3D-reconstructions of Bast's Valve and Membranous Labyrinth: Insights for Vestibular Implantation and Meniere's Disease

Differential Volume Increase of Endolymphatic Compartments in Ménière's Disease Is Inversely Associated With Membrane Thickness

OBJECTIVES

Our aim in this study was to characterize the morphology of the endolymphatic compartment on histopathology in individuals with Ménière's disease (MD) and to determine why hydrops of the saccule is more pronounced than that of other compartments of the inner ear in MD.

METHODS

Temporal bones from 9 patients with idiopathic MD and from 10 individuals without MD/endolymphatic hydrops were examined. The inner ear fluid compartments in normal ears, and ears with MD were three-dimensionally reconstructed and their volume was calculated. The thickness of the membranes of the labyrinth was measured, and both ruptures of the membranes and patency of the utriculoendolymphatic (UEV; Bast's) valve were assessed.

RESULTS

In ears with MD, the saccule and the cochlear duct were most frequently hydropic; the utricle was involved approximately half as frequently. In ears without MD, the Reissner's membrane and the membranous wall of the saccule were thinner than that of the utricle and of the lateral semicircular canal ( p < 0.01). The lateral semicircular canal did not show signs of hydrops. In all ears with MD in which the utricle exceeded the average volume of normals (6 of 12), the UEV was open or there was a rupture in the utricle.

CONCLUSION

Increases in endolymphatic pressure may cause a primary swelling of the apical cochlear duct and saccule, both of which have relatively thin membranes. Hydrops in the utricle may occur less frequently because of a thicker wall, because of a functioning UEV, and when the saccule has already occupied most of the vestibular perilymphatic space.

Volume ratio and distribution rate in patients with orthostatic vertigo/dizziness using MR imaging: a comparison with vertiginous diseases

BACKGROUND

Orthostatic dizziness/vertigo (ODV) is characterized by lightheadedness owing to postural changes.

AIMS/OBJECTIVES

To measure the endolymphatic space (ELS)/total fluid space (TFS) volume ratio and the distribution rate of endolymphatic fluid (ELF) of patients with ODV and compare them with those of control subjects (CS).

MATERIALS AND METHODS

This study included 22 patients (44 ears) with ODV and 52 controls (104 ears, CS). The ELS/TFS volume ratio (%) and distribution rate (%) of the inner ear components were measured using 3-dimensional magnetic resonance imaging.

RESULTS

In the ODV group, the mean ELS/TFS volume ratios of the cochlea, vestibule, and semi-circular canals (SCCs) were 12.1%, 18.6%, and 18.1%, respectively; the mean ELS distribution rates for the cochlea, vestibule, and SCCs were 27.3%, 26.2%, and 46.6%, respectively. The ELS distribution rate of the vestibule was significantly lower (p < .01) and the ELS distribution rate of the SCCs was significantly higher in the ODV than in the CS group (p < .01).

CONCLUSIONS AND SIGNIFICANCE

The ELS distribution rate in the vestibule + SCCs among patients with ODV did not differ from that in the CS; ELF in the vestibule moved to the SCCs, and a large amount of ELF was distributed only in the SCCs.

First evidence of the link between internal and external structure of the human inner ear otolith system using 3D morphometric modeling

Our sense of balance is among the most central of our sensory systems, particularly in the evolution of human positional behavior. The peripheral vestibular system (PVS) comprises the organs responsible for this sense; the semicircular canals (detecting angular acceleration) and otolith organs (utricle and saccule; detecting linear acceleration, vibration, and head tilt). Reconstructing vestibular evolution in the human lineage, however, is problematic. In contrast to considerable study of the canals, relationships between external bone and internal membranous otolith organs (otolith system) remain largely unexplored. This limits our understanding of vestibular functional morphology. This study combines spherical harmonic modeling and landmark-based shape analyses to model the configuration of the human otolith system. Our approach serves two aims: (1) test the hypothesis that bony form covaries with internal membranous anatomy; and (2) create a 3D morphometric model visualizing bony and membranous structure. Results demonstrate significant associations between bony and membranous tissues of the otolith system. These data provide the first evidence that external structure of the human otolith system is directly related to internal anatomy, suggesting a basic biological relationship. Our results visualize this structural relationship, offering new avenues into vestibular biomechanical modeling and assessing the evolution of the human balance system.