Optical coherence tomography imaging demonstrates endolymphatic hydrops in the lateral and posterior semicircular canals in noise-exposed mice

Abstract

Optical Coherence Tomography (OCT) has been used to characterize cochlear endolymphatic hydrops (ELH) with distention of Reissner’s membrane in mice after noise exposure. Noise exposure has been correlated with vestibular dysfunction, so we hypothesized that noise exposure can lead to ELH in the vestibular system. Little work has been performed using OCT to image the membranous labyrinth in the lateral and posterior semicircular canals (SCCs). We show that OCT with 12.5 µm axial resolution and 13.2 µm lateral resolution can image the SCCs and delineate the membranous labyrinth in anesthetized mice. A high-resolution OCT system with 2.45 µm axial and 3.95 µm lateral resolution provides improved distinction between the endolymphatic and perilymphatic fluid spaces that enables quantification of the endolymph to perilymph (E/P) area ratio in the SCCs. The LSCC E/P ratio in noise exposed mice (5.16 ± 0.67, mean ± standard deviation, n = 12) is significantly increased (p = 0.0014, unpaired Student’s t-test) compared to control mice (4.26 ± 0.41, n = 10). Similarly, the PSCC E/P ratio in noise exposed mice (4.92 ± 0.52, n = 12) is significantly increased (p = 3.65e-6, unpaired Student’s t-test) compared to control mice (4.00 ± 0.37, n = 11). Furthermore, the PSCC and LSCC E/P ratios correlate significantly (R² = 0.284, p = 0.0063, linear regression). These data demonstrate that noise exposure leads to increased E/P ratio, a measurement of ELH, in both the LSCC and PSCC in mice, and this corresponds to ELH present in the cochlea after noise exposure. Therefore, noise exposure leads to ELH in both the cochlea and the vestibular system, suggesting a pathway for noise exposure to cause vestibular dysfunction.