Vestibular dysfunction in Pendred syndrome is inconsistent and variable. A mouse model of Pendred syndrome (Slc26a4 Δ/Δ mice) is known to manifest variable degrees of vestibular dysfunction, as evidenced by gait unsteadiness, circling behavior, and head tilting. Scanning electron microscopic studies of the vestibular end organs have demonstrated abnormally enlarged otoconia, while the vestibular hair cells looked normal for 2 months after birth. In this study, we performed X-ray computed microtomography (microCT) at 10-micron resolution with three-dimensional image reconstruction of the otoconia as well as the bony labyrinth, to elucidate the etiology of the equilibrium disturbance observed in the Slc26a4 Δ/Δ mice. The otic capsules of the Slc26a4 Δ/+ and Slc26a4 Δ/Δ mice were imaged by microCT at 1 day, 8 days, and 3 months of age. Multiplanar reconstructed images were used to calculate the width of the saccule and utricle, and delineate the shape, size, and location of the otoconia. The ossicles, osseous labyrinth, and otoconia were clearly visualized by microCT. The Slc26a4 Δ/Δ mice exhibited an enlarged saccule and utricle as compared to the Slc26a4 Δ/+ mice. In the utricle of the Slc26a4 Δ/Δ mice, nearly 20 giant otoconia were discretely distributed on P8. The number of otoconia decreased with age. In the saccule, otoconia were fewer in number than that in the utricle, or altogether absent, on P8. No ectopic otoconia were observed in any of the semicircular canals. We succeeded in non-destructive delineation of the giant otoconia in the Slc26a4 Δ/Δ mice by microCT, with extremely few artifacts. We believe that these results will be useful for elucidating the etiology for equilibrium disorder in Pendred syndrome.
