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

Abstract

Hypothesis/Background: Bast's valve is a poorly understood inner ear structure located at the junction between pars superior and inferior in the membranous labyrinth. Anatomically precise three-dimensional reconstructions (3D-reconstructions) of Bast's valve can help illuminate the morphology of the valve, and point toward its role in normal physiology and pathological states such as endolymphatic hydrops. This is of particular relevance to the development of a vestibular implant, a device intended to rehabilitate deficits in the vestibular system. Methods: Six postmortem human temporal bones from healthy donors were scanned using a micro-computed tomography (microCT) scanner. The microCT data allowed 3D-reconstructions of the membranous labyrinth, with a particular focus on Bast's valve, vestibule, and cochlear duct.Results: The microCT images of Bast's valve showed a rigid lip containing a core of soft tissue, opposing the thin membranous wall of the utricle. The maximum recorded length and width of the rigid lip were 440.4 mm and 88 mm, respectively. The 3D-reconstructions illustrated the slit-like opening of Bast's valve into the utricle, the twisting course of the basal turn of the cochlear duct, and the spatial orientation of utricle and saccule with respect to the stapes footplate.Conclusions: The present study provided a novel anatomical perspective on the microscopic structure of Bast's valve. The interplay between endolymphatic hydrops and Bast's valve is an ongoing area of research, but defining this anatomy in 3D will play a key role in furthering our understanding of the disease process. Implications for vestibular implantation are explored through the various 3D-reconstructions.

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

“…Although there have been varying hypotheses for the role of the utriculoendolymphatic valve (Bast's valve) in health and disease, the role of Bast's valve in regulating endolymph physiology remains unknown (17). We evaluated the status of the valve to determine whether it could be involved in the pathophysiology of endolymphatic hydrops (see also: Limitations of the study).…”

“…endolymph physiology remains unknown (17). We evaluated the status of the valve to determine whether it could be involved in the pathophysiology of endolymphatic hydrops (see also: Limitations of the study).…”

Expression of AQP8 in serum of patients with Meniere's disease and its value in evaluating the degree of hydrolabyrinth and predicting prognosis

“…Traditionally, endolymphatic hydrops has been viewed as an objective histopathological evidence of Meniere's disease, but histopathology can only be performed after death and cannot be used to evaluate patients with episodes of vertigo. The development of active Meniere's disease and its time gap from autopsy assessments limit our understanding of disease progression 8,9 . Many otologic biomarkers are currently used to differentiate Meniere's disease from vestibular migraine and assess the progression of Meniere's disease 10,11 .…”

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

“…Following centuries of research using such methods, x-ray computed tomography revolutionized 3D visualization of inner ear structure through virtual segmentation and reconstructions of form. More recently, high-resolution micro-computed tomography (μCT) and synchrotron-phase contrast imaging have allowed the visualization of previously poorly understood structures of the membranous labyrinth 15 – 18 . Specifically, the combination of μCT modalities with 3D digital modeling and shape analyses has established the spatial configuration of the ML 9 , 19 and morphological structure of the ductus reuniens (DR), a link between the peripheral hearing and balance mechanisms 20 .…”