Evaluation of the structure of the otoconial layer using micro-computed tomography
Introduction
Benign paroxysmal positional vertigo (BPPV) is one of the most common peripheral vestibular diseases and has an estimated lifetime prevalence of 2.4% [1]. BPPV is caused by dislocated otoconia that fall from utricular macula and float into the semicircular canals, thereby inducing transient vertigo elicited after quick changes in head position [2]. BPPV can occur in both sexes at any age, yet it is most common in middle-aged and elderly females [1]. Recently, the occurrence and/or recurrence of BPPV has been reported to be associated with osteopenia/osteoporosis and/or vitamin D deficiency [3], [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16]. Calcium metabolism is important for the synthesis and absorption of otoconia, as they are composed of calcium carbonate. Therefore, it is suggested that peri‑menopause conditions that cause deterioration of serum levels of estrogen are primarily responsible for the disturbance of calcium metabolism and may induce changes in otolith organs [17]. Animal studies have shown that bilateral ovariectomy (OVX), which causes the deterioration of estrogen, leads to the morphological changes of otoconia [18,19]. Honda et al. reported that the mouse otoconial layer could be visualized using micro-computed tomography (µCT) with minimum artifacts [20]. However, it is currently unknown whether µCT is useful for the detection of morphological changes in the otoconial layer. Thus, we investigated this issue in mice, and we also aimed to determine whether µCT is useful for evaluating changes in the otoconial layer after OVX.
Section snippets
Materials and methods
The study protocol was approved by the Ethics Committee for Animal Experiments at Ehime University. The animals received human care as required by the institutional guidelines and the Guide for the Care and Use of Laboratory Animals [21].
Bone mass density
Fig. 2 shows the BMD values of the femurs for the OVX and sham groups that were measured during the experiment. The femur BMD was 27.6 ± 0.7 mg/cm3 at 2 weeks, 29.9 ± 0.4 mg/cm3 at 4 weeks, and 29.3 ± 0.9 mg/cm3 at 8 weeks in the sham group. In the OVX group, the femur BMD value was 27.3 ± 0.7 mg/cm3 at 2 weeks, and it remained stable during the experiment. The BMD values of the femurs in the OVX group were significantly lower compared to those of the sham operated mice at 4 and 8 weeks after
Discussion
In this study, the volume of the utricular otoconial layer increased 4 weeks after OVX, and the changes could be detected using µCT. To our knowledge, this is the first report to show the utility of µCT for the detection of morphologic changes in the otoconial layer after OVX.
Using scanning electron microscopy (SEM), a previous study showed that the size of the utricular otoconia layer increased in rats that had undergone OVX [18]. Yang et al. also reported that estrogen deficiency leads to
Conclusion
We investigated the morphological changes in the otoconial layer after bilateral OVX. The volume of the utricle otoconial layer significantly increased 4 weeks after OVX compared to the sham group. The µCT and histological results were significantly correlated, suggesting that µCT is useful for the detection of morphological changes in the otoconial layer with minimum artifacts.
Declaration of Competing Interest
None declared.
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