferred attacks at specific areas (anisotropic dissolution) of human and artificial otoconia. Owing to successive reduction of material, all the dissolution mechanisms finally produce fragments and remnants of otoconia. It can be assumed that the organic component of otoconia is not significantly attacked under the given conditions. Artificial otoconia serve as a suitable model system mimicking chemical attacks on biogenic specimens. The underlying principles of calcite dissolution under in vitro conditions may play a role in otoconia degeneration processes such as BPPV.